“What of Darwin? Never wavering from his strong principles of infinitesimal evolutionary change and continuity, in his The Descent of Man (1871) Darwin himself advanced a “Caruso” theory for the evolution of language:
males who could sing better were sexually selected by females, and this, in turn, led to perfection of the vocal apparatus, like the peacock’s tail.
Better vocal competence went hand in hand with a general increase in brain size that led, in turn, to language— language used for internal mental thought:
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 progenitor 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 advancement 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. (Darwin 1871, 57)
Darwin’s Caruso theory has recently undergone something of a revival."
Why Only Us
Language and Evolution
Robert C. Berwick