Biology | Page 8

existing organism. Biological investigators have long since
ceased to regard the fact of organic evolution as open to serious
discussion. The transmutation of species is not an hypothesis or
assumption, it is a fact accurately observed in our laboratories; and the
theory of evolution is only questioned in the same very general way in
which all the great generalizations of science are held open to
modification as knowledge advances. But it is a very large question
what has caused and determined evolution. Here, too, the fundamental
problem is, how far the process may be mechanically explicable or
comprehensible, how far it is susceptible of formulation in

physico-chemical 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 brought to a standstill, not merely by

specific difficulties in the application of his theory, but also by a certain
instinctive or temperamental dissatisfaction with such a general
conclusion as the one I have indicated; and many able naturalists feel
the same difficulty to-day. Whether this be justified or not, it is
undoubtedly the fact that few working naturalists feel convinced that
the problem of organic evolution has been fully solved. One of the
questions with which research is seriously engaged is whether
variations or mutations are indeterminate, as Darwin on the whole
believed, or whether they may be in greater or less degree determinate,
proceeding along definite lines as if impelled by a vis a tergo. The
theory of "orthogenesis," proposed by Naegeli and Eimer, makes the
latter assumption; and it has found a considerable number of adherents
among recent biological investigators, including some of our own
colleagues, who have made important contributions to the investigation
of this fundamental question. It is too soon to venture a prediction as to
the ultimate result. That evolution has been orthogenetic in the case of
certain groups, seems to be well established, but many difficulties stand
in the way of its acceptance as a general principle of explanation. The
uncertainty that still hangs over this question and that of the heredity of
acquired characters bears witness to the unsettled state of opinion
regarding the whole problem, and to the inadequacy of the attempts
thus far made to find its consistent and adequate solution.
Here, too, accordingly, we find ourselves confronted with wide gaps in
our knowledge which open the way to vitalistic or transcendental
theories of development. I think we should resist the temptation