58i
Whatever force there may be in this argument, it is
scarcely consistent with the principles laid down by Mr.
Spencer; for, if we assume that the race is so adapted
to external conditions that further change is not required
with reference to them, it does not follow that the struggle
with enemies will naturally afford a special opportunity
for the action of Natural Selection. For Mr. Spencer lays
down two different definitions of the survival of the fittest,
according to one of which a species survives by virtue
of its enormous fertility. Now we have already pointed
out that a great output of life is a necessary condition of
the action of Natural Selection, and that if a great output
of life is sufficient to secure the survival of a species
without any modification, then one of the conditions
necessary for the action of Natural Selection prevents it
from coming on the scene. But let us, for the sake of
argument, assume that a great output of life may act in
two ways,—either by leading up to Natural Selection or
by dispensing with its action. In which case is the output
of life most likely to act to the exclusion of Natural
Selection ? A great output of life, accompanied with a
corresponding output of “ fortuitous ” variations, would
affect nothing in adapting a species to a new locality
apart from Natural Selection. But a great output of life
would preserve the species from extinction through the
attack of enemies. Where there is a fixed balance be
tween species living in the same locality, there is a
correlation between the output of life and the destruc
tion to which a species is liable.
Nor is it true to say that a great output of life will lead
to the transmutation of species by Natural Selection in
consequence of the competition between individuals of
the same species, for the normal population of a district
is correlated to the number of enemies ; while an excep-