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 some are used and some are
disused. Centres of use and disuse must be centres of evolution.
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