PERPETUATION OF LIVING BEINGS. 121 



consideration of the production of those natural races 

 which everybody admits to exist. The question is, 

 whether in nature there are causes competent to pro- 

 duce races, just in the same way as man is able to 

 produce, by selection, such races of animals as we have 

 already noticed. 



When a variety has arisen, the Conditions of Exist- 

 ence 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 furnished by the physical, the 

 inorganic world, and there are conditions of existence 

 which are furnished by the organic world. There is, 

 •in the first place, Climate ; under that head I include 

 only temperature and the varied amount of moisture of 

 particular places. In the next place there is what is 

 technically called Station, which means — given the 

 climate, the particular kind of place in which an ani- 

 mal or a plant lives or grows ; for example, the station 

 of a fish is in the water, of a fresh-water fish in fresh 

 water; the station of a marine fish is in the sea, and a 

 marine animal may have a station higher or deeper. 

 So again with land animals : the difterences in their 

 stations are those of diff"erent soils and neighbour- 

 hoods; some being best adapted to a calcareous, and 

 others to an arenaceous soil. The third condition of 

 existence is Food, by which I mean food in the 

 broadest sense, the supply of the materials necessary to 

 the existence of an organic being ; in the case of a 

 plant the inorganic matters, such as carbonic acid, 

 water, ammonia, and the earthy salts or saUnes ; in the 

 case of the animal the inorganic and organic matters, 



