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