The Descent of Man

modified, so as to become suitable to the erect
or semi- erect position.
I have now endeavoured to shew that some of
the most distinctive characters of man have in
all probability been acquired, either directly, or
more commonly indirectly, through natural
selection. We should bear in mind that modifications
in structure or constitution which do
not serve to adapt an organism to its habits of
life, to the food which it consumes, or passively
to the surrounding conditions, cannot have
been thus acquired. We must not, however, be
too confident in deciding what modifications
are of service to each being: we should remember
how little we know about the use of many
parts, or what changes in the blood or tissues
may serve to fit an organism for a new climate
or new kinds of food. Nor must we forget the
principle of correlation, by which, as Isidore
Geoffroy has shewn in the case of man, many
strange deviations of structure are tied to-