e 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 enthusiasm
a multitude of inimitable contrivances in nature, this same reason tells
us, though we may easily er