ently succeed. Now variations ascribed
mainly to use and disuse can be supposed capable of being accumulated,
for use and disuse are fairly constant for long periods among the
individuals of the same species, and often over large areas; moreover,
conditions of existence involving changes of habit, and thus of
organisation, come for the most part gradually; so that time is given
during which the organism can endeavour to adapt itself in the requisite
respects, instead of being shocked out of existence by too sudden change.
Variations, on the other hand, that are ascribed to mere chance cannot be
supposed as likely to be accumulated, for chance is notoriously
inconstant, and would not purvey the variations in sufficiently unbroken
succession, or in a sufficient number of individuals, modified similarly
in all the necessary correlations at the same time and place to admit of
their being accumulated. It is vital therefore to the theory of
evolution, as was early pointed out by the late Professor Fleeming Jenkin
and by Mr. Herbert Spencer, that variations should be supposed to have a
definite and persistent principle underlying them, which shall tend to
engender similar and simultaneous modification, however small, in the
vast majority of individuals composing any species. The existence of
such a principle and its permanence is the only thing that can be
supposed capable of acting as rudder and compass to the accumulation of
variations, and of making it hold steadily on one course for each
species, till eventually many havens, far remote from one another, are
safely reached.

It is obvious that the having fatally impaired the theory of his
predecessors could not warrant Mr. Darwin in claiming, as he most
fatuously did, the theory of evolution. That he is still generally
believed to have been the originator of this theory is due to the fact
that he claimed it, and that a powerful literary backing at once came
forward to support him. It seems at first sight improbable that those
who too zealously urged his claims were unaware that so much had been
written on the subject, but when we find even Mr. Wallace himself as
profoundly ignorant on this subject as he still either is, or affects to
be, there is no limit assignable to the ignorance or affected ignorance
of the kind of biologists who would write reviews in leading journals
thirty years ago. Mr. Wallace writes:--

"A few great naturalists, struck by the very slight di