m 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.

Says Osborne in his "Cartwright Lectures"[A]: "It is evident that
use and disuse characterize all the centres of evolution; that
changes of structure are slowly following on changes of function or
habit. In eight independent regions of evolution in the human body
there are upward of twenty developing organs, upward of thirty
degenerating organs." Now this parallelism, through a long series of
generations, between the evolution of organs, their advance or
degeneration, and the use or disuse of these same organs, that is,
of the habits of the individual, is certainly of great significance.
It must have an explanation; and the most natural one would seem to
be the transmission of the effects of use and disuse.

[Footnote A: American Naturalist, vols. xxv. and xxvi.]

On the whole Osborne's verdict would seem just: The Neo-Lamarckian
theory fails to explain heredity, Weismann's theory does not explain
evolution. But, if the effects of use and disuse are transmitted,
correlation of variation is to be expected. Muscle, nerve, and
ganglion all vary in correlation because they are all used together
and in like degree. Evolution and degeneration of muscles in hand
and foot go on side by side, because