NATURAL SELECTION 125 



seems. It requires certain favourable congenital variations, 

 among others a certain hardness of the soles of the feet, or a 

 tendency to harden under certain conditions. Otherwise lame- 

 ness would ensue ; disease or capture by enemies would follow 

 in due course. Now among the offspring of a pair who suc- 

 ceeded in this new mode of life, some would have feet of the 

 right sort, together with the other characteristics required, and 

 would survive. Others would be ill-adapted for an upright 

 posture and the associated habits. Nevertheless they would have 

 to follow their parents' mode of life. The species, at the time of 

 which we are thinking, has long advanced beyond the stage at 

 which the young are flung upon the world directly they are 

 born. They cannot, therefore, revert to the trees because 

 walking is painful, and, at last, impossible for them. Their 

 parents choose for them their line of life, thus deciding within 

 certain limits the line of development of the species. 



Not only parental care but also the gregarious habit, so com- Force of 

 mon among animals, helps, so to speak, to give the species a fashlon 

 continuous policy and so to promote evolution. Here, too, a gregarious 

 few examples may make clear what is meant. animals 



Among a herd of primitive ruminants some individual bulls 

 may have had, where the horns now are, an exceptional thickness 

 of bone and over it a certain epidermal callosity, not sufficient 

 without special treatment to enable them to drive rivals from 

 the field, but sufficient to make them enjoy sparring, so that the 

 parts would get hardened and enlarged during their advance to 

 maturity. Those of inferior natural endowments would improve 

 much less quickly or break down altogether. Thus congenital 

 hardness of head increased by practice in butting would become a 

 character having selection-value, and bulls that were not richly 

 endowed in this respect would leave no offspring behind them. 

 Among animals living in herds there are special facilities for 

 sexual selection by battle. All the males must fight or efface 

 themselves : there is no standing out. And thus if they are to 

 survive, males must vary in a certain direction, viz., towards 

 hardness of head and weapons for butting. Hence by gradual 

 accumulation will arise horns or branching antlers. 



