BUFFON AND THE PROBLEM OF SPECIES 561 



identity of species (the possibility of interbreeding) did not essentially 

 depend upon morphological similarity, he could with consistency sup- 

 pose the descendants of a given pair to have departed to a very great 

 (though not to an indefinite) degree, in the course of ages, from the 

 form and external characters of their ancestors. It was, in other 

 words, characteristic of his biological system that he set up an absolute 

 distinction between species and varieties, gave an extreme extension to 

 the notion of a variety, and sought to reduce the number of separate 

 species as much as possible, by assuming — until the establishment of 

 the sterility of the hybrids should prove the contrary — that most of the 

 Linnaean species were merely varieties descended from a relatively small 

 number of original specific types. Near the close of his essay " De la 

 degeneration des animaux" (1766), Buffon writes: 



To account for the origin of these animals [certain of those found in 

 America] we must go back to the time when the two continents were not yet 

 separated and call to mind the earliest changes which took place in the surface 

 of the globe; and we must think of the two hundred existing species of quadru- 

 peds as reduced to thirty-eight families. And though this is not at all the state 

 of nature as we now find it, but a state much more ancient, at which we can 

 arrive only by induction and by analogies . . . difficult to lay hold of, we shall 

 attempt nevertheless to ascend to these first ages of nature by the aid of the 

 facts and monuments which yet remain to us. 30 



Here, clearly, is an evolutionary program, strictly limited by the 

 assumption that there are irreducible ultimate species, yet tolerably 

 ambitious : to regard all known kinds of quadrupeds as derived from 

 thirty-eight original types, by modification in the course of natural 

 descent; and to determine the general causes and conditions of the 

 production of species in the ordinary sense, i. e., of relatively stable 

 varieties. These ideas occurred to Buffon too late to be made use of in 

 his general plan for the classification of the quadrupeds; that plan, 

 it will be remembered, was formed while he was unluckily under the 

 influence of the principle of continuity. But in the volumes on birds, 

 of which the first appeared in 1770, he had the opportunity for a fresh 

 start ; and he took advantage of it to introduce a method of distinguish- 

 ing and classifying species which — within the limits already indicated 

 — is expressly evolutionary in its principles. 



For the natural history of the birds I have thought that I ought to form a 

 plan different from that which I followed in the case of the quadrupeds. Instead 

 of treating of the birds ... by distinct and separate species, I shall bring several 

 of them together under a single genus. Except for the domesticated birds, all 

 the others will be reunited with the species nearest to them and presented 

 together as being approximately of the same nature and the same family. . . . 

 When I speak of the number of lines of parentage, I mean the number of species 

 so closely resembling one another that they may be regarded as collateral 

 branches of a single stock, or of stocks so close to one another that they may 

 be supposed to have a common ancestry and to have issued from that same 

 original stock with which they are connected by so many points of resemblance 



30 Vol. XIV., 1766, p. 358. 



