Use-inheritance is normally so weak that it appears to be quite helpless
when opposed to any other factor of evolution. Natural selection evolves
and maintains the instincts of ants and termites in spite of
use-inheritance to a more wonderful degree than it evolves the instincts
of almost any other animal with the fullest help of use-inheritance. It
develops seldom-used horns or natural armour just as readily as
constantly-used hoofs or teeth. Sexual selection evolves elaborate
structures like the peacock's tail in spite of disuse and natural
selection combined. Artificial selection appears to enlarge or diminish
used parts or disused parts with equal facility. The assistance of
use-inheritance seems to be as unnecessary as its opposition is
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 of, which otherwise would scarcely be continued
for many generations, except by the favourably-varying branches of a
family: which again is selection rather than use-inheritance.
Where is the necessity for even the remains of the Lamarckian doctrine
of inherited habit? Seeing how powerful the general principle of
selection has shown itself in cases where use-inheritance could have
given no aid or must even have offered its most strenuous opposition,
why should it not equally be able to develop used organs or repress
disused organs or faculties without the assistance of a relatively weak
ally? Selection evolved the remarkable protective coverings of the
armadillo, turtle, crocodile, porcupine, hedgehog, &c.; it formed alike
the rose and its thorn, the nut and its shell; it developed the
peacock's tail and the deer's antlers, the protective mimicry of various
insects and butterflies, and the wonderful instincts of the white ants;
it gave the serpent its deadly poison and the violet its grateful odour;
it painted the gorgeous plumage of the Impeyan pheasant and the
beautiful colours and decorations of countless birds and insects and
flowers. These, and a thousand other achievements, it has evidently
accomplished without the help of use-inheritance. Why should it be
thought incapable of reducing a pigeon's wing or enlarging a duck's
leg? Why should it be credited with the help of an officious ally in
effecting comparatively slight changes, when great and striking
modifications are effected without any such aid?