Chap. XXI.] AND CONCLUDING REMARKS. 373 



is the high standard of intellectual power and of moral 

 disposition which he has attained. But every one who 

 admits the general principle of evolution, must see that 

 the mental powers of the higher animals, which are the 

 same in kind with those of mankind, 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. The development of these powers in animals 

 does not offer any special difficulty ; for with our domesti- 

 cated animals, the mental faculties are certainly variable, 

 and the variations are inherited. No one doubts that 

 these faculties are of the utmost importance to animals in 

 a state of nature. Therefore the conditions are favorable 

 for their development through natural selection. The 

 same ccmclusion may be extended to man ; the intellect 

 must have been all-important to him, even at a very 

 remote period, enabling him to use language, to invent 

 and make weapons, tools, traps, etc. ; by which means, in 

 combination with 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, through a previous considerable 

 advance, the half-art and half-instinct of language came 

 into use ; for the continued use of language will have re- 

 acted on the brain, and produced an inherited effect ; and 

 this again will have reacted on the improvement of lan- 

 guage. The large size of the brain in man, in comparison 

 with that of the lower animals, relatively to the size of 

 their bodies, may be attributed in chief part, as Mr. 

 Chauncey Wright has well remarked,' to the early use of 

 some simple form of language — that wondei-ful engine 

 which affixes signs to all sorts of objects and qualities, 



1 On the " Limits of Natural Selection," in the ' North American Re- 

 view,' Oct. 1870, p. 295. 



