“It seems to be the well-established result of enquiries into the various tribes of organized beings, that the perpetuation of hybrids, whether of plants or animals, so as to produce new and intermediate tribes, is impossible.
“Now, unless all these observations are erroneous, or capable of some explanation that has not yet been pointed out, they lead, with the strongest force of analogical reasoning, to the conclusion, that a number of different tribes, such as the various races of men, must either be incapable of intermixing their stock, and thus always fated to remain separate from each other; or, if the contrary should be the fact, that all the races to whom the remark applies, are proved by it to belong to the same species.
“I believe it may be asserted, without the least chance of contradiction, that mankind, of all races and varieties, are equally capable of propagating their offspring by intermarriages, and that such connexions are equally prolific, whether contracted between individuals of the same or of the most dissimilar varieties. If there is any difference, it is probably in favour of the latter.”
This conclusion is repeated a little further on.
“It appears to be unquestionable that intermediate races of men exist and are propagated, and that no impediment whatever exists to the perpetuation of mankind when the most dissimilar varieties are blended together. We hence derive a conclusive proof—unless there be, in the instance of human races, an exception to the universally prevalent law of organized nature—that all the tribes of men are of one family.
“Perhaps the solution of the problem which we have undertaken to discuss might be left on this issue, or considered as obtained by this argument. But further light may be thrown on the subject, by a careful analysis of the facts which can be collected relative to the nature and origination of varieties; and it may be satisfactory to my readers to survey this field of enquiry.”
Granting, then, the truth of the limitation of species to be established, and taking as the definition of species the power of continual propagation, we have it proved at the commencement of the work, that “all human races are of one species;” the only question which remains is, whether, admitting them to be of one species, the deduction that they have a common origin is necessary; or, if not necessary, whether it is proved in the course of the author’s work. It does not appear to us a necessary conclusion; for there appears no reason à priori why the Creator should not as well form separately an indefinite number of creatures of the same species as a single pair. This point is not adverted to in the work before us; and whenever identity of origin is assumed, it is upon the same grounds from which identity of species is deduced. In fact, they are generally coupled; thus, at page 487, we have the expression—
“If now it should appear, on enquiry, that one common mind, or psychical nature, belongs to the whole human family, a very strong argument would thence arise, on the ground of analogy, for their community of species and origin.”
And in the last page we have—
“We are entitled to draw confidently the conclusion, that all human races are of one species and one family.”