430 THE CAUSES OF THE XI 
can prove—and this comes to the same thing— 
that varieties exist in nature within the limits of 
species, and, what is more, that when a variety has 
come into existence in nature, there are natural ~ 
causes and conditions, which are amply competent 
to play the part of a selective breeder; and al- 
though that is not quite the evidence that one 
would like to have—though it is not direct testi- 
mony—yet it is exceeding good and exceedingly — 
powerful evidence in its way. 
As to the first point, of varieties existing 
among natural species, 1 might appeal to the 
universal experience of every naturalist, and of ~ 
any person who has ever turned any attention 
at all to the characteristics of plants and animals 
in a state of nature; but I may as well take 
a few definite cases, and I will begin with Man 
himself. 
I am one of those who believe that, at present, 
there is no evidence whatever for saying, that man- 
kind sprang originally from any more than a single 
pair; I must say, that I cannot see any good 
ground whatever, or even any tenable sort of evi- 
dence, for believing that there is more than one 
species of Man. Nevertheless, as you know, just 
as there are numbers of varieties in animals, so 
there are remarkable varieties of men. I speak 
not merely of those broad and distinct variations 
which you see at a glance. Everybody, of course, 
knows the difference between a Negro and a white 
