IO 6
The displacement of one species by another may be
due to a struggle between the two ; but it may also arise
from an independent effort of the two species to adapt
themselves to new conditions in which one species fails
and another succeeds ; or again, it may arise from the fact
that one species is already fitted for new conditions and
another species is not. The first of these phenomena may
be described literally as a struggle between two conflicting
species. In the other instances the two species struggle
with the difficulties of their new conditions without refer
ence to one another, and only in a metaphorical sense can
be said to struggle with each other.
We have now to consider how far these facts may be
regarded as affording a proof of the transmutation of
species by means of Natural Selection.
In the first place it should be observed that the displace
ment of one species by another does not necessarily imply
that the victorious species is in any way more fit to live,
or more adapted to its external conditions than the other.
It simply shows that one species has the power to exter
minate the other. Mr. Wallace contends that “the dis
placement of one species by another can be illustrated by
innumerable cases, and that they all go to establish the
fact that forms less fitted to survive succumb in their com
petition with forms better fitted.” Now, if this means that
the one has some advantage over the other, the assertion
simply declares what is the most obvious of facts ; but if it
means that the surviving species is in any other way more
fitted to live, more adapted to external conditions, this is
to assert what in very many cases is not true. There is no
reason for supposing that the black rat is any less fit to
live, any less adapted to the conditions by which it is
surrounded, than the brown rat. For in their native
country the two varieties live together; in some countries