VIII THE DEVELOPMENT OF HUMAN RACES 171 
secure its prey, to escape from its enemies, to resist the 
inclemencies of the seasons, and to rear a numerous and 
healthy offspring. Buta change now takes place. A series 
of cold winters, for instance, come on, making food scarce, 
and bringing an immigration of some other animals to com- 
pete with the former inhabitants of the district. The new 
immigrant is swift of foot, and surpasses its rivals in the 
pursuit of game; the winter nights are colder, and require a 
thicker fur as a protection, and more nourishing food to keep 
up the heat of the system. Our supposed perfect animal is 
no longer in harmony with its universe; it is in danger of 
dying of cold or of starvation. But the animal varies in its 
offspring. Some of these are swifter than others—they still 
manage to catch food enough; some are hardier and more 
thickly furred—they manage in the cold nights to keep warm 
enough ; the slow, the weak, and the thinly clad soon die 
off. Again and again, in each succeeding generation, the 
same thing takes place. By this natural process, which is so 
inevitable that it cannot be conceived not to act, those best 
adapted to live, live; those least adapted, die. It is some- 
times said that we have no direct evidence of the action of 
this selecting power in nature. But it seems to me we have 
better evidence than even direct observation would be, 
because it is more universal, viz., the evidence of necessity. 
It must be so ; for, as all wild animals increase in a geomet- 
rical ratio, while their actual numbers remain on _ the 
average stationary, it follows that as many die annually as 
are born. If, therefore, we deny natural selection, it can 
only be by asserting that, in such a case as I have supposed, 
the strong, the healthy, the swift, the well-clad, the well 
organised animals in every respect, have no advantage over 
—do not on the average live longer than—the weak, the 
unhealthy, the slow, the ill-clad, and the imperfectly organised 
individuals ; and this no sane man has yet been found hardy 
enough to assert. But this is not all; for the offspring on 
the average resemble their parents, and the selected portion 
of each succeeding generation will therefore be stronger, 
swifter, and more thickly furred than the last; and if this 
process goes on for thousands of generations, our animal will 
have again become thoroughly in harmony with the new con- 
