Nor ought we to marvel if all the
contrivances in nature be not, as far as we can judge, absolutely perfect;
as in the case even of the human eye; or if some of them be abhorrent to
our ideas of fitness. We need not marvel at the sting of the bee, when
used against the enemy, causing the bee's own death; at drones being
produced in such great numbers for one single act, and being then
slaughtered by their sterile sisters; at the astonishing waste of pollen by
our fir-trees; at the instinctive hatred of the queen-bee for her own
fertile daughters; at ichneumonidae feeding within the living bodies of
caterpillars; and at other such cases. The wonder, indeed, is, on the
theory of natural selection, that more cases of the want of absolute
perfection have not been detected.
The complex and little known laws governing the production of varieties are
the same, as far as we can judge, with the laws which have governed the
production of distinct species. In both cases physical conditions seem to
have produced some direct and definite effect, but how much we cannot say.
Thus, when varieties enter any new station, they occasionally assume some
of the characters proper to the species of that station. With both
varieties and species, use and disuse seem to have produced a considerable
effect; for it is impossible to resist this conclusion when we look, for
instance, at the logger-headed duck, which has wings incapable of flight,
in nearly the same condition as in the domestic duck; or when we look at
the burrowing tucu-tucu, which is occasionally blind, and then at certain
moles, which are habitually blind and have their eyes covered with skin; or
when we look at the blind animals inhabiting the dark caves of America and
Europe.
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