"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." The great point as to identity of species being proved, it would be certainly more simple, and more in unison with the economy of nature, to suppose that all were descended from one pair, than that numerous identical members of a common species were simultaneously created. On the other hand, a physiological difficulty occurs, in viewing a race as descended from a single pair, from the fact universally recognised in the later periods of history, viz. the degeneration, and, in the end, destruction or indefinite deterioration of both physical and mental faculties, by continual intermarriage. The houses of Braganza and Hapsburg are notorious instances of this; and, as far as we are aware, there are no counter instances. "Marry A gentler scion to the wildest stock, And make conceive a bark of baser kind By bud of nobler race; this is an art Which does mend nature, change it rather, but The art itself is nature." The matter is incapable of absolute proof--we mean inductive proof; for it is in this point that the work before us regards it. Any arguments, such as similarity of habits, of languages, of opinions, which may be used to deduce community of origin, would be equally explained by community of species; for, supposing that different individuals of the same species were simultaneously created, the same physical formation would necessarily engender similar habits, and the power of intermarriage would induce a similarity of language, long before any period to which our histories go back. Taking, then, as a fair assumption, that, if identical in species, mankind have a common origin, we get in the outset of the book the conclusion stated at the end, viz. that all human races are of one species and one family. The great body of the work is, therefore, only accessory and corroborative; and its value would consist not so much in proving the affirmative of the author's thesis, as in placing in a prominent point of view the principal facts known respecting the natural history of man.