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logic of which was irresistible, assuming the premises to
be true. It left untouched some of the greatest difficulties
associated with Organic Evolution—the origin of life, the
laws of variation, the mysteries of reproduction. It ex
plained all by assuming that the variations necessarily
associated with reproduction were the source of heritable
variations—that selection in nature acted in the same
fashion, for the most part, as selection in art; and that
similar results might be looked for—nay, still greater,
inasmuch as the works of nature are greater than the
works of man.
The third reason for the success of this theory lies in the
fact that it was promulgated by men who were not mere
theorists, but careful observers of the actual world of
nature. But experience warns us that scientific observers
of the calibre of Darwin and of Wallace, who have done
good work as careful observers of nature, have sometimes
promulgated scientific theories which have not been
sustained.
Another reason is found in the elasticity of the terms
employed and the indefiniteness of the definitions which
are often given. It prevailed moreover because the effect
of its promulgation was to depreciate the influence of other
factors of Organic Evolution. But I venture to go a step
further back, and to say that the theory of Natural
Selection has prevailed because scant justice has been
done to the arguments for Organic Evolution, which were
used before the date of the publication of The Origin of
Species.
It is candidly admitted by believers in Natural Selec
tion that, if it should be proved that Natural Selection
was not after all a law of nature, it would not affect the
arguments for Organic Evolution ; it would only imply
that some factors, other than Natural Selection, had