IX.] RETROGRESSIVE DEVELOPMEXT IN NATURE. 2^) 



thing will happen. In these, as with the various species of 

 pheasants which have been domesticated, the young animals 

 are the wildest : the instinct to escape has been inherited 

 almost unaltered, and the process of taming must begin afresh 

 with each individual. The tameness of the adult animal is here 

 still an acquired character, i. e. one acquired during the lifetime 

 of the individual, and is not inherent, or rather, it is not the re- 

 sult of those changes in the potentialities of the germ which 

 are gradually produced by universal crossing. The tameness 

 comes about just as in wild animals taken young, such as 

 foxes, wolves, rats, or finches, all of which are tameable up to 

 a certain point, and become accustomed to the absence of 

 enemies. 



It is also interesting to note that loss of the instinct which 

 impels animals to seek their food may sometimes occur. Both 

 food itself and the power of obtaining it are essential to life, and 

 the instinct of seeking food may be looked upon as the first and 

 earliest developed of any : yet it may be partially or even 

 entirely lost. The young of many birds no longer possess the 

 instinct ; they open their bills and cry, and they swallow food 

 placed in their mouths, but they have no idea of picking it up 

 if scattered on the floor of their cage ; the sight of food does 

 not result in any impulse to eat. At this early period of life 

 such birds have not learned the art of feeding themselves, and 

 this is not unnatural ; for they leave the egg in a very unde- 

 veloped condition, and their parents feed them by putting food 

 into their mouths. A part of the food-seeking instinct has thus 

 become superfluous and has disappeared. It may be objected 

 that the little creatures are too undeveloped to feed themselves ; 

 this is true, and it is the reason why the parents feed them and 

 why their instinct is undeveloped. But many other birds, 

 fowls, for instance, run about directly they are out of the egg 

 and pick up food for themselves ; here the food-seeking in- 

 stinct is unimpaired. 



One of the most remarkable cases of degeneration of the 

 food-seeking instinct is found in certain ants. It has been 

 known ever since the beginning of this century that some 

 species of ants keep slaves, for instance, the reddish ant found 

 in the meadows of Switzerland and Alsace {Polyergiis ritfescens). 

 It is not a large but a strong species, which has adopted the 



