GENERAL SUMMARY AND CONCLUSION. 697 



must see that the mental powers of the higher animals, 

 which are the same in kind with those of man, though so 

 different in degree, are capable of advancement. Thus 

 the interval between the mental powers of one of the 

 higher apes and of a fish, or between those of an ant and 

 scale-insect, is immense ; yet their development does not 

 offer any special difficulty ; for with our domesticated 

 animals the mental faculties are certainly variable, and 

 the variations are inherited. No one doubts that they are 

 of the utmost importance to animals in a state of nature. 

 Therefore, the conditions are favorable for their develop- 

 ment through natural selection. The same conclusion 

 may be extended to man; the intellect must have been all- 

 important to him, even at a very remote period, as enabling 

 him to invent and use language, to make weapons, tools, 

 traps, etc., whereby with tlie aid of his social habits he 

 long ago became the most dominant of all living creatures. 



A great stride in the development of the intellect will 

 have followed, as soon as the half -art and half -instinct 

 of language came into use; for the continued use of lan- 

 guage will have reacted on the brain and produced an 

 inherited effect; and this again will have reacted on the 

 improvement of language. As Mr. Ohauncey Wright* has 

 well remarked, the largeness of the brain in man relatively 

 to his body, compared with the lower animals, may be 

 attributed in chief part to the early use of some simple 

 form of language that wonderful engine which affixes 

 signs to all sorts of objects and qualities, and excites trains 

 of thought which would never arise from the mere impression 

 of the senses, or if they did arise could not be followed out. 

 The higher intellectual powers of man, such as those of 

 ratiocination, abstraction, self-consciousness, etc., probably 

 follow from the continued improvement and exercise of the 

 other mental faculties. 



The development of the moral qualities is a more inter- 

 esting problem. The foundation lies in the social instincts, 

 including under this term the family ties. These instincts 

 are highly complex, and in the case of the lower animals 

 give special tendencies toward certain definite actions; but 

 the more important elements are love and the distinct 



* " On the Limits of Natural Selecticfh," in the " North American 

 Review," Oct., 1870, p. 295. 



