Darwin also attributes the thickened sole in infants, "long before
birth," to "the inherited effects of pressure during a long series of
generations."[50] But disuse should make the infant's sole _thin_, and
it is this thinness that should be inherited. If we suppose the
inheritance of the thickened soles of later life to be transferred to an
earlier period, we have the anomaly of the inherited effects of disuse
at that earlier period being overpowered by the untimely inheritance of
the effects of use at another. On the other hand, it is clear that
natural selection would favour thickened soles for walking on, and might
also promote an early development which would ensure their being ready
in good time for actual use; for variations in the direction of delay
would be cut off, while variations in the other direction would be
preserved. Anyhow, the mere transference of a character to an earlier
period is no proof of use-inheritance. The real question 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?