dualistic philosophers who are perpetually reiterating this
cry for more certain evidence, anywhere indicate where possibly such
evidence is to be sought. Where in all the world can we discover
"facts" which will speak more plainly or significantly for the truth
of transmutation than the facts of comparative morphology and
physiology; than the facts of the rudimentary organs and of embryonic
development; than the facts revealed by fossils and the geographical
distribution of organisms--in short, than the collective recognised
facts of the most diverse provinces of biological science?

But I am in error--the certain proof that Virchow demands in order to
be perfectly satisfied with the evidence, is to be supplied by
"experiment, the test as well as the highest means of evidence." This
demand, that the doctrine of descent should be grounded on experiment,
is so perverse and shows such ignorance of the very essence of our
theory, that though we have never been surprised at hearing it
continually repeated by ignorant laymen, from the lips of a Virchow it
has positively astounded us. What can in this case be proved by
experiment, and what can experiment prove?

"The variability of species, the transformation of species, the
transition of a species into one or more new varieties," is the
answer. Now, so far as these facts can be proved by experiment, they
actually have long since been experimentally proved in the completest
manner. For what are the numberless trials of artificial selection for
breeding purposes which men have practised for thousand of years in
breeding domestic animals and cultivated plants, but physiological
experiments which prove the transformation of species? As an example
we may refer to the different races of horses and pigeons. The swift
race-horse and the heavy pack-horse, the graceful carriage-horse and
the sturdy cart-horse, the huge dray-horse and the dwarfed pony--these
and many other "races" are so different from each other, that if we
had found them wild we should certainly have described them as quite
different varieties of one species, or even representatives of
different species. Undoubtedly, these so-called "races" and "sports"
of the horse tribe differ from each other in a much greater degree
than do the zebra, the quagga, the mountain horse, and the other wild
varieties of the horse, which every zoologist distinguishes as "bonae
species." And yet all these artificial varieties, which man