ion is whether the
thickened sole was gained by natural selection or by the inherited
effects of pressure, and the mere transference or hastened appearance of
the thickening does not in any degree solve this question. It merely
excludes the effect of disuse during lifetime, and thus presents a
fallacious appearance of being decisive. The thickened sole of the
unborn infant, however, like the lanugo or hairy covering, is probably a
result of the direct inheritance of ancestral stages of evolution, of
which the embryo presents a condensed epitome. While the relative
thinness of the infant's sole might be pointed to as the effect of
_disuse_ during a long series of generations, its thickness is rather an
illustration of atavism still resisting the effects of long-continued
disuse. There is nothing to show that the inheritable portion of the
full original thickness was not gained by natural selection rather than
by the directly inherited effect of use; and the latter, being
cumulative and indiscriminative in its action, would apparently have
made the sole very much thicker and harder than it is. If natural
selection were not supreme in such cases, how could we account for the
effects of pressure resulting in hard hoofs in some cases and only soft
pads in others?

A SOURCE OF MENTAL CONFUSION.

Of course in a certain sense this thickening of the sole has resulted
from use. In one sense or other, most--or perhaps all--of the results of
natural selection are inherited effects of use or disuse. Natural
selection preserves that which is of use and which is used, while it
eliminates that which is useless and is not used. The most confident
assertions of the effects of use and disuse in modifying the heritable
type, appear to rest on this indefeasible basis. Darwin's statements
concerning the effects of use and disuse in evolution can frequently be
read in two senses. They often command assent as undeniable truisms as
they stand, but are of course written in another and more debatable
sense. Thus in the case of the shortened wings and thickened legs of the
domestic duck, I believe equally with Darwin and Spencer that "no one
will dispute that they have resulted from the lessened use of the wings
and the increased use of the legs." "Use" is at bottom the determining
circumstance in evolution generally. The trunk of the elephant, the fin
of the fish, the wing of the bird, the cunning hand of man and his
complicated brain--and, i