In Darwin's Shadow: The Life and Science of Alfred Russel Wallace ...

Breaching the Walls of the Species Citadel / 105
Through the study of comparative anatomy Buffon also looked to the underlying
unity of type by which one could infer a degree of relationship
among species. These observations led to the principle of homology, where
organisms have similar anatomy due to similar ancestry, such as the wing of
a bat, the arm of a human, and the flipper of a whale. All show similar
structure due to similar ancestry, though the environments to which they have
adapted are radically different:
If we choose the body of some animal or even that of man himself to serve as
a model with which to compare the bodies of other organized beings, we shall
find that...there exists a certain primitive and general design, which we can
trace for a long way....Evenintheparts which contribute most to give variety
to the external form of animals, there is a prodigious degree of resemblance,
which irresistibly brings to our mind the idea of an original pattern after which
all animals seem to have been conceived. The foot of the horse in appearance
so different from the hand of man, is nevertheless composed of the same bones,
and we have at the extremities of our fingers the same small hoofshaped bone
which terminates the foot of that animal. 63
From these many and diverse quotes, all taken from the Histoire Naturelle,
one might be tempted to conclude that Buffon was an evolutionist, a genius
out of time, but this is not the case. Instead of reaching the conclusion of
descent with modification through an argument from homology, Buffon asks
“whether this does not seem to show that the Creator in making all these used
but a single main idea, though varying it in every conceivable manner?” 64
Further, the causative environmental agents that create variations do not lead
to new species in Buffon’s model, but instead are degenerations of originally
created kinds that came into existence shortly after the cooling of the earth
some 75,000 years ago. For Buffon there are species, and there are varieties
within species, but he knew of no mechanism by which varieties could become
new species and thus never developed an evolutionary theory. Even in
the “ape to man” passage earlier, Buffon notes that the “missing links” between
species prove the fixity of the same. He continued: “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 today see the representatives, the
descendants of these intermediate species? Why is it that only the two extremes
remain?” Buffon answers his own question: “Though it can not be
demonstrated that the production of a species by degeneration from another
species is an impossibility for nature, the number of probabilities against it is