No doubt similar structures, adapted for the same purpose, have often
been independently acquired through variation and natural selection
by distinct species; but this view will not explain close similarity
between distinct species in a multitude of unimportant details.
Now if we bear in mind the numerous points of structure having no
relation to expression, in which all the races of man closely agree,
and then add to them the numerous points, some of the highest
importance and many of the most trifling value, on which the movements
of expression directly or indirectly depend, it seems to me improbable
in the highest degree that so much similarity, or rather identity
of structure, could have been acquired by independent means.
Yet this must have been the case if the races of man are descended
from several aboriginally distinct species. It is far more probable
that the many points of close similarity in the various races are due
to inheritance from a single parent-form, which had already assumed
a human character.
It is a curious, though perhaps an idle speculation, how early in the long
line of our progenitors the various expressive movements, now exhibited
by man, were successively acquired.
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