344 MIND IN EVOLUTION CHAP. 



life, though inherited tendency is its foundation through- 

 out, far outruns in subtle complexity any possible achieve- 

 ment of instinct. 



One hesitates to dogmatise about animal societies until 

 they have been more thoroughly studied, but what we know 

 of them goes to show that the division of labour the 

 most notable form of social differentiation in the animal 

 world is based, in the cases where it is most elaborate, 

 on differences of structure. This is conspicuously the 

 case with the Social Hymenoptera, where the distribution 

 of functions between fertile females, infertile females, and 

 males is the basis of the whole order. The further 

 differentiations which appear among ants as between 

 " workers " and " warriors," " mistresses " and " slaves," 

 are also directly correlated with differences of physical 

 structure. The division of labour in these cases would 

 thus seem in its main lines to follow rather than to over- 

 ride the inherited tendencies to which physical structures 

 give rise. On the other hand, the rudimentary division 

 that we find among the higher vertebrates is not sufficient 

 to justify us in speaking of a social " system " at all. 

 The habit of fixing sentinels is the typical case. Probably 

 we must ascribe this to a kind of tradition as much as to 

 heredity, the habit once formed being kept up in each 

 flock or herd from generation to generation, by the simple 

 practice of forcing the younger members as they grow up 

 to take their turn at watching while the others feed. It 

 is a special adjustment to the needs of a gregarious life, 

 part instinctive, part traditional, part, very likely, intel- 

 ligent. One such adjustment, however, does not make a 

 system with a complex ramification of duties. Lastly, the 

 submissign to a chief, which we find conspicuous among 

 apes, seems to be of the same habitual character. The 

 .most active and capable member of a troop tends to 

 acquire a certain primacy. Here again there seems to be 

 something of habit, and perhaps something of intelligence, 

 operating on the hereditary tendency to follow and 

 imitate. If there were evidence that the chieftainship 

 became hereditary, and that apes would tolerate and 

 grovel before a rot faineant, we should have to consider 



