ed them before you
obviously directly contradict any form of the hypothesis of evolution
which stands in need of these two postulates.

But, one great service that has been rendered by Mr. Darwin to the
doctrine of evolution in general is this: he has shown that there are
two chief factors in the process of evolution: one of them is the
tendency to vary, the existence of which in all living forms may be
proved by observation; the other is the influence of surrounding
conditions upon what I may call the parent form and the variations which
are thus evolved from it. The cause of the production of variations is a
matter not at all properly understood at present. Whether variation
depends upon some intricate machinery--if I may use the phrase--of the
living organism itself, or whether it arises through the influence of
conditions upon that form, is not certain, and the question may, for the
present, be left open. But the important point is that granting the
existence of the tendency to the production of variations; then, whether
the variations which are produced shall survive and supplant the parent,
or whether the parent form shall survive and supplant the variations, is
a matter which depends entirely on those conditions which give rise to
the struggle for existence. If the surrounding conditions are such that
the parent form is more competent to deal with them, and flourish in
them than the derived forms, then, in the struggle for existence, the
parent form will maintain itself and the derived forms will be
exterminated. But if, on the contrary, the conditions are such as to be
more favourable to a derived than to the parent form, the parent form
will be extirpated and the derived form will take its place. In the
first case, there will be no progression, no change of structure,
through any imaginable series of ages; in the second place there will be
modification of change and form.

Thus the existence of these persistent types, as I have termed them, is
no real obstacle in the way of the theory of evolution. Take the case of
the scorpions to which I have just referred. No doubt, since the
Carboniferous epoch, conditions have always obtained, such as existed
when the scorpions of that epoch flourished; conditions in which
scorpions find themselves better off, more competent to deal with the
difficulties in their way, than any variation from the scorpion type
which they may have produced; and, for that reason, the scorpio