What I have just said of the turkey might also be said of the rabbit. The wild rabbit lives all around us—in our downs, in our woods—and he does not resemble, or resembles but little, our domestic rabbit. These, you know, are both great and small, with short hair, and with silky hair; that they are black and white, yellow and gray, spotted and of uniform color. In a word, this species comprehends a great number of different races, all constituting one and the same species with the wild stock which still lives around us.
From these facts, that could be multiplied, we have to draw an important consequence, to which I call your attention:
A pair of rabbits, left in a plain where they would encounter no enemies, in a few years would fill it with their descendants, and, in a little while, all France would be easily peopled. We have just seen that a single stalk of coffee gave birth to all the coffee trees now found in America.
The wild turkeys and their domestic offspring, the wild rabbits and their captive descendants, may then be considered by the naturalist as equally arising from a primitive pair.
Gentlemen, this is the stamp of a species. Whenever you see a greater or less number of individuals, or groups of animals, or vegetables, if, for one reason or another, you can look upon them as descendants of a single primitive pair, you may say you have before you a species; if from group to group there are differences, you say these are the races of that species.
Observe carefully, gentlemen, that, in thus expressing myself, I have not stated for certain the existence of this primitive pair of the stock of rabbits or of the stock of turkeys. I affirm no such thing, because neither experiment nor observation—the two guides we should always follow in science—can aid us on this point. I only say to you, every thing is as if they had been derived from a single pair.
You see, after all, the question of species and of race is not very difficult to comprehend, nor even very difficult to settle when we know the wild type, when we have the historic data which enable us to connect with this type the more or less different groups which domestication has detached. But when we do not know the wild type, when the historic data are lost, the question, on the contrary, becomes extremely difficult at the first step, because differences that we encounter from individual to individual, and, above all, from group to group, might be considered as specific differences.
Happily, Physiology comes now to our relief. We encounter here one of those great and beautiful general laws upon which the established order depends, and which we admire more the more we study. This is the law of cross breeding—a law which governs animals as well as vegetables, and is, of course, applicable to man himself.
You know what is meant by the word crossing. We mean by it all marriage occurring between animals that belong either to two
