VI. The Meaning of Homology.
The similarities and homologies of structure existing between man and other animals, and between other animals and still others, are not accidental and causeless. They are not resemblances scattered arbitrarily among the multitudinous forms of life by the capricious levities of chance. That all animals commence existence as an egg and are all made up of cells composed of the same protoplasmic substance, and all inhale oxygen and exhale carbon dioxide, and are all seeking pleasure and seeking to avoid pain, are more than ordinary facts. They are filled with inferences. That vertebrate animals, differing in externals as widely as herring and Englishmen, are all built according to the same fundamental plan, with marrow-filled backbones and exactly two pairs of limbs branching in the same way, is an astonishing coincidence. That the wing of the bird, the foreleg of the dog, the flipper of the whale, and the fore-limb of the toad and crocodile, have essentially the same bones as the human arm has is a fact which may be without significance to blind men, but to no one else. The metamorphosis of the frog from a fish, of the insect from a worm, and of a poet from a senseless cell, are transformations simply marvellous in meaning. And it is not easy, since Darwin, to understand how such lessons could remain long unintelligible, even to stones and simpletons. Not many generations have passed, however, since these revelations, now so distinct and wonderful, fell on the listless minds of men as ineffectually as the glories of the flower fall on the sightless sockets of the blind.
It is hardly two generations since the highest intelligences on the earth conceived that not only the different varieties of men—the black, the white, and the orange—but all the orders and genera of the animal world, and not only animals, but plants, had all been somehow simultaneously and arbitrarily brought into existence in some indistinct antiquity, and that they had from the beginning all existed with practically the same features and in approximately the same conditions as those with which and in which they are found to-day. The universe was conceived to be a fixed and stupid something, born as we see it, incapable of growth, and indulging in nothing but repetitions. There were no necessary coherencies and consanguinities, no cosmical tendencies operating eternally and universally. All was whimsical and arbitrary. It was not known that anything had grown or evolved. All things were believed to have been given beginning and assigned to their respective places in the universe by a potential and all-clever creator. The serpent was limbless because it had officiously allowed Eve to include in her dietary that which had been expressly forbidden. The quadruped walked with its face towards the earth as a structural reminder of its subjection to the biped, who was supposed to be especially skilled in keeping his eyes rolled heavenward. The flowers flung out their colours, not for the benefit of the bugs and bees, and the stars paraded, not because they were moved to do so by their own eternal urgings, but because man had eyes capable of being affected by them. Man was an erect and featherless vertebrate because his hypothetical maker was erect and featherless. (I wonder whether, if a clam should conceive a creator, it would have the magnanimity to make him an insect or a vertebrate, or anything other than a great big clam.)