-formula that for a time he regarded Natural Selection
as almost the sole factor in evolution, variations being pre-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 selection. I do not believe that the theory of evolution would
have made its way so easily and so quickly after Darwin took up the
cudgels in favour of it, if he had not been able to support it by a
principle which was capable of solving, in a simple manner, the greatest
riddle that living nature presents to us,--I mean the purposiveness
of every living form relative to the conditions of its life and its
marvellously exact adaptation to these.

Everyone knows that Darwin was not alone in discovering the principle
of selection, and that the same idea occurred simultaneously and
independently to Alfred Russel Wallace. At the memorable meeting of the
Linnean Society on 1st July, 1858, two papers were read (communicated by
Lyell and Hooker) both setting forth the same idea of selection. One
was written by Charles Darwi