The Descent of Man

It must not be supposed that the resemblances
between man and certain apes in the above and
in many other points—such as in having a naked
forehead, long tresses on the head, etc.,—
are all necessarily the result of unbroken inheritance
from a common progenitor, or of subsequent
reversion. Many of these resemblances
are more probably due to analogous variation,
which follows, as I have elsewhere attempted
to shew (10. 'Origin of Species,' 5th edit. 1869,
p.194. 'The Variation of Animals and Plants
under Domestication,' vol. ii. 1868, p. 348.),
from co-descended organisms having a similar
constitution, and having been acted on by like
causes inducing similar modifications. With
respect to the similar direction of the hair on
the fore-arms of man and certain monkeys, as
this character is common to almost all the anthropomorphous
apes, it may probably be attributed
to inheritance; but this is not certain, as
some very distinct American monkeys are thus
characterised.