For in the first explanation, one species drives out the
other, and neither is modified. In the second explanation,
the withdrawal of the protection and stimulus of culture
does not lead to reversion to a wild ancestral form, but
to extinction.
No evidence is given, in connection with the struggle of
one species with another, of any modification of the
triumphant species. If there were such evidence, it is
astonishing that it is not adduced in this connection.
But one case is cited by Mr. Wallace, in which a distinct
attempt is made by one of the combatants to adapt itself
so as to be able to co-exist with its opponent. In the
forests of Denmark, wherever the soil is suitable for the
beech, it drives out the birch.
“ The latter loses its branches at the touch of the beech, and
devotes all its strength to the upper part, where it towers above the
beech. It may live long in this way, but it succumbs ultimately in
the fight—of old age if of nothing else, for the life of the birch in
Denmark is shorter than that of the beech. . . . The tufted,
bushy top of the beech preserves a deep shade at its base. Hardly
any young plants can grow under the beech except its own shoots ;
and while the beech can flourish under the shade of the birch, which
allows the rays of the sun to pass to the soil below, the latter dies
immediately under the beech. The birch is only saved from total
extinction by the fact that it can grow where the beech cannot;
forests of birch are only found now in sterile sandy tracks.”—
(Wallace. Darwinism, p. 21.)
Here we have no case of a transmutation of species by
adaptation to new and unfavourable conditions such as
Natural Selection ought to achieve for the birch, if it were
the powerful agent which the theory presupposes. But
the attempt is made. The birch loses its branches at the
touch of the beech and devotes all its strength to the
upper part, where it towers above the beech. But the
attempt, in spite of all its efforts, fails. Even if the
attempt had succeeded, the transmutation would not have
