There remains, however, this difficulty. After an organ has ceased being
used, and has become in consequence much reduced, how can it be still
further reduced in size until the merest vestige is left; and how can it be
finally quite obliterated? It is scarcely possible that disuse can go on
producing any further effect after the organ has once been rendered
functionless. Some additional explanation is here requisite which I cannot
give. If, for instance, it could be proved that every part of the
organisation tends to vary in a greater degree towards diminution than
toward augmentation of size, then we should be able to understand how an
organ which has become useless would be rendered, independently of the
effects of disuse, rudimentary and would at last be wholly suppressed; for
the variations towards diminished size would no longer be checked by
natural selection. The principle of the economy of growth, explained in a
former chapter, by which the materials forming any part, if not useful to
the possessor, are saved as far as is possible, will perhaps come into play
in rendering a useless part rudimentary. But this principle will almost
necessarily be confined to the earlier stages of the process of reduction;
for we cannot suppose that a minute papilla, for instance, representing in
a male flower the pistil of the female flower, and formed merely of
cellular tissue, could be further reduced or absorbed for the sake of
economising nutriment.
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