47° ZOOLOGY 



mobile hands, means the making and use of tools, of dwellings, 

 and getting numerous forms of mastery over nature. It is 

 scarcely possible to overstate the importance of tools in human 

 evolution. Each new implement is a kind of new bodily organ 

 and a stimulant to greater intelligence. The brain working 

 through language makes it possible to communicate experi- 

 ences, and to develop ideas and the power of thinking and 

 reasoning. In the more intimate parental relations brought 

 about by homes, all this insures the education and training of the 

 young in the discoveries of the race. The increase of the 

 cerebral cortex and the closer association of the different parts 

 of this cortex are in some way related to the better consciousness 

 and memory in man. The use of language and the power of 

 abstract reasoning have been chief agencies in the further 

 increase in size and complexity of the brain. 



470. Mental Life of Man, Instincts, Habits, Reason. — 



Fundamentally, the mental life of man, no less than that of the 

 lower animals, is the function of the brain and its accompanying 

 systems of organs. He has the same nervous arcs by which 

 stimulus, conduction, reaction, satisfactions and dissatisfactions, 

 and the coordinations of these are made possible. His reflexes 

 and inherited reaction patterns are much the same, and the 

 appetites and feelings do not differ fundamentally. All the 

 higher animals experience much the same hunger, thirst, sex 

 impulses, satiety and pains. All have fears, aversions, loves 

 and jealousies, and anger, — the basis of which at least is in- 

 herited. That portion of these qualities and tendencies which 

 is inherited we call instinctive. Much of the mental life of 

 man, quite as really as in the lower animals, is of these more 

 mysterious impulses (instincts) that we do not get by our own 

 experiences, but which belong to our make-up in some way as an 

 inheritance from the past of our ancestors. We do not always 

 realize how much our own life is controlled by these inherited 

 instincts. They predispose us to do certain things in particular 

 ways. Much of man's life and activities is made up of habitual 

 actions that have been acquired through trial and experience, 

 and the crystallizing of these through memory. The child 



