But in all probability most of us are more conversant with the ways of the domesticated cat than with those of the golden eagle. The cat produces its first litter of three or four before it is a year old. Its kitten-producing life lasts, say, for eight years, and it may, on a low estimate, be supposed to produce a litter of four kittens once in each year. In all a cat will have, on a fair estimate, thirty-two kittens, and may be a great-great-great-great-great-great-grandmother in her lifetime, yet we do not observe in town or village such an alarming increase in the cats from year to year. Their number is pretty stationary, kept so by the enormous destruction of their progeny. The enormous capacity for reproduction of a race of animals, where for a time their surroundings are favourable, will be appreciated by the lowland farmers whose fields were laid waste a few years ago by armies of short-tailed field-mice, whose natural enemies, the hawks, the cats, and the weasels, had been extensively shot or trapped.
The struggle to survive among the savage tribes of man must be excessive. Whole races come and go, and their survivors again fall victims to privations, disease, or natural enemies, before the white man with his better brain and capacity for adaptation.
The third idea in the law of natural selection--namely, that inborn variations are transmitted--is also a fact that is universally admitted not only among biologists at the present day, but by those who trust only to their everyday experience. “The child has its father’s temper,” or “its mother’s eyes,” are expressions heard in every nursery, while the innumerable cases of the transmission of inborn drooping eyelids and supernumerary fingers and toes show the same thing in a more striking manner.
The law of selection is therefore no mere unproved fancy, it is a statement of fact, and of one which is so obviously true that it is now almost universally admitted, not only among specialists, but by most intelligent and educated persons. It was understood, and its significance partly appreciated by Malthus, and I find that even he acknowledges a prior claim of Franklin’s.[2] Romanes[3] tells us that the idea occurred in 1813 to Dr. Wells, and in 1831 to Mr. Patrick Matthew, and the wonder is that other thinkers have passed unnoticed such an obvious phenomenon.