supposed; gradually, however, he came to recognise that there was some
validity in the factors which had been emphasized by Lamarck and by Buffon,
and in his well-known summing up in the sixth edition of the "Origin" he
says of the transformation of species: "This has been effected chiefly
through the natural selection of numerous successive, slight, favourable
variations; aided in an important manner by the inherited effects of the
use and disuse of parts; and in an unimportant manner, that is, in relation
to adaptive structures, whether past or present, by the direct action of
external conditions, and by variations which seem to us in our ignorance to
arise spontaneously."

To sum up: the idea of organic evolution, older than Aristotle, slowly
developed from the stage of suggestion to the stage of verification, and
the first convincing verification was Darwin's; from being an a priori
anticipation it has become an interpretation of nature, and Darwin is still
the chief interpreter; from being a modal interpretation it has advanced to
the rank of a causal theory, the most convincing part of which men will
never cease to call Darwinism.


III. THE SELECTION THEORY

By August Weismann.
Professor of Zoology in the University of Freiburg (Baden).

I. THE IDEA OF SELECTION.

Many and diverse were the discoveries made by Charles Darwin in the course
of a long and strenuous life, but none of them has had so far-reaching an
influence on the science and thought of his time as the theory of