To his great task he brought a patience that is almost without parallel. One of his biographers, Grant Allen, tells us that: “His uncle and father-in-law, Josiah Wedgwood, suggested to him that the apparent sinking of stones on the surface might really be due to earthworm castings. So, as soon as he had some land of his own to experiment upon, he began in 1842, to spread broken chalk over a field at Down, in which, twenty-nine years later in 1871, a trench was dug to test the results. “What other naturalist,” asks Allen, ever waited so long and so patiently to discover the upshot of a single experiment? Is it wonderful that a man who worked like that should succeed, not by faith but by logical power, in removing mountains?” Darwin studied domestic animals. He observed how many, and how widely different, races there are of horses, dogs, swine, poultry in general and pigeons in particular. In each instance the many varieties are derived from an original common stock, as domestic fowls from the Indian jungle fowl, and pigeons from the old-world rock-dove. “Derived,” but how--by what process? In the case of domestic creatures this was not difficult to answer. It is accomplished by breeders “selecting” the individuals to be bred from. In the case of pigeons, which Darwin laid particular stress on the fancier seemed to be able to obtain almost any kind of a bird by selecting as parents those pigeons which had the desired characteristics developed to the most pronounced degree, and then again selecting in the same way from their progeny. In this way were produced birds so different from each other and their ancestors as the tumbler, the fantail, the pouter, and about a hundred and fifty other varieties. The same with horses. If the breeder desired draught horses, he selected for parents those animals with massive shoulders and sturdy limbs. When a racer wins a “classic” race, it is at once sent to the stud-farm. Although in the zenith of its powers it races no more; it is “selected” for another and more important role--the reproduction and, it is hoped, the accentuation of the characteristics which enabled it to outrun its competitors. All this impressed on Darwin’s mind the importance of the word “selection,” which appears in the title of his theory and the subtitle of his epoch-making book. Could it be possible that nature contained some principle or combination of principles, which performed among wild animals a part analogous to that of the breeder, among domestic animals? Darwin discovered that this is precisely what takes place. His famous theory may be formulated under the three following heads: (1) Heredity. (2) Variation. (3) The struggle for existence, with its resultant, survival of the fittest. Darwin requires very little of heredity, and what he does ask is beyond dispute. It is enough for his theory if like begets like and “figs do not grow on thistles.”