56 A STUDY IN HEREDITY 



after they become useless, and therefore exempted 

 from selection. Thus birds have possessed wings 

 for millions of years ; they are of little use to tame 

 birds ; but an enormous period would have to 

 elapse before our tame birds became wingless. 

 But characters that have recently appeared are 

 very apt to vanish in a generation or two. Thus 

 the children of an abnormally big man and woman 

 are generally smaller than their parents ; a sixth 

 finger seldom persists long in a family. As com- 

 pared to the characters of wild animals and plants, 

 the special characters of the tame and cultivated 

 varieties are of very recent origin. We have, 

 besides, exceptional opportunities of observing 

 their evolution. We know what the prize breed 

 started from ; we generally have the parent variety 

 to compare it with ; and the evolution, having 

 been on very simple lines, is, in the absence of 

 complexity, easy to study. Thus race-horses have 

 only recently been evolved ; we know exactly how 

 they differ from their progenitor, the ordinary horse, 

 which is with us still. The same is true of all the 

 other prize breeds of animals. Now let us ask 

 ourselves, what would happen if, instead of care- 

 fully selecting for breeding purposes our race-horses 

 and other prize breeds of animals, we bred indis- 

 criminately, allowing the inferior animals to have 

 as much influence on posterity as the superior ? 



