70 



DOMESTICATED ANIMALS AND PLANTS 



If the great problem in existence is the perpetuation of the 

 species, then the individual helps the object forward in either 

 one of two ways, — by reproduction to insure new numbers, or 

 by improving conditions of life, thus reducing selection and 

 lengthening existence. 



The number of any race at any given time, therefore, is quite 

 as much dependent upon the length of life as it is upon the rate 

 of reproduction ; ^ indeed, many disappearing races of men are 

 slowly failing in the face of rapid reproduction because the in- 

 dividuals are not well enough conditioned to attain full and ripe 

 maturity and establish and maintain good conditions of life. 



This principle is of special application in the breeding yards. 

 Suppose, for example, the farmer has three classes of cows of 

 different degrees of fertility, — one that will raise but two calves, 

 one that will raise four, and one that will raise six, before thc\ 

 die or stop breeding ; and suppose, for sake of the illustration, 

 that the descendants will do the same respectively. Remem- 

 bering now that only half the descendants will be females, let 

 us see how the account would stand with these three classes 

 of cows and their descendants, say, at the end of the fifth 

 generation .2 



The Meaning of Relative Fertility 



It is easy to see that cows of the third class and their de- 

 scendants would not only soon constitute the herd but afford 

 abundant material for selection in the meantime. It is so with 



1 Race suicide that is now so much talked about is not so much a matter of 

 the size of families as is commonly supposed ; it is quite as much involved in 

 the matter of health and long life. ^ See " Principles of Breeding," p. 199. 



