Chap. II. 
MENTAL POWERS. 
57 
idiots , 35 and in tlie 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 without 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 Yogt, 4 Memoire sur les Microcephales/ 1867, p. 169. With 
respect to savages, I have given some facts in my ‘ Journal of 
Researches/ &c., 1845, p. 206. 
36 See clear evidence on this head in the two works so often quoted* 
by Brehm and Rengger. 
