THE PHILOSOPHICAL DIMENSIONS OF THE ORIGIN OF SPECIES.
John N. Deely
University of Ottawa
Ottawa, Canada
PART ONE
" Les philosophes pour lesquels la catรฉgorie du pรฉrimรฉ est un critรจre mรฉtaphysique, et la pensรฉe a le devoir de vieillir en oubliant, peuvent-ils comprendre que si nous consultons les anciens c'est pour recourir ร une fraรฎcheur de regard au-jourd'hui perdue? Nulle thรฉsaurisation d'expรฉrience, aucun des avantages et aucune des grรขces du vieillissement de la pensรฉe ne sauraient remplacer la grรขce propre de sa jeunesse, la virginitรฉ de l'observation, l'รฉlan intuitif de l'intelligence non fatiguรฉe encore vers la savoureuse nouveautรฉ du rรฉel."
(Jacques Maritain)
PROBABLY it is not possible for educated men not to accept John Dewey's statement that " few words in our language foreshorten intellectual history as much as does the word species."1 Whether the word " foreshorten" here refers to a near-sightedness of modern scholarship in this area of intellectual history, or to the truth of Dewey's contention that Darwin's work by combining the word origin with the word species " embodied an intellectual revolt and introduced a new intellectual temper,"2 however, is another question which is worthy of consideration.
To this extent, Dewey's contention is certainly true and accurate: in the whole matter of evolution, the mass of data which scientific research has uncovered and attested has had a cumulative effect in making an ancient and traditional problem about the nature of species a currently insistent one, and
1 John Dewey, " The Influence of Darwinism on Philosophy," in The Influence of Darwin on Philosophy (New York: Holt, 1910), p. 3.
2 Ibid., p. 1.
STRUCTURAL OUTLINE
I. The State of the Question. II. Approach to the Problem. III. The Logic of Evolutionary Science. V. Specific Structures in an Evolving World. VI. The Error of Univocally Ontologized Kind-Essences. VII. The Operational Displacement of Typological Thought in its Implications for Hierarchy. VIII. The Two Hierarchies. IX. Conclusion.
one which, in the contemporary mind, serves to exemplify in a clear and striking manner the incompatibility of modern science and traditional philosophy.
I. The State of the Question
Whether there is an incompatibility between modern science and traditional philosophy is an interesting question, and one which admits of no single, simple answer; but the evolution of species may not be an illustration thereof, and it is certainly not a clear and striking illustration; for it is not entirely accurate to oppose the modern conception of species to the conception entertained by the ancients, particularly Aristotle, and to claim on this basis (as so many do) that the entire classical metaphysical approach to the essential structures of existence has been shown to be a cultural illusion.
As a matter of fact, the intention guiding the theoretical efforts of the ancients was simply different from that which preoccupies the evolutionary biologists. The ancients dealt with the problem of species primarily in terms of knowledge, by reference to the question of whether the mind can lay hold in concepts of the necessities truly governing the ontological structure of the world; and in judgments, of the existence exercised by things independently of those conceptions which we form. By contrast, modem biology has approached the problem of species simply in terms of their reality in the nature of things, especially in the community of living things, and only secondarily has it given thought to the epistemological value of specific concepts.
It is true, of course, that the ancients did regard the specific structures of extramental realities as fixed once and for all, and this on the basis both of inadequate observational data and cultural assumptions. But the question of species as addressed by modern biology was only placed rather late in Western history, beginning with the work of John Ray, Carolus Linnaeus, and Comte de Buffon, in the seventeenth and eighteenth centuries.
This point may be illustrated textually, and its capital importance
indeed makes such illustration incumbent on us. First of all, with respect to the species problematic of traditional philosophy so far as it traces its roots to Aristotle, Mortimer J. Adler, whose reputation as an authority on the Western intellectual tradition is well known, has made a comprehensive analytical survey of all the texts in Aristotle and St. Thomas dealing with the problem of species, and has formulated this judgment: " the word ' species,' as used in the philosophy of nature, never refers to an existent thing.. . ." 3 " The notion of species is strictly a logical concept; . . . any use of the word ' species' to signify anything other than the concept species itself, is a derivative mode of signification. Strictly speaking, the concept species is never used ontologically; the word ' species ' can be. ..." 4
Philosophically, and still speaking within the explicitly Aristotelian tradition of natural philosophy, Jacques Maritain concurs in this assessment: " the notion of species is in itself a logical notion, concerning the mode of existence of things in our mind, or insofar as they are known (intentiones secundae). This notion, logical in itself, can be employed either from the logical or the ontological point of view." 5 But even " the ' species ontologically considered ' is not exactly the ' specific nature,' but rather an application of the logical notion of species . . .";6 so that, even in the case of species understood in the ontological sense, for a traditional natural philosophy transparent to itself, " species remains still a logical entity, but this second intention is then related to the ontological order of essences or of primae intentiones." 7
In the second place, with respect to the species problematic of evolutionary biology, Ernst Mayr, in what Julian Huxley has
3 Mortimer J. Adler, The Problem of Species (New York: Sheed and Ward, 1940), p. 14. The reader is asked to refer immediately to my comments on this work in fn. 124 below, second paragraph.
4 Mortimer J. Adler, "The Solution of the Problem of Species," The Thomist, III (April, 1941), p. 298, fn. 27.
5 Jacques Maritain, " Foreword " to Adler's The Problem of Species, p. ix.
6 Jacques Maritain, " Concerning a ' Critical Review'," The Thomist, III (January, 1941), fn. 2 p. 46.
7 Ibid., p. 47, fn. 4.
called " a masterly and illuminating statement of contemporary thinking about species and their basic role as integrated units of evolution," expresses the scientific concern for the meta-logical reality of species by pointing out that a typological species-concept based on essential properties common to individuals of the type is impossible to employ if one seeks directly to encompass the multidimensional dynamics of reproductive populations as ecological units; while on the other hand, " internal cohesion of the gene pool " within such populations and " the biological causation of the discontinuities " between such populations provides an intelligible ensemble of interaction resulting in a properly biological species-concept devoid at once of both the arbitrary and the purely noetic type or " essential kind." 8 " Whoever, like Darwin, denies that species are non-arbitrarily defined units of nature not only evades the issue but fails to find and solve some of the most interesting problems of biology." 9 For contemporary evolutionary science, the ecological population clusters and the discontinuities observed between them " are not, as sometimes contended, abstractions or inventions of the classifier."10 " It must be stressed that this discontinuity exists whether it is or is not used by the systematists for their purposes, and for that matter whether it is studied at all." 11
In organisms which reproduce sexually and by crossfertilization, the reality of species as biological units can also be demonstrated by a quite different method. . . . These communities consist of individuals united by the bonds of sexual unions, as well as of common descent and common parenthood. . . . A species is, consequently, not merely a group and a category of classification. It is also a supraindividual biological entity, which, in principle, can be arrived at regardless of the possession of common morphological characteristics.12
8 Ernst Mayr, Animal Species and Evolution (Cambridge, Mass.: Harvard, 1963), p. 21.
9 Ibid., p. 29.
10 Theodosius Dobzhansky, Genetics and the Origin of Species (3rd rev. ed.; New York: Columbia, 1951), p. 5.
11 Ibid., p. 255.
12 Ibid., p. 6, emphasis added.
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These texts make it clear, I think, that John Dewey's simple opposition of traditional philosophy and modern science as knowledges of nature mutually incompatible by reason of their respective conceptions of species was premature, although certainly justified in the light of Darwin's original opinion and long-sustained view:
I look at the term species as one arbitrarily given, for the sake of convenience, to a set of individuals closely resembling each other, and . . . it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, for convenience sake.13
So long as evolutionary science maintained that species were conveniences pure and simple, arbitrarily chosen points in the continuum of nature rather than natural articulations thereof, the species problematic did provide a clear and striking illustration of a radical incompatibility between traditional philosophy and modern science. In traditional terms, Darwin's position was that specific distinctions are entirely quoad nos, and not at all secundum se. Such a position could not in any sense coexist with the first principles of traditional philosophy.
To accept this view [of Darwin's] is to deny the doctrine of substantial forms; for, according to it, all things would differ only accidentally. If we are to maintain a hylomorphic conception of nature, we must preserve the integrity of substantial forms, both secundum se and quoad nos.14
The traditional notion of species, logical in itself (" typological," in Mayr's terms15), could, if employed from an ontological
13 Charles Darwin, The Origin of Species (New York: Modern Library Giant G27, n. d.), p. 46. (Original publication date was 1859).
14 Adler, The Problem of Species, p. 23.
15 Actually, this correspondence is not quite precise. For Mayr, " typological thought" is thinking in terms of reified ideal types. On the other hand, when Maritain speaks of " the order of typological discrimination " (e. g., see The Degrees of Knowledge, 1959 English ed., p. 177), he is speaking of the order of intelligible necessities discriminable at the heart of natural existents. At the same time, since, as we shall see below, esp. in Sec. VI, Maritain's doctrine on the nature and number of species does seem to include a large element of unwarranted reification of epistemological constructs, the correspondence is not entirely imprecise either. See fns. 16 and 22 infra, and the references there cited. In itself, however, the word " typology " as employed by the two authors is as diverse as the two species problematics we are here limning
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point of view, be used to designate specific natures as the fundament in things which mediates the universal intention of pure intellection as an index in some respect (which respect, however, it is for ontology and never logic to determine16) of
16 See Adler, " Solution of the Problem of Species," pp. 302-3: " We are concerned with the problem of the ontological vs. the logical, as that occurs in epistemology. I am here thinking of the problem of how these two spheres of knowledge are ordered to one another. The oft-cited fact that the science of logic considers, in its own way, everything which falls within the scope of all other bodies of knowledge (i. e., all knowledge of the real--vd. Aristotle, Metaphysics, IV, 2, 1004b17-26, and St. Thomas, In IV Met., lect. IV, n. 574), does not solve this problem. Although the spheres of logic and of ontology (in the broadest sense) are co-extensive, the two kinds of science are not simultaneous: each in its own way has a certain priority over the other. Thus, in the order of analysis, the logician has priority with regard to the notion of species, for species is exclusively a second intention; and when the philosopher of nature or the natural scientist uses this notion, he borrows it from the logician. This is seen in the fact that any employment of the word " species " or the word " specific " in the first intention is a derivative usage. (The concept species is a second intention even when it lends its significance to the word " species " as used in the first intention to designate a specific nature; and even when it enters, as a second intentional note, into the signification of a concept, such as man, which is primarily a first intention.) But, in the order of learning and discovery, first intentions are prior to second intentions, and here the student of nature, philosopher or scientist, takes priority. Nature itself is prior to knowledge of nature, and knowledge of nature, in turn, is prior to knowledge of knowledge. If there were not in fact substances differing specifically (i. e., diverse in specific nature), we could not in truth form concepts of these natures, which contained the intention of specificity, and hence we could never have derived the concept species itself. This fact about priority is extremely important to the philosophy of nature. Although he must listen to the logician with regard to species and genus, the philosopher of nature speaks first when it comes to saying how many specific natures there are, how they share generic natures, how they are ordered, etc. There need be no conflict between logic and ontology in the consideration of these problems, in which they both have an interest; but there will be conflict, with consequent confusions and errors, unless the two spheres of knowledge are well-ordered to one another. Thus, it is not for the logician alone to say whether the concept man is truly a specific concept; he can say what the formal properties of any concept must be in order for it to be a species or a genus; but the interpretation of the facts of nature in the light of strictly ontological principles is indispensable for the final determination whether this or that concept is a species or a genus. Logicians, or readers of logic, who fail to realize this fall into grave error, the sort of error which can become an obstacle to truth in the philosophy of nature, in so far as the student of nature must employ the logical concepts of species and genus. But falsity in the philosophy of nature can also cause errors in logic; if the logician is misled by the naturalist to make wrong discriminations among concepts (e. g., between those which are and those which are not properly specific), he may develop a false or confused analysis of species and genus. In fact, both of these mistakes have actually happened in the history of philosophia perennis: falsity in the philosophy of nature has caused errors in logic, and errors in logic have been an obstacle to reaching the truth about nature." See ibid., fn. 87 p. 347; and in this present essay fn. 22 infra, and Sects. VI and VIII esp.; also The Problem of Species, Chs. II and III, pp. 12-47, esp. Ch. Ill, " Our Knowledge of Species," pp. 32-47 where the alternative positions are set out and their implications clearly indicated. See also pp. x, xii, 43, 47, 94 fn. 129a, 180, 210, 224. And fn. 249 infra.
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all or none: such usage, however, is always derivative and secondary; for in the domain of material beings species as such cannot exist, and even the specific nature for philosophy " is not an ens, but an ens entis." 17 Moreover, since (1) the logical species concept, employed from an ontological point of view and in the perspective of reasons for being, intelligibly considered refers exclusively to natural entities which differ radically in kind, i. e., to things in which an observable or manifest difference in kind is based on and explained by the fact that one of the two beings being compared has a factor or element in its fundamental constitution or make-up that is totally absent from the constitution of the other--in other words, to natural kinds recognizable as different not simply in the order of existence exercised, but in their metaphysical composition in the pure line of essence taken in itself; since, in addition (2) beings which differ in this way differ in essential grade by a whole step (since, logically, essential differentiation involves positive and negative differences rooted in the same perfection, so that there can never be more than two essential species in a single genus; or, more exactly, since such differentiation involves " two, not three, distinct perfections, of which one radical kind possesses both and is, therefore, the higher, and the other possesses only one and is, therefore, the lower "18), while yet remaining, as forms educible from matter, not sufficiently determined in their intelligible note to exist except under
17 Adler, The Problem of Species, p. 14.
18 Mortimer J. Adler, " The Hierarchy of Essences," The Review of Metaphysics, VI (September, 1952), p. 17. This point will be developed in Sec. VIII infra.
the supraessential determinations inseparably involved at the very level of first act inasmuch as they are constituted by the accidents caused by or the simple variegated determinateness of the signate matter involved in generation 19 (so that " it is the absence of complete determination, and the incapacities for self-individuation which call for matter . . . which are the last cause of the essential complexity of entia mobilia"20); by reason of these two conditions, the real existence of natural beings radically distinct from the standpoint of constitutive intelligible notes has always depended in traditional philosophy on an inductive procedure viewed, exactly as in modern science, " as a process of concluding from instances or particular evidences that a nominal definition is real or, in other words, that the kind for which a definition can be notionally or verbally formulated really exists." 21
Considering for the moment only the case of the two essential kinds that divide a single genus, the inductive procedure by which the formulated definitions can be established must involve instances that differentiate one species from another. To do this, the instances must provide evidence of a hierarchical relation between the traits or perfections possessed by one sub-class of things and those possessed by another, the two groups being accepted as belonging to the same generic class. In short, in the realm of essential kinds, the specifying signs must also hierarchize or be signs of hierarchy.22
18 See Adler, The Problem of Species, pp. 188-195, esp. pp. 193-4.
20 Charles De Koninck, Le Problรจme de I'lndรฉterminisme (Quebec, 1937; Extrait des rapports de la Sixiรจme Session [1935], de L'Acadรฉmie Canadienne Saint-Thomas d'Aquin), p. 125.
21 Adler, " The Hierarchy of Essences," p. 26.
22 Ibid., p. 28. This point is extremely important, and an inescapable consequence of essential constitution through genus and difference. In fact, it is probably not too extreme to say that only someone unfamiliar with the available literature or who has not grasped the main implications of the metaphysics of essential composition could call it into question. Thus Adler could write that, from a strictly traditional point of view, " it may be that the principle of perfect hierarchy is self-evidently true--immediately known by anyone who fully understands the notion of species itself." (" Solution of the Problem of Species," p. 329; see also pp. 285-7, 307 ff., 337 fn. 72, 338 fn. 73, 338 fn. 73a, 347 fn. 87.) We will return to this point of the necessity for strictly essential kinds to be ordered in a unilinear hierarchy when discussing in Section VIII below the modes of difference. Here we may note that Adler's point, also follows from the fact that the human species is the causa cognoscendi (non autem essendi) of the whole hierarchy of essences. See Charles de Koninck, " Rรฉflexions sur le problรจme de I'indรฉterminisme," Revue Thomiste, XLIII (1937), p. 235: " II n'y a point intermรฉdiaire entre ' รชtre', ' vivre ', ' connaรฎtre ' et ' intelliger '. Le caractรจre absolu de cette gradation trouve d'ailleurs son fondement dans l'idรฉe de I'homme dont l'รขme est formellement sensitive, vรฉgรฉtative et forme de corporรฉitรฉ. Parce que l'รขme de I'homme est tout cela, non seulement รฉminentment mais formellement, ces degrรฉs d'รชtre sont susceptible d'รชtre distinctement rรฉalisรฉs hors de lui." As Adler has so thoroughly pointed out, " the point here being made is extremely important. It has traditionally been supposed that there are essential perfections which we do not know, and hence that we are justified in employing accidental perfections in the differentiation of species, i. e., by using properties or even contingent accidents as signs of substantial differences even when we do not know what these substantial differences might be. But this supposition is absolutely invalid on the ground that human nature virtually includes all inferior natures and actually possesses the essential perfections of all inferior things eminenter. Since we claim to know the structure of human nature adequately, we cannot consistently say that there are inferior species whose substantial perfections are rooted in essential perfections not known to us. Hence we are entitled to employ proper or contingent accidents as signs of substantial [i. e., essential] differences only with regard to those which are rooted in known essential perfections--known through our knowledge of man. In fact there are no others." (" Solution of the Problem of Species," fn. 73a p. 338. Cf. The Problem of Species, pp. 109-111; and fn. 16 supra. Some interesting external qualifications are placed on this line of argument in his later study " The Hierarchy of Essences," fn. 11 p. 20, pp. 28-9, fn. 20 p. 29.) A main point of this present article will be to point out that strict adherence to the principle of parsimony in our account of essential kinds imposes this same conclusion quite apart from Adler's reasonings--see esp. Sec. VI below.
Since, so far as the species problematic of traditional philosophy is concerned, everything depends on the notion of hierarchy bound up with the metaphysical constitution and consequent ordering of specific natures in their purely intelligible line, we may point out explicitly that it involves four principal notes: 23
1. an absolutely unilinear ordering in which each radical kind (" infima species ") is higher or lower than another, and no two are coordinate;
2. a discontinuous ordering in which proximate radical kinds are separated by a unit difference, so that there is no medium between them;
23 Cf. The Problem of Species, pp. 109-10.
3. the distinction of radical kinds by the presence or absence of properties which signify through interaction the unit differences, and not by the possession of the same property in different degrees;
4. the virtual inclusion by a radical kind (specific nature) of all lower radical kinds, so that a given radical kind will have all the strict properties belonging to inferior radical kinds, in addition to which it will have the distinctive property that constitutes its superiority.
Turning now to the contemporary species problematic, let us set up as well as we can a parallel contrast.
The biological notion of species, metalogical in itself (concrete as well as nonarbitrary, in Mayr's terms), could, if employed from an epistemological point of view, be used to indicate specific natures as taxonomic categories (taxa) which mediate the population structures of interacting individuals as indices in some respects (which respects, however, it is for genetics and never taxonomy to determine) of specific discontinuity: such usage, however, is always derivative and secondary, for " the evidence is usually morphological, but to conclude that one therefore is using or should use a morphological concept of the category (not taxon) species [i. e., of the specific population as well as of the taxonomic class] is either a confusion in thought or an unjustified relapse into typology."24 Moreover, (1) since the metalogical species concept is itself a collective concept englobing the multidimensional dynamics of population behavior, what the taxonomist must seize on as a specifying " property " is never a unit formal difference but an aggregate of morphological characters which taken together are distinctive. In doing so, because he employs a concept which is in itself indifferent to the pure line of intelligibility and bears consequently no immediate reference to the possible distinction
24 George Gaylord Simpson, Principles of Animal Taxonomy (New York: Columbia, 1961), p. 150. See Mayr's comments in Animal Species and Evolution, pp. 27-9, on the problem of classifying a-sexual organisms, where " arbitrariness and subjectivity cannot be avoided." (Further references in fn. 151 below.)
of substantial from accidental beings (both separable and inseparable) , and of these from property (as necessary accident), he is concerned with evidence for the distinction of natural kinds, as Simpson points out, only so far as it is susceptible of judgment " in the light of known consequences of the genetical situation," i.e., the situation of generation, " stated in the definition [of the ecological population]." 25 This amounts to saying that the metalogical species concept employed from a logical (taxonomic) point of view and in the perspective of reasons for being biologically considered (as resulting in discontinuities between populations) refers to natural entities which differ in kind without being concerned to further discriminate whether that difference in kind is only apparent 26 or real, either radical (as defined above), or superficial. By way of contrast, then, just as the traditional species problematic was centered on the discrimination of natural kinds which were such both in the order of existence exercised and in the pure line of essence considered in itself, so the evolutionary species
25 Ibid.
26 The terms here introduced must be defined at least nominally and as they will be used throughout this essay. In Section VIII, these definitions will be correlated with and justified in terms of the possible modes of difference. At that point we will also justify our equation of " radical kind" with the traditional notion of " essential kind," and per consequens of " accidental kinds" in the traditional sense with both apparent and superficial differences in kind. The definitions are as follows. (1) Apparent difference in kind: When, between two things being compared, the difference in degree in a certain respect is large, and when, in addition, in that same respect, the intermediate degrees which are always possible are in fact absent or missing (i. e., not realized by actual specimens), then the large gap in the series of degrees may confer upon the two things being compared the appearance of a difference in kind; really they differ in degree and not in kind. (2) Superficial difference in kind: An observable or manifest difference in kind may be based on and explained by an underlying difference in degree, in which one degree is above and the other below a critical threshold in a continuum of degrees. (3) Radical difference in kind: An observable or manifest difference in kind may be based on and explained by the fact that one of the two things being compared has a factor or element in its constitution that is totally absent from the constitution of the other; in consequence of which the two things, with respect to their fundamental constitution or make-up, can also be said to differ in kind.
These preliminary definitions are taken from M. J. Adler's analysis of the modes of difference in The Difference of Man and the Difference It Makes (New York: Holt, 1967), pp. 15, 19-35, and 60-65, esp. pp. 23-5.
problematic is centered on the discrimination of natural kinds which are such in the order of existence exercised, without regard for the pure line of essence taken in itself. Additionally (2) speaking in the traditional language, and still for purposes of contrast, natural kinds of the first sort would have to be referred to as " essential natural kinds" and constitute an exclusive category; natural kinds of the second sort, indifferently apparent or real in either sense, would have to be referred to as " accidental natural kinds" and constitute an inclusive category.
Thus the real existence of natural kinds depends, for evolutionary science as for traditional philosophy, on induction " so far as it is a process of inferring from observable particulars generalizations about the articulations of nature "; but now it is a question of beings really distinct only from the standpoint of relatively constant and peculiar attributes which when taken as an aggregate " typify " an ecological unit by reference to the genetical situation of its individual members.
So far as accidental natural kinds are concerned . . . the inductive principle is derived from the character of accidental differentiation and definition. Since differentiation [of this sort] involves positive differences rooted in contrary perfections [i. e., any distinct respect in which the being of a thing or the understanding of it can be completed or made more determinate], and since each of these positive differences is conjoined with a generic term signifying a distinct perfection, the evidence for an accidental natural kind would consist, in the simplest case, of instances which show a constant conjunction of two traits, combined with instances in which the contrary of one of these traits is conjoined with the trait that appears to be generic. . . . In their taxonomic inquiries, the empirical sciences deal, for the most part, with more complex cases in which the accidental definition, to be tested or established inductively, consists not of one generic term and one positive difference, but of a genus combined with a number of positive differences which are supposed to signify inseparable traits. The problem is not whether the trait signified by the genus is always accompanied by the traits signified by the set of differences, but whether when it is accompanied by one of them, it is also accompanied by the others that are proposed by the definition as being co-present . . . the accidental definition in question asserts that in
a certain natural class of things there is a natural sub-class constituted by a number of inseparable traits. . . . Furthermore, since each sub-class is determined by positive differences each signifying the possession of a distinct trait, there need not be only two subclasses within a given class. In the accidental order, a genus can have more than two species, the differentiating traits of each being as a set contrary to the sets of differentiating traits in all the others.27
We may complete our parallel contrast here by pointing out what notion of hierarchy is necessarily bound up with the existential constitution and consequent ordering of individuals as genetic members of ecological populations. Because the logical species concept employed derivatively from an ontological point of view regards only things radically different in kind, it orders species according to what are properties with a strictly ontological status in the metaphysical composition of essences. Since properties in this sense are convertible with the formal perfection which establishes a radical kind in and as its grade of being, and grades of being differ as higher and lower by a unit difference, the species of the traditional problematic (however many or few) constitute an order of species which is necessarily a unilinear hierarchy, " a perfect hierarchy of specific natures, in which each member is, in essential grade of being, higher or lower than a proximate inferior or superior, and in which no two specific natures are of coordinate grade in any respect except that in which all corporeal substances are of the same grade, namely, as corporeal (i. e., as falling within the same natural genus, signified by the presence of prime matter in their substantial composition)."28 (At the same time, it must be noted that these levels or grades of being existentially considered had no absolute limits but defined probability zones for statistical variations 29).
By contrast, because the metalogical or biological species concept employed derivatively from a taxonomic point of view regards whatever things factually differ in kind in any one or
27 Adler, " The Hierarchy of Essences," pp. 27-8.
28 Adler, " Solution of the Problem of Species," pp. 285-6.
29 De Koninck, Le Problรจme de I'Indรฉterminisme, p. 126. Cited in Adler, The Problem of Species, pp. 80-82.
combination of the three possible modes of difference, it orders species according to whatever characteristics in the aggregate are revealed as proper to a population in the light of what is known of its genetical situation. When the groups so ordered are arranged in a taxonomic hierarchy, the generic levels interrupt the specific orderings no matter how these are set up among themselves; and against the generic background of the taxonomic hierarchy, moreover, the specific or natural groupings may be variously ordered but never in such a manner that that the natural kinds are each one higher or lower than some one other, which is its proximate inferior or superior. Thus the taxonomic hierarchy of evolutionary science, derivatively based on the metalogical species concept, involves, like the ontological hierarchy of traditional philosophy, derivatively based on the logical species concept, four principal notes, contrasting almost point by point with the principal notes of the perfect hierarchy:
1. in some cases the natural kinds are related coordinately in a genus, as contraries are: this is consequent on the fact that their specifying properties are related as contraries;
2. in some cases, the natural kinds are related as higher or lower than one another, but in a scale of continuous degrees of the same difference: this is consequent on the fact that two natural kinds may have the same specifying properties but in different degrees;
3. in some cases, the species are ambivalently related as higher and lower than one another in different respects: this is consequent on the fact that each of two natural kinds may possess and lack specifying properties respectively lacked and possessed by the other;
4. ambivalently related species may also be coordinate in other respects without contrariety: this is consequent on the fact that they may also possess certain characteristics in common, while differing in others.30
30 Cf. Adler, The Problem of Species, pp. 125-6: " It should be noted that the cause of these four types of ordering,--contrariety, continuity, multilinearity and coordination, all of which are incompatible with [perfect] hierarchy--is the same in each case. But that there are four types of ordering here--in contradistinction to the unity of hierarchical ordering--is due to the fact that the specifying ' property ' is never a unit, but an ' aggregate of properties.' Though the properties of any one species are a constant aggregate, inseparable from that kind of substance, the members of a given aggregate are not all related to the members of an aggregate specifying another substance in the same way. Because of the fourfold diversity of relationships among the members of such aggregates, there is a fourfold ordering of substantial species. These four types of ordering are not exclusive of one another; nor are they necessarily combined. In different respects, two species may be related in all four ways; or only in one, or two, or three.
" Furthermore, this fourfold ordering of species does not mean that one group of species may not be hierarchically related to another group, for it is not inconsistent if their genera constitute a hierarchy. Thus, for instance, all plants, generically, as plants, may be hierarchically inferior to all animals, considered generically; and this may be true even for subordinate genera of plants or animals, although as a matter of fact the latter truth may be more difficult to evidence. But that is not the point here being affirmed. It is rather that, within any proximate genus, the species, considered as species of that genus, are susceptible to a fourfold ordering, and are not hierarchically disposed."
If, then, one contrasts the two species problematics in terms of hierarchy alone, their different preoccupations leading to different results emerge rather clearly:
If manifold differentiae are employed, instead of single differentia, two items may each be superior and inferior to the other in different respects. If one tries to order a set of items, which are distinguished inter se by manifold differentiae, no single arrangement of them is possible. There will be several ways of ordering them as lower and higher in being, according to the particular characteristics chosen. I call this the fact of multilinear, in contrast to unilinear, ordering. A hierarchy is imperfect if it is subject to generic interruptions and multilinearity, [and] a hierarchy of accidental terms is necessarily imperfect in both these respects.31
Thus modern evolutionary science differs from Darwin, on the one hand, by affirming the reality of species as non-arbitrary articulations of nature; but it differs, on the other
31 Adler, " Solution of the Problem of Species," fn. 57 pp. 323-4. For the reasons why a hierarchy of accidental terms--superficial and merely apparent kinds--is necessarily imperfect in both these respects, see ibid., fn. 122 p. 367; also The Difference of Man and the Difference It Makes, p. 57; and A. O. Lovejoy, The Great Chain of Being (Cambridge, Mass.: Harvard, 1948), pp. 253-4, 269-70, 275-7.
hand, from Aristotle as well, by denying the possibility of an all or none aspect of specific differentiation.
The reconciliation between Darwinian evolutionary science and Aristotelian philosophy, for reasons we have seen, was a hopeless and impossible task. Their incompatibility, as Dewey suggested, was direct and absolute. Between post-Darwinian biology (contemporary evolutionary science) and Aristotelian philosophy, however, there lies a difference of primary and secondary contexts, or if you like, an inversion of primary and secondary questions.
From this it is clear that if the evolution of species ascertained by modern science does indeed illustrate a fundamental incompatibility between that science and traditional philosophy, it does not do so in the direct and straightforward manner that it seemed to do when Dewey assessed " the influence of Darwinism" in the first half of our century. It is certainly naive of any contemporary writer assessing the concept of evolution in philosophy to flatly affirm, as Oliver Reiser does, that " Dewey is certainly correct in his analysis, in his early essay (1910) on ' The Influence of Darwin on Philosophy.' "32
It may be, of course, when the complex differences we have outlined separating the primary concern of traditional natural philosophy and of modern natural science with respect to species are all accounted for and seen in the light of their mutual ramifications, that a fundamental incompatibility--a mutual negation, in effect--may stand out. That is the question which will occupy the rest of our analysis.
II. Approach to the Problem
The problem we have set ourselves seems to me to involve several distinct facets or phases of analysis, related to each other in such a way that each arises in terms of the previous one. First of all (Sec. Ill), it is necessary to come to terms with
32 Oliver L. Reiser, " The Concept of Evolution in Philosophy," in A Book That Shook the World, Anniversary Essays on Charles Darwin's " Origin of Species," Ralph Buchsbaum, ed. (Pittsburgh: University of Pittsburgh Press, 1958), p. 38.
Dewey's contention that the logic immanent to traditional philosophy and the order of questioning which it imposes are together " outlawed, flanked, dismissed--what you will " 33 by the " genetic and experimental logic "34 immanent to " the Darwinian mode of thinking."35 Is the bearing of " Darwinian ideas," of species as products of processes, upon philosophy such that it " dismisses one type of problems and substitutes for it another type? "36 Is this what is implied in our sketch of the inverted concerns of traditional philosophy and modern science with respect to species?
If our answer to this question is affirmative, then our central problem of whether the evolution of species illustrates a fundamental incompatibility between traditional philosophy and modern science will be settled, and we may get on with the task of radical " reconstruction in philosophy." If our answer is negative, then before any attempt to mediate between the differently posed species problematics of traditional philosophy and modern science, it will be necessary to state clearly the theoretical framework which underpins the modem species concept and problematic, and to show how this framework incarnates in its own way the logic of rational understanding formally delineated in the preceding stage (Sec. IV).
We will then be in a position to state the contemporary species problem in its own terms (Sec. V), preparatory to an attempt to take up the implications of the reality of specific structures as modern biology delineates them, in order to see whether it is in fact a reality too dark for the illuminative power of the essential principles of the metaphysics and natural philosophy of the scholastic tradition (Sec. VI) . Rather than contrast the results worked out within two altogether differently specified problematics, such as the ancient and modern species problematics are, in order to judge earlier conclusions on the basis of principles heterogeneous to those conclusions, it
33 John Dewey, " The Influence of Darwinism on Philosophy," p. 13.
34 Ibid., p. 18.
35 Ibid.
36 Ibid., p. 13.
would seem more useful (and more genuinely philosophical), in short, to work the other way round and see if the fundamental categories of traditional ontology, rather than particular conclusions, can be shown to be adequate to the implications of the modern way of stating the issues. Only then will we be in a fair position to adjudicate whether or not the data of evolution are thinkable only by some kind of process philosophy which abandons hope of any transcendent or metaphysical perspective in the traditional sense of the term.
This will be the most difficult phase of the analytic. In order to carry it through, we shall have to essay a hylomorphic analysis of the structure of interaction in terms of what can be said at the level of existence exercised prior to any analysis of the pure line of essence taken in itself--that is, without first answering definitely questions about the constitution, order, and number of radically distinct natural kinds. Novel and difficult as such a task must prove, there is no other way to mediate between the contemporary and traditional species problematics other than by a concrete proof that both can be stated analogically within the traditional categories of philosophy. By transposing the traditional question of essence onto the level of the structured exercise of existence, moreover, we may expect to gain a fresh angle on the traditional problem of subsistentia. The reason for this should be clear:
If the word " essence " be used to signify what is the proximate subject of the act of existence, then, in the case of composite substances, essence as the subject of existence must be the individual nature rather than the specific nature. In other words, in the case of composite substances, essence as the quiddity or principle of intelligibility, and essence as the proximate subject of existence, are not the same nature. . . .37
We should also find ourselves, thanks to this same transposition, in a position to show that the projected disproportion supposedly involved in the causal succession of " higher " from " lower " forms is a one-sided and misleading problematic, a
37 Adler, The Problem of Species, p. 18, text and fn. 6.
caricature in fact of the Aristotelian-Thomistic understanding of the reciprocal activation of causes. The actual coming to terms with this " higher from lower " causality problematic, however, will have to be delayed in our analytic until we reach the point where the modern species problematic re-engages through its secondary implications the central concern of the traditional problematic (Sec. VIII).
To this end it will be appropriate to consider the contribution of mathematics to the contemporary formulation of the species problem (Sec. VII), showing how the effective assessment of the workings of natural selection entails an arrangement of natural kinds in an overall hierarchy, and does so ineluctably; from here it is an easy transition to the traditional problematic of radical natural kinds, and thus, from the very heart of the modern species problem by a line of continuous analysis, we shall arrive at the problem of the two hierarchies, the point where the traditional preoccupations become meaningful against the backdrop of modern preoccupations (Sec. VIII).
We will then be in a position finally to answer our guiding question as to whether the evolution of species illustrates any alleged incompatibility between modern science and traditional philosophy (Sec. IX).
III. The Logic of Rational Understanding
It is both startling and interesting to find Dewey point out, on the one hand, that in seeking a logic of science " there are but two alternative courses: we must either find the appropriate objects and organs of knowledge in the mutual interactions of changing things; or else, to escape the infection of change, we must seek them in some transcendent or supernal region ";38 and then, on the other hand, to single out Aristotle and the scholastics who followed him as the prime example of men following the latter course.
As a matter of the scholarship proper to philosophical
38 John Dewey, art. cit., pp. 6-7, Dewey's own emphasis.
history, it is not difficult to show that such a view entirely misses the doctrinal differences between the Platonic and Aristotelian explanatory modes.39
But--what is more fundamental--it is necessary to say that such a view betrays a misunderstanding of the Aristotelian Organon that is almost total. What Aristotle essayed was in fact a delineation of the necessary steps involved in the securing of a rational understanding in the mutual interactions of the beings of nature. And ever since Aristotle, " the scientific study of natural objects has always followed the procedures of methodological behaviorism for the simple reason that no other procedures are possible "--except in myth-making--though " the word ' behaviorism' itself is new and dates from the time when students of man decided to forsake introspective methods."40
What Adler is here referring to as " methodological behaviorism " is Aristotle's doctrine of scientia (rational understanding, be it scientific or philosophical) as reasoned facts, a doctrine articulated in terms of the four scientific questions and the four causes.41
Since our concern here is with the logic of rational knowledge of nature simply for the purpose of demonstrating that there is
39 See the essay " Evolution as World-View and as Philosophy," esp. Section II, A-H, in The Problem of Evolution: A Study of the Philosophical Repercussions of Evolutionary Science, by Raymond J. Nogar and John N. Deely (New York: Appleton-Century-Crofts, 1970) . Also R. J. Nogar, The Wisdom of Evolution (New York: Doubleday, 1963), pp. 315-6. See also Richard McKeon, " Aristotle's Conception of the Development and the Nature of Scientific Method," Journal of the History of Ideas, VIII (January, 1947), pp. 3-44. We will return to this point in the present essay at fn. 85 below.
40 Adler, The Difference of Man, p. 150.
41 See Aristotle's Analytica Posteriora, esp. Bk. I, ch. 13, " The difference between knowledge of the fact and knowledge of the reasoned fact"; Bk. II, ch. 1, " The four possible forms of inquiry," and ch. II, " The several causes as middle term." A brilliant exposition of the phases of investigation required for rational understanding is Benedict Ashley's " Does Natural Science Attain Nature or Only the Phenomena," in The Philosophy of Physics, V. E. Smith, ed. (New York: St. John's University Press, 1961), pp. 63-82. Further exemplification may be found in William A. Wallace, " Some Demonstrations in the Science of Nature," The Thomist Reader, 1957, pp. 90-118.
no " new logic " implied by evolutionary thinking distinct from and opposed to the traditional philosophical logic, it will suffice to provide a formal summary of the set of questions which Aristotle discriminated as necessarily and sequentially involved in the development of a rational comprehension of any aspect of reality whatsoever, and it will be easy in terms of this formal exposition to show in the next section that evolutionary science has in fact unfolded and is progressing along the lines of inquiry and according to the stages marked by Aristotle. Since this has also been true of traditional natural philosophy, it will be clear that whatever be the reason behind the divergent orientations of the ancient and modern species problematics, it is certainly not a consequence of some potent " new logic " dismissing the problems of the " old logic " and substituting for them a diverse type of problem.
Keeping with Adler's phrase for economy, we may say that, according to the notion of methodological behaviorism, there are only four possible questions implied in the attempt to gain adequate rational knowledge of anything at all, and their sense is such that each by being answered poses the next one. These four questions may be stated thus: 1) Does a possible subject of investigation exist (an sit) ? 2) What is it (quid sit) ? 3) What is unique or distinctive about it (quale sit) ? 4) Why is it as it is (propter quid sit) ?
The sense of these four questions and the rationale of their sequence may be stated as follows.
The first of these questions requires that one isolate a subject for investigation. It is mainly a descriptive question. In responding to it, we move through four steps, from an observation of something, to a consideration of the activity which produced or sustains the object, to a postulation of a power or faculty which gives rise to the activity, to a recognition of a nature in which the preceding three are finally rooted. Thus, regularly occurring processes of change and stability are the sign of a natural kind or unit.
Once we know that there is a subject of possible investigation we proceed to an initial determination of what it is. Thus the
second question is a demand for classification of the isolated subject and entails essentially a comparative process in its answer.
In answering this second question, therefore, the third question automatically arises, because in any thorough classification we recognize not only the general features of a subject but also its unique features; and the more thorough our classification the more clearly does the distinctive character of the subject classified emerge. Thus the fourth question becomes possible: why does it differ as it does?
The answer to the fourth question is the most difficult, by virtue of the principle that " the simplicity or complexity of a question derives from the range of answers that can be given to it";42 and it alone constitutes scientific or philosophical knowledge in the strictest sense. Its answer constitutes an explanation in the full sense, because it involves the assignation of reasons for being. In the order of nature, however, such reasons are always four, so that, from the standpoint of possible answers, the fourth question is never simple but itself a complex of four questions, which may be simply expressed thus: 1) What is it made out of, or, what is its composition? 2) How is it put together, or, how is it organized? 3) What agents are involved in its production and modification? 4) By what activities does it sustain itself and what are its developmental stages, or, what are its typical modes of behavior?
The " reasons for being " called for by these questions were the Aristotelian meaning of cause in the general sense and were named specifically the material, formal, efficient, and ' final'43
42 Adler, The Difference of Man, p. 19.
43 Cf. J. H. Randall, Aristotle (New York: Columbia, 1962), p. 229: " 'final causes,' as they were developed during the predominance of the religious traditions, tended to become a way of showing how under the ministrations of God's providence everything in the universe conduces to the self-centered purposes of man. In sharp contrast, Aristotle's natural teleology is, in the technical sense, wholly ' immanent.' No kind of thing, no species, is subordinated to the purposes and interests of any other kind. In biological theory, the end served by the structure of any specific kind of living thing is the good--ultimately, the ' survival'--of that kind of thing. Hence Aristotle's concern is always to examine how the structure, the way of acting, the ' nature," of any species conduces toward the preservation of that species, and enables it to survive, to exist and to continue to function in its own distinctive way. This Aristotelian emphasis on the way in which kinds of living things are adapted to their environment brings Aristotle's thought very close to the functional explanations advanced by evolutionary thinkers: in both cases the emphasis is placed on the survival value of the arrangement in question.
" It might be well to add, that such functional and Ideological conceptions are just the notions that modern biologists, no matter how ' mechanistic' their explanatory theory, actually have to employ in describing the subject matter they are attempting to explain. Teleological relations, the relations between means and ends, or ' functional structures,' are an encountered fact. Like all facts, they have to be explained in terms of certain mechanisms that are involved." Cf. further Ernst Mayr, "Cause and Effect in Biology," Science, 134 (10 November 1961), pp. 1501-1506.
causes, in that order. They constitute a factorial in contrast with a reductive analysis.
These are four kinds of reason, four kinds of answer, four necessary conditions--necessary for understanding the process: we need to know all four if we are to find it intelligible. Only one of the four, the By What, the agent, the efficient cause, is a " cause " in the popular sense today--if " cause " have any clear meaning in our ordinary language. The unfortunate neglect of the other three has been due to the dominance of mechanical thinking [and mathematicist explanation of nature] since the day of Newton, complicated by the popular heritage of Hume and John Stuart Mill.44
The essential nature of this factorial or " process " analysis was summed up by the ancients in the famous axiom, causae sunt ad invicem causae (" causes are causes one to another," or " causes are reciprocally active "). In this way, Aristotle and his followers, both Arabian and Latin, expressed their basic disaccord with Platonism and sought to replace sequences of simple causal or logical (and mathematically perfectly expressible) relations required in absolutizing Forms by organized causal or logical frameworks, which ideally and when complete should be self-contained in the sense of necessitating no reference to anything outside the system.45
44 J. H. Randall, Aristotle, p. 125: " It is worth noting, incidentally, that the empiricist notion of causation as constant succession, of ' cause' as the invariable antecedent of its effect, is wholly lacking in Aristotle."
45 Elsasser makes a comment which has bearing in this connection: " to introduce logical complexity on a purely abstract basis . . . brings us much closer to the preoccupations of the naturalist than we are in the absence of this idea, and it separates us to some extent from the more rigorous methods [but only in the sense of more formally reducible to mathematics and the style of causation mathematics allows for--see Sec. VII below] of the physical scientist."--Atom and Organism (Princeton: The University Press, 1966), p. 137.
It is important to see, in contemporary terms, that such factorial process analysis has a wider reference than the quantitative analysis of various material systems to which cybernetic or " feedback" ideas are applied;46 such insight depends on a clear grasp of the careful analysis essayed by the ancients of the ontological conditions for reciprocal activation of the causes. Just as their metaphysical analysis showed that the common condition of beings was such that they were both actual and potential under different formalities, so their analysis of physical interactions showed that the same reality can be both cause and effect under certain circumstances. Following Aristotle, Aquinas set the matter forth thus:
It must be recognized that as there are four causes, two of them correspond to each other because the efficient cause is the principle of change and the final cause the termination of change; and likewise the other two correspond to one another, for the form gives being and the matter secures being. The agent thus is the cause of the end, and the end, cause of the agent: the former is true as regards being, because in initiating motion the agent continues to the attainment of a term; while the later is true, not as regards being, but as regards the formality or intelligible character of causality, since the agent is cause insofar as it acts, but it acts only in a determinate fashion, and in this sense has its very causality from the term. Form and matter are causes in relation to each other and with regard to being: the form is the cause of matter by giving it existence, but matter is a cause of form in sustaining it.47
Thus, the ancients explained the circularity of natural causation by distinguishing. Causes are reciprocally active, are causes one to another, either according to being (as material
46 See R. J. Nogar and J. N. Deely, The Problem of Evolution, Section IV, The Metaphysical Issues, Third Reading, " The Shape of Biological Thought," by C. H. Waddington, and the Contextualizing Comments thereon.
47 In V Met., lect. 2, n. 775.
and formal cause), or according to becoming (agent in respect to determinate productions), or according to causality in its intelligible ground (as the effect or end product in respect to the agent). But not every combination of causes exhibits this circularity of reciprocal activation: only the end and agent (final cause by bounding the agent's efficacy, the agent by exercise) and matter and form (matter by sustaining form, form by actuating matter, so that in mutually communicating they have being as partial principles in the whole itself). In other combinations, causes need not be reciprocally active.
All this may be summarized in the simple observation that considered in their respective correlations, the four causes refer to the two aspects of every natural subject which must be accounted for in any adequate explanation, namely, its structure and its function; while to say that two things are correlated is merely to say that insofar as one implies the other they cannot be described separately.
Throughout its various stages, of course, methodological behaviorism requires governance by what we now refer to as the principle of parsimony or " Occam's razor," and what the ancients had no catch phrase for but expressed in the proposition " entia non multiplicanda sunt sine necessitate."48 In this respect, and in this respect alone, there has been a certain variation possible in the logic of rational understanding:
In the case of inert bodies, plants, and non-human animals, the procedures of methodological behaviorism have always been followed by natural scientists, ancient and modern, even though the principle of parsimony has not always been observed and though scientists of an earlier generation are usually regarded by more recent ones as having been fanciful or imprecise with regard to the powers or dispositions they attributed to inert or animate bodies. To say that the procedures of methodological behaviorism
48 See Bernard Wuellner's references to this under the " principle of economy" in Summary of Scholastic Principles (Chicago: Loyola University Press, 1956), nn. 35, 79, 291, 292. Two of Wuellner's formulations of this principle are of particular interest in our context: a) " distinctions between beings and constituents of beings are not to be multiplied without good reason "; b) " Hence, essential or real distinction is not to be affirmed without a clear sign." (p. 79)
have always been followed in the scientific study of natural objects . . . is misleading if it allows anyone to think that some other procedure might have been used instead. That is not the case: no other procedure is possible if it is to be scientific in character, and not just an adventure in myth-making.49
It is clear, then, that as modes of rational understanding, both science in the modern sense and philosophy (the ancients spoke simply of scientia naturalis) must subscribe to so-called methodological behaviorism as the immanent logic of rational understanding. From one point of view, there can be no difference between a philosophical analysis of nature and a study of nature in the scientific sense: all explanation, when it is not mathematical, assigns reasons for being.
Yet from another point of view, there is a sense in which natural philosophy and natural science do subdivide the order of rational knowledge of nature. The question of the difference between philosophy and science and of the relations which their respective explanations sustain is a difficult one which, perhaps more than any other, has exercised contemporary reflections. It is not even agreed among those who treat this question that philosophy constitutes a mode of rational understanding in its own right; but I think that once it is seen that, with respect to the sensible, natural world, just as there are some questions for which laboratory or field research is indispensable (e. g., how does photosynthesis take place? what is the average life-span of a star? or are there extinct life forms?), so also there are other questions for which such research is adventitious (e. g., what is change? what is chance? how does chance differ from fortune? what is place? in what sense do relations exist?), then it is necessary to admit that (a) in relation to experience science and philosophy differ between themselves according to the manner in which their respective explanations depend thereon, and that (b) both belong to the order of rational understanding, sharing formally in an identical set and sequence of questions.50
49 Adler, The Difference of Man, pp. 149-50.
50 We should recognize, too, that not all questions can be assigned preclusively to either science or philosophy; there are also, so to speak, " hybrid" questions, questions for which laboratory or field research are superfluous in certain respects and helpful in others--such questions as, what is good for man? what role does chance play in the constitution of the world? or our own problem, what are the natural kinds of common experience?
This assertion depends, of course, on there being a real analytical distinction between knowledge and experience. That there is such a distinction is plain from the fact that experience functions both as a source and as a test of our knowledge in both philosophy and science, which would be impossible if the two were not somehow distinct. In fact, this difference between experience and knowledge lies at the base of rational understanding, inasmuch as it defines the respective spheres or orders of observation and explanation.
Thus, according to Aristotle and traditional philosophy there is only one logic of rational understanding and only one set of possible questions which this logic imposes. All inquiry takes its start in discovery and finds its realization in the assignation of reasons for being. Of course, one cannot determine in advance the content of the answers possible by a purely formal assessment of the eight possible questions: that depends on the structure and diversity of the universe, which is practically infinite. From the side of its content or matter, mankind's knowledge is so extensive that it mocks encyclopedias and overflows libraries; so difficult that a man does well to devote his life to mastery of some part of it; and so incomplete and inadequate that it is subject to endless additions and repeated revisions. But from the side of its form, we have in Aristotle's four scientific questions and four causes the vindication of Bernard Lonergan's contention, " thoroughly understand what it is to understand, and not only will you understand the broad lines of all there is to be understood but also will you possess a fixed base, an invariant pattern, opening upon all further developments of understanding."51
51 Bernard J. F. Lonergan, Insight (rev. ed.; New York: Philosophical Library, 1958), pp. xxviii and 748. Maritain observes that " from this point of view it may also be said that the work which metaphysics is called upon to do today is to put an end to that kind of incompatibility of temper which the humanism of the classical age had created between science and wisdom." (The Degrees of Knowledge, p. xi)
Dewey could well point out that with certain qualifications, " the influence of Darwin upon philosophy resides in his having conquered the phenomena of life for the principle of transition "; but it is noetic nonsense to speak of Darwin as having " thereby freed the new logic for application to mind and morals and life." 52 To demonstrate this it will be sufficient to assay the historical development and theoretical structure of evolutionary biology. To that assay we may now turn.
IV. The Framework of Evolutionary Science
According to the Aristotelian schema, the history of evolutionary biology, like that of any other science, must have passed through three analytically distinguishable phases recognizable in terms of principal (not exclusive) preoccupation successively with the first three " scientific questions," before it reached an incipient maturity wherein reasons for being became the dominant concern. And the extent to which the science at a given time conducts its inquiry into causes along all four of the possible lines will in turn be an index of its degree of maturity. It would be possible to draw an analogy between the predominantly fact-finding phase of the science (an sit) and its " infancy "; between the phase preoccupied especially with classifications and definitions (quid sit) and the " childhood " of the science; between the brief phase where the distinctive difficulties to be explained come into focus (quale sit) and the " adolescence " of the science; and between the phase where the science organizes research along the lines of the difficulties in search of their proper explanations (propter quid sit) and the " adulthood " of the science.
This analogy is the more helpful if we realize that even as infancy conditions childhood and childhood adolescence, so even as adults what we are and do remains conditioned by the previous stages. So also in the work of rational understanding. No stage is ever completely surpassed, but different questions come into dominance.
52 " The Influence of Darwinism on Philosophy," pp. 8-9.
Such, according to the " old logic," is the order of questioning leading to rational knowledge of the natural world, including man. In the rise of evolutionary science, do we find this immanent pattern confirmed, or do we find it supplanted by a " new logic " which substitutes another type and pattern of problems entirely?
For the sake of brevity, and because our main interest is philosophical rather than historical, I think we are justified at this point in taking as our object of analysis a summary of the development of evolutionary science made by one of the authorities in the field, in lieu of an extended treatment of the primary sources which would deflect too far the thrust of our proper analytic.
I have in mind for our purpose a brief text by Sir Julian Huxley,53 which will carry us up to the fourth of Aristotle's questions. Huxley introduces his " brief methodological divagation " thus:
The method of approach to any scientific problem is clearly of extreme importance, and will to a large extent determine the type of discovery made. Putting the matter the other way round, the method of approach is itself largely dictated by the type of answer you want to obtain: it is, in fact, a kind of question. Furthermore, the question will alter with time and with the progress of discovery: when one method has yielded the main crop of answers that it could be expected to provide, it is time to ask another kind of question, by adopting a new method.
He then goes on " to summarize the various methods of approach adopted in biology." In this summary, it is not hard to discern the immanent pattern of rational understanding, of Aristotle's four questions.
The question, An sit?:
The original approach inevitably was descriptive: biologists set out to describe as fully and accurately as possible the variety of organisms and the phenomena which they exhibit. This approach is designed to answer the basic question, What are the facts?
53 Julian Huxley, " Evolution, Cultural and Biological," in Knowledge, Morality, and Destiny (New York: Mentor, 1957), pp. 56-84. The cited passages are taken passim, from pp. 68-70.
The question, Quid sit?, in biology was developed in two phases, first on the supposition of the absolute fixity of forms, and then, when classification ceased to be possible on this basis, on the supposition of the fluidity of forms. The important thing to note here is that it was the attempt to answer this classification question that forced the abandonment of the Porphyrian-Linnean classificatory systems and not the introduction of any " new logic " opposed to the pattern Aristotle discerned at the base of rational progress in understanding.
a) The descriptive approach was soon supplemented by the comparative. This was first focussed round the question of grouping or classification. What pattern or system of characters does an assemblage of organisms have in common; and what distinct types are there at the various levels of characterization? This led to the classification of organisms in a hierarchical system of groups--species grouped in genera, genera in families, families in orders, orders in classes, and so on.
b) Implicit in such a system was the idea of physical relationship. With the acceptance of the fact of evolution, this implicit postulate became explicit, and the question posed by the comparative method became correspondingly altered; behind common patterns, men were reaching for common origins. The result was a phylogenetic classification intended to express evolutionary descent and relationships rather than just a convenient pigeonholing system. The animals placed in the order of Carnivora, for instance, were all presumed to be descended from a single common carnivore ancestor, and a common mammalian ancestor was postulated for them and all the other orders placed in the class Mammalia.
Once the phylogenetic character of taxonomic divisions was recognized and the materials rearranged accordingly, the third question, Quale sit?, leading to the search for causes, automatically emerged: " However, while common ancestry accounted for the shared resemblances of a group, the problem of the differences exhibited by its members remained."
Thus began the search for reasons for the facts, Propter quid sit?, as a dominant phase of evolutionary inquiry:
For this, a new method of approach was needed, a method which we may call that of differential analysis. It asked the question,
What is the cause of the differences between the members of a group? . . . However, there are limits to the usefulness of such differential analytic methods . . . we must utilize other methods of approach--constitutive as well as differential, integrative as well as analytic.
What Huxley here refers to as constitutive, differential, integrative, and analytic methods of approach to the question of the reasons for the differences within biological populations are in fact organizing evolutionary explanations according to the formal pattern of Aristotle's four causes. This is perhaps most easily seen in C. H. Waddington's analysis of the entire process of evolution as the intersection of four main sub-processes.54 According to Waddington, further developments of evolutionary theory require incorporating a circular concept of causality, consisting, as he explains, of four basic systems: the genetic system, corresponding analogously to Aristotle's sense of material cause; the epigenetic system, corresponding to formal cause; the natural selective system, analogous to efficient causality; and the exploitive system, corresponding to Aristotle's final cause. " Most biologists at the present day, in expounding evolutionary theory, seem to be content to leave it that the mechanism by which evolution has been brought about is composed of these two major factors: the genetic system with random mutation on the one hand and natural selection on the other. The evolutionary pressures exerted by these two factors are exhibited as being quite external to the nature of the organisms involved."55 " Now, with such a
54 See C. H. Waddington, " Evolutionary Adaptation," in The Evolution of Life, Vol. I of Evolution After Darwin, Sol Tax, ed. (Chicago: University of Chicago Press, 1960), pp. 381-402. Also " The Biological Evolutionary System," Ch. 9 of The Ethical Animal (New York: Atheneum, 1961), pp. 84-100. Today, notes Waddington (" The Biological Evolutionary System," p. 96), " the recent developments of neo-Mendelian evolutionary theory, which have often been referred to by their adherents as the ' synthetic ' theory "--sometimes, too, as the neo-Darwinian theory--" have merited that title mainly because of the wide range of the ' evidences for evolution' for which they could account, rather than for any tendency to exhibit the various factors involved in the evolutionary process as aspects of a unified general system."
55" The Biological Evolutionary System," p. 88 (see full reference in fn. 54 immediately above).
mechanism," Waddington continues, " it would appear difficult to find any principle which would produce any specific direction of evolutionary change. All evolution would appear to be a purely contingent phenomenon, which just happened to go the way that it did. . . ."56
" In my opinion, biology has already made all the discoveries of matters of principle which can be reached by this way of formulating the situation. The time seems to have come when we need to take into account two further aspects of the evolutionary mechanism,"57 namely, the " epigenetic system, which translates the information in the fertilized egg and that which impinges on it from the environment into the characters of the reproducing adult," and " an exploitive system, by which an animal chooses and modifies the environment to which it will submit itself." 58
" Biological evolution, then, is carried out by an ' evolutionary system' which involves four major factors," not two.59
This formulation of the nature of the evolutionary system incorporates all the features which have been shown to be essential by modern genetics, and brings into the picture nothing to which present day biology can take exception. However, by drawing attention to factors which are often somewhat neglected, and changing the emphasis on others, it issues in an outlook which is of a very different type from that which has been conventional in the
56 Ibid., p. 89. See the discussion in Section VII of this present article.
57 Ibid. See Section VII below.
58 Ibid., pp. 94-6. " Very much remains to be done in working out the theory of evolution from this more inclusive point of view. But one general point is already clear. We can now see that the system by which evolution is brought about has itself some degree of organisation, in the sense that its subsystems are mutually interacting, and, in fact, mutually interdependent. In the recent past we have been working with a theory in which the obvious organisation of the living world had to be engendered ab initio out of non-organised basic components--' random' mutation, on the one hand, and an essentially unconnected natural selection on the other. We had to rely on a Maxwell demon, and persuade ourselves not merely that natural selection could show some of the properties of such a useful deus ex machina but that it had them so fully developed that we needed nothing further. This was a rather uncomfortable position, and we can now escape from it." See Randall's discussion of final cause and the reference to Mayr cited in fn. 43 above, and the discussion on reductionism in Section VII below.
59 Ibid., p. 94.
last few decades. The theory of evolution, and indeed the whole of biology, has always provided a battleground for two rather contrasting methods of analysis. On the one hand, there is the tendency toward what may be regarded as, in a broad sense, ' atomicity '--an analysis into entities which are independent of one another in their essential nature, and which have, when they interact, only external relations with one another. The alternative approach expects to find that it is dealing with organized systems, in which the factors determine, at least in part, each others' essential characters, and enter into cyclic interaction-systems involving internal relations.60
It would be a mistake to consider that what is being asserted here is an explicit recognition on Waddington's part of an Aristotelian pattern as the necessary form of evolutionary theory.61 It would be an even greater misunderstanding to regard the equation of Waddington's genetic, epigenetic, natural selective, and exploitive systems with what Aristotle termed material, formal, efficient, and final causes as some sort of " concordism."
In fact, it would be impossible to show an equivalence between an empirical formulation and a purely formal pattern, for what is empirical is just what is not or at least is no longer purely formal. The point of the formal notion of the four causes is that they name a set of relationships necessarily involved in any phenomenon whatever as understandable. Whether one takes as one's focus of inquiry society, the human person, the extraterrestrial objects of astronomy, patterns of culture--it is
60 Ibid., p. 96.
61 In fact, there seems no reason for thinking he is at all acquainted with the Aristotelian treatises on methodology. Waddington finds no perfect parallels of the direction of his thought. In " the type of thinking which I suggest is called for in evolution theory," he writes, " the contrast is not so much between mechanism and vitalism, but rather between mechanism and organicism. Or possibly one could even use the Marxist terms, mechanical materialism and dialectical materialism. The view which I am urging . . . is much more in tune with the thought of Whitehead than with that of Driesch or Bergson." (Ibid., pp. 99-100). Waddington is plainly groping here. My point is that the Aristotelian method provides exactly the parallel he is groping for. Cf. Randall, Aristotle; and Ashley, " Change and Process," Second Reading in Part II, Sec. IV of The Problem of Evolution by Nogar and Deely. Also Ashley's " Does Natural Science Attain Nature or Only the Phenomena? "
impossible to arrive at an adequate formulation without detailing " structure " (with its correlative " composition " and " organization "), which is the immediate referent of cause as material and formal; and " function" (with its correlative " agent " and " product "), which is the immediate referent of cause as efficient and final.
Thus when we are told that " in modern evolutionary studies, concern has shifted from the organism as a describable object to the more sophisticated view of it as a morphological expression of the genetic and environmental status of an evolving population"62 (for the very good reason that " in sexual organisms," which are the majority by far, " Mendelian populations, rather than individuals, have become the units of the adaptively most decisive forms of natural selection "63), it is certain that these populations, in order to be intelligible, must be seen as possessing a structure and typified by a function, involving composition, organization, activities, and determinate results; and that none of these aspects may be left out or treated as peripheral if our understanding as rational is to be adequate to the reality.
But this is exactly the point of Waddington's formulation of biological evolution as involving four major factors, not just two.
Moreover, the fact that in modern evolutionary studies concern has shifted away from the organism as a describable object should not be used--as it unfortunately sometimes is-- as a flight from the organism as a describable object rationally intelligible in its own right as structured and functional; for as a matter of fact, the whole element of necessity in the view of populations as evolving devolves upon the structural stability of the organism " as a describable object." In short, populations are labile only by reason of the fact that the individual organism taken as such is stable.
62 Glenn L. Jepsen, " Foreword " to Genetics, Paleontology and, Evolution, edited by Jepsen, Ernst Mayr, and George Gaylord Simpson (New York: Atheneum, 1963), p. ix.
63 Dobzhansky, Genetics and the Origin of Species, p. 260.
Since the whole character of evolutionary studies as scientific depends on this point (science, after all, is of the necessary: that is what it means to assign causes--to see why the facts are as they are and not otherwise 64), it is important to be clear on what is at issue here, before passing on to a statement of specific structures in an evolving world.
When Waddington tells us that to take explicit account of the epigenetic and exploitive systems is a matter of changing the emphasis on the factors natural selection and mutation by drawing attention to neglected factors and of seeing why the automatic character of the evolutionary process is not external to the nature of the organisms involved, I think he is doing no more than recalling that the rational explanation of the individual organism as a morphological expression of the status of an evolving population logically involves the possibility of a rational understanding of the individual organism as a describable object which is the subject of processes. Put otherwise, if the individual organism as a describable object is the morphological expression of an evolving population, then that individual organism itself must be rationally intelligible as undergoing constant change. But in any such analysis it will
64 Moreover, for those philosophers who flatly assert " there is no science of the singular " (usually, it is worth adding, philosophers who hold for a large number of infima species in the scholastic sense), it is worth pointing out that in the first place, " nihil est adeo contingens, quin in se aliquid necessarium habet" (Summa, I, 86, 3) --which translates, " there is nothing so contingent that it has no aspect under which it may be seen as necessary" (another way of saying that the principle of causality holds absolutely throughout the order of finite being)--and in the second place, ubi necessitas, ibi scientia possibilis. See the remarks on this connection hi " Evolution as World-View and as Philosophy," esp. sec. C, in The Problem of Evolution by Nogar and Deely. In the particular context of biological evolutionary theory, for example, Dobzhansky points out that today, " biology not only recognizes the absolute individuality of every person and every living being, but in fact supplies evidence for a rational explanation of uniqueness " (Mankind Evolving, New Haven: Yale, 1962, p. 29), without denying that, from the scientific standpoint, " the uniqueness and unrepeatability of individuals are aspects falling primarily within the province of philosophers and artists " (Genetics and the Origin of Species, p. 4)--well, of artists anyway. See further Gardner Murphy's remarks on " The Consequences of Mutations " in Human Potentialities (New York: Basic Books, 1958), pp. 228-31; and Gordon Allport's study of Becoming (New Haven: Yale, 1955).
be necessary to take account both of the structure and of the function of the individual organism; for to say it is a " describable object" (albeit not the principal center of interest in the evolutionary process as a whole) is to say that it has parts put together in a certain way (material and formal cause) as the result of certain agencies working through certain stages (efficient and final cause). Thus the fact that populations as describable objects have a recognizable structure and function is possible only by reason of the fact that the individual members of the population have them first.
This may seem an obvious point, but it is one which is in practice overlooked by any formulation of the evolutionary mechanism which singles out the genetic system with random mutation and natural selection as the sole principal factors, to which the functioning of individuals is subordinate and secondary. To see the functionings of the individual as a mere part of the selective process and not as forming a distinct major evolutionary factor in its own right, in short, inevitably distorts one's conception of the real workings of the evolutionary system as a whole.
This is clearly illustrated in Simpson's proposition that at the descriptive level, " natural selection is the only objectively established anti-chance evolutionary factor."65 The individual as a describable object plainly lies " at the descriptive level"; and the individual as the morphological expression of the genetic and environmental status of an evolving population is plainly an evolutionary factor. But the development of this individual as such is not a mere random transition; it is a definite passage from fertilized ovum to mature adult, turning circumstance so far as possible to its own benefit for becoming what it can be and potentially is. Consequently, the individual is not only an evolutionary factor at the descriptive level; he is veritably an anti-chance factor. Underlying the long-range adaptive population trends controlled by the natural selective system lies in every case the phenotype which is adaptive, but
65 George Gaylord Simpson, This View of Life (New York: Harcourt, 1963), p. 228.
which is under the direct control not of the natural selective system at all but of the epigenetic system. There are two anti-chance factors in evolution, therefore, both located at the descriptive level: one at the level of the individual organism as such--epigenesis, the source of homeostasis and teleonomy; and another at the level of populations--natural or evolutionary selection, the process whereby the occurrence of favorable mutations increases the adaptive fitness of organisms to meet the requirements of their environments and subsequently to better survive and reproduce.
Thus the adaptive flexibility and evolutionary advance observed at the level of the population is only possible by reason of the structural stability and limited adaptive range of the individual organism; and the fact that in modern studies concern has shifted away from the individual organism ought not to blind us to the implications of the fact that species evolve through individual reproductions of organisms as " describable objects." As Dr. Nogar among others has pointed out:
Although it is true that the path of evolution is best traced in paleontology, the process by which evolution has taken place must be found in the individual reproductions of organisms. Species evolve through individual generations, even though whole populations are involved in the total process of species change. The method, often called the mechanics of evolution, is not treated by paleontology but by the sciences of heredity and development. What actually takes place in the process of change which is called evolution can only be ascertained by those sciences which study the origin and development of individual organisms [or better, not without them].66
66 Raymond J. Nogar, The Wisdom of Evolution, pp. 290-91: " There are many departments of biological science which contribute to an understanding of the origin and development of organic systems. It is true that ultimately the problem of evolution concerns only heritable characters. Among the developmental sciences, certainly genetics plays a dominant role today. Genetics is classically defined as the science of variation and inheritance in organisms. Its object is to determine to what extent the variable characters of plants and animals are inherited from parents to offspring, to what extent they are from environmental influence, and by what biological mechanisms such characters are transmitted from generation to generation. But the problem of development of organisms is much more broad than these considerations. Cytology, the study of the cell, embryology, the study of the growth of the embryo (seed) to maturity, and physiology of growth are all involved in the full developmental picture. All the facets of reproduction, heredity and development are at issue in the question of individual origins." Thus even this list of the disciplines involved is but representative and not at all exhaustive.
Probably there is no way to make this point clearer than by considering directly in what manner evolutionary studies meet the ancient requirement that science be of the necessary. In what sense is evolution a necessary and not merely contingent fact? In what sense does the idea of evolution intend an aspect of reality which does not just happen to be as it is but could not be otherwise?
The answer to this question is not far to seek. It lies in what Dobzhansky has described as " the splendid simplicity and deductive character of the idea of natural selection." 67 In fact, the core of evolutionary theory, that aspect of the science which expresses the root necessity behind the evolutionary character of reality, may be expressed in a quasi-syllogistic involving four facts of observation and three immediate deductions therefrom.68
First Fact: the reproductive prodigality of the biotic community. This says that all organisms tend to increase in a geometric ratio (a crucial factor, it may be noted, in a species' survival of recurrent catastrophes of disease and weather).
Second Fact: population constancy. Generally, the numbers of adults in the populations of any given area remain relatively constant from year to year; and what increase or decrease can be observed is arithmetic, never geometric.
First Deduction: the " struggle for existence," a metaphorical expression for the deduction which follows from the above data, namely, that natural populations, though locally variable to some degree, remain so far short of their reproductive potential that there clearly is in each generation an excess of offspring that fail to attain reproductive status. Due to the limited
67 Theodosius Dobzhansky, Mankind Evolving, p. 130.
68 The following analysis is largely an amplification and development of the structure of argument suggested by Julian Huxley in the recent re-edition of his classic, Evolution: The Modern Synthesis (New York: Science Editions, 1964), pp. 13-28.
economic resources of any given ecological niche or environment, " reproduction results in more offspring being reproduced than can survive to reproduce again; and this in turn results in what Darwin called the struggle for existence." 69
In essence, this " struggle for life " is convertible with the positive orientation of each organism toward self-development and reproduction:
Thus trees " struggle " against the danger of being felled by wind by developing stronger root systems; mammals and birds " struggle " against cold by developing heat insulation, temperature regulation, or by remaining dormant during winter months; desert plants " struggle " against dryness by having leaves transformed into spines. Plants and animals " compete " for food when food is scarce, but they do not necessarily fight against one another.70
Depending upon the adaptive exigencies prevailing at any given time, living beings may " struggle for existence " not only by fighting each other but also by helping each other; and in fact " competition in evolution often or usually is entirely passive." 71
Epigenesis, the positive, dynamic orientation of each individual organism toward self-development and perpetuation through progeny: " Here is the crucial point in the conceptual scheme which Darwin gave to biology. The apparently designed nature and purpose of living organisms . . . is all ultimately directed at survival in order to reproduce." 72 Yet the
69 Julian Huxley, Evolution In Action (New York: Mentor, 1953), p. 33. Conversely, of course, " any living species, race or population tends to expand in numbers as soon as it encounters a favorable environment." (Dobzhansky, Evolution, Genetics, and Man, New York: Science Editions, 1963, p. 333). Australians are among the more vocal witnesses of this phenomenon.
70 Dobzhansky, Evolution, Genetics, and Man, pp. 112-13.
71 George Gaylord Simpson, The Meaning of Evolution (New Haven: Yale, 1949), p. 222 fn. 3.
72 G. G. Simpson, C. S. Pittendrigh, and L. H. Tiffany, Life: An Introduction to Biology (New York: Harcourt, 1957), p. 34. On the metaphysical dimensions of this formulation, see Jacques Maritain, A Preface to Metaphysics (New York: Mentor, 1962), " The Principle of Finality: First Aspect," pp. 103 ff.; and " The Principle of Finality (Second Aspect)," pp. 107 ff. See also fn. 160 of " Evolution as World-View and as Philosophy " in Nogar and Deely, The Problem of Evolution, on natural selection as a definition of the role of chance in the constitution of nature.
notion of an intrinsic source of structure and function produced by the generator in the process of generation and which establishes both the tendency for development and limitations of the generated's capacity for development is just that sense of "nature " which has always been fundamental for traditional philosophy.73
Third Fact: Appreciable variation. This is simply a pointing out that the struggle for survival in nature is not among identical individuals but is waged among organisms which are slightly different at least from one another.
Second Deduction: differential elimination. By taking the first deduction in conjunction with this third fact, we have the premises for a deduction that there is a differential elimination of the offspring in each generation: on the average, organisms with unfavorable variations will be eliminated in greater numbers than those with favorable variations. " The statistical probability of survival or elimination, despite accidents, will depend on the degree of adaptedness of individuals and groups to the environments in which they live ";74 and even a very high percentage of non-selective or random elimination in no way invalidates the general selection principle from holding for the remaining fraction.
By way of historical comment, we may note that this largely negative process of differential elimination was what Darwin originally termed " natural selection" and proposed as the mechanism of the evolutionary process. But elimination of the less fit does not make the more fit novelties, and an evolutionary mechanism which eliminates without explaining how the
73 See Raymond J. Nogar, " Evolution: Scientific and Philosophical Dimensions," in Philosophy of Biology, V. E. Smith, ed. (New York: St. John's University Press, 1962), pp. 23-66, esp. pp. 49-63; also Benedict Ashley, " Change and Process '' in Part II, Section IV of The Problem of Evolution; James A. Weisheipl, Nature and Gravitation (River Forest, Ill.: Aquinas Institute, 1955); and " The Concept of Nature," The New Scholasticism, XXVIII (October, 1954), pp. 377-408; " Natural and Compulsory Movement," The New Scholasticism, XXIX (1955), pp. 50-81; " Space and Gravitation," The New Scholasticism, XXIX (April, 1955), pp. 175-223. See also fn. 77 below.
74 Dobzhansky, Mankind Evolving, p. 128.
more suitable variants are linked with the processes of biological inheritance could not in the end account for genuine origins of species. What eluded Darwin to the end was a satisfactory explanation of how a variation arising within a given population would be preserved from reabsorption--like a drop of ink in the ocean--in the succeeding generations. How could surface variability be radical? What was required was a stable basis within the inheritance factors, and the factors of inheritance were unknown when Darwin published (unless you happened to live in the right monastery and also be Monk Mendel's friend), save for the ancient and general axiom, generans generat simile sibi.
Thus, between natural selection as first proposed by Darwin and the concept of selection put forward today in the evolutionary synthesis, " the great biological fact of inheritance makes all the difference." 75
Fourth Fact: particulate inheritance. Mendel's discovery of the particulate nature of inheritance held the answer to
75 Simpson, Pittendrigh, and Tiffany, Life, p. 33. Cf. C. H. Waddington, " Evolutionary Adaptation," in The Evolution of Life, pp. 385-6: " The development of evolutionary theory in the last hundred years has in fact proceeded along quite other lines. Darwin's major contribution was, of course, the suggestion that evolution can be explained by the natural selection of random variations. Natural selection, which was at first considered as though it were a hypothesis that was in need of experimental or observational confirmation, turns out on closer inspection to be a tautology, a statement of an inevitable although previously unrecognized relation. It states that the fittest individuals in a population (defined as those which leave most offspring) will leave most offspring. Once the statement is made, its truth is apparent. This fact in no way reduces the magnitude of Darwin's achievement; only after it was clearly formulated, could biologists realise the enormous power of the principle as a weapon of explanation. However, his theory required a second component--namely, a process by which random hereditary variation would be produced. This he was unable himself to provide, since the phenomena of biological heredity were in his day very little understood. With the rise of Mendelism, the lacuna was made good. Heredity depends on chromosomal genes, and these are found in fact to behave as the theory requires, altering occasionally at unpredictable times and in ways which produce a large, and, it is usually stated, ' random ' variety of characters in the offspring bearing the altered genes. On these two foundations--natural selection operating on variation which arises from the random mutation of Mendelian genes--the present-day neo-Darwinist or ' synthetic' theory of evolution has been built up."
Darwin's dilemma over the origin and the stability of novelties. Research along Mendelian lines revealed that the sex cells contain the sum total of physical heredity, and that within the sex cells the specific carriers of heredity are self-replicating molecular entities called genes. Although these function as interacting and cooperative sets in the unit-organism's development by controlling the metabolic pattern as such, they are transmitted (and therefore inherited) as more or less discrete, unblending units. Once it had become known that biological heredity is basically " the transmission of self-reproducing entities, genes,"76 and the Mendelian laws had revealed that during the process of hereditary transmission the genetic units do not blend but segregate, recombining more or less randomly in the establishment of the hereditary endowment or " genotype " of a new organism,77 the problem of a stable hereditary basis for novel variations became soluble. Here, in the particulate character of hereditary transmission, lay precisely " that point in the process of origins whereby the relation between the generator and the generated can be investigated and conceptualized." 78
In order to find a stable basis for novelty, and so understand the inception and possible sustainment of evolutionary change,
76 Dobzhansky, Mankind Evolving, p. 77.
77 The totality of the genes an organism possesses is referred to as its genotype or genetic endowment. The genotype is contrasted with the so-called phenotype, which is not transmissible biologically and comprises the total of everything that can be observed or inferred about an organism excepting only its genes. On the basis of this distinction, which is altogether fundamental to the understanding of heredity, it follows that the total range of phenotypes which a given genotype can engender in all possible environments constitutes the norm of reaction of the genotype, so that whatever change is induced in the phenotype is of necessity within the norm of reaction circumscribed by the genotype, i. e., fixed in the zygote at fertilization. Thus the limitation on any given organism's substantial developmental variation potential, its reaction range, is established once and for all at the moment of that organism's genetic origin. " No matter what the prehistory might be," writes Nogar, " there remains a stable, unique, and typical order in the process of generation which gives to the entity both its capacity and its limitations for development." (" Evolution: Scientific and Philosophical Dimensions," p. 58. See further references in fn. 73 above.)
78 Nogar, " Evolution: Scientific and Philosophical Dimensions," p. 55, italicized.
one need know nothing about the parents who mate beyond the sex cells which they produce.
In this narrowed perspective it became relatively easy to identify the imprecise or " mutant " gene as the ultimate source of all heritable variation, and so the root of evolutionary novelty at the adaptive level. " Since all developmental processes are gene controlled, any morphological or physiological trait may be altered by mutation." 79
A mutation is simply a gene which has replicated imprecisely without losing the capacity to further reproduce.79a In this way what was originally a variant becomes a strain, and what in a parent organism was " essentially a dislocation taking place in the delicate self-reproducing mechanism of the gene " 80 may become for succeeding generations " the origin of an hereditary trait which did not exist at all in the parents of the mutant." 81
The frequency, range, and nature of genetic mutations have
79 Dobzhansky, Genetics and the Origin of Species, p. 29. Moreover, it is known at present that mutations form a spectrum, ranging from drastic changes lethal in early development stages to changes so minute that their detection presents serious technical problems. In fact, a great majority of mutations cause no changes in the chromosomes visible under even the best microscopes; so that one will obtain at best a grossly distorted picture of the characteristics of the mutation process if he restricts his observations to the data of " common sense " and only considers mutational changes in their phenotypic manifestation, that is, only by reference to visible departure from the ancestral condition in the structural and physiological characters. Since, as we shall see below, the effects of the mutation process on organic evolution are cumulative, it would hardly be possible to achieve a clear understanding of the evolutionary progression if one were unaware of the presence of slight mutants which, at any given time level, remain invisible to the unaided eye for the simple reason that they fall within the ' normal' range of individual variability.
79a In many respects, the nature of mutation remains profoundly mysterious. So far as has been determined, genetic mutation " is a random affair, and takes place in all directions," often manifesting itself " as uncaused or at least as unpredictable as the jumping of an electron from one orbit to another inside an atom." (Huxley, Evolution in Action, p. 36.) About all that we can say with assurance is that the extreme atomic complexity of the genetic unit linked with a high sensitivity to forces external to itself (i. e., by definition, to environmental forces) makes it inevitable that the self-copying process will be occasionally inexact.
80 Dobzhansky, Evolution, Genetics, and Man, p. 107.
81 L. C. Dunn and Theodosius Dobzhansky, Heredity, Race, and Society (rev. and enlarged ed.; New York: Mentor, 1952), p. 77.
been the object of many special studies and are far from being exhaustively understood.82 What is clear, however, is that mutation is the ultimate source of all hereditary variation. Thus Simpson can say that " modern geneticists have supplied what seems to have been the last lacking basic information necessary for an explanation of evolution essentially complete on, at least, the descriptive level.83 For, if the forms of the universe are immanent, and not transcendent principles separate from matter, the constancy and variation of natural kinds center around the relationship between the parent and the progeny; and just as species as existing kinds can be no more fixed than this relationship, so our ideas of them ought to be " no more and no less permanent, stable, unique, and constant than the relation of generator-generated manifested under closest scrutiny." 84
For the sake of the larger philosophical context, a digression here seems called for again with regard to Dewey's assessment of the conflict between modern science and traditional philosophy over the permanence of species. Earlier I suggested that Dewey seemed to have misunderstood or missed entirely the nature of the doctrinal dispute between Plato and Aristotle.85
82 Without being able to go into the matter here, we may at least note in passing that recent advances in research on the DNA molecule have led to some dramatic breakthroughs in our understanding of the genetic structure and function. A very readable account of the background of recent researches in this area which requires no technical knowledge to follow can be found in Theodosius Dobzhansky, Heredity and the Nature of Man (New York: Harcourt, 1964). Also Isaac Asimov, The Genetic Code (New York: New American Library, 1962). A more technical account can be found in B. Wallace and Th. Dobzhansky, Radiations, Genes, and Man (New York: Holt, 1959).
83 George Gaylord Simpson, This View of Life (New York: Harcourt, 1963), p. 201.
84 Raymond Nogar, " Evolution: Scientific and Philosophical Dimensions," p. 59.
85 See fn. 39 above for references. It might be added here that, according to a recent study by Frederick M. Anderson, " Dewey's Experiment With Greek Philosophy " in International Philosophical Quarterly, VII (March, 1967), pp. 86-100, " In all of his writings about the Greek philosophers, there is but one essay by Dewey that contains some sustained study of specific writings: John Dewey, ' The " Socratic Dialogues " of Plato,' in Studies in the History of Ideas (New York: Columbia Univ. Press, 1925), II, 1-23." (Anderson, fn. 1 p. 86). One may reasonably suspect that Dewey lacked the inclination or information or both to grasp the nature of the dispute in philosophy of nature between Plato and Aristotle. See further John Anton, " John Dewey and Ancient Philosophies," Philosophy and Phenomenological Research, 25 (1965), pp. 477-499.
page 119
Here this suggestion can now be laid bare in its ground. In metaphysics, their disagreement was but the conflict between the answers they gave as mathematical interpreter of nature and naturalist or philosopher of nature, respectively, to the question as to where the properties of natural objects are to be verified, in a world of ideas knowable with mathematical precision and certitude, or in the changing world of nature itself? Are the forms of entities themselves things or only principles of things? How to interpret the universal datum, agens facit simile sibi, omne generans generat simile sibi? Both Aristotle and Plato forthrightly posited the eternity of species for there was then no known evidence to the contrary; but they characteristically differed in their respective explanations of this fixity. Plato assigned it to noetic reasons and defended it in terms of the requirements of intellectual understanding. Aristotle, without denying that science bears on the necessary, assigned the fixity of forms to their stable and unchanging environment--the eternal heavens. His ecology was wrong, but he looked to the right source and conceived the relationship between permanence and instability of natural kinds rightly in giving the universal axiom, agens facit simile sibi, an absolutistic interpretation, as Dobzhansky observes:
If the environment were absolutely constant, one could conceive of formation of ideal genotypes each of which would be perfectly adapted to a certain niche in this environment. In such a static world, evolution might accomplish its task and come to a standstill; doing away with the mutation process would be the ultimate improvement. The world of reality is, however, not static. A species perfectly adapted at present may be destroyed by a change in the environment if no hereditary variability is available in the hour of need. Depending upon the speed and character of environmental changes, and also upon the reproductive biology of the species, greater or lesser mutability will be favored. The store of potential variability, and the rate at which the potential variability becomes actualized will be controlled by natural selection [in the sense to be defined in our Third Deduction below].86
86 Dobzhansky, Genetics and the Origin of Species, p. 74, emphasis added. See fn. 154 infra.
Thus Dr. Nogar could point out that " surprisingly enough, the fundamental issues involved in the doctrinal differences between Plato's system and Aristotle's view are raised again today by the advances of evolutionary theory."87 Yet, as Ashley also points out, " the Thomists who today are the main proponents of this position "--i. e., Aristotle's position--" often seem to express it in a manner which tends back toward the Platonic view that Aristotle opposed." 88 In this light, as Adler comments, " we can discount what is excessive in Dewey's statement . . . but we must also remember that, in Darwin's time and even today there was and is the ' scholastic' position, claiming the authority of Aristotle and St. Thomas, which . . . overemphasizes, as well as mislocates, the immutability of nature." 89
87 Nogar, The Wisdom of Evolution, p. 316. This is spelled out in philosophical and historical detail in the essay on " Evolution as World-View and as Philosophy," esp. div. II, ' From classical antiquity to Darwin's world,' Part I of The Problem of Evolution by Nogar and Deely.
88 Ashley, " Change and Process," Third Heading in Part II, Section IV of The Problem of Evolution. Ashley goes on to say: " In spite of this commitment to a view of nature which emphasized its dynamism, Aristotle and the medieval Aristotelians failed to follow out its full implications. They were restrained both by the lingering influence of Hellenic religious attitudes and by the actual state of astronomy in their day which had been developed under Pythagoreans and Platonists. This astronomy accepted the mythological view that the cosmos is divided into two fundamentally different regions, the sublunar region in which alone radical change can take place, and the heavenly spheres in which no change can take place, except pure mechanical change (the frictionless motion of the unalterable spheres, motion which is absolutely uniform and capable of perfect mathematical expression). Thus mechanism and mathematicism were realized in the principal parts of the universe, while dynamic naturalism applied only to a restricted and inferior region. This drastic restriction of dynamic naturalism in Aristotle's world view survived through the middle ages. St. Thomas Aquinas recognized it as hypothetical rather than definitive, but Thomists abandoned it only reluctantly as modern science made it completely untenable. Contemporary Thomists have made only a feeble effort to rethink the consequences of the Aristotelian view of change for the modern world-picture, and have been largely content to argue that changes in empirical science cannot affect the metaphysical principles of Thomism, which, it is claimed, rest on a superior ground."
In this respect, see Sections VI and VIII below.
89 Adler, The Problem of Species, p. 272. E. g., see Desmond Murray, Species Revalued (London: Blackfriars, 1955) .
We shall pick up the thread of what is here in the nature of digression when we come to Sec. VI below; for the present it suffices to note that, for the philosophy authentically recognized as traditional,
nature is a principle, that is to say a relation of the generator to the generated, and cosmic natures are no more fixed than this relation. True to the Aristotelian principle that there is no other way to know how fixed this relation is than to observe nature, Aquinas and his students repudiated, in theory, the Platonic tendency to identify temporal natures with eternal essences.90
In the absence of the beneficent regularity of the celestial spheres as causa regitiva of generations and corruptions in this sublunary region, therefore,
nature, as the relative relation of the generator to the generated, parent to the progeny in organic beings, is dynamic and changing, and must be conceived as of the temporal order. It is important that the permanence and stability of natural bodies be acknowledged, for regularity and unicity of type are evident. But the permanence and stability, even of species, is no greater than the stability of the relation of the generator to the generated. A mathematical or metaphysical conception of essence as an absolutely fixed and eternal idea cannot be superimposed upon natural bodies, except in the sense of an ideal (logical) type, and one must be careful here not to drift into the idealism of Plato and imagine that the real horse is the idea, and the domestic horse is but a shadow of reality. As an archetype or idea, the horse can be conceived of as free of the ravages of time, but the natural history of the horse family shows it to be about 60 million years old with an estimated evolutionary rate of 0.15 genera per million years.91
Summing up, then, our " fourth fact," the discovery of the particulate nature of biological inheritance, we may simply say
90 Nogar, The Wisdom, of Evolution, p. 318, emphasis added. Nogar has particularly in mind the text of Aquinas's In II Phys. The core of Dr. Nogar's interpretation, which rests on a scholarly grasp of the continuity of the philosophical project across the dimensions of history, is a strictly philosophical contention, namely, that evolutionary science is a substantial development but not a destruction of the root principles structuring the Aristotelian Physica.
91 Ibid., pp. 318-9.
that " mutation causes changes in the genes and variants of the gene structure; these are the raw materials of evolution. In those organisms which reproduce sexually, these variants are combined and recombined to form countless different genotypes." 92 Thus, " if self-copying serves as the basis of continuity and specificity in life, and reproduction generates its expansive force, mutation is the ultimate source of all its heritable variation." 93
The principles of heredity, then, plus the datum of mutation, constitute what is referred to as " the great biological fact of
92 Theodosius Dobzhansky, The Biological Basis of Human Freedom, (New York: Columbia, 1956), p. 56. See Genetics and the Origin of Species, p. 8: " The number of conceivable combinations of genes present in different organisms is, of course, immense. The actually existing combinations amount to only an infinitesimal fraction of the potentially possible, or at least conceivable, ones. All these combinations may be thought of as forming a multidimensional space within which every existing or possible organism may be said to have a place."
93 Julian Huxley, Evolution in Action (New York: Mentor, 1953), pp. 33-4. In this connection, Simpson finds it " a rather astonishing observation that the supply of this basic material for evolution seems to have no particular relationship to the demand," i. e., that " the results of mutations do not tend to correspond at all closely with the needs or opportunities of the mutating organism." (The Meaning of Evolution, p. 164.) But is this really so astonishing? Alluding to the same fact, Dunn and Dobzhansky make the following comments (Heredity, Race, and Society, pp. 81-2): " Perplexing questions which may then be asked are these: Why should harmful and useful mutations occur indiscriminately at all times? Would it not be vastly more advantageous for life and for its evolution if only useful mutations were to take place only when and where they are needed? " " The answers to these questions are not difficult. This is not a perfect world. Mutations are changes . . . which alter the structure of the genes and their effects on body or mind. To produce only mutations that would be useful in the environment in which the descendants of a given individual are going to live would require the genes not only to possess wisdom but foresight. This is just too much to expect and, in any case, nature has not seen fit to endow mortal creatures with providential powers. All kinds of mutational changes of which a gene is capable do occur in it or in its descendants, given the vast stretches of time through which the hereditary material continues. A few of these changes will be useful to the organism in some environments. A majority of changes will be harmful, just because tinkering with a delicate mechanism is more likely to spoil it than to improve it. A more biological reason is that the mutations which are useful in today's environments took place in the past and have become incorporated in the ' normal ' hereditary constitution." " Harmful mutations and hereditary diseases are thus the price which the species pay for the plasticity which makes continued evolution possible." See further Dobzhansky, Genetics and the Origin of Species, p. 83.
inheritance": some variation has a stable basis radicated within the inheritance factors, and that fraction is available for transmission to subsequent generations.
By taking this fact in conjunction with the second deduction (differential elimination), we have the premises for a third and final deduction, and we are in a position to circumscribe the element of necessity in the idea of evolution.
Third Deduction: evolutionary selection. Since Darwin coined the phrase " natural selection" precisely to fit the second deduction above, which reveals less the creative and positive thrust of evolutionary change than it does the conservative and negative phase of the process, since, too, this idea carried over into the social order as a pseudo-scientific support for a vicious philosophy of " social Darwinism," since, moreover, we are separated from this Darwinian prototype of evolutionary explanation by decisive discoveries and a hundred years, even though Julian Huxley insists that " biologists may with good heart continue to be Darwinians and to employ the term Natural Selection, "94 it seems to me historically less ambiguous and philosophically more exact to leave the term " natural selection " to history and to designating the aspect of reality for which it was so exactly tailored to fit, and to express the conceptual keystone in the structure of the modern synthesis in a different phrase, more precise because in turn tailor-made to fit the new aspect of reality which post-Darwinian research brought to light with so much labor. Rather than continuing to speak of natural selection, therefore, I submit we should prefer the phrase evolutionary selection to intend the realization that there must be a differential transmission of inherited variation, so that automatically " the hereditary endowment of the succeeding generations will differ from that of the preceding generations in the direction of superior fitness " 95--of greater chance of reproductive success. This is so because inheritable variations, no less than non-inheritable ones, inevitably differ in the degree of biological
94 Evolution: The Modern Synthesis, p. 28.
95 Dobzhansky, Evolution, Genetics, and Man, p. 112.
advantage they confer--in other words, in their survival value; and so the struggle for survival results in their differential elimination--in Darwin's words, natural selection; but differential elimination for one organism is differential survival for another, and so natural selection clears the field for the transmission of adaptively superior heritable variations--in other words, for evolutionary selection. Thus in modern theory the emphasis is not on differential survival but on differential transmission, on reproduction.96
Since, however, biologists continue to prefer the original Darwinian expression, notwithstanding this altered sense, it is important to be clear in one's own mind what is intended:
The term Natural Selection thus is seen to have two rather different meanings. In a broad sense it covers all cases of differential survival [second deduction]; but from the evolutionary point of view it covers only the differential transmission of inheritable variation [third deduction].97
The existential stability of life forms, then, is seen to depend on the pattern of generation or reproduction, which is itself determined by the ecology, the relation to environment, of any given form. As the ecological resources change, beyond certain adaptive limits the life-form must itself change correlatively, or suffer extinction. The rhythm of successful adaptive change cannot be faster than the rhythm of the environmental change; it may even be somewhat slower. But anyone who has watched for the disappearance of his local mountain range or for the onset of a new ice age knows that the argument against the mutability of particular forms, be they oysters or elephants, on the grounds that " like generates like," is either naive or the last hurrah of scholastics whose thought bears witness to a cultural unconscious wherein the eternal heavens still have their implications for the changes which occur below the moon.
96 Mayr, in his Animal Species and Evolution, comments: " Therefore, modern evolutionists include in natural selection any factor that contributes to differential reproduction " (p. 183). To see the necessity in the process is one step, to explain it adequately, another: it is for this second step that Waddington's qualifications are in line.
97 Huxley, Evolution: The Modern Synthesis, p. 16.
The perspective of the geologist together with that of the geneticist reveal what may well be termed by the philosopher the basis for the prior possibility of paleontological data:
The process of adaptation may be looked at as a series of conflicts between the organism and its environment. The environment is in a state of flux, and its changes, whether slow or rapid, make the genotypes of bygone generations no longer fit for survival. The ensuing contradictions can be resolved either through extinction of the species, or through reorganization of its genotype.98
Mutations, however, " create genotypes that have not gone through a process of adjustment in the evolutionary history ";99 so that there is no need to conceive of the potential variability of a natural kind as restricted within the boundaries of some " original type " (usually conceived as an immediate creation of God), and to go on from this gratuitous postulation to observe that " the substantial form would then be viewed as an ontological impulse realizing itself in various patterns along the line of a certain phylum." 100 Such evolution could, indeed, " only take place within the limits of the phylum or the ontological species in question."101 Yet as the author of this view himself has elsewhere well remarked, " the proper task of a straightforward philosophy is to assign the reasons for what is given to it and to gain an understanding of that datum, not to ' elucidate ' a universe of fictions," be they possible or not.102 It is therefore not only scientifically more exact but, in the light of available evidences, philosophically more sound to simply remark that " evolution is possible because some mutants and their combinations happen to produce adaptively valuable
98 Dobzhansky, Genetics and the Origin of Species, pp. 73-4.
99 Ibid., p. 83.
100 Jacques Maritain, " Substantial Forms and Evolution," in The Range of Reason (New York: Scribner's, 1952), p. 37.
101 Ibid., pp. 37-8.
102 Jacques Maritain, The Degrees of Knowledge, trans. from the 4th French ed. under the general supervision of Gerald Phelan (New York: Scribner's, 1959), p. 106. As I shall try to show in Section VI below, it is a question here of how seriously one is to take the principle of parsimony. See fns. 161 and 163 infra.
phenotypes [epigenetic systems] in environments which the species encounters in space or in time." 103
Dobzhansky is unusually vehement in making this last point. " Evolution is change in the heredity, in the genetic endowment of succeeding generations," he points out; " no understanding of evolution is possible except with the foundation of a knowledge of heredity." 104 With a slightly different emphasis, Sir Julian Huxley makes the same point with equal vehemence: " The discovery of the principle of natural selection "--caveat lector --" made evolution comprehensible; together with the discoveries of modern genetics, it has made all other explanations of evolution untenable." 105
At the cost of getting a bit ahead of ourselves, let us note here quickly and parenthetically that " one thing no single mutation has done is to produce a new species, genus, or family. This is because species and supraspecific categories differ always in many genes, and hence arise by the summation of many mutational steps."105a (The objection that this view involves contradiction because it implies generation of a " higher " by a " lower " species [leaving aside for the moment the detail that species as such neither exist nor generate, save among the angels, if such there be, and even then there would still be no generation] will be disposed of in Section VIII below.)
Such, then, is the theoretical framework of contemporary evolutionary thought. I have called it a " quasi-syllogistic," and by this I wanted to call attention to and stress the logical
103 Dobzhansky, Genetics and the Origin of Species, p. 83. Nor will it do here to say I am committing the error of settling properly philosophical questions by appeal to scientific fact in itself unrelated to the intelligible issue. It is for the philosopher to relate such facts to his own knowledge and principles, not to casually dismiss them as of no interest. In short, if the philosopher neglects the task of drawing out from the properly physical data of science an intelligible content which is in fact there to be seen, he has no one to blame but himself (even if he is not to blame: vessels of clay are not the best containers for the workings of understanding) . See fn. 163 infra.
104 Dobzhansky, The Biological Basis of Human Freedom, pp. 10 and 11.
105 Evolution in Action, p. 35.
105a Dobzhansky, Genetics and the Origin of Species, p. 31.
rigor and structural interdependence with which the seven factors which are the foundation of the science hold together. It will be useful to diagram this structural interdependence to make sure the syllogistic analogy is clear. To do this, let us represent the sequence of facts and deductions as a progression of major and minor premises, in which the first two " premises " are empirical, and where each " deduction " becomes in turn a major premise to be coupled with an empirical minor premise to yield a further necessary step. Pictured thus, the materials we have just summarized exhibit the following pattern:
MAJOR: Reproductive Prodigality (1st Fact)
MINOR: Population Constancy (2nd Fact)
CONCLUSION: Struggle For Existence (1st Deduction)
MAJOR: Struggle For Existence (1st Deduction)
MINOR: Appreciable Variation (3rd Fact)
CONCLUSION: Differential Elimination/Survival (2nd Deduction)
MAJOR: Differential Survival (2nd Deduction)
MINOR: Particulate Inheritance (4th Fact)
CONCLUSION: Evolutionary Selection (3rd Deduction)
[leading to] EVOLUTION AS REASONED FACT
Here, then, the full philosophical weight of contemporary evolutionary biology makes itself felt. We are in confrontation with a 'phenomenon of necessity giving to nature as a totality a depth-dimension, that is, a radically developmental structuring made secure by the very tendency to both endure (agere sequitur esse) and stamp the environment with its image (agens facit simile sibi) which characterizes the existence of each individual entity regarded, as it were, in isolation.
Such at least must be our conclusion if we may take as a criterion of unqualified knowledge the following text from Aristotle:
We suppose ourselves to possess unqualified scientific knowledge of a thing, as opposed to knowing it in the accidental way in which the sophist knows, when we think that we know the cause on which the fact depends, as the cause of that fact and of no other, and, further, that the fact could not be other than it is. Now that scientific knowing is something of this sort is evident--witness those who falsely claim it and those who actually possess it, since the former merely imagine themselves to be, while the latter are also actually, in the condition described. Consequently the object of unqualified knowledge cannot be other than it is.106
Thus Dobzhansky, writing on the character of evolutionary selection, could remark almost syllogistically:
[Major:] Its ironclad necessity was clearly expressed by Darwin in an argument that can be reduced to a few sentences. Any organism needs food in order to live; the resources are always limited; the number of individuals of any species is therefore also limited. Any species is capable of increasing in number in a geometric progression; sooner or later the state will be reached when only a part of the progeny will be able to survive. [Minor:] The statistical probability of survival or elimination, despite accidents, will depend on the degree of the adaptedness of individuals and groups to the environment in which they live. This degree of adaptedness is in part conditioned by the genetic endowment. [Conclusion:] Therefore, carriers of some genotypes will survive, or will be eliminated, more or less frequently than will the carriers of other genotypes, and the succeeding generations will not be descended equally from all the genotypes in the preceding generations, but relatively more from the better adapted ones. Therefore, the incidence of better adapted forms will tend to increase and the incidence of the less well adapted ones to decrease.107
At the strictly biological level and throughout the living community, developmental succession in transcendental relation to environmental succession is a necessary phenomenon. In this
106 Aristotle, Analytica Posteriora Bk. I, ch. 2, 71 b 8-15.
107 Dobzhansky, Mankind Evolving, p. 128.
we possess a key insight into the fundamental structure of the world.108 Bergson writes:
There is no doubt that life as a whole is an evolution, that is, an unceasing transformation. But life can progress only by means of the living, which are its depositaries. Innumerable living beings, almost alike, have to repeat each other in space and in time for the novelty they are working out to grow and mature. It is like a book that advances toward a new edition by going through thousands of reprints with thousands of copies. There is, however, this difference between the two cases, that the successive impressions are identical, as well as the simultaneous copies of the same impression, whereas representatives of one and the same species are never entirely the same, either in different points of space or at different moments of time.109
From every point of view, the balance of life is struck so subtly within the very being of every living creature that it is difficult to realize how ultimately each life is connected with a great many other lives. Perhaps this is why the idea of evolution is dealt with so reluctantly by many thinkers, and why an understanding of heredity can make all the difference in one's philosophical attitude toward the evolutionary problematic. In any event, it can be said that, once the genetic basis of evolutionary problems is clearly understood, one sees how logical evolutionary events really are; and that traditional scholastic thought was seriously mistaken in its tendency to regard all deviations from the parental pattern as strictly accidental in the sense of not entering into the organism's fundamental
108 Traditionally, in terms of the convertibility of the act of being with unity, a set of " transcendental " notions have been worked out which are " nothing but being itself explicitated in a certain way " (Ralph A. Powell, Truth or Absolute Nothing, River Forest, Ill.: Aquinas Institute, 1958, p. 26). Here, I am suggesting that, having recognized that " all things are either one or many, and of the many each is one " (Aristotle, Metaphysica, Bk. Ill, ch. 4, 1001 b 6), but now in light of the distinctively modern discovery that all natural units are transformable, i. e., that there are no praeter-lunar regions exempt from radical transformations, it is possible to work out evolution as a transcendental of the interaction situation, i. e., a transcendental convertible with being not as a unity, but as a plurality. It is the " esse " consequent on the interagere of beings.
109 Henri Bergson, Creative Evolution, authorized trans, by Arthur Mitchell York: Modern Library, 1944), p. 252.
developmental process nor consequently into its " essential definition."
Let us therefore consider in the framework of evolutionary science the role and structure of species in an evolving world, preparatory to an attempt to illumine those very notions in terms of the principles of traditional philosophy.
V. Specific Structures in an Evolving World
In another work,110 I have attempted to show that, with the exception of a tendency to typological thinking, in the sense of reification of ideal notions of natural kinds (which, so far as Aristotelianism was concerned, by right should have been abandoned with the unchanging heavens that were its mainstay, but which so far as Platonism was concerned rested on an ambition to substitute the constructivistically explanatory mode of reason in its noblest or mathematical form for the properly philosophical or natural physical mode of explanation which discriminates reasons for being in the very order of experience), the key sources of reasoned opposition to the evolution of nature did not draw on the thought of classical antiquity or on the scholasticism which extended it into medieval times. The chief obstacles to the reasoned development of evolutionary evidence stemmed in every case from what has been well described as " the nationalistic atmosphere of the seventeenth and eighteenth centuries which was impatient of distinctions between different types of knowledge," 111 and in general even more from the scientific than from the religious temper of that modern Age of Enlightenment, inasmuch as it was the former and not the latter which was the source of the conviction that not just astronomy or physics but any study, be it " a work of ethics, politics, criticism, or even eloquence, other things being equal, is merely so much more beautiful and perfect if it is written in the geometric spirit." 112
110 See Part I of Nogar's and Deely's The Problem of Evolution.
111 Benedict M. Ashley, " Aristotle's Sluggish Earth, Part II: Media of Demonstration," The New Scholasticism (April, 1958), p. 234.
112 Fontenelle, Preface to On the Usefulness of Mathematics and Physics; quoted in E. Cassirer, The Mind of the Enlightenment (Princeton: The University Press, 1951), p. 16.
Thus Loren Eiseley has pointed out that " variation, selection, the struggle for existence were all known before Darwin. They were seen, however, within the context of a different world view." 113 Thus " it was not natural selection that was born in 1859, as the world believes. Instead it was natural selection without balance," 114 i. e., a vision of the world-order as being in a dynamic, relative equilibrium rather than a permanent and mechanical one.
From a philosophical standpoint, this amounted to a returning to Aristotle's epigenetic view of individual development115
113 Loren Eiseley, The Firmament of Time (New York: Atheneum, 1962), p. 72.
114 Ibid., p. 81.
115 Mayr points out (Animal Species and Evolution, p. 4) that " more important for the development of the synthetic theory than the rejection of ill-founded special theories of evolution was the rejection of two basic philosophical concepts that were formerly widespread if not universally held: preformism and typological thinking." We have already indicated the very different bases of typological thinking in Mayr's sense in the philosophy of Aristotle and that of Plato, it being in the former case a function of the conception of the heavens as unchanging and in the latter case a function of the conception of the forms of nature as transcendent to nature itself. (See fn. 154 infra.)
So far as the philosophical concept of preformism is concerned, it is a concept which never played a role in Aristotle's conception of individual development. This is an historical note of some importance: " Long before the materials of generation were known in any physiological detail, two dominant theories of development dominated the thought of biologists and naturalists. Hippocrates (460-377 B.C.), over two thousand years ago, suggested that in generation the semen came from all parts of the body and that all the parts produced pangenes or particles representing each part. Each part was preformed to be what it became in the adult offspring. This was called the theory of pangenesis and theories like this were known as preformistic theories of development. In this way, Hippocrates hoped to explain both the replication of type and the obvious variations.
" Aristotle, in turn, rejected the theory of pangenes and the idea of preformism in reproduction. Still without accurate materials for an exploration of this problem, he reasoned that since the semen cannot have the same character as the parts from which they come, the process of reproduction must involve a true ' creative' process of unfolding what is only potentially there from the parent. Holding that the whole organism is greater than any of its parts, he reasoned that the best way to explain both the repetition of type and the production of novelty was to recognize the potential factor in the reproductive material and regard the developmental process as the progressive eduction or actualization of adult form. This unfolding of organic development became known as epigenesis. It is interesting to note that during the entire history of biology, experts have been divided between the theory of epigenesis and the theory of preformation. Darwin, in his Origin of Species, revived a theory of pangenes very similar to that of Hippocrates." (Raymond J. Nogar " Preformism vs. Epigenesis " in The Wisdom of Evolution, p. 292. For a presentation of the history of this question, see E. S. Russell, The Interpretation of Development and Heredity, London: Oxford, 1930, esp. ch. Ill).
minus " the features of Aristotelianism which were the survival of mechanism and mathematicism in his view of the world " and which were his patrimony as a student of the Academy;116 minus, that is to say, the unchanging environmental reference of the celestial, immutable spheres which were (as causa regitiva) the sole guarantee that the relation of generator-generated would be absolute and not just relative across the ages.
That is why, if one keeps to a philosophical standpoint the history of which is transparent to itself, since Darwin neither inaugurated a new logic of scientific questions nor freed in principle the phenomena of life for the possibility of transition (the astronomers had done that), but simply attempted to indicate the network of causes which made transition necessary, it is simply naive to assert that " the influence of Darwin upon philosophy resides in his having conquered the phenomena of life for the principle of transition, and thereby freed the new logic for application to mind and morals and life";117 the influence of Darwin on philosophy resides rather in a return to the conception of science as reasoned facts, distinct from and superordinate to mathematized facts.
When one turns to an assessment of specific structures in an evolving world and seeks to gather the lines of evidence bearing on their reality and role, it is important to be absolutely clear on the real nature of the Darwinian revolution as a renewed attempt to seek out proper causes, or as a reestablishment of " the independence of explanation and prediction,"118 in a
116 Ashley, " Change and Process." See fn. 87 above.
117 John Dewey, " The Influence of Darwinism on Philosophy," pp. 8-9.
118 Ernst Mayr, " Cause and Effect in Biology," Science, 184 (November 10, 1961), p. 1504. See also Michael Scriven, " Explanation and Prediction in Evolutionary Theory," Science, 130 (28 August 1959), pp. 477-482.
period convinced by its distinctive contributions to knowledge that geometry provided the only entry into philosophy. Thus a recent author aptly points out:
Much of the sound and fury surrounding evolutionary theory is due to a misapprehension of sorts. Evolution initially had no pretensions to the status of a Weltanschauung, nor did it seek to serve as a substitute for the Christian doctrine of creation. . . . The theory of evolution actually grew out of a conflict between two distinct and opposing biological theories. It was a family quarrel. The dominant biological theory was that of a fixed and immediate creation of species. This of course has little or no reference to the theological doctrine of creatio ex nihilo. Nor is the concept of the fixity of species a logical deduction from the philosophical doctrine of the immutability of essence, although the genus and species of Linnaeus do carry some of the logical and conventional characteristics of the Aristotelian genera and species.119
Ultimately, of course, it is necessary to face this question of what relation does the stable or labile nature of species have with the philosophical doctrine of the immutability of essence: this is the whole question of the mutual import of the modern and traditional species problematics. Everything that has been said up to now moves in this direction and will be confirmed or infirmed depending on our success in articulating an answer.
But to attempt a delineation of that question would be fatuous if we do not first see what has been the outcome of this " family quarrel," and secure our understanding of the articulations of nature in terms thereof. On any other course, it is at best premature and at worst gratuitous to assert that " biological species from Linnaeus to the present have little in common with the philosophical species because they have no (philosophically speaking) specific differences but only accidental differences," 120 for " to say that wherever we have only nominal
119 William E. Carlo, Philosophy, Science and Knowledge (Milwaukee: Bruce, 1967), p. 118. At the same time, it is necessary to add that, while agreeing completely with Dr. Carlo's historical point here, I must disagree almost equally completely with his general assessment of the evolutionary question (op. cit., ch. VI, " Evolutionary Theory and Philosophy," pp. 115-126.)
120 Ibid., p. 120.
definitions the objects are not species, is to conclude from our ignorance to the nature of things." 121
Our immediate question therefore must be: what is the meta-logical status of real natural kinds, prescinding for the moment from the possible distinction of " radical " and " superficial:; (in the senses we have already defined) ? What is the status of our intuitive, " common-sense " conviction " that there is a diversity of species in the corporeal world, and that this diversity is manifested in the activity of bodies "? 122 For if our reasoning here is not to be circular and a begging of the question, " the issue concerning our knowledge cannot be resolved " (i. e., it is impossible to say in a founded fashion, for example, that " the philosopher knows in advance--I mean by purely philosophic means--that there is a diversity of species in the corporeal world " 123) " unless there are extrinsic (ontological) criteria for judging whether what is known . . . exists as an infima species. Hence, unless such extrinsic criteria can be found . . . neither the ontological nor the epistemological problem concerning species can be solved. One thing is clear: . . . the nature of our knowledge, its relative perfection or imperfection, is no basis for inferring anything about the nature of things, so far as specific distinctions go." 124
121 Adler, The Problem of Species, p. 43.
122 Jacques Maritain, " Foreword " to Adler's The Problem of Species, p. xi.
123 Ibid.
124 Adler, The Problem of Species, p. 210. See fn. 16 supra, and references cited therein. Also St. Thomas, Summa Theol., I, q. 76, a. 3 ad 4; and I, q. 85, a. 3 ad 4: " dicendum quod universale, secundum quod accipitur cum intentione universalitatis est quidem quodammodo principium cognoscendi, prout intentio universalitatis consequitur modum intelligendi qui est per abstractionem. Non autem est necesse quod omne quod est principium cognoscendi, sit principium essendi, ut Plato existimavit: cum quandoque cognoscamus causam per effectum et substantiam per accidentia. Unde universale sic acceptum, secundum sententiam Aristotelis, non est principium essendi, neque substantia, ut patet in VII Metaphysica " (ch. 13, 1038 b 8-16; lect. 13 of Aquinas's Commentarium, nn. 1570-76). To this must be added Adler's decisive demonstration that " the sign which tells us whether distinctions are accidental or essential" is the fact that, whenever a bifurcate division rests on a non-essential difference in a nature, " these two distinctions cannot be ordered in a single way---this fact shows that the distinctions are accidental." (" Solution of the Problem of Species," fn. 72 p. 337). See The Problem of Species, pp. 157-163, for the full force of this proof; and at this point, it is necessary to insert a caveat.
Dr. Adler's reflections on the problem of specific natures and the hierarchy of essences have been continuously sustained and developed over more than thirty years. In fact, they constitute the most profound contribution to the question yet made, but their very nature is such that the early writings cannot be rightly understood unless taken together with the later, much briefer essays. To judge Dr. Adler's position on the book The Problem of Species alone, therefore, would not only be a mistake, it would necessarily result in a serious misunderstanding. There are four essays which, in my opinion, must be taken as a unit, and it is necessary for the serious reader to accomplish for himself the interrelations and corrections that obtain among them. These four works are, in chronological order: The Problem of Species; " Solution of the Problem of Species"; " The Hierarchy of Essences"; and " The Philosophers Give All the Answers and Establish None," ch. 4 of The Difference of Man and the Difference It Makes. Together, these four constitute the necessary point of departure for philosophical work in this area, whether one accepts their conclusions or not. What Kant said of his own work on metaphysics in his Prolegomena, I say here of Adler's work on the philosophical problem of species: " He who undertakes to judge or, still more, to construct a theory of species and essential differences must satisfy the demands there made, either by adopting Adler's solution or by thoroughly refuting it and substituting another. To evade it is impossible." Cf. Immanuel Kant, Prolegomena to Any Future Metaphysics (New York: Library of Liberal Arts edition, 1950), p. 11.
" The question, in short, concerns the criteria by which we are able to select that one from a series of nominal definitions which signifies a species, a real essence." 125 " The method then that we must adopt is to attempt to recognize the natural groups, following the indications afforded by the instincts of mankind, which led them for instance to form the class of Birds and the class of Fishes, each of which groups combines a multitude of differentiae, and is not defined by a single one as in a dichotomy." 126
If this is what we mean by knowledge " that there is a diversity of species in nature manifested by the activity of bodies "--and it seems to me we must at least and first of all mean this--then unless and until this sense of species as natural groups or kinds can be put on a causal (which is to say a minimally ontological) footing and elevated to the level of reasoned fact, there can be no possibility of further discriminating between " natural " species (as radical kinds) and " systematic " species (as superficial kinds). For a distinction
125Adler, The Problem of Species, p. 37.
126 Aristotle, De partibus animalium, Bk. I, ch. 3, 643 b 10-13.
which contributes no clarification to the issue being discussed is a useless and merely verbal distinction; and such is the case for anyone who asserts, on the one hand, that there are other natural species besides man, that there are species which have not only " accidental " differences accessible to " science " but also specific differences " philosophically speaking," yet, on the other hand, when pressed to defend his views concerning the reality of these " natural " as distinct from " systematic" groupings finds it impossible to illustrate his point with a single specific example.127 " There is not only evasion here, but hopelessness." 128
If we are concerned with rendering intelligible the articulations of the living world in rational terms, then, " we must not consider the diversity of natural things as proceeding from the various logical notions or intentions which flow from our manner of understanding, because reason can apprehend one and the same thing in various ways." 129
The subjectivist is usually primarily concerned about the workability of his units and will set the limits of his species where the discontinuities corresponding to his criteria, which are usually external [i. e., epistemological], are most obvious to him. The believer in the reality of species, on the other hand, will strive ideally to find the achievements of nature in their integrity, i. e., the species as they really exist, and to prepare descriptions expressing these realities. In other words, while the subjectivist adapts nature to his concept of order and practicality, the realist makes an effort to adjust his concept, descriptions, and circumscriptions to the entities as they exist. Of the two outlooks, the latter is certainly to be preferred, if workable.130
127 Adler, in " The Hierarchy of Essences," p. 26, makes this point
crushingly via
the simple observation that, so far as induction is a process of inferring
from
observable particulars to generalization about kinds, whatever the kinds
may be
and whether the generalization is necessary and certain or contingent and probable,
in every case " induction with respect to kinds can be viewed as a
process of
concluding from instances or particular evidences that a nominal
definition is
real or, in other words, that the kind for which a definition can be
nationally or
verbally formulated really exists " (my emphasis).
128 Adler, The Problem of Species, p. 211.
129 Thomas Aquinas, Summa Theol., I, q. 76, a. 3 ad 4.
130 Jean R. Beaudry, " The Species Concept: Its Evolution and Present Status," Revue Canadienne de Biologie, 19 (September 1960), p. 234. Beaudry goes on to add: " Nature, however, has evolved with an utter disregard of the practical problems that would face its students, and it is sometimes found that its realities are so complex, elusive, or inconvenient that they cannot be satisfactorily encompassed into the units of the systems which have been invented for the purposes of its study. If objectivity requires that these systems be adapted to nature, and not that nature be adapted to them, the limitations of our conceptual means, of our methods of graphic representation, of our systems of codification, impose boundaries to our quest for the ideal, beyond which confusion replaces order. Such appears to be the situation in taxonomy when we attempt to make a classification too highly phylogenetic, or to codify all the facets of the multifarious species. A compromise then has to be reached between the ideal and the workable. Realistic systems of classification and applied species concepts embody this idea, where necessary." In this connection, see R. J. Nogar, The Wisdom of Evolution, pp. 324-35. It should be noted that Dr. Nogar's remark on p. 332 that, with such an animal as the domestic cat, for example, " if the root reason for all the characteristics were known, a logical or dialectical definition with genus and specific difference "--proximate genus and essential difference in the traditional sense, he means-- " could be assigned," is a remark not only contrary to the major thrust of his own analysis (and a remark inserted for the sake of an old teacher, I suspect), but a violation of the principle of parsimony. In fact, with felix domestica as with every other plant, animal, and human population, there is every reason to consider that the unifying intelligible reason for all morphological, physiological and ecological characteristics lies not in the organism as a distinguishable natural unity but in the relation between the organism and its proper environmental niche--if you like, in the " economic system " of the organism. (It is in this sense and this sense alone, moreover, that Darwinism can be regarded as having provided a " scientific base " for the Marxian ideology).
And it is workable if and to the extent that the reasons for the differences of the natural groups, the true and proper causes, can be assigned in the patient work of research. Such at least was the conviction of Aristotle: " The best course appears to be that we should follow the method already mentioned, and begin with the phenomena presented by each group of animals, and, when this is done, proceed afterwards to state the causes of those phenomena, and to deal with their evolution." 131 Such, too, is the conviction of evolutionary science, and it is striking that a survey of the definitions and statements concerning species made by the leading evolutionists today can conclude that " all of them imply the reality of species and entirely neglect the idea that it is only a construct of the human mind," 132 and that all of them are concerned with a causal account of this reality.
131 Aristotle, De partibus animalium, Bk. I, ch. 1, 640 a 14-16.
132 Beaudry, art. cit., p. 224.
It is perhaps even more striking that, in the end, the modern species problematic finds itself compelled, even as we shall see does the traditional problematic, to reject and abandon " the idea that species are always distinguishable by means of morphological or external characters."133
Striking and decisive parallels, no doubt, but not surprising ones: for both are linked to the common aim of rational understanding by a common logic and bounded, formally speaking, by a common set of problems. What their divergence is in this matter we shall finally see, but first we must follow the indications afforded by the instincts of mankind, which recognize a difference between elephants and oysters and seaweed and cactus as between natural groups or kinds; and recognizing these differences, see what can be said about their reasons for being. In the end, to see why there are natural kinds is to see what they are. Then we may ask if they further divide before the mind in some distinctively philosophical sense. What, then, in the present state of research, is the causal status of the natural articulations of nature?
At the outset of their work, but precisely because they were concerned from the first with the assignation of truly proper causes, evolutionists tended to confuse two essentially different problems--species transformation and species multiplication-- in a single concept. This confusion was even written into the title of Darwin's classic text, The Origin of Species.
Subsequent research made it clear, however, that the question of evolutionary change as such (the transformation of species in time] is fundamentally distinct from the question of the origin and multiplication of species as such. The essential aspect of species transformation is the continuous genetic and adaptive change within the population composing the species; while the essential note of species multiplication is the development of reproductive isolation (discontinuity) between populations of the species, i. e., the splitting up of an originally uniform species into several daughter species--the multiplication of species in space.
133 Ibid., p. 226.
" The problem of the multiplication of species, then, is to explain how a natural population is divided into several that are reproductively isolated, or, more generally, how to explain the origin of a natural population that is reproductively isolated from pre-existing species." 134 This problem--like the " higher from lower forms " question which we shall address in Sec. VIII --resists resolution as long as one approaches it primarily in the non-dimensional terms of " formal perfection " univocally conceived and bridgeless discontinuity. Just as at the level of radical kinds, as we shall see, " evolution would be shocking only for a strictly Aristotelian conception of the causal process reduced to the transmission of an identical form--while the individual existence of the effect is overlooked,"135 so in a similar manner here at the level of natural kinds as yet undifferentiated further according to the possible categories of modes of real difference--superficial and radical--the typological impasse, the impasse consequent upon the insufficiently critical reification of cognitive intentions, is transcended as soon as it is reconceptualized in terms of the population structure of species. In both cases, the discourse is governed throughout by the analogous realization of the formal axiom, causae sunt ad invicem causae.
In its main lines, the view of species as interaction-structured populations is not hard to sketch, and it underpins causally the " instincts " of mankind which lead men to form the class of birds and the class of fishes, and so on.
As we have seen, the process of differential gene transmission is the key to the necessity of biological evolution, because it is the source and stable basis for the establishment of novel variations. When variation reaches the threshold of specific discontinuity in the evolution of a given life form, however, the intervention of so-called isolating mechanisms, " the evolutionary devices for preventing interbreeding between closely related and formerly united populations," 136 must usually intervene in
134 Mayr, Animal Species and Evolution, p. 431.
135 Joseph de Finance, Existence et Libertรฉ (Paris: Vitte, 1955), p. 263.
136 Simpson, The Meaning of Evolution, p. 238.
the process of differential gene transmission if the threshold is to be actually crossed. Basically, this amounts to saying that some degree of spatial isolation is ordinarily prerequisite (requisitum ut in pluribus) to species formation. Dobzhansky succinctly comments: " It is the geographic separation of races which prevents them from crossing and exchanging genes at rates which would result in fusion of these races into a single variable population. . . . Yet as races diverge more and more, they become adapted to different environments in their respective territories or to the different modes of life," until finally behavioral and psychological traits are established which (sometimes along with anatomical configurations) serve to insure against free gene exchange even should the geographical barriers between the distinct populations be in one way or another removed.137
In other words, the real problem in attempting to experimentally and causally ground our insight into the metalogical status of natural kinds in an evolutionary world, into the process of speciation, becomes one of determining (relative to reproductive activity between genetically consonant groups) the threshold of behavioral disparity which will effectively sustain the variance of gene frequencies in the respective gene pools: it is not a question of an absolute, formal discretion, but rather of a sometimes ambiguous behavioral frontier.138
137 Dobzhansky, Evolution, Genetics, and Man (New York: John Wiley & Sons, Science Editions, 1963), pp. 183-4. Cf. Genetics and the Origin of Species, pp. 205 and 255: " The real problem is how much gene exchange between the diverging populations is possible without arresting and reversing the divergence." " The patterns with superior adaptive values form the ' adaptive peaks '; the peaks are separated by the ' adaptive valleys' which symbolize the gene combinations that are unfit for survival and perpetuation. The reproductive isolating mechanisms, as well as the geographic isolation, interdict promiscuous formation of the gene combinations corresponding to the adaptive valleys, and keep the existing genotypes more or less limited to the existing peaks. The observed discontinuity in the body structures and in the ways of life is a result of adaptation to the discontinuity of the secular environments on our planet."
138 Cf. Mayr, Animal Species and Evolution, p. 523: " The range of a species is delimited by a line beyond which the selective factors of the environment prevent successful reproduction. This line is called the species border. Single individuals may appear annually in considerable number beyond this line, yet fail to establish themselves permanently. Even if they succeed in founding new colonies, these are sooner of later eliminated in an adverse season. As a result, the species border, though fluctuating back and forth, remains a dynamically stable line," i. e., so long as the environment does not suffer fundamental change.
Contextualizing these considerations within the general framework of the basic theory established by contemporary evolutionary science, we may say:
A mutation produces discrete differences and to this extent its appearance [like that of an individual organism as such] is an instantaneous and discontinuous evolutionary event, whether its effects be small or large. But it is populations, not individuals, that evolve. For a given mutation, regardless of its " size " [i. e., visible morphological impact] to become involved in the origin of a new and especially of a highly distinctive group of animals it must spread through a population and while doing so and thereafter it must become integrated in a new sort of genetic system.139 It is very nearly impossible to imagine these processes occurring except by transition over a long sequence of generations, and certainly no conclusive, or even really suggestive, opposite example is provided by the paleontological record.140
139 Thus Dobzhansky comments (Evolution, Genetics, and Man, pp. 147 and 177): " What natural selection does is to establish proportions of the genotypes at which the average fitness of an individual in the population is the highest attainable one, but the high fitness of the population as a whole is purchased at the price of producing some genetically unfit individuals (the homozygotes)." " The gene pool of a sexual population comes, therefore, to consist of genes that are coadapted, that is, that fit well together when present in heterozygous individuals. . . . The process of coadaptation makes a species something more than a collection of individuals." Simpson himself adds at this point in his text the following footnote: " This special aspect of evolution is expertly treated in C. D. Darlington, The Evolution of Genetic Systems (Cambridge, England: The University Press, 1939). See also C. H. Waddington, An Introduction to Modern Genetics (New York: Macmillan, 1939); and his " Evolution of Developmental Systems " (Nature, [147] 1941), 108-110."
140 Simpson, The Meaning of Evolution, pp. 233-4. Simpson's descriptive analysis of the physical causality involved and the conclusion to which it leads him (namely, that " it is very nearly impossible to imagine these processes [effecting speciation] occurring except by transition over a long sequence of generations") receives prima facie reinforcement in W. H. Kane's metaphysical analysis of " Existence and Causality": " A cause which is limited in being can produce something similar to itself, but not something diverse, and so it cannot produce an effect distinct from itself as such, that is, as distinct." The reason is that " secondary causes do not produce the whole effect and all that is in it, but always presuppose something, and then produce as their proper effects, not existence as such, but other perfections which limit and determine existence." " Hence an agent which is limited and determined with respect to genus, species, and accident has limited power determined to effects which are similar to itself as the agent, and it acts to produce something similar to itself." (The Thomist, XXVIII [Jan., 1964], pp. 90 and 89.) William C. Boyd provides in effect an empiriological formulation of these abstract considerations in application to the concrete evolutionary data in his consideration of " The Contributions of Genetics to Anthropology ": " It is true that we now think of evolution as resulting from the action of selection on genetic mutations. But this does not mean that there are no limits to what the mechanism can accomplish. The genes of any animal that survives and competes successfully with its fellows in the struggle for existence must be reasonably harmonious with one another, for anything else is not compatible with the continued existence and reproduction of the animal. Each creature is like its ancestors in all but a few respects. The differences which have arisen must necessarily coexist in harmony with the more extensive, more complex elements which are not different. Each character is dependent on the interaction of many genes, so that it will be easier to continue a line of evolutionary change for which many of the modifiers are already present [orthoselection] than to start off on an entirely new line. Species are not constructed de novo, but on the basis of genotypes already existing. In most cases no sort of modification which is within the capabilities of the existing genes and possible mutations would be definitely advantageous, and in many other cases only one particular modification would be an advantage." (In Anthropology Today, Sol Tax, ed. [Chicago: the University of Chicago Press, 1962], p. 66). Thus the adaptive flexibility and evolutionary advance observed at the level of the population is only possible by reason of the structural stability and limited adaptive range of the individual organism as such. Cf. Raymond J. Nogar, " Evolution: Scientific and Philosophical Dimensions," pp. 23-66, esp. p. 58.
page 142
Thus, " with the aid of isolating mechanisms, natural selection directs and guides the variety away from the parent stock and on to the development of new forms of life." 141 It is necessary to keep clearly in mind in this case, as in every case of causal analysis, that the principles of explanation do not lie at a simply visual level but in the order of reason. In terms of the proper causes involved in this question of the existential articulations of nature, " visible characters, and especially the macroscopic ones, will always be the most convenient . . . but where nonexistent or poorly developed, the invisible or less convenient should be resorted to, because the species exist whether visibly expressed or not," and " the essential sets of genes which constitute the species cannot be seen."142
141 Nogar, The Wisdom of Evolution, p. 90.
142 Beaudry, art. cit., pp. 235 and 234, respectively.
A large fraction of the difficulties experienced with many modern definitions of species reside in the fact that these definitions insist not on the essence of species but on their limits with other species. As implied above, a definition based on essence automatically sets up limits which stem from within, whereas one based on limits or barriers with other species, which are at least partly extrinsic, does not necessarily suppose identity of essence. The essence of the process of speciation is thus not the development of reproductive isolation, but the development of a different genetical identity within a group. The development of this genetical identity necessitates isolation which, however, may primarily be spatial, i. e., geographical. But a segment of a population isolated by distance does not, because of that, become a distinct species. It only becomes so when it has developed its different essential genetical identity, suddenly or gradually. When this takes place suddenly ([as sometimes in plants] through polyploidy), reproductive isolation often accompanies it, but it is doubtful that it should always do so.143
Mayr summarized the status of research on the metalogical character of natural kinds by referring to them as the causal keystone of the evolutionary process, even as natural selection is the conceptual keystone of evolutionary explanation:
The evolutionary significance of species is now quite clear. Although the evolutionist may speak of broad phenomena, such as trends, adaptations, specializations, and regressions, they are really not separable from the progression of entities that display these trends, the species. The species are the real units of evolution, as the temporary incarnation of harmonious, well-integrated gene-complexes. And speciation, the production of new gene complexes capable of ecological shifts, is the method by which evolution advances. Without speciation there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress. The species, then, is the keystone of evolution.144
We shall see in Section VII that this means that hierarchization is an ontological characteristic of evolutionary advance, therefore establishing the temporal prerequisite and structural
143 Ibid., p. 227.
144 Mayr, Animal Species and Evolution, p. 621. See also ibid., " The Role of Species," pp. 422-3; and " The Species as a Potential Evolutionary Pioneer," pp. 587-588.
preconditions for the emergence of man, as well as providing the clue to the problem of choosing for non-subjective reasons a criterion of evolutionary progress; but it is just at that juncture that the primary concerns of modern biology meet those of traditional philosophy in the question of species, and we shall have to deal at that point with the problem of the two hierarchies, one imperfect, one perfect (in the senses already defined in Sec. I above), in their existential interarticulation. What focusses our immediate attention is Dobzhansky's critical remark to the effect that " modern systematics has vindicated the intuitive conviction which workers in this field always had, and which was expressed concisely by Bateson (1922): ' Though we cannot strictly define species, they yet have properties which varieties have not, . . . and the distinction is not merely one of degree.' "145
145 Dobzhansky, Genetics and the Origin of Species, p. 259, my emphasis. " Although individuals, limited in existence to only a short interval of time, are the prime reality with which a biologist is confronted, a more intimate acquaintance with the living world discloses a fact almost as striking as the diversity itself. This is the discontinuity of the variation among organisms. If we assemble as many individuals at a given time as we can, we notice at once that the observed variation does not form any kind of continuous distribution. Instead, a multitude of separate, discrete, distributions are found. The living world is not a single array in which any two variants are connected by unbroken series of intergrades, but an array of more or less distinctly separate arrays, intermediates between which are absent or at least rare. Each array is a cluster of individuals which possess some common characteristics. Small clusters are grouped together into larger secondary ones, these into still larger ones, and so on in an hierarchical order." (Dobzhansky, Genetics and the Origin of Species, p. 4). " Formation of discrete groups is so nearly universal that it must be regarded as a fundamental characteristic of organic diversity." (Ibid., p. 6.) " Scientifically considered," therefore, in every dimension of the living world, " the similarities and the differences are incommensurable. Both have to be studied. It is folly to neglect either." (Mankind Evolving, p. 219) " Hence, the living world is not a formless mass of randomly combining genes and traits, but a great array of families of related gene combinations, which are clustered on a large but finite number of adaptive peaks. Each living species may be thought of as occupying one of the available peaks in the field of gene combinations. The adaptive valleys are deserted and empty." (Genetics and the Origin of Species, pp. 9 f.) " Biologists have exploited the discontinuity of variation to devise a scientific classification of organisms. The hierarchical nature of the observed discontinuity evidently lends itself admirably to this purpose. For the sake of convenience the discrete clusters are designated races, species, genera, families, and so forth. The classification thus arrived at is to some extent an artificial one, because it is a matter of convenience and convention which cluster is to be designated a genus, family, or order. But the clusters themselves, and the discontinuities observed between them, are not, as sometimes contended, abstractions or inventions of the classifier." (Ibid., p. 5) " It must be stressed that this discontinuity [in the living world] exists regardless of whether it is or is not used by the systematists for their purposes, and for that matter whether it is studied at all. The discontinuity, the absence of immense multitudes of potentially possible gene combinations, is an objectively ascertainable fact." (Ibid., p. 255.) " The hierarchic nature of biological classification reflects the objectively ascertainable discontinuity of adaptive niches, in other words the discontinuity of ways and means by which organisms that inhabit the world derive their livelihood from the environment." (Ibid., p. 10)
It is interesting in this regard to contrast the conclusions of those quintessentially " modern " philosophers who have indeed broken with the Aristotelian pattern of questions and substituted in their place a new set of problems centered on the universe of discourse rather than the universe of being. Those thinkers who really seek to inaugurate a new type of questioning based on a new type of logic, as Dewey wrongly thought of Darwin as having done, arrive at a very different assessment of the status of natural kinds than does the causal assessment typical of traditional and contemporary approaches alike. Anthony Quinton, Fellow of New College and University Lecturer in Philosophy at Oxford, may be cited as an archetypical case of a ' philosopher' who got off at the celebrated " linguistic turn ":
The devices with which we classify the objects of experience are influenced in their formation by our interests as well as by the intrinsic nature of the things themselves. Thus a difference in kind in the natural order reflects only a dissimiliarity that is definite and interesting enough to lead us to invent a special word to mark it with . . . such a difference could be said to rest on the solidity with which the conceptual distinctions we have chosen to introduce are entrenched in our way of thinking about the world. Natural differences in kind can still be important, even if they are all, in Adler's sense, no more than apparent [i. e., differences of degree].146
In the language of Beaudry, this is unquestionably the subjectivist outlook, which differs from the realist outlook in its
146 Anthony Quinton, " Mortimer Adler's Machine," New York Review of Books, XI (21 November 1968), p. 4. See references to Waddington's criticism of the linguistic approach to nature in fn. 148 below.
indifference to the logic involved in the process of determining whether two things differ in degree or kind, and to the wealth of empirical evidence that is now available to decide how natural kinds stand in their intrinsic nature prior to and independently of our personal and psychological interests. By contrast, Beaudry's " realist " considers that our affirmation of real and not just seeming differences in kind in the natural order rests today principally on the intrinsic nature of the things themselves, by virtue of the fact that " the development of genetical and evolutionary principles has permitted the study of individuals and populations not only by means of their external characters, and their distribution in space and time, but also through their internal organization and the dynamics of their interrelationships." 147
There is no doubt that the species is something objective, that it is constituted by a substance incorporated in a mass. The existence of many such specific substances has been abundantly revealed by genetic studies. . . . The masses formed by these substances are not unitary entities but collective ones. . . . The distinctness of the individuals does not destroy the reality of the mass, since the individuals are not independent but are all interrelated in space and in time by physical links, in the form of gametes, which transmit the essential sets of genes to the distinct parts. The existence of a multiplicity of these different essential sets of genes is expressed through different integrated groups of external and internal characters, which are often sharply discontinuous but not completely so. The sophisticated arguments of various kinds of philosophers cannot hold when confronted with the impressive bodies of data collected by hundreds of experimentalists, about the reality of species, and summarized in books such as those of Clausen (1951), Clausen, Keck, and Hiesey (1940, 1945,1948), Clausen and Hiesey (1958), Cuenot (1936, 1951), Dobzhansky (1951), Huxley (1942), Mayr (1942), Simpson (1944), Stebbins (1950), and many others.148
147 Beaudry, art. cit., pp. 219-20.
148 Ibid., p. 225. " The idea that species are always distinguishable by means of morphological or external characters has had to be rejected. Different basic sets of genes can originate without accompanying visible manifestations." (p. 226) One may be permitted to marvel at Mr. Quinton's unflinching readiness to entrench genetic origins " in our way of thinking about the world "--after all, are not genes words? What Waddington refers to as " the inadequacy of the fashionable method of linguistic analysis " in respect of the problems presented by living things may be found spelled out in chs. 3-7 of The Ethical Animal, pp. 34-71, esp. ch. 4, pp. 46-9. (The quoted remark is from p. 83.) Moreover, Dr. Waddington's familiarity not only with the doctrines of both Logical Positivism and Linguistic Analysis but also with many of the key personalities expounding those doctrines (he was a personal friend of Wittgenstein, for example--see esp. " Squaring the Vienna Circle," ch. 3 of The Ethical Animal, pp. 34-45), makes his conclusions from the standpoint of an evolutionary biologist all the more interesting for the philosopher. The linguist, of course, need not be bothered with what pertains to the universe of being in its intrinsic determinations--until, of course, they happen to become " entrenched in our way of thinking about the world." Then we may be assured that Quinton et al., like those other " scholarly men" mentioned by Kant (Prolegomena, ed. cit., p. 3), will be on hand " to inform the world of what has been done."
From the standpoint of explanation by proper causes, then, there are three stages or levels in the evolutionary process and establishment of species: the origin of genetic diversity constitutes the first level; once arisen, the mutations are scattered throughout the population--they enter its gene pool, where they come under influence of selection, migration, and geographical isolation, thus establishing the second level of the evolutionary speciation process, where the impact of environment effects the historical changes in the living populations; finally a third level is reached when the sustained operation of isolating mechanisms achieves a relative fixation of the diversity cumulatively attained on the preceding two levels, so that a stabilization through a new genetic equilibrium is effected both within and among the evolving groups.
The essential feature of the process of speciation, " of the transformation of races into species, is, then, the development of reproductive isolation between Mendelian populations ";149 while the essence of the species itself " resides in the common, basic genetic endowment of its members, which is always expressed in interbreeding, actual or potential." 150 In this way, a species constitutes a group unity structured intrinsically through interaction, that is, a concrete universal. " The species can thus be succinctly defined as follows: it is a community of
149 Dobzhansky, Evolution, Genetics, and Man, p. 184.
150 Beaudry, art. cit., p. 232.
individuals possessing common essential sets of genes, and actually or potentially related [proximally] through interbreeding."151
Dobzhansky goes so far as to conclude that " it is, then, not a paradox to say that if some one should succeed in inventing a universally applicable, static definition of species, he would cast serious doubts on the validity of the theory of evolution "152--which introduces us to our pivotal consideration.
151 Ibid. Mayr (Animal Species and Evolution, pp. 27-9) points out " The Difficulties Posed by Asexuality" and which have led some authors to go " so far as to abandon the biological [i. e., genetic] species concept altogether and return to the morphological species for sexual and asexual organisms," but sums up by pointing out further that " the advantages of the biological species concept are far greater than its shortcomings. Difficulties are rather infrequent in most groups of animals and are well circumscribed where they do occur. . . . Indeed, the biological species concept, even where it has to be based on inference, nearly always permits the delimitation of a sounder taxonomic species than does the morphological concept." See also Beaudry's remarks on " Self-fertilization, Apomixis, and the Species," pp. 232-3. Finally, it should be mentioned that, as Stebbins in particular has pointed out (G. L. Stebbins, Variation and Evolution in Plants, New York: Columbia, 1950, esp. pp. 189-90), in the framework of the basic genetic view several different species definitions--whether in terms of ecology, geography, even morphology--remain legitimate and possible. As Maritain remarks in quite another context (The Degrees of Knowledge, p. 200), "the capacity of a doctrine to integrate whatever is positive in systems which invoke different principles might perhaps be taken as an indication of its truth."
152 Dobzhansky, Evolution, Genetics, and Man, p. 182. Thus we are able (by clearing away the mists of metaphor) to correct and verify a philosophic no less than scientific insight formulated by Bergson relative to the evolutionary question in an initial--if not altogether satisfactory--manner as early as 1907, namely, the intrinsic natural necessity for continual causal play throughout a natural developmental process (cf. Creative Evolution, pp. 33 f. and 252). With customary clarity, Dobzhansky (Genetics and the Origin of Species, p. 17, inter alia) cuts through ambiguities in this matter: " Methods of experimental genetics apply directly only to forms which can be crossed and which produce hybrids. Genetic analysis is, accordingly, limited to differences on the individual, racial, specific, and at most generic levels, which are usually regarded as the province of microevolution. A geneticist can approach macroevolutionary phenomena only by inference from the known microevolutionary ones. It is obviously impossible to reproduce in the laboratory the evolution of, for example, the horse tribe, or for that matter of the genus [of fruit fly] Drosophila. All that is possible is to examine the evidence bearing on macroevolution which has been accumulated by paleontologists and morphologists, and to attempt to decide whether it agrees with the hypothesis that all evolutionary changes are compounded of microevolutionary ones. This difficult but important task has been brilliantly accomplished in recent years by Simpson (1949) for paleontological and by Schmalhausen (1949) and Rensch (1947) for comparative anatomical and embryological evidence. The three authors find nothing in the known macroevolutionary phenomena that would require other than the known genetic principles for causal explanation. The words ' macroevolution' and ' microevolution ' are relative terms, and have only descriptive meaning; they imply no difference in the underlying causal agencies." For a detailed and interdisciplinary report on the research in this connection, cf. Glen L. Jepsen, George Gaylord Simpson, and Ernst Mayr, eds., Genetics, Paleontology, and Evolution (New York: Atheneum Books, 1963). The most important single work covering this matter is, however, George Gaylord Simpson's masterful The Major Features of Evolution, which has in 1965 gone through its fourth printing. Naturally, there are informed pockets of opinion which simply reject the majority view, even though in this case the majority is near-unanimity and the dissenting minority can point to no known processes at work in the world of life other than those detailed and accounted for by the proponents of the ' synthetic' theory. A most recent exposition of the arguments for dissent, such as they are, can be found in Emile Guyenot's The Origin of Species (New York: Walker and Company, 1964). This author concedes a microevolution continually operative among races and even species, but, finding no direct proof for " evolution hi depth " which involves modifications of genera, families, etc., he rejects the synthetic view. The intervening variable of geologic time which is necessary for large scale evolution obviously counts for little in the interpretation of such thinkers as this. Yet the fact remains that " with respect to the evolution which has actually taken place in the history of the earth, an observer of only the now-living animals and plants is still in a position of judging a long movie film by only the last picture frame." (Dobzhansky, Evolution, Genetics and Man, p. 284.) See fn. 66 above.
Can this genetic and authentically causal conception of specific structures be assimilated and expressed in terms of the essential principles of traditional ontology, or is it contrarily related to their texture and sense?
(to be concluded)
