The Descent of Man

THE DIRECT AND DEFINITE ACTION OF
CHANGED CONDITIONS.
This is a most perplexing subject. It cannot be
denied that changed conditions produce some,
and occasionally a considerable effect, on organisms
of all kinds; and it seems at first probable
that if sufficient time were allowed this
would be the invariable result. But I have failed
to obtain clear evidence in favour of this conclusion;
and valid reasons may be urged on the
other side, at least as far as the innumerable
structures are concerned, which are adapted for
special ends. There can, however, be no doubt
that changed conditions induce an almost indefinite
amount of fluctuating variability, by
which the whole organisation is rendered in
some degree plastic.
In the United States, above 1,000,000 soldiers,
who served in the late war, were measured,
and the States in which they were born and
reared were recorded. (17. 'Investigations in