refused to admit that there was any domain from which science could be
excluded as a trespasser; we have to take account of the development of
philosophical thought, and even of theological and religious movements; we
should also, if we are wise enough, consider social changes. In short, we
must abandon the idea that we can understand the history of any science as
such, without reference to contemporary evolution in other departments of
activity.

While there were many evolutionists before Darwin, few of them were expert
naturalists and few were known outside a small circle; what was of much
more importance was that the genetic view of nature was insinuating itself
in regard to other than biological orders of facts, here a little and there
a little, and that the scientific spirit had ripened since the days when
Cuvier laughed Lamarck out of court. How was it that Darwin succeeded
where others had failed? Because, in the first place, he had clear
visions--"pensees de la jeunesse, executees par l'age mur"--which a
University curriculum had not made impossible, which the "Beagle" voyage
made vivid, which an unrivalled British doggedness made real--visions of
the web of life, of the fountain of change within the organism, of the
struggle for existence and its winnowing, and of the spreading genealogical
tree. Because, in the second place, he put so much grit into the
verification of his visions, putting them to the proof in an argument which
is of its kind--direct demonstration being out of the question--quite
unequalled. Because, in the third place, he broke down the opposition
which the most scientific had felt to the seductive modal formula of
evolution by bringing forward a more plausible theory of the process than
had been previously suggested. Nor can one forget, since questions of this
magnitude are human and not merely academic, that he wrote so that all men
could understand.