([Footnote] * I say 'help' to furnish: for I by no means believe that it
was any original difference of cerebral quality, or quantity which
caused that divergence between the human and the pithecoid stirpes,
which has ended in the present enormous gulf between them. It is no
doubt perfectly true, in a certain sense, that all difference of
function is a result of difference of structure; or, in other words, of
difference in the combination of the primary molecular forces of living
substance; and, starting from this undeniable axiom, objectors
occasionally, and with much seeming plausibility, argue that the vast
intellectual chasm between the Ape and Man implies a corresponding
structural chasm in the organs of the intellectual functions; so that,
it is said, the non-discovery of such vast differences proves, not that
they are absent, but that Science is incompetent to detect them. A very
little consideration, however, will, I think, show the fallacy of this
reasoning. Its validity hangs upon the assumption, that intellectual
power depends altogether on the brain--whereas the brain is only one
condition out of many on which intellectual manifestations depend; the
others being, chiefly, the organs of the senses and the motor
apparatuses, especially those which are concerned in prehension and in
the production of articulate speech.

A man born dumb, notwithstanding his great cerebral mass and his
inheritance of strong intellectual instincts, would be capable of few
higher intellectual manifestations than an Orang or a Chimpanzee, if he
were confined to the society of dumb associates. And yet there might not
be the slightest discernible difference between his brain and that of a
highly intelligent and cultivated person. The dumbness might be the
result of a defective structure of the mouth, or of the tongue, or a
mere defective innervation of these parts; or it might result from
congenital deafness, caused by some minute defect of the internal ear,