or mechanistic terms. The most essential part of
this problem relates to the origin of organic adaptations, the
production of the fit. With Kant, Cuvier and Linnaeus believed this
problem scientifically insoluble. Lamarck attempted to find a solution
in his theory of the inheritance of the effects of use, disuse and
other "acquired characters"; but his theory was insecurely based and
also begged the question, since the power of adaptation through which
use, disuse and the like produce their effects is precisely that which
must be explained. Darwin believed he had found a partial solution in
his theory of natural selection, and he was hailed by Haeckel as the
biological Newton who had set at naught the _obiter dictum_ of Kant.
But Darwin himself did not consider natural selection as an adequate
explanation, since he called to its aid the subsidiary hypotheses of
sexual selection and the inheritance of acquired characters. If I
correctly judge, the first of these hypotheses must be considered as
of limited application if it is not seriously discredited, while the
second can at best receive the Scotch verdict, not proven. In any
case, natural selection must fight its own battles.

Latter day biologists have come to see clearly that the inadequacy of
natural selection lies in its failure to explain the origin of the
fit; and Darwin himself recognized clearly enough that it is not an
originative or creative principle. It is only a condition of survival,
and hence a condition of progress. But whether we conceive with Darwin
that selection has acted mainly upon slight individual variations, or
with DeVries that it has operated with larger and more stable
mutations, any adequate general theory of evolution must explain the
origin of the fit. Now, under the theory of natural selection, pure
and simple, adaptation or fitness has a merely casual or accidental
character. In itself the fit has no more significance than the unfit.
It is only one out of many possibilities of change, and evolution by
natural selection resolves itself into a series of lucky accidents.
For Agassiz or Cuvier the fit is that which was designed to fit. For
natural selection, pure and simple, the fit is that which happens to
fit. I, for one, am unable to find a logical flaw in this conception
of the fit; and perhaps we may be forced to accept it as sufficient.
But I believe that naturalists do not yet rest content with it. Darwin
himself was repeatedly brou