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The Metaphysics of Evolution*

Abstract

Extreme variation in the meaning of the term “species” throughout the history of biology has often frustrated attempts of historians, philosophers and biologists to communicate with one another about the transition in biological thinking from the static species concept to the modern notion of evolving species. The most important change which has underlain all the other fluctuations in the meaning of the word “species” is the change from it denoting such metaphysical entities as essences, Forms or Natures to denoting classes of individual organisms. Several authors have taken notice of the role of metaphysics in the work of particular biologists. An attempt will be made in this paper to present a systematic investigation of the role which metaphysics has played in the work of representative biologists throughout the history of biology, especially as it relates to their species concepts.

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1 Throughout this paper I will be talking about “metaphysics” and “metaphysical entities”. By “metaphysics” I mean the study of the basic kinds of entities which one has to postulate to explain everything that exists, what their nature is, why the postulation of their existence is necessary, and so on. This is “metaphysics” in the good sense. But because so many of the entities which philosophers have postulated have gradually lost whatever empirical content they might have had at one time, the term “metaphysics”, especially “metaphysical entity”, has taken on a bad connotation. By “metaphysical entity” I mean any entity postulated as one of the basic constituents of the world but which turns out to have no empirical content. The identifying of a genuine metaphysical entity is not always easy, especially when the system of which it is part is first being formulated. Hertz's hidden bodies and Wittgenstein's objects are obvious cases of metaphysical entities. As it turns out, so are Aristotle's essences. But who could have predicted that aether and caloric would go the way of metaphysical entities, whereas electrons and genes would retain their status as theoretical entities. The difference is not between those that turn out to exist and those that do not but between those that retain characteristics by which their existence or non-existence could be determined by observation, no matter how indirect, and those that do not.

2 Several biologists have been treated separately, for example, Mayr Ernst's excellent paper, “Agassiz, Darwin and Evolution”, Harvard Library Bulletin, xiii (1959), 165194. See abo several papers in Glass Bentley, Temkin Owsei and Straus William L. Jr., (eds.), Forerunners of Darwin: 1745–1859 (Baltimore, 1959).Lovejoy Arthur O. treats the effect on biology of the Great Chain of Being and the Principle of Plenitude exhaustively in his The Great Chain of Being (Cambridge, Mass., 1936).

3 The disparity between the essentialist view of species and that of a Darwinian evolutionist can be seen clearly in the following quotation from Joseph H. W. B., An Introduction to Logic (London, 1916), 28.

“Biologists do not seem always to have asked themselves which they mean when they write about evolution. Do individual men evolve, or is it the human nature which is displayed in them all? and if the latter, and men are descended from animals whose nature was not human nature, what is the relation of the two, or are human nature and pithecanthropous nature the same common nature? and if so, are there many species or only one?” The difficulty is with Aristotelian metaphysics. Neither individuals nor natures evolve. Whole classes of organisms change during successive generations to such an extent that members of early generations are no longer classed in the same species with their later progeny.

4 These characterizations of the philosophy of Plato and Aristotle are, of course, extremely simplified but I hope not to the point of falsification. Similarly, there are several interpretations of the philosophies of these two men. I have chosen the traditional interpretation to describe in each case because these were the doctrines that affected biologists.

5 It is the failure to appreciate the metaphysical referent of “species” which robs a muchcited paper by Conway Zirkle of much of its explanatory value, “Species before Darwin”, Proc. Am. Phil. Soc., ciii (1959), 638. Although Zirkle is aware of the danger of inferring the meaning of a term from its etymology, he says:

“The first scholars who used the word ‘species’ wrote in Latin and, when they switched to their vernaculars, they carried the Latin word with them. Thus, the word ‘species’ in our modern languages is only a bit of naturalized Latin. ‘Species’ comes from ‘specere’ meaning to look at, to behold. The species of an object then are merely its appearances, not its inward essence. Thus the word used to label the concept introduced an uncertainty principle into the concept itself because, from the very earliest times, appearances proverbially have been deceitful.

“The word ‘species’ also was used within the framework of the dualistic philosophy that dominated both classical and Christian thinking. In this setting, the appearances of an object—its species—seemed superficial, and the appearances were contrasted routinely with some inner reality—with some inner Platonic ideal. Thus, if species turned out to be epherneral, if they changed erratically into other species, it really meant very little. It was only to be expected. Naturally, in such a setting all species took on some of the qualities of the specious.”

On the contrary, just because appearances were thought to be deceitful, philosophers had as the primary object of the word “species” the inner essence or Form and not the fleeting appearances.

6 Because of a prejudice against change that has permeated Western thought, many scientists assumed, unlike Galileo, that remaining at rest needed no explanation but beginning to move or continuing to move did. This prejudice was reflected in biology by the assumption that no mechanism had to be provided for species being static but a very powerful mechanism had to be provided for any claim that species evolved. Biologists now realize that a species not evolving for long periods of time stands just as much in need of explanation as a species evolving in that period of time.

7 Aristotle, De Anima, 415a26. All Aristotle citations are from the W. D. Ross edition.

8 Everett W. Hall, “The Scientific Revolution in Biology”, reprinted in Madden Edward H. (ed.), The Structure of Scientific Thought (Boston, 1960), 123.

9 Zirkle, op. cit. (5), 640, 637, 639.

10 Aristotle, De Generatione Animalium, 747a25.

11 Aristotle, Historia Animalium, 607a1.

12 Ibid., 585b33 and Aristotle, op. cit. (10), 721b33. Zirkle condenses these two examples into one, op. cit. (5), 637.

13 Theophrastus, Enquiry into Plants, II, iv, 1 and Causes of Plants, I, ix, 2. All citations from Theophrastus will be from SirHort's Arthur translation of the Enquiry into Plants (Cambridge, 1916) and Dengler R. E.'s translation of the first book of the Causes of Plants (Philadelphia, 1927). There is no English translation of the remainder of the Causes, although several Latin versions are easily available; e.g. Wimmer Fredericus, Theophrasti Erestii Opera (Paris, 1866).

14 Ibid., Enquiry, II, ii, 9; see also Enquiry, VIII, viii, 2.

15 As these statements indicate, the Greeks were none too clear concerning the mechanisms of reproduction. For further explanation see the next section of this paper.

16 Aristotle, op. cit. (ii), 550b26; op. cit. (10), 732a26.

17 Theophrastus, Enquiry (13), III, i, 1&5; Causes (13), I, v.

18 Aristotle, op. cit. (10), 721a3.

19 Theophrastus, Enquiry (13), II, i, I.

20 Ibid., II, iv, 4.

21 Aristotle, op. cit. (10), 721a3 & 762b25; op. cit. (11), 551b26 & 551a13; Theophrastus, Enquiry (13), II, iv, 4. Given the extremely close connection between plants and the soil and Aristotle's authority as to the spontaneous generation of lower animals from inorganic matter, one would have expected Theophrastus to have assumed extreme spontaneous generation among plants. Such is not the case. Although Theophrastus admitted that on rare occasions a plant might arise directly from certain metaphysical principles latent in the soil, the most probable explanation of putative causes of spontaneous generation was that seeds were already present in the soil but unnoticed. Enquiry (13), III, i, 2 & 5; Causes (13), I, v.

22 Hantz H. D., The Biological Motivation in Aristotle (New York, 1930); Randall John Herman Jr., Aristotle (New York, 1960); and Grene Marjorie, A Portrait of Aristotle (Chicago, 1963).

23 One apparent difficulty for Aristotelian metaphysics (which several authors have noted) can be handled merely by distinguishing between species as essences changing and individuals changing their species. At one extreme is the philosopher Caws Peter, The Philosophy of Science (Princeton, 1965), 41, who ignores all of the phenomena previously discussed when he says:

“It used to be thought, nevertheless, that there were [sharp] borderlines [between species], and that they could not under any circumstances be crossed; every living thing belonged to its fixed species, every inanimate object to its fixed class, and a man to his station in life. This doctrine was undermined by the theory of evolution, which envisaged species as developing out of earlier species and themselves subject to further changes.”

On the contrary, although species as essences were believed to be fixed with sharp borderlines, these borderlines were quite commonly crossed by individual organisms.

Conway Zirkle, op. cit. (5), 636 & 638 goes to the other extreme and confuses individuals changing their species with species changing. See footnote (5) as well as Arber Agnes, Herbals, Their Origin and Evolution (Cambridge, 1938), 5. In none of the examples given by Zirkle are essences Changing. Either individuals of one species are giving rise to individuals of another species or else the individuals are themselves becoming members of another species directly. Species in the Aristotelian sense remain in the face of all this change constant, static and immutable. That is the whole purpose of essences.

24 Aristotle, De Partibus Animalium, 640a17 & 642a15; De Mundo, 403b26; Physica, 198a22.

25 Ibid., 198b23; see also 196b29 & 197b14.

26 Ibid., 198a25; see also Copleston Frederick, A History of Philosophy (Westminster, 1960), i, 313, and Ross W. D., Aristotle (London, 1937), 74.

27 Aristotle, op. cit. (11), 547b18; see also op. cit. (10), 761a15–763b15.

28 Aristotle, Metaphysics, 1034b4.

29 The force of this statement is dissipated, however, when it is discovered that Harvey considered anything capable of beginning life an “egg”. Harvey William, Exercitationes de Generations Animalium (London, 1651).

30 Raven C. E., John Ray, Naturalist (Cambridge, 1942), 375, 462, 469, 471.

31 This aspect of the static species concept has been well documented. See Edward Poulton, “What is a Species?”, Proc. Ent. Soc. Lond., xciv; Ernst Mayr, op. cit. (2); Conway Zirkle, op. cit. (5). Although Zirkle's mode of expression is confusing, his conclusion about the relation between a belief in the phenomena which he refers to as “species changing” and the formulation of evolutionary theory is still apt:

“One fact in the history of the species concept should be emphasized. The early belief that species were ephemeral and mutable did not promote a belief in evolution. A scientific theory of evolution became possible only after the stability of species was established. Evolution demands that species change but it demands that they change in an orderly fashion.” Zirkle, op. cit. (5), 643. I owe the Poulton reference to Ernst Mayr.

32 Ray John, Historia Plantarum (London, 1686), i, 40.

33 Linnaeus Carolus, Systema Natura, facsimile of the first edition, trans, by Engel-Lederboer M. S. J. and Nieuwkoop Engel (Leyden, 1964).

33a Glass, op. cit. (2), 151.

34 Crombie A. C., “The Notion of Species in Medieval Philosophy and Science”, VIem Congrès international d'histoire des sciences, Actes, i (1950), 261269. Biologists have a tendency to adopt philosophical views only long after they have become outmoded in philosophical circles. For example, Cesalpino (1519–1603) re-introduced Aristotelian essentialism with all its trappings just when philosophers as well as physicists were at last freeing themselves of it. Similarly, nominalism was at its height in the fourteenth century with William of Ockham (1280–1349). It took over 400 years for this philosophical view to filter down (or up) to biologists. The trend is still exhibited today, although the assimilation gap has narrowed considerably. The controversy over operationalism now cropping up in biological journals was fought thirty years ago by philosophers and physicists and, some time later, by psychologists.

35 This same line of reasoning is common in contemporary biology, but the word of approbation has changed from “real” to “objective” or “nonarbitrary”. The issues are the same. See the last section of this paper and Hull David L., “The Effect of Essentialism on Taxonomy”, Brit. Jour. Phil. Sci., xv & xvi (1965).

36 Leclerc Louis, de Buffon Comte, Histoire Naturelle (Paris, 1749), i, 38 & 20. The translation for this and other quotations from Buffon are those of Lovejoy A. O., “Buffon and the Problem of Species”, Popular Science Monthly, Ixxix (1911), 464473, 554567, also reprinted in Glass, op. cit. (2), 84113.Wilkie J. S., “The Idea of Evolution in the Writings of Buffon”, Annals of Science, xii (1956), 4862, goes over much the same ground as Lovejoy but fails to mention Lovejoy's article.

37 Buffon, op. cit., (36), 38 & 20. In stating this objection, Buffon himself makes a logical error, an error which Aristotle would never have made. No matter how much one increases one's divisions in classification, one does not come down to the individual organism without changing logical relations. Taxa are related to each other by inclusion; individuals to taxa by membership. Buck Roger and Hull David L., “The Logical Structure of the Linnaean Hierarchy”, Systematic Zoology, xv (1966), 97111.

38 Buffon, Histoire Naturelle (Paris, 1749), ii, 10.

39 Later Buffon will have to moderate his position as far as the effectiveness of his criterion, but species nevertheless remain real.

40 Crombie, op. cit. (34), 261, also cites the importance of the transition from essentialist explanation in terms of substance and attribute to nominalist explanation in terms of relations.

41 Buffon, Histoire Naturelle (Paris, 1753), iv, 383.

42 Buffon's doctrine of pangenesis undoubtedly played an important role in his overall conceptual outlook, but not everything can be treated in a survey paper such as this one. Similarly, an exhaustive treatment of the relation between metaphysics and the species concept in biology should also treat certain key figures in Germany such as Maupertuis, Oken and Goethe. See Bentley Glass, “Maupertuis, Pioneer of Genetics and Evolution” and “Heredity and Variation in the Eighteenth Century Concept of the Species”, both in Glass, op. cit. (2), 1583 & 144172, as well as Temkin Owsei, “German Concepts of Ontogeny and History around 1800”, Bulletin of the History of Medicine, xxiv.

43 Buffon, Histoire Naturelle (Paris, 1765), xiii, 1, 7, 9.

44 Buffon, Histoire des Oiseaux (Paris, 1770), i, preface; Buffon, Histoire Naturelle (Paris, 1766), xiv, 358.

45 Ernst Mayr has repeatedly pointed out this error. See Mayr Ernst, Animal Species and Evolution (Cambridge, 1965), 600. He cites Goldschmidt R. B., “Evolution as Viewed by One Geneticist”, Amer. Sci., xl (1952), 91, as a contemporary biologist still making this error.

46 For an explanation of the quotation marks around “evolutionism”, see later in this section as well as Charles C. Gillispie, “Lamarck and Darwin in the History of Science”, in Glass, op. cit. (2), 265291.

47 Quoted from Coleman William, Georges Cuvier—Zoologist (Cambridge, Mass., 1964), 144.

48 Ellegard Alvar, “The Darwinian Theory and Nineteenth Century Philosophies of Science”, Journal of the History of Ideas, xviii (1957), 362393.

49 Owen Richard, “Darwin on the Origin of Species”, Edinburgh Review, iii (1860), 257. Recently so-called Baconian philosophy of science has been resurrected to criticize the work of evolutionary taxonomists. The objection is no longer that the evidence for the general fact of evolution is insufficient but that phylogeny cannot be reconstructed with sufficient certainty and in sufficient detail to warrant attempts to classify phylogenetically. See for example, Cain A. J., “Logic and Memory in Linnaeus's System of Taxonomy”, Proc. Linn. Soc. Lond., clxix (1958), 144163; “Deductive and Inductive Methods in Post-Linnaean Taxonomy”, Proc. Linn. Soc., Lond., clxx (1959), 185217; “The Post-Linnaean Development of Taxonomy”, Proc. Lin. Soc., Lond., clxx (1959), 234244; see also Sokal R. R. and Sneath P. H. A., Principles of Numerical Taxonomy (San Francisco, 1963). For criticism of this view see Mayr Ernst, “Numerical Phenetics and Taxonomic Theory”, Systematic Zoology, xiv (1965), 7397, and Hull D. L., “Certainty and Circularity in Evolutionary Taxonomy”, Evolution, xxi (1967), 174189.

50 Cuvier Georges, Leçons d'anatomie comparée (Paris, 1835), i, 64.

51 Cuvier Georges, Discours sur les révolutions de la surface du globe et sur les changements qu'elles ont produits dans le règne animal (3rd edn., Paris, 1830), 95.

52 Georges Cuvier, “Essay on Zoological Analogies”, quoted in Appendix B, Coleman, op. cit. (47), 189. For a general explanation of the errors in this view of scientific laws, see Hempel Carl G., “Geometry and Empirical Science”, The American Mathematical Monthly, lli (1945), 717, reprinted in Madden Edward H. (ed.), The Structure of Scientific Thought (Boston, 1960), 7180. For a comparable explanation which has the biologist specifically in mind, see Hull, op. cit. (49).

53 Coleman, op. cit. (47), 176.

54 Lamarck J. B., Système des Animaux sans vertèbres (Paris, 1806), 14.

55 Gillispie, op. cit. (46), 271.

56 Lamarck J. B., Philosophie Zoologique (1st edn., Paris, 1809), trans. Elliot Hugh (New York, 1963), 213; Gillispie, op. cit. (46), 275.

57 There is considerable truth to Gillispie's statement, “In one sense, therefore, the hiatus that one feels in Professor Lovejoy's work between the temporalizing of the chain of being and the foundation of evolution is inevitable. The latter is not the outcome of the former.” Gillispie, op. cit. (46), 290.

58 Lamarck, op. cit. (56), 59, 70.

59 Ibid., 66.

60 Ibid., 22.

61 Ibid., 67, 133.

62 Ibid., 92, 82, 74.

63 Ibid., 23, 92.

64 Ibid., 103.

65 Ibid., 173.

66 Ibid., 51.

67 Ibid., 176, 178; Lamarck also mentions rather casually, “This direct creation is confined to those living bodies which are at the beginning of the animal and vegetable scales, and perhaps of some of their branches.” Ibid., 237; see also 247.

68 Occasionally even at this late date an arrangement of largely contemporary forms is presented as if it were a phylogenetic tree; e.g. Prosser C. Ladd and Brown Frank A., Comparative Animal Physiology (Philadelphia, 1962), 2. I owe this reference to Miss Judy Todd.

69 Lamarck, op. cit. (56), 44, 183.

70 I do not mean to deny that the principle of plenitude is also operative here. There is, however, an important intermediary between it and Lamarck's decision about the existence of extinct species.

71 Darwin Charles, The Autobiography of Charles Darwin (New York, 1958), 140.

72 Darwin Charles, The Life and Letters of Charles Darwin (London, 1888), iii, 120.

73 Passmore John, “Darwin's Impact on British Metaphysics”, Victorian Studies, iii (1959), 4154, comments on the irony of these passages, noting that Spencer's philosophy is largely non-Darwinian.

74 Mayr Ernst, “Review of Himmelfarb's ‘Darwin and the Darwinian Revolution’,” Sci. Amer., cci (1959), 215.

75 Darwin Charles, op. cit. (71), 140.

76 Ayer A. J., “The Structure of Darwinism”, New Biology, xxii (Baltimore, 1959), 2544, points out just what role deduction played in Darwin's theory. The key issue in any estimation of Darwin as a logician is the difference between deduction and induction. The difference emphasized by Aristotle and successive logicians such as Whewell William, The Philosophy of the Inductive Sciences (2nd edn., London, 1847), ii, 9293, is that deduction supposedly goes from the general to the particular and induction from the particular to the general. Such a characterization is grossly inadequate.

77 Mayr Ernst, “Introduction to ‘On the Origin of Species’ by Charles Darwin” (Cambridge, Mass., 1966), xviii.

78 Himmelfarb Gertrude, Darwin and the Darwinian Revolution (Garden City, New York, 1959), 274.

79 Kaplan Abraham, The Conduct of Inquiry (San Francisco, 1964), especially chapters VI & VIII.

80 Darwin himself evinced admiration for John Herschel, William Whewell and, by praising Huxley's lectures on logic, for John Stuart Mill. Darwin, op. cit. (71), 66, 104; Darwin, op. cit. (72), iii, 3. But all three of these authors held views on inductive inferences incompatible with Darwin's actual practice in the Origin. Both Herschel and Whewell were adamantly opposed to Darwin's way of doing science. Even Mill, although he says that Darwin does not violate the rules of induction, says that it is because Darwin is not concerned with proof but with hypothesis. See Loewenberg James R., “The Mosaic of Darwinian Thought”, Victorian Studies, iii, 16, and Ellegard, op. cit. (48). Passmore Strangely, op. cit. (73), 42, thinks that Darwin and Whewell were largely in accord in their views of philosophy of science. What is at issue here is the nature and role of inductive inferences.

81 For example, Darwin feels called upon to say, “I do not believe that any animal in the world performs an action for the exclusive good of another of a distinct species …” Darwin, op. cit. (77), 211. Neither did Aristotle.

82 Hull, op. cit. (35).

83 Darwin, op. cit. (77), 207, 208.

84 Ibid., 119.

85 Ibid., 484, 485.

86 Ibid., 484.

87 Ibid., 248; see Wittgenstein Ludwig, Philosophical Investigations (New York, 1953), for the opposite view.

88 Darwin, op. cit. (77), 248.

89 Ibid., 245; and the controversy still rages. For a summary of the arguments concerning vicious circularity see Hull, op. cit. (49).

90 Almost all of the various metaphysical viewpoints sketched in this paper can be found expressed in the writings of biologists since Darwin. For example, Thompson W. R., “The Philosophical Foundations of Systematics”, The Canadian Entomologist, Ixxxiv (1952), 116, argues for a position very much like Aristotelian essentialism. Hatch Mellville, “The Species Concept”, The Amer. Nat., lxxv (1941), is clearly a nominalist. Gilmour J. S.L., “Taxonomy and Philosophy”, New Systematics (Oxford, 1940), Julian Huxley, ed., 461–474, recommends a sense data version of Idealism; i.e. phenomenalism. Bather F. A., “Biological Classification: Past and Future”, Proc. Geological Soc., Ixxxiii, Ixi–civ, has definite idealist overtones. The two biologists who hold positions closest to that of Darwin and who, though they would be the last to admit it, have gone a long way toward providing an explicitly formulated metaphysics for evolutionary theory as a biological theory are Simpson G. G., Principles of Animal Taxonomy (New York, 1961) and Ernst Mayr, op. cit. (45). It is precisely for this reason that a philosopher, Grene Marjorie, “Two Evolutionary Theories”, Brit. Jour. Phil. Sci., ix (1959), 110127, 185193, has seen fit to take issue with at least the first of these two biologists.

* I wish to thank Ernst Mayr for criticizing an early draught of this paper and Yukio Kachi for his assistance in checking the translations of certain Greek passages. Early versions of this paper were read before the Philosophy Department of the University of Texas and the palaeozoologists at the University of Chicago. Their comments and criticisms were also much appreciated.

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