structure of another. But natural selection can and does often produce
structures for the direct injury of other species, as we see in the
fang of the adder, and in the ovipositor of the ichneumon, by which its
eggs are deposited
in the living bodies of other insects. If it could be proved that any
part of the structure of any one species had been formed for the
exclusive good of another species, it would annihilate my theory, for
such could not have been produced through natural selection. Although
many statements may be found in works on natural history to this
effect, I cannot find even one which seems to me of any weight. It is
admitted that the rattlesnake has a poison-fang for its own defence and
for the destruction of its prey; but some authors suppose that at the
same time this snake is furnished with a rattle for its own injury,
namely, to warn its prey to escape. I would almost as soon believe that
the cat curls the end of its tail when preparing to spring, in order to
warn the doomed mouse. But I have not space here to enter on this and
other such cases.
Natural selection will never produce in a being anything injurious to
itself, for natural selection acts solely by and for the good of each.
No organ will be formed, as Paley has remarked, for the purpose of
causing pain or for doing an injury to its possessor. If a fair balance
be struck between the good and evil caused by each part, each will be
found on the whole advantageous. After the lapse of time, under
changing conditions of life, if any part comes to be injurious, it will
be modified; or if it be not so, the being will become extinct, as
myriads have become extinct.
Natural selection tends only to make each organic being as perfect as,
or slightly more perfect than, the other inhabitants of the same
country with which it has to struggle for existence. And we see that
this is the degree of perfection attained under nature. The endemic
productions of New Zealand, for instance, are perfect one compared with
another; but they are now rapidly yielding before the advancing legions
of plants
and animals introduced from Europe. Natural selection will not produce
absolute perfection, nor do we always meet, as far as we can judge,
with this high standard under nature. The correction for the aberration
of light is said, on high authority, not to be perfect even in that
most perfect organ, the eye. If our reason leads us to admire with
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