Popular Science Monthly/Volume 79/November 1911/Buffon and the Problem of Species I
|BUFFON AND THE PROBLEM OF SPECIES
By Professor ARTHUR O. LOVEJOY
THE JOHNS HOPKINS UNIVERSITY
THERE is no chapter of the history of the theory of organic evolution more confused or more controverted than that which relates to the position of Buffon. Upon one point, indeed, nearly all expositors of the "Histoire Naturelle" are agreed—namely, that Buffon's own expressions on the subject, if taken at their face value, contradict one another. But upon the questions whether his utterances were meant to be taken at their face value; whether, by a due consideration of dates, the contradictions can not be regarded as consecutive steps in a logical progress of doctrine; whether he was in the main a partisan or an opponent of transformism: upon these questions both the biographers of Buffon and the historians of evolutionism are greatly at variance.
The rival interpretations fall into six groups: (1) Older writers of the anti-evolutionary school, such as Cuvier and Flourens, while admitting that (in the words of Flourens) "the ideas of Buffon were constantly subject to profound mutations," were wont to maintain that in the last analysis and in the long run he must be counted among the defenders of the doctrine of immutability of species. Among recent writers Packard gives a similar account; while he recognizes "tentative" evolutionistic utterances in the "Histoire Naturelle," he opines that Buffon himself "did not always take them seriously, but rather jotted them down as passing thoughts." (2) One of the earlier French evolutionists, Isidore Geoffroy St. Hilaire, contended that there was no mere fluctuation in Buffon's teaching, but simply an orderly movement of thought from one position to another.
The successive phases of opinion through which, according to Isidore Geoffroy, Buffon passed were three. At the beginning of his work (1749) and down to 1756 or later, he "still shared the views of Linnæus" and affirmed consistently the theory of immutability. From 1761 to 1766 he asserted the hypothesis of variability in an extreme form. Later he became convinced that "in setting himself free from the prevailing notions," he had, "like all other innovators, gone what to the opposite extreme "; and in all his writings subsequent to 1766 he held to a doctrine of "limited mutability," to the "permanence of the essential features" of species and "the variability of details." This division of Buffon's opinions into three periods, of which the middle one was characterized by an extreme evolutionism, has been accepted by a number of later writers. It is apparently adopted by Osborn, though not to the exclusion of other interpretations inconsistent with it. (3) By several recent writers—such as Samuel Butler, de Lanessan, Giard, Clodd—Geoffroy's scheme of three periods is rejected, and Buffon is declared to have been an evolutionist throughout virtually his whole career as a writer. Those who take this view explain away his apparent self-contradictions by various suppositions. Giard, for example, holds that Buffon began as a transformist, but was led by his difficulties with the ecclesiastical authorities (in 1751) to conceal his real position for a number of years, becoming bolder and more outspoken after 1761, when his fame was securely established. In other words, Giard proposes an alternative division into three periods, in which the middle phase is the least evolutionistic. Samuel Butler, who has taken the most extreme ground of all in favor of the view that Buffon was a whole-hearted evolutionist, endeavors at great length and with much ingenuity to show that all the anti-evolutionary passages in the "Histoire Naturelle" are ironical. According to this interpretation Buffon must almost be said to have woven a sort of cryptogram into his work. "His irony is not the ill-natured irony of one who is merely amusing himself at other people's expense, but the serious and legitimate irony of one who must either limit the circle of those to whom he appeals, or must know how to make the same language appeal differently to the different capacities of his readers, and who trusts to the good sense of the discerning to understand the difficulty of his position, and make due allowance for it." In other words, Buffon threw in sufficiently frequent affirmations of the immutability of species to deceive, or at least to quiet, the doctors of the Sorbonne, and in the very act of doing so he made it evident to the judicious reader that the opposite conclusion was the one to be accepted.
The three remaining interpretations of Buffon's position are less subtle and ingenious. (1) The author of the most comprehensive recent history of biological theories tells us that, though Buffon "speculated aboiut the origination of one species from another," he did not "especially interest himself in the question of the mutability of species; his too little developed sense for the historical [i. e., the genetic] aspect of nature did not permit him to put clearly before himself such a question as that concerning the origin of species. How should he have done so, since he did not even believe in the existence of species, but recognized only individuals?" (5) Dacqué, in what is at many points the least inaccurate of the histories of evolutionism, declares that Buffon brought forward no more profound ideas than his contemporaries "upon the interconnection of the phenomena of organic nature," though he did something to clarify the conception of geological evolution, and "regarded species as variable within certain limits." (6) The writer who (so far as I know) has most recently discussed the subject, Landrieu, seems finally to give up as hopeless the attempt to reduce Buffon's utterances to harmony and coherency. He adds, however, that in spite of these inconsistencies, "Buffon retains the indisputable honor of having been the first zoologist to admit the possibility of specific variations due to environmental influences and extending beyond the limits of species."
All of these accounts of the matter seem to me to be either inadequate or erroneous, though all may be said in some measure to be founded on fact. Most of them—especially of the more recent ones—wholly ignore two essential considerations in relation to Buffon's biological conceptions, in the light of which all that he wrote must be interpreted. In attempting to present a more adequate and more correct analysis of Buffon's opinions, I shall be obliged to tax the reader's patience with many and lengthy citations. Where there has been so much disagreement, it is necessary to present the proofs for nearly every statement propounded. And where so much error has arisen through the citation of brief passages in disregard of their contexts, it is important that pains be taken to quote or summarize so much of each text as appears to be in any way relevant to the question under consideration.
1. The first volume of the great treatise (1749) opened with a preliminary disquisition on the methodology of the science, a "Discours de la manière d'étudier et de traiter l'histoire naturelle." In this Buffon gave a salutary emphasis to the demand for a more "philosophical" way of studying botany and zoology than had been exemplified by Linnæus and Tournefort and the other great systematists. Description and classification, Buffon insisted, were the least part, though a necessary part, of "natural history."
But these judicious and stimulating, if slightly vague, appeals for the conversion of natural history into a science of causal relations and generalized laws, were not the principal purpose of the preliminary discourse. The thought of Buffon at the time when he wrote that essay seems to have been dominated above all by a single idea, which was also one of the two or three ruling ideas of the whole of the first half of the eighteenth century—namely, the Leibnitian "principle of continuity'* (lex continui). In the intellectual fashions of this period, next to the blessed word "Nature" the most sacred phrase was "the Great Chain of Beings"; indeed, one of the truths that man was supposed to know most surely about nature was that she "makes no leaps." In the form, especially, of the neo-Platonic and Spinozistic metaphysical assumption that all possible forms must exist, the principle was much older than the philosophy of Leibniz; but it owed to him and his disciples a more definite formulation and a greatly increased popular currency. It declared that all entities are arranged in a graded scale of similarity, so that for every being that exists there also exists some other (in the strict version of the principle, one and only one other) from which its difference is infinitesimal, i. e., less than any assignable difference. A typical statement of the doctrine is Bonnet's:
Between the lowest and the highest degree of corporeal or spiritual perfection there is an almost infinite number of intermediate degrees. The series of these degrees constitutes the Universal Chain. It unites all beings, binds together all worlds, embraces all spheres. One Being alone is outside of this chain, and that is He who made it. . . . There are no breaks (sauts) in nature; all is graduated, everything shades off into the next thing. If, between any two beings whatever, there existed a gap, what would be the reason of the transition from the one to the other? There is, therefore, no being above or below which there is not some other that approximates it with respect to some characters and diverges from it with respect to others.
All this (as Bonnet's language intimates) was held by the Leibnitian philosophy to be logically implied by the still more fundamental "principle of sufficient reason." For if the gradations found in nature were discontinuous, if between any two beings an intermediate type were logically capable of existing, but actually non-existent, the universe would stand convicted of irrationality. A thing for the existence of which there was just as much "reason" as there was for the existence of certain other things would have failed of realization, while the others arbitrarily enjoyed the privilege of actuality. The principle of continuity owed its vogue in part, also, to the influence of the Leibnitian calculus, which had brought infinitesimals and the notion of the continuum peculiarly into fashion.
Applied primarily to the "monads" of Leibniz's metaphysics, the principle found a multitude of other applications. It served, for example, as the chief basis of the arguments for optimism of which the early eighteenth century was so fond. Pope's "Essay on Man" is full of the argument from the necessity of continuity to the necessity of imperfections and apparent evils.
Vast chain of being! which from God began;
Nature's ethereal, human, angel, man,
Beast, bird, fish, insect, whom no eye can see,
No glass can reach; from infinite to thee,
From thee to nothing. On superior powers
Were we to press, inferior might on ours;
Or in the full creation leave a void,
Where, one step broken, the great scale's destroyed.
For the limitations of man's lot the sufficient consolation is that the principle of continuity requires them; in a system
Where all must full or not coherent be,
And all that rises, rise in due degree,—
Then in the scale of reasoning life 'tis plain
There must be, somewhere, such a rank as man.
From the assumption of the same principle sprang the inquiries from which the science of anthropology may be said eventually to have originated. As a historian of the beginnings of that science has said:
The question concerning the line of demarcation between man and the animal kingdom was plainly forced upon anthropology by the philosophy of Leibniz. The lex continui demanded the discovery of that "grade" (nuance) of existence among the higher organisms which comes nearest to the human species. And so there began the celebrated quest of the "missing link." In the first phase of this quest, the missing link was sought at the lower limits of humanity itself. It was held to be not impossible that among some of the more remote peoples semi-human beings might be found, such as had now and then been described in travelers' tales. Some voyagers had testified to having seen with their own eyes men with tails; others had encountered tribes incapable of speech. Linnæus mentions a homo troglodytes concerning whom it was not established with certainty whether he was more nearly related to the pygmies or to the orang-outang. The most eminent men of science down to a late period in the eighteenth century hesitated to reject absolutely the possibility of the existence of such beings.
It was, then, the application of this principle to natural history that was Buffon's main object in his preliminary discourse. The consequences of it, when it was applied in this field, were simple and evident and drastic: there can be no such thing as a "natural," or even a consistent "system" of classification, since there are no sharp-cut differences in nature, and since, therefore, species and genera are not real entities but only figments of the imagination. It is easy, Buffon wrote, to see the essential fault in the work of the systematists, the inventors of "methods" as a class.
It consists in an error in metaphysics in the very principle underlying these methods. This error is due to a failure to apprehend nature's processes, which take place always by gradations (nuances), and to the desire to judge of a whole by one of its parts.
Man, placing himself at the head of all created things and then observing one after another all the objects composing the universe,
will see with astonishment that it is possible to descend by almost insensible degrees from the most perfect creature to the most formless matter; . . . he will recognize that these imperceptible shadings are the great work of nature; he will find them—these gradations—not only in the magnitudes and the forms, but also in the movements, in the generations and the successions, of every species. If the meaning of this idea be fully apprehended, it will be clearly seen that it is impossible to draw up a general system, a perfect method, for natural history. . . . For in order to make a system or arrangement, everything must be included, and the whole must be divided into different classes, these classes into genera, and the genera into species—and all this according to an order in which there must necessarily be something arbitrary. But nature proceeds by unknown gradations, and consequently can not wholly lend herself to these divisions—passing, as she does, from one species to another species, and often from one genus to another genus, by imperceptible shadings; so that there will be found a great number of intermediate species and of objects belonging half in one class and half in another. Objects of this sort, to which it is impossible to assign a place, necessarily render vain the attempt at a universal system.
In short, the whole notion of species is inconsistent with the conception of nature as a graded continuum of forms in which there are no breaks.
In general, the more one increases the number of one's divisions, in the case of natural products, the nearer one comes to the truth; since in reality individuals alone exist in nature, while genera, orders, classes, exist only in our imagination.
The vogue of the principle of continuity in the eighteenth century was, unquestionably, an important influence tending to prepare men's minds for the acceptance of the conception of evolution; but the two doctrines were by no means synonymous, nor did the adoption of the former necessarily imply adherence to the latter. The lex continui is historically important because it led to one of the early notable departures in modern thought from what may be called a Platonistic habit of mind, that had, in a hundred subtle ways, dominated most European philosophy and science for many centuries; it meant, in some degree, the abandonment of the fashion of thinking of the universe as tied up in neat and orderly parcels, the rejection of rigid categories and absolute antitheses, as inadequate instruments for the description of the complexity and fluidity and individuatedness of things. In other words, the principle of continuity, though itself the product of the extreme of philosophical rationalism, tended in a mild way towards a sort of antirationalism, towards a distrust of over-sharp distinctions and oversimple conceptions, towards a sense of certain incommensurability between the richness of reality and the methods of conceptual thought. And in the nineteenth century this same tendency, in vastly more extreme forms, has been far more conspicuously furthered by the influence of the doctrine of evolution. But the idea of continuity as generally held in the time of Buff on had no reference to temporal sequences and by no means involved, in the minds of those who accepted it, any definite belief in the descent of what are commonly called species from other species. If the presupposition of continuous gradations and imperceptible transitions had been explicitly brought to bear upon genetic problems in biology, it would naturally though not necessarily have suggested some sort of theory of descent. But, curious as the fact may appear, the presupposition was ordinarily not brought into connection with genetic problems at all; it was taken in an essentially static sense.
And it seems to have been taken in this sense by Buffon in the introductory discourse in his first volume. A single obscure phrase, which I have already quoted, might be regarded as hinting at the conception of organic evolution, if the general tenor of the essay lent any confirmation to such an interpretation. But nowhere else in this writing is it even' remotely suggested that the conception of the continuity of forms involves the conception of the descent of so-called species from one another. It is scarcely conceivable that if Buffon had had before his mind so momentous a new idea as that of evolution, he should not have contrived to give a far plainer intimation of it than a single vague remark that imperceptible gradations are found not only in the forms but also in the generations and the successions of every species. At this time, at all events—whatever he may have been later—Buffon was fairly outspoken in the expression of even heterodox hypotheses; it was only subsequently that he was condemned by the Sorbonne, on account of opinions propounded in his "Théorie de la Terre," contained in the same volume as the preliminary discourse. It is significant, moreover, that at this date he saw no hint of any evolutionary significance in the homologies of the vertebrate skeleton; he had as yet learned nothing from comparative anatomy. This is shown in the argument by which he defends his own method of arranging species—a method which wholly ignored anatomical considerations and merely proceeded from the more familiar to the less familiar animals.
Is it not better to make the dog, which is fissiped, follow (as he does in fact) the horse, which is soliped, rather than have the horse followed by the zebra, which perhaps has nothing in common with the horse except that it is soliped? . . . Does a lion, because it is fissiped, resemble a rat, which is also fissiped, more closely than a horse resembles a dog?
It is probable, then, that in writing the opening discourse of his great work Buffon was innocent of any idea of organic evolution; it is certain that he did not convey that idea in any such way that a reader of his time might be expected to recognize it. Nor did he make any use of the conception of the descent of species in his "Théorie de la Terre," of the same date—where he might naturally have been expected to introduce the doctrine, if he held it; on the contrary he implies (p. 197) the equal antiquity of all species—though he does so in a way which, I confess, might plausibly be taken as ironical. The truth is that when under the influence of the principle of continuity Buffon's mind overshot the problem of the origin of species altogether. There were no such things as species: upon this point he was clear. There was therefore no need of explaining their genesis. As for the further question, how successive generations of offspring are related in form to their forebears, that was a question upon which the principle of continuity had, strictly speaking, nothing to say. That offspring varied somewhat, and usually slightly, from their parents every one knew; to this extent the conformity of the laws of heredity to the law of continuity was a common-place of every-day observation. Beyond this, no definite genetic or embryological consequences seemed necessarily to follow from the maxim natura non facit saltus.
The most important thing, however, to remark concerning Buffon's position in his first volume is that it is a position which he speedily abandoned, and to which he never returned. Its most characteristic point was the contention that nature knows only individuals and that species are entia rationis merely. The most characteristic point of nearly all his subsequent references to the subject is the contention that species are real entities, definable in exact and strictly objective terms, and necessary to take account of in any study of natural history.
This change already was manifest in the second volume, published in the same year as the preliminary discourse (1749). In this volume Buffon propounded his celebrated definition of species, which was destined to have so great an influence upon the biological ideas of the later eighteenth century.
We should regard two animals as belongng to the same species if, by means of copulation, they can perpetuate themselves and preserve the likeness of the species; and we should regard them as belonging to different species if they are incapable of producing progeny by the same means. Thus the fox will be known to be a different species from the dog, if it proves to be the fact that from the mating of a male and a female of these two kinds of animals no offspring is born; and even if there should result a hybrid offspring, a sort of mule, this would suffice to prove that fox and dog are not of the same species—inasmuch as this mule would be sterile (ne produirait rien). For we have assumed that, in order that a species might be constituted, there was necessary a continuous perpetual and unvarying reproduction (une production continue, perpétuelle, invariable)—similar, in a word, to that of the other animals.
This language, it will be observed, implies not only that species are real entities, but also that they are constant and invariable entities. The same implication may be found again later in the volume; Buffon thus concludes the exposition of his embryological hypotheses—which embraced a theory of pangenesis:
The reference here is primarily to the continuance rather than the invariability of species. But the latter seems also to be implied; and certainly Buffon does not improve the opportunity to introduce a hint of the doctrine of mutability—as he could hardly have failed to do if he had at this time held that doctrine and had been desirous of propagating it. It must be remembered that these passages also were written before Buffon's opinions had been censured by the Sorbonne.
No account of Buffon's position in the history of biology can be other than misleading which fails to note the decisive significance, for nearly all of his positions from the second volume onward, of the peculiarly Buffonian criterion of identity and diversity of species. Unless this criterion (and the implied distinction between species and varieties, which latter term covers many Linnæan species) be borne in mind, most of the pages in the "Histoire Naturelle" which have an evolutionistic sound are likely to misinterpreted. This is what has happened in a number of the studies of Buffon's relation to evolutionism. The error is especially conspicuously in Samuel Butler's "Evolution Old and New." Butler has devoted nearly one hundred pages to a review of Buffon's utterances on the subject; yet he nowhere lets his reader know that Buffon was the propounder of a new definition of species, which set up a radical distinction between species and varieties, and implied that a species was a definite, objective, "natural" entity. The oversight is not due to any neglect of Buffon's to emphasize and reiterate his definition. He recurs to it frequently in later volumes. His sense of its importance was such that the question of hybridism and the limits of fertility in cross breeding was one of the very few subjects which he can be said to have studied experimentally on his own account. He writes, for example, in 1755:
We do not know whether or not the zebra can breed with the horse or ass; whether the large-tailed Barbary sheep would be fertile if crossed with our own; whether the chamois is not a wild goat; . . . whether the differences between apes are really specific or whether the apes are not like dogs, one species with many different breeds. . . . Our ignorance concerning these questions is almost inevitable, as the experiments which would settle them require more time, care and money than can be spared from the fortune of an ordinary man. I have spent many years in experiments of this kind, and will give my results when I come to speak of mules. But I may as well say at once that I have thrown but little light on the subject and have been for the most part unsuccessful.
(To be concluded)
- In his "Histoire Naturelle Générale, "Vol. II., 1859. His account is translated in Butler's "Evolution Old and New."
- "From the Greeks to Darwin," 130-135.
- In his "Evolution Old and New."
- "Rádl, "Gesch. der biologischen Theorien," I., 1905, pp. 117-118.
- "Der Descendenzgedanke u. seine Geschichte," 1903—a little book less known than it deserves to be.
- In his "Lamarck, fondateur de l'évolution," 1909, pp. 275-283. May I improve this occasion to express the hope that both French and English writers may some day be broken of the habit of talking of "evolution" when they mean "evolutionism"? Both languages chance to be provided with a suffix for distinguishing a theory which affirms, or relates to, a given fact from the fact itself; it seems a pity to throw away this instrument of linguistic precision. It is surely absurd (not to say profane) to speak of Lamarck or any other mortal as "the founder of evolution"; or of the eighteenth century as "the beginning of evolution."
- This implied that there must be one, and can be only one, sample of every possible kind or degree of entity. To consider Leibniz's attitude toward this form of the principle would involve too much technical metaphysics.
- "Contemplation de la Nature" (1764), 2d ed., 1769, I., 26-27.
- Günther, "Die Wissenschaft vom Menschen im 18ten Jahrhundert," p. 30.
- "Hist. Nat., Vol. I., 1749, p. 20.
- These words are Buffon's nearest approach in the introductory discourse to a suggestion of the mutability of species. De Lanessan has interpreted them as an affirmation of transformism; but they are too vague to justify such a construction.
- "Hist. Nat.," Vol. I., 1749, p. 13. Much the same thing had, however, been said by Eay over sixty years before; cf. "Historia Plantarum," 1686, I., p. 50.
- Op. cit., p. 38.
- This fact has often been overlooked by interpreters of eighteenth century writers. When we find such a writer saying that "nature passes from one species to another by gradual and almost imperceptible transitions, "it is by no means safe to assume that the phrase contains any reference to genealogical transitions, or that the writer meant by his words to affirm the transformation of species through the summation of slight individual variations. Misapprehension upon this point has caused some eighteenth century authors to be quite undeservedly set down as evolutionists.
- "Hist. Nat.," Vol. L, p. 36.
- Rádl's account, already quoted, of Buffon's attitude towards transformism and towards the conception of species, is apparently based chiefly upon the first volume. For virtually all of Buffon 's views, except his early and quickly repudiated one, Rádl's statement is almost the exact reverse of the truth.
- "Hist. Nat.," Vol. II., 1749, p. 10.
- "Hist. Nat.," Vol. II., p. 425.
- Vol. V., p. 63. The passage is given by Butler, but he shows no sense of its general significance.