HUMAN SELECTION. 95 



ference of food or training, since it is by selection alone that 

 our various breeds of domestic animals have in most cases been 

 produced. 



On the other hand, the person who undertook to produce simi- 

 lar results by food and training alone, without allowing selection 

 to have any part in the process, would have to act in a very differ- 

 ent manner. He would first divide his horses into two lots as 

 nearly as possible identical in all points, and thereafter subject 

 the one lot to daily exercise in drawing loads at a slow pace, the 

 other lot to equally constant exercise in running, and he might 

 also supply them with different kinds of food if he thought it 

 calculated to aid in producing the required effect. In each suc- 

 cessive generation he must make no selection of the swiftest or 

 the strongest, but must either keep the whole progeny of each lot, 

 or carefully choose an average sample of each to be again sub- 

 jected to the same discipline. It is quite certain that the very 

 different kinds of exercise would have some effect on the individ- 

 uals so trained, enlarging and strengthening a different set of 

 muscles in each, and if this effect were transmitted to the off- 

 spring, then there ought to be in this case also a steady advance 

 toward the racer and the cart-horse type. Such an experiment, 

 however, has never been tried, and we can not therefore say posi- 

 tively what would be the result ; but those who accept the theory 

 of the non-heredity of acquired characters would predict with 

 confidence that after thirty or forty generations of training with- 

 out selection, the last two lots of colts would have made little or 

 no advance toward the two types required, but would be practi- 

 cally indistinguishable. 



It is exceedingly difficult to find any actual cases to illustrate 

 this point, since either natural or artificial selection has almost 

 always been present. The apparent effects of disuse in causing 

 the diminution of certain organs, such as the reduced wings of 

 some birds in oceanic islands and the very sinall or aborted eyes 

 of some of the animals inhabiting extensive caverns, can be as 

 well explained by the withdrawal of the cumulative agency of 

 natural selection and by economy of growth, as by the direct 

 effects of disuse. The following facts, however, seem to show 

 that special skill derived from practice, when continued for sev- 

 eral generations, is not inherited, and does not therefore tend to 

 increase. The wonderful skill of most of the North American 

 Indians in following a trail by indications quite imperceptible to 

 the ordinary European has been dwelt upon by many writers, 

 but it is now admitted that the white trappers equal and often 

 excel them, though these trappers have in almost every case ac- 

 quired their skill in a comparatively short period, without any 

 of the inherited experience which might belong to the Indian. 



