BENTHAM TO NIETZSCHE Natural selection can easily be illustrated, and observed, in the case of characteristics within a single species Suppose that there is a population of moths, some happening to be dark and others happening to be pale, who live on birch trees and are preyed upon by birds While the trees retain their natural silver colour, the better-camouflaged pale moths will have a better chance of survival, and will therefore come to form the greater part of the population If, however, the trees become blackened with soot, the odds of survival will tilt in favour of the dark moths As they survive in more than average numbers, it will appear from the outside that the species is changing its colour, from being characteristically pale to being characteristically dark Darwin believed that over a long period of time natural selection could go further and create whole new species of plants and animals This would, indeed, be a process so slow as to be in the normal sense unobservable; but recent discoveries in geology made plausible the idea that the earth had existed for a sufficient length of time for species to come into and go out of existence in this manner Evolution could thus explain not only the likenesses and differences between existing species, but also the difference between the species now extant and defunct species from earlier ages that were being discovered in fossil form throughout the world Even the most complex organs and instincts, Darwin claimed, could be explained by the accumulation of innumerable slight variations, each good for the individual 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 any variation of 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 (OS 152) The case for Darwin’s theory was greatly strengthened after his death, first when the laws of population genetics established by Gregor Mendel became generally known, and then when the identification of DNA enabled molecular geneticists to elucidate the mechanisms of heredity The story of Darwinism belongs to the history of science, not the history of 27