SELECTION 583 



circulating the blood ; but apparently we have not yet, in any 

 line, approached a limit so high that variation is not abundantly 

 able to present still higher values. How long this may go on is 

 a question both of scientific and of utilitarian interest, but it will 

 be remembered that variation is supposed not to be reducible 

 below some 85 or 89 per cent of its original amount. 1 



Selection for definite purposes often against valuable qualities, 

 especially fertility, 2 vigor, and longevity. So intent are we upon 

 securing some coveted character, as early maturity, size, milking 

 or feeding quality, that we overlook other less visible but none 

 the less essential qualities. This is best seen among our meat- 

 producing animals. For example, it is the heavy-fleshed, early- 

 maturing sow pig that finds her way to the prize ring and ulti- 

 mately to the fashionable breeding pen. Now this is not the 

 most prolific type of swine, and under this policy of selection, 

 primarily for flesh and fat, it is not surprising that, of all our 

 animals, those bred for meat production are lowest in fertility. 

 We know of no fundamental reason why it must be so ; it simply 

 is so because fertility has been so generally neglected in the 

 exclusive standards and methods of selection employed. 



" Fertility," " vigor," and "longevity" are all relative terms. 

 All animals and plants have some degree of vigor, and nearly 

 all are able to reproduce, at least to some extent. The evils on 

 this score arise not from the non-breeder, or the individual that 

 succumbs in early life, but from those individuals which, though 

 not entirely wanting, are yet deficient in those fundamental 

 qualities that are of necessity correlated with propagation of a 

 vigorous, lasting, and prosperous race. It is the " shy breeder" 

 that comes to nothing, and that is the root of many of the evils 

 of the breeding herd. 



The relative values of prolific and of shy breeders may be 

 brought out by comparing three cows, for example, one of which 

 will produce two calves before she stops breeding, another four, 

 and another six. After five generations the fertile female 

 descendants of each would be as follows, assuming that one half 



1 Pearson, Grammar of Science, p. 483. 



2 The word " fertility " is used in preference to " fecundity " because the latter 

 term refers especially to females. 



