that Darwin's originality was greatest, for
he revealed to naturalists the many different forms--often very
subtle--which natural selection takes, and with the insight of a
disciplined scientific imagination he realised what a mighty engine of
progress it has been and is.

(IV) As an epoch-marking contribution, not only to AEtiology but to
Natural History in the widest sense, we rank the picture which Darwin
gave to the world of the web of life, that is to say, of the
inter-relations and linkages in Nature. For the Biology of the
individual--if that be not a contradiction in terms--no idea is more
fundamental than that of the correlation of organs, but Darwin's most
characteristic contribution was not less fundamental,--it was the idea
of the correlation of organisms. This, again, was not novel; we find
it in the works of naturalists like Christian Conrad Sprengel,
Gilbert White, and Alexander von Humboldt, but the realisation of its
full import was distinctly Darwinian.

_As Regards the General Idea of Organic Evolution_

While it is true, as Prof. H. F. Osborn puts it, that "'Before and
after Darwin' will always be the _ante et post urbem conditam_ of
biological history," it is also true that the general idea of organic
evolution is very ancient. In his admirable sketch _From the Greeks to
Darwin_,[1] Prof. Osborn has shown that several of the ancient
philosophers looked upon Nature as a gradual development and as still
in process of change. In the suggestions of Empedocles, to take the
best instance, there were "four sparks of truth,--first, that the
development of life was a gradual process; second, that plants were
evolved before animals; third, that imperfect forms were gradually
replaced (not succeeded) by perfect forms; fourth, that the natural
cause of the production of perfect forms was the extinction of the
imperfect."[2] But the fundamental idea of one stage giving origin to
another was absent. As the blue AEgean teemed with treasures of beauty
and threw many upon its shores, so did Nature produce like a fertile
artist what had to be rejected as well as what was able to survive,
but the idea of one species emerging out of another was not yet
conceived.

Aristotle's views of Nature[3] seem to have been more definitely
evolutionist than those of his predecessors, in this sense, at least,
that he recognised not only an ascending scale, but a genetic series
from polyp to man and an age-long movement towar