Page:Popular Science Monthly Volume 79.djvu/560
556 THE POPULAR SCIENCE MONTHLY
writers — dealing somewhat less than fairly with their readers — have failed to mention that his rejection of the evolutionary hypothesis was not put forth by him as resting exclusively upon these religious con- siderations. If the words just quoted stood alone, it would, indeed, be scarcely possible to take them seriously. But they do not stand alone; they are directly followed by arguments of quite another order against the possibility of the descent of one real species from another ; and the essence of the most emphasized of these arguments lies in the Buffonian conception of the nature of species, already expounded in the second volume. In other words, the fact of the sterility of hybrids, and certain other purely factual considerations, were urged by Buffon as conclusive objections against the theory of descent.
Specifically, his arguments against evolution are three: (1) Within recorded history no new true species (in his own sense of the term) have been known to appear. (2) There is one entirely definite and constant line of demarcation between species : it is that indicated by the infertility of hybrids.
This is the most fixed point that we possess in natural history. No other resemblances or differences among living beings are so constant or so real or so certain. These, therefore, will constitute the only lines of division to be found in this work.
But why, it may be asked, should the sterility of hybrids be a proof of the wholly separate descent of the two species engendering such hybrids ? This question Buffon does not neglect to answer. An " im- mense and perhaps an infinite number of combinations " would need to be assumed before one could conceive that " two animals, male and fe- male, had not only so far departed from their original type as to be- long no longer to the same species — that is to say, to be no longer able to reproduce by mating with those animals which they formerly re- sembled — but had also both diverged to exactly the same degree, and to just that degree necessary to make it possible for them to produce only by mating with one another." The logic of this is to me, I con- fess, a trifle obscure; but it is evident that Buffon conceived that the evolution from a given species of a new species infertile with the first could come about only through a highly improbable conjunction of cir- cumstances. (3) Buffon's third reason for maintaining the fixity of species is the argument from the " missing links."
If one species had been produced by another, if, for example, the ass species came from the horse, the result could have been brought about only slowly and by gradations. There would therefore be between the horse and the ass a large number of intermediate animals. Why, then, do we not to-day see the repre- sentatives, the descendants, of these intermediate species? Why is it that only the two extremes remain?
Taking these three arguments into account, then, Buffon arrives at this conclusion :
Though it can not be demonstrated that the production of a species by