Chap. II. MENTAL POWEES. 57 



idiots, 35 and in the barbarous races of mankind, to imi- 

 tate whatever they hear deserves notice. As monkeys 

 certainly understand much that is said to them by man, 

 and as in a state of nature they utter signal-cries of 

 danger to their fellows, 36 it does not appear altogether 

 incredible, that some unusually wise ape-like animal 

 should have thought of imitating the growl of a beast 

 of prey, so as to indicate to his fellow monkeys the 

 nature of the expected danger. And this would have 

 been a first step in the formation of a language. 



As the voice was used more and more, the vocal 

 organs would have been strengthened and perfected 

 through the principle of the inherited effects of use ; 

 and this would have reacted on the power of speech. 

 But the relation between the continued use of language 

 and the development of the brain has no doubt been far 

 more important. The mental powers in some early pro- 

 genitor of man must have been more highly developed 

 than in any existing ape, before even the most imperfect 

 form of speech could have come into use ; but we may 

 confidently believe that the continued use and .advance- 

 ment of this power would have reacted on the mind by 

 enabling and encouraging it to carry on long trains of 

 thought. A long and complex train of thought can no 

 more be carried on wdthout the aid of words, whether 

 spoken or silent, than a long calculation without the 

 use of figures or algebra. It appears, also, that even 

 ordinary trains of thought almost require some form of 

 language, for the dumb, deaf, and^ blind girl, Laura 

 Bridgman, was observed to use her fingers whilst dream- 



35 Vogt, 'Memoire sur les Microcephales,' 1867, p. 169. With 

 respect to savages, I have given some facts in my ' Journal of 

 Eesearches,' &c, 1845, p. 206. 



36 See clear evidence on this head in the two works so often quoted, 

 by Brehm and Kengger. 



