We must say another word about Isidore Geoffroy Saint-Hilaire’s opinion on the important question of cross-breeding in mankind. After having reproached Cuvier, and with reason, with having often, in the interest of particular views, admitted, as regards mankind, a flagrant contravention of the biological laws which his genius proclaimed for other animals, Isidore Geoffroy seems to us to have, in his turn, fallen into a contradiction of the same kind. He especially calls _hybrids_ the crosses which occur from the cross of two different species, and he remarks, besides, that hybrids have generally tolerably decided characteristics, which are partly those of the father and partly those of the mother; so that the offspring, he adds, can resemble one more than the other, but not _exclusively_ either of them: the cross is always to be found in it. On the contrary, it is not _always_ so with the cross between two varieties of the same species; the produce has often the characteristics of both its parents, but very frequently, also, it resembles one of them exclusively. For these beings who are the offspring of two varieties of the same species, and _who very frequently reproduce entire the type of one of their parents_ to the exclusion of the other, Isidore Geoffroy reserved the name of _homoïdes_. Well, we ask him this,--in taking, as an example, the offspring of a union between a white and a black, shall we find in it the characteristics of a homoïd cross? Will it never resemble exclusively one of the two founders? Are not the characteristics of the Mulatto perfectly represented, perfectly defined, and always medium? Are not exceptions, if any can be quoted, of extreme rarity?[251] In the name of this consistency, ought not Isidore Geoffroy to have seen in a Mulatto something besides a homoïd mongrel, and to doubt even more that the different races of mankind constituted only varieties of the same species? However, let us examine into hybridity so far as it may serve to produce new, or modify existing races, as Blumenbach and Flourens have admitted.[252] Let us only remark that these two authors, like most monogenists, in placing hybridity, as the modifying cause, in the same rank as climate or medium, commit a great error. Hybridity, even in giving it the creative power which some have desired, goes entirely into the second rank, for it supposes a pre-existing plurality. It can only act, in the end, by weakening differences, by creating a middle term to two extremes. It cannot of itself produce variety of origin, it is the consequence of it, and we shall see that the part it takes on this matter is extremely restricted.