Published online by Cambridge University Press: 05 January 2009
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.
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), 165–194.Google Scholar See abo several papers in Glass, Bentley, Temkin, Owsei and Straus, William L. Jr., (eds.), Forerunners of Darwin: 1745–1859 (Baltimore, 1959).Google ScholarLovejoy, 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).Google Scholar
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.Google Scholar
“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.Google Scholar 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.Google Scholar
9 Zirkle, , op. cit. (5), 640, 637, 639.Google Scholar
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.Google Scholar
13 Theophrastus, Enquiry into Plants, II, iv, 1Google Scholar and Causes of Plants, I, ix, 2.Google Scholar All citations from Theophrastus will be from SirHort's, Arthur translation of the Enquiry into Plants (Cambridge, 1916)Google Scholar and Dengler, R. E.'s translation of the first book of the Causes of Plants (Philadelphia, 1927).Google Scholar 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).Google Scholar
14 Ibid., Enquiry, II, ii, 9; see also Enquiry, VIII, viii, 2.Google Scholar
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&5Google Scholar; 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.Google Scholar 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 & 5Google Scholar; Causes (13), I, v.
22 Hantz, H. D., The Biological Motivation in Aristotle (New York, 1930)Google Scholar; Randall, John Herman Jr., Aristotle (New York, 1960)Google Scholar; and Grene, Marjorie, A Portrait of Aristotle (Chicago, 1963).Google Scholar
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), 41Google Scholar, 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.Google Scholar 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, 313Google Scholar, and Ross, W. D., Aristotle (London, 1937), 74.Google Scholar
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).Google Scholar
30 Raven, C. E., John Ray, Naturalist (Cambridge, 1942), 375, 462, 469, 471.Google Scholar
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.Google Scholar I owe the Poulton reference to Ernst Mayr.
32 Ray, John, Historia Plantarum (London, 1686), i, 40.Google Scholar
33 Linnaeus, Carolus, Systema Natura, facsimile of the first edition, trans, by Engel-Lederboer, M. S. J. and Nieuwkoop, Engel (Leyden, 1964).Google Scholar
33a Glass, op. cit. (2), 151.Google Scholar
34 Crombie, A. C., “The Notion of Species in Medieval Philosophy and Science”, VIem Congrès international d'histoire des sciences, Actes, i (1950), 261–269.Google Scholar 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).Google Scholar
36 Leclerc, Louis, de Buffon, Comte, Histoire Naturelle (Paris, 1749), i, 38 & 20.Google Scholar 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), 464–473, 554–567Google Scholar, also reprinted in Glass, op. cit. (2), 84–113.Google ScholarWilkie, J. S., “The Idea of Evolution in the Writings of Buffon”, Annals of Science, xii (1956), 48–62CrossRefGoogle Scholar, goes over much the same ground as Lovejoy but fails to mention Lovejoy's article.
37 Buffon, , op. cit., (36), 38 & 20.Google Scholar 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), 97–111.CrossRefGoogle Scholar
38 Buffon, , Histoire Naturelle (Paris, 1749), ii, 10.Google Scholar
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), 261Google Scholar, 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.Google Scholar
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), 15–83 & 144–172Google Scholar, as well as Temkin, Owsei, “German Concepts of Ontogeny and History around 1800”, Bulletin of the History of Medicine, xxiv.Google Scholar
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45 Ernst Mayr has repeatedly pointed out this error. See Mayr, Ernst, Animal Species and Evolution (Cambridge, 1965), 600.Google Scholar He cites Goldschmidt, R. B., “Evolution as Viewed by One Geneticist”, Amer. Sci., xl (1952), 91Google Scholar, 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), 265–291.Google Scholar
47 Quoted from Coleman, William, Georges Cuvier—Zoologist (Cambridge, Mass., 1964), 144.CrossRefGoogle Scholar
48 Ellegard, Alvar, “The Darwinian Theory and Nineteenth Century Philosophies of Science”, Journal of the History of Ideas, xviii (1957), 362–393.CrossRefGoogle Scholar
49 Owen, Richard, “Darwin on the Origin of Species”, Edinburgh Review, iii (1860), 257.Google Scholar 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), 144–163CrossRefGoogle Scholar; “Deductive and Inductive Methods in Post-Linnaean Taxonomy”, Proc. Linn. Soc., Lond., clxx (1959), 185–217Google Scholar; “The Post-Linnaean Development of Taxonomy”, Proc. Lin. Soc., Lond., clxx (1959), 234–244Google Scholar; see also Sokal, R. R. and Sneath, P. H. A., Principles of Numerical Taxonomy (San Francisco, 1963).Google Scholar For criticism of this view see Mayr, Ernst, “Numerical Phenetics and Taxonomic Theory”, Systematic Zoology, xiv (1965), 73–97CrossRefGoogle Scholar, and Hull, D. L., “Certainty and Circularity in Evolutionary Taxonomy”, Evolution, xxi (1967), 174–189.CrossRefGoogle Scholar
50 Cuvier, Georges, Leçons d'anatomie comparée (Paris, 1835), i, 64.Google Scholar
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52 Georges Cuvier, “Essay on Zoological Analogies”, quoted in Appendix B, Coleman, , op. cit. (47), 189.Google Scholar 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), 7–17CrossRefGoogle Scholar, reprinted in Madden, Edward H. (ed.), The Structure of Scientific Thought (Boston, 1960), 71–80.Google Scholar For a comparable explanation which has the biologist specifically in mind, see Hull, op. cit. (49).
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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.
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.Google Scholar I owe this reference to Miss Judy Todd.
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76 Ayer, A. J., “The Structure of Darwinism”, New Biology, xxii (Baltimore, 1959), 25–44Google Scholar, 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, 92–93Google Scholar, 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.Google Scholar
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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, 104Google Scholar; Darwin, , op. cit. (72), iii, 3.Google Scholar 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, 16Google Scholar, and Ellegard, op. cit. (48). Passmore, Strangely, op. cit. (73), 42Google Scholar, 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.Google Scholar 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)Google Scholar, for the opposite view.
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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), 1–16CrossRefGoogle Scholar, argues for a position very much like Aristotelian essentialism. Hatch, Mellville, “The Species Concept”, The Amer. Nat., lxxv (1941)Google Scholar, is clearly a nominalist. Gilmour, J. S.L., “Taxonomy and Philosophy”, New Systematics (Oxford, 1940)Google Scholar, 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–civGoogle Scholar, 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)Google Scholar 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), 110–127, 185–193CrossRefGoogle Scholar, has seen fit to take issue with at least the first of these two biologists.
