s
ineffective.

The alleged inheritance of the effects of use and disuse in our domestic
animals must be very slow and slight.[51] Darwin tells us that "there
is no good evidence that this ever follows in the course of a single
generation." "Several generations must be subjected to changed habits
for any appreciable result."[52] What does this mean? One of two things.
Either the tendency is very weak, or it is non-existent. If it is so
weak that we cannot detect its alleged effects till several generations
have elapsed, during which time the more powerful agency of selection
has been at work, how are we to distinguish the effects of the minor
factor from that of the major? Are we to conclude that use-inheritance
_plus_ selection will modify races, just as Voltaire firmly held that
incantations, together with sufficient arsenic, would destroy flocks of
sheep? Is it not a significant fact that the alleged instances of
use-inheritance so often prove to be self-conflicting in their details?

For satisfactory proof of the prevalence of a law of use-inheritance we
require normal instances where selection is clearly inadequate to
produce the change, or where it is scarcely allowed time or opportunity
to act, as in the immediate offspring of the modified individual. Of the
first kind of cases there seems to be a plentiful lack. Of the latter
kind, according to Darwin, there appears to be none--a circumstance
which contrasts strangely and suspiciously with the many decisive cases
in which variation from unknown causes has been inherited most
strikingly in the immediate offspring. It must be expected, indeed, that
among these innumerable cases some will accidentally mimic the alleged
effects of use-inheritance.

If Darwin had felt certain that the effects of habit or use tended in
any marked degree to be conveyed directly and cumulatively to succeeding
generations, he could hardly have given us such cautious, half-hearted
encouragement of good habits as the following:--"It is not improbable
that after long practice virtuous tendencies may be inherited." "Habits,
moreover followed during many generations probably tend to be
inherited."[53] This is probable, independently of use-inheritance. The
"many generations" specified or implied, will allow time for the play of
selective as well as of cumulatively-educative influences. There must
apparently be a constitutional or inheritable predisposition or fitness
for the habits spoken