58 EVOLUTION AND MAN S PLACE IN NATURE 



environment, but no deviation either from the general 

 plan of structure, or from the laivs of sensori-motor 

 activity. 



Differences in the functions of animal life depend on 

 differences of structure, involving differences in work 

 ing apparatus. Capacity of sensory impression, and 

 power of muscular activity, are common to all. For 

 these, there is a common dependence on brain and 

 nerve, all nerve fibres being co-ordinated in a nerve 

 centre. Nerve centres are more or less complicated 

 as differentiation of bodily structure is extended. The 

 more elaborate the bodily differentiation, the more 

 elaborate the nerve distribution and the more compli 

 cated the central arrangements. Only in this way 

 is diversity of function provided for in the animal 

 structure. Functions depend upon structure. As 

 these are multiplied, there is variation in terminal 

 organs of sensibility, and increased complication in 

 muscular arrangements. Special senses are only 

 modifications of the sense of touch ; detailed muscular 

 distribution answers to all diversities in sensibility. 1 

 In this way, a definite conclusion is reached as to 

 man s physical nature, in accordance with the 

 inductions of comparative anatomy and physiology. 

 The superiority of human organism appears in its 

 structure, not in the conditions under which its 

 functions are fulfilled. In the scale of organic life, 

 Man holds conspicuously the chief place ; in the line 

 of history, his appearance must be accounted for in 

 accordance with his rank. His superiority in organism 

 is altogether impressive, as indicated by comparative 

 size and weight of brain, by complexity of structure 



1 I have discussed details in The Relations of the Mind and Brain. 



