Let us take a group of individuals more or less similar, but always capable of contracting fertile unions, and let us, with M. Chevreul, trace it in imagination to its origin. We shall see it divided into families, each of which will have risen either mediately or immediately from one pair of parents. We shall see that the number of these families decrease at each generation, and rising still higher we shall at length find the initial term of a single primitive pair.
Has this really been the case? Has each species indeed arisen from one single pair, or have several pairs, resembling each other perfectly both morphologically and physiologically, appeared simultaneously or successively? These are questions of fact which science neither can nor ought to approach, for neither experiment nor observation is able to furnish us with the smallest data requisite for the solution.
But what science may affirm is that from all appearances each species has had, as point of departure, a single primitive pair.
CHAPTER IX.
CROSSING BETWEEN HUMAN GROUPS.—UNITY OF THE HUMAN SPECIES.
I. We now know what are species and race; the phenomena exhibited by mongrels and hybrids furnish us with an experimental means of distinguishing them. We can, therefore, now reply to the question which has necessitated this discussion: Are there one or many human species? Are the human groups races or species?
Unless we pretend that man alone of all organised beings is free from the laws which, in every other case, govern and regulate the laws of reproduction, and consequently, unless we make him a solitary exception precisely in that order of facts which most closely unites all other beings, we shall be forced to admit that he also obeys the laws of crossing.
Thus, if the human groups represent a more or less considerable number of species, we ought to prove in the crossings of their species the existence of the characteristic phenomena of hybridism. If these groups are only races of a single species, we ought, in crossings between them, to meet with the phenomena exhibited by mongrels.
II. It is scarcely necessary to recall what nearly four centuries of experience and observation have taught us. It may be recapitulated in a very few words.
Since Columbus commenced the era of great geographical discoveries, the White, the highest division of mankind, has penetrated to almost every part of the globe. He has everywhere met human groups which differed considerably from himself in every kind of character; he has everywhere mixed with them, and mixed races have everywhere sprung up in his track.