XI PHENOMENA OF ORGANIC NATURE 433 
any plant and any animal may vary in nature; 
that varieties may arise in the way I have described 
—as spontaneous varieties—-and that those varie- 
ties may be perpetuated in the same way that I 
have shown you spontaneous varieties are perpetu- 
ated ; I say, therefore, that there can be no doubt 
as to the origin and perpetuation of varieties in 
nature. 
But the question now is :—Does selection take 
place in nature? Is there anything like the 
operation of man in exercising selective breeding, 
taking place in nature? You will observe that, 
at present, I say nothing about species ; I wish to 
confine myself to the consideration of the pro- 
duction of those natural races which everybody 
admits to exist. The question is, whether in 
nature there are causes competent. to produce 
races, just in the same way as man is able to pro- 
duce by selection, such races of animals as we 
have already noticed. | 
When a variety has arisen, the CONDITIONS OF 
EXISTENCE are such as to exercise an influence 
which is exactly comparable to that of artificial 
selection. By Conditions of Existence I mean 
two things—there are conditions which are fur- 
nished by the physical, the inorganic world, and 
_ there are conditions of existence which are fur- 
nished by the organic world. There is, in the first 
place, CLIMATE ; under that head I include only 
temperature and the varied amount of moisture 
VOL. II FF 
