To sum up our knowledge of the ethnological past of man:  so far as the light is bright, it shows him substantially as he is now; and, when it grows dim, it permits us to see no sign that he was other than he is now.

It is a general belief that men of different stocks differ as much physiologically as they do morphologically; but it is very hard to prove, in any particular case, how much of a supposed national characteristic is due to inherent physiological peculiarities, and how much to the influence of circumstances.  There is much evidence to show, however, that some stocks enjoy a partial or complete immunity from diseases which destroy, or decimate, others.  Thus there seems good ground for the belief that Negroes are remarkably exempt from yellow fever; and that, among Europeans, the melanochrous people are less obnoxious to its ravages than the xanthochrous.  But many writers, not content with physiological differences of this kind, undertake to prove the existence of others of far greater moment; and, indeed, to show that certain stocks of mankind exhibit, more or less distinctly, the physiological characters of true species.  Unions between these stocks, and still more between the half-breeds arising from their mixture, are affirmed to be either infertile, or less fertile than those which take place between males and females of either stock under the same circumstances.  Some go so far as to assert that no mixed breeds of mankind can maintain themselves without the assistance of one or other of the parent stocks, and that, consequently, they must inevitably be obliterated in the long run.

Here, again, it is exceedingly difficult to obtain trustworthy evidence, and to free the effects of the pure physiological experiment from adventitious influences.  The only trial which, by a strange chance, was kept clear of all such influences—­the only instance in which two distinct stocks of mankind were crossed, and their progeny intermarried without any admixture from without—­is the famous case of the Pitcairn Islanders, who were the progeny of Bligh’s English sailors by Tahitian women.  The results of this experiment, as everybody knows, are dead against those who maintain the doctrine of human hybridity, seeing that the Pitcairn Islanders, even though they necessarily contracted consanguineous marriages, throve and multiplied exceedingly.

But those who are disposed to believe in this doctrine should study the evidence brought forward in its support by M. Broca, its latest and ablest advocate, and compare this evidence with that which the botanists, as represented by a Gaertner, or by a Darwin, think it indispensable to obtain before they will admit the infertility of crosses between two allied kinds of plants.  They will then, I think, be satisfied that the doctrine in question rests upon a very unsafe foundation; that the facts adduced in its support are capable of many other interpretations; and, indeed, that from the very nature of the case, demonstrative evidence one way or the other is almost unattainable. A priori, I should be disposed to expect a certain amount of infertility between some of the extreme modifications of mankind; and still more between the offsprings of their intermixture. A posteriori, I cannot discover any satisfactory proof that such infertility exists.