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 ;1 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 they 
_ 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.? 
THE MEANING OF RELATIVE FERTILITY 
Bae oul 7 =e 
First Second Third Fourth Fifth 
FirS€ 40. core 3 I I I I I I 
Second . . . 2 a 4 8 16 32 
Ahindy sa eo 3 3 9 27 81 243 
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. 2 See ‘Principles of Breeding,” p. 199- 
