“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 degree,” he writes. But if we look at the whole tree of life, Darwin says, we can find innumerable gradations from extremely simple eyes consisting of hardly more than a nerveless cluster of pigment cells, which are rudimentary light sensors, to the marvels of the human eye, which are more impressive pieces of work than the human telescope.”