The Origin of Species

Abstract

MR. MURPHY has mistaken my meaning, which I will try to make clear by an example. Suppose one brood of an ancient species of Gallinæ to have exhibited, as a sport, a partial infertility with the rest of the species, while the birds composing the brood remained abundantly fertile among themselves. Suppose the main body of that species to have become, by natural selection, our pheasants, while the isolated brood became the ancestors of our grouse. Suppose one brood of these grouse to have become partially infertile with the main body of grouse, and to have been the ancestors of our red grouse, while the main body of the grouse became, by natural selection, our black grouse. If, as I believe, variation does not produce or increase infertility, the black grouse will still be only partially infertile with the pheasant, and the red only partially infertile with the black grouse; but it seems probable, primâ facie, that the second spontaneous infertility would remove the red grouse further from the pheasant, so that thsse would be quite infertile. But this is merely argument from analogy; there is no evidence of the result of such superposed “sports,” and retrogression to greater fertility seems possible.