400 EVOLUTION OE MENTAL CHAKACTEES 



about. To begin with, the pre-human ancestor was favourably- 

 situated for such a development because he was a generalized 

 and not a specialized type. Once specialization of form has set 

 in, as it has among the anthropoid apes, there are two bars to 

 such a development as occurred in man. The specialization of 

 bodily form in order to cope with a peculiar environment renders 

 the body less adaptable to any changes in the environment 

 which may take place. Further, unless the body is of the nature 

 of an instrument capable of being readily employed to perform 

 various functions, the intellect is unable to manifest itself. We 

 have only to think of the specialized fore and hind limbs of most 

 mammalian types to see how poor an instrument the body would 

 in those cases make in the service of the intellect. 



Under these favourable circumstances, evolution took this 

 momentous turn. We can understand how, since the pre-human 

 ancestor depended for his survival almost solely upon his intellect, 

 there would be a high premium upon intellectual development. 

 It is reasonable to suppose that he lived in groups of polygamous 

 families and that differential fertihty thus intensified selection. 

 There is, of course, never at any time only a single factor governing 

 selection, and though undoubtedly intellect was the chief factor 

 in selection, climatic and other factors were, as we have noticed, 

 also in operation, bringing about those changes in bodily form 

 that we have observed. 



The instincts of the pre-human ancestor were doubtless, in 

 common with those of other mammals, of a generalized type 

 compared with what we find among some lower groups of animals. 

 The tendency has been for them to become even more generalized, 

 though not on the whole any less powerful. It seems likely, for 

 instance, that the instinct of flight was definitely associated with 

 the snakes among other objects from the attacks of which pre- 

 sumably the ancestor was at one time in danger. We assume 

 this because we occasionally meet with cases in which this 

 specialization of the instinct of flight still obtains. The instinct 

 of flight has now become wholly generalized, being aroused by 

 general conditions and not by specialized occurrences. If it is 

 correct to think of the ancestor as living in groups of families, 

 for the leadership of which there must have been continual 

 struggles, we may conclude that the instincts of pugnacity and 

 of self-assertion were favoured, and we may make other similar 



