is absorbed, or a muscle becomes small or flabby,
it proves, so far, that the average effect of use through enormous ages
is _not_ transmitted. When the fibula of a dog's leg thickens by 400 per
cent. to a size "equal to or greater than" that of the removed tibia
which previously did the work,[69] it shows that in spite of disuse for
countless generations, the "almost filiform" bone has retained a
potentiality of development which is fully equal to that possessed by
the larger one which has been constantly used. When, after being reared
on the ailanthus, the caterpillars of the _Bombyx hesperus_ die of
hunger rather than return to their natural food, the inherited effect of
ancestral habit does not seem to be particularly strong. Neither is
there any strongly-inherited effect of long-continued ancestral wildness
in many animals which are easily tamed.

WOULD NATURAL SELECTION FAVOUR USE-INHERITANCE?

If use-inheritance is really one of the factors of evolution, it is
certainly a subordinate one, and an utterly helpless one, whenever it
comes into conflict with the great ruling principle of Selection. Would
this dominant cause of evolution have favoured a tendency to
use-inheritance if such had appeared, or would it have discouraged and
destroyed it? We have already seen that use-inheritance is unnecessary,
since natural selection will be far more effective in bringing about
advantageous modifications; and if it can be shown that use-inheritance
would often be an evil, it then becomes probable that on the whole
natural selection would more strongly discourage and eliminate it as a
hostile factor than it might occasionally favour such a tendency as a
totally unnecessary aid.

USE-INHERITANCE AN EVIL.

Use-inheritance would crudely and indiscriminately proportion parts to
actual work done--or rather to the varying _nourishment and growth_
resulting from a multiplicity of causes--and this in its various details
would often conflict most seriously with the real necessities of the
case, such as occasional passive strength, or appropriate shape,
lightness and general adaptation. If its accumulated effects were not
corrected by natural or sexual selection, horns and antlers would
disappear in favour of enlarged hoofs. The elephant's tusks would become
smaller than its teeth. Men would have callosities for sitting on, like
certain monkeys, and huge corns or hoofs for walking on. Bones would
often be modified disastrousl