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 



