y. Thus the condyle of the human jaw would
become larger than the body of the jaw, because as the fulcrum of the
lever it receives more pressure. Some organs (like the heart, which is
always at work) would become inconveniently or unnecessarily large.
Other absolutely indispensable organs, which are comparatively passive
or are very seldom used, would dwindle until their weakness caused the
ruin of the individual or the extinction of the species. In eliminating
various evil results of use-inheritance, natural selection would be
eliminating use-inheritance itself. The displacement of Lamarck's theory
by Darwin's shows that the effects of use-inheritance often differ from
those required by natural selection; and it is clear that the latter
factor must at least have reduced use-inheritance to the very minor
position of comparative feebleness and harmlessness assigned to it by
Darwin.

Use-inheritance would be ruinous through causing unequal variation in
co-operative parts--of which Mr. Spencer may accept his own instances of
the jaws and teeth, and the cave-crab's lost eyes and persistent
eye-stalks, as typical examples. That the variation would be unequal
seems almost self-evident from the varying rapidity and extent of the
effects of use and disuse on different tissues and on different parts of
the general structure. The optic nerve may atrophy in a few months from
disuse consequent on the loss of the eye. Some of the bones of the
rudimentary hind legs of the whale are still in existence after disuse
for an enormous period. Evidently use-inheritance could not equally
modify the turtle and its shell, or the brain and its skull; and in
minor matters there would be the same incongruity of effect. Thus, if
the molar teeth lengthened from extra use the incisors could not meet.
Unequal and indiscriminate variation would throw the machinery of the
organism out of gear in innumerable ways.

Use-inheritance would perpetuate various evils. We are taught, for
instance, that it perpetuates short-sight, inferior senses, epilepsy,
insanity, nervous disorders, and so forth. It would apparently transmit
the evil effects of over-exertion, disuse, hardship, exposure, disease
and accident, as well as the defects of age or immaturity.

Would it not be better on the whole if each individual took a fresh
start as far as possible on the advantageous typical lines laid down by
natural selection? Through the long stages of evolution from prima