150 EVOLUTION AND MAN S PLACE IN NATURE 



involved by including the whole range of animal ac 

 tivity. But this is not the consideration which has 

 influenced Darwin. His restriction to the higher 

 mammalia arises from the structure of an evolution 

 theory. Within such a theory, evolution of organic 

 structure from its simplest form upwards, towards a 

 more highly elaborated organism, constitutes a vast 

 epoch in the history of progress, carrying within itself, 

 under operation of natural law, provision for the life of 

 a later epoch. Ac&rding to the implications of this 

 theory, the evolution of mind is a Iate_j3ventj for 

 which all antecedent stages in natural history_had been 

 preparing. This is, indeed, the meaning of natural 

 selection. It is the action of environment on organism, 

 constitutionally adapted for modification under pres 

 sure of external demands. This, according to Darwin, 

 is the key to the progress manifest in the annals of 

 natural history. Hence the restriction to the higher 

 mammals, when inclusion of the functions of human 

 life is attempted. On the other hand, when Wallace 

 admits his inability to claim that the rational life can 

 be included within this scheme of evolution, it is 

 because he fails to find, in the forms of life most 

 closely allied, sufficient promise to account for evolu 

 tion of the mental powers of man. 



Granting evolution of organic life on the earth, 

 what account can be given of the appearance of 

 mind or intelligence ? In the contrast between 

 sensible discrimination and rational, we have a 

 serviceable definition of intelligence. It seems also 

 as if in advancing into this higher field of research, 

 we were passing away from organic structure and 

 its functions, inasmuch as physiology of brain has 



