left no trace nor sign. We have generally no conception at all of
the amount of extermination and degeneration which have taken place
in past ages.

I grant frankly that I do not believe that the forms which I have
selected represent exactly the ancestors of man. They have all been
more or less modified. I claim only that in the balance and relative
development of their organic systems--muscular, digestive, nervous,
etc.--they give us a very fair idea of what our ancestor at each
stage must have been. But it is on this balance and relative
development of the different systems, that is, whether an animal is
more reproductive, digestive, or nervous, that my argument will in
the main be based.

But if the older ancestors have so generally disappeared, and their
surviving relatives have been so greatly modified, how can we make
even a shrewd guess at the ancestry of higher forms? The genealogy
of the animal kingdom has been really the study of centuries,
although the earlier zoölogists did not know that this was to be the
result of their labors. The first work of the naturalist was
necessarily to classify the plants and animals which he found, and
catalogue and tabulate them so that they might be easily recognized,
and that later discovered forms might readily find a place in the
system. Hypotheses and theories were looked upon with suspicion.
"Even Linnæus," says Romanes, "was express in his limitations of
true scientific work in natural history to the collecting and
arranging of species of plants and animals." The question, "What is
it?" came first; then, "How did it come to be what it is?" We are
just awakening to the question, "Why this progressive system of
forms, and what does it all mean?"