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 comes into competition.

And we see that this is the standard 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 by Muller not to be perfect even in that most perfect organ, the human eye.