To suppose that the eye, with all its inimitable contrivances for
adjusting the focus to different distances, for admitting different
amounts of light, and for the correction of spherical and chromatic
aberration, could have been formed by natural selection, seems, I
freely confess, absurd in the highest possible degree. Yet reason
tells me, that if numerous gradations from a perfect and complex eye
to one very imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye does vary ever
so slightly, and the variations be inherited, which is certainly the
case; and if variation or modification in the organ be ever useful to
an animal under changing conditions of life, then the difficulty of
believing that a perfect and complex eye could be formed by natural
selection, though insuperable by our imagination, can hardly be
considered real.
