n short, all organs and faculties
whatsoever--can only have been moulded and developed by use--by
usefulness and by using--but not necessarily by use-inheritance, not
necessarily by directly inherited effects of use or disuse of parts in
the individual. So, too, reduced or rudimentary organs are due to
disuse, but it by no means follows that the diminution is caused by any
direct tendency to the inheritance of the effects of disuse in the
individual. The effects of natural selection are commonly expressible as
effects of use and disuse, just as adaptation in nature is expressible
in the language of teleology. But use-inheritance is no more proven by
one of these necessary coincidences than special design is by the
other. The inevitable simulation of use-inheritance may be entirely
deceptive.

Darwin thinks that "there can be no doubt that use in our domestic
animals has strengthened and enlarged certain parts, and disuse
diminished them; and that such modifications are inherited." Undoubtedly
"such" or _similar_ modifications have often been inherited, but how can
Darwin possibly tell that they are not due to the simulation of
use-inheritance by natural or artificial selection acting upon general
variability? Of the inevitability of selection and of its generally
adaptive tendencies "there can be no doubt," and panmixia would tend to
reduce disused parts; so that there _must always_ remain grave doubts of
the alleged inheritance of the similar effects of use and disuse, unless
we can accomplish the extremely difficult feat of excluding both natural
and artificial selection as causes of enlargement, and panmixia and
selection as causes of dwindling.

WEAKNESS OF USE-INHERITANCE.

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 i