39. The doctrine which proceeds from the idea of human beings of one individuality alone six thousand years old is not admissible in the present state of knowledge. The principal considerations which contradict it are drawn from physical and moral order.
From a physiological point of view, certain races present particular characteristics, which do not allow of a common origin being assigned to them. There are differences which are evidently not produced by climate variations, since white people who are born in a land of black people do not become black. The heat of the sun broils and burns the skin, but has never transformed a white man into a black man, flattened the nose, changed the form of the features of the face, or rendered the hair crimped and woolly, from that which was naturally long and silky. One knows today that the color of the black race is produced by a peculiar tissue under the skin, appertaining to the species.
It is necessary then to consider the Black, Mongolian, and Caucasian races as having each its own particular origin, and of having been born successively or simultaneously upon different parts of the globe; and their mingling has produced mixed secondary races. The physiological characters of primitive races are the evident indications that they are the result of special types. The same considerations apply then to man, as well as to animals, as to the plurality of origins (chap. X, from item 2 on).