; while the operation of natural selection has also determined
the organ which can bear a corresponding loss without detriment to
the organism as a whole."[A]
[Footnote A: Weismann, Essays, p. 88.]
Here again natural selection of individuals, not the diminished
supply of nutriment, has to determine which of many muscles shall be
poorly fed and which favored. But natural selection can favor
special organs only indirectly through the individuals which possess
such organs. Variation is fortuitous, and there is nothing, except
natural selection, to combine or direct them. And, I think, we have
already seen that any theory which neglects or excludes such
directing and combining agencies must be unsatisfactory and
inadequate. Weismann has promised us an explanation of correlation
of variation in accordance with his theory; and if such an
explanation can be made, it would remove one of the strongest
objections. But for the present the objection has very great weight.
Furthermore, as Osborne has insisted, linear variations, or
variations proceeding along certain single and well-marked lines,
would seem inexplicable by, if not fatal to, Weismann's theory. And
yet Osborne, Cope, and others have shown that the teeth of mammals
have developed steadily along well-marked lines. They have
apparently not resulted at all by selection from a host of
fortuitous variations.
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