Chimpanzee and of Man is almost insignificant, when compared with that
between the Chimpanzee brain and that of a Lemur.

It must not be overlooked, however, that there is a very striking
difference in absolute mass and weight between the lowest human brain
and that of the highest ape--a difference which is all the more
remarkable when we recollect that a full grown Gorilla is probably
pretty nearly twice as heavy as a Bosjes man, or as many an European
woman. It may be doubted whether a healthy human adult brain ever
weighed less than thirty-one or two ounces, or that the heaviest
Gorilla brain has exceeded twenty ounces.

This is a very noteworthy circumstance, and doubtless will one day help
to furnish an explanation of the great gulf which intervenes between
the lowest man and the highest ape in intellectual power;* but it has
little systematic value, for the simple reason that, as may be
concluded from what has been already said respecting cranial capacity,
the difference in weight of brain between the highest and the lowest
men is far greater, both relatively and absolutely, than that between
the lowest man and the highest ape. The latter, as has been seen, is
represented by, say twelve ounces of cerebral substance absolutely, or
by 32:20 relatively; but as the largest recorded human brain weighed
between 65 and 66 ounces, the former difference is represented by more
than 33 ounces absolutely, or by 65:32 relatively. Regarded
systematically, the cerebral differences of man and apes are not of more
than generic value; his Family distinction resting chiefly on his
dentition, his pelvis, and his lower limbs.

[Footnote] * I say 'help' to furnish: for I by no means
believe that it was any original difference of cerebral