distinct classes have something in common in structure and much in common
in constitution, analogy would lead us one step further, and to infer as
probable that all living creatures are descended from a single prototype.

I hope that the reader will pause before coming to any final and hostile
conclusion on the theory of natural selection. The reader may consult my
'Origin of Species' for a general sketch of the whole subject; but in that
work he has to take many statements on trust. In considering the theory of
natural selection, he will assuredly meet with weighty difficulties, but
these difficulties relate chiefly to subjects--such as the degree of
perfection of the geological record, the means of distribution, the
possibility of transitions in organs, etc.--on which we are confessedly
ignorant; nor do we know how ignorant we are. If we are much more ignorant
than is generally supposed, most of these difficulties wholly disappear.
Let the reader reflect on the difficulty of looking at whole classes of
facts from a new point of view. Let him observe how slowly, but surely, the
noble views of Lyell on the gradual changes now in progress on the earth's
surface have been accepted as sufficient to account for all that we see in
its past history. The present action of natural selection may seem more or
less probable; but I believe in the truth of the theory, because it
collects, under one point of view, and gives a rational explanation of,
many apparently independent classes of facts. (Introduction/4. In treating
the several subjects included in the present and my other works I have
continually been led to ask for information from many zoologists,
botanists, geologists, breeders of animals, and horticulturists, and I have
invariably received from them the most generous assistance. Without such
aid I could have effected little. I have repeatedly applied for information
and specimens to foreigners, and to British merchants and officers of the
Government residing in distant lands, and, with the rarest exceptions, I
have received prompt, open-handed, and valuable assistance. I cannot