I established first that the life or death of societies was the result of internal causes. I have said what these causes are, and described their essential nature, in order that they may be more easily recognized. I have shown that they are generally referred to a wrong source; and in looking for some sign that could always distinguish them, and indicate their presence, I found it in the capacity to create a civilization. As it seemed impossible to discover a clear conception of this term, it was necessary to define it, as I have done. My next step must be to study the natural and unvarying phenomenon which I have identified as the latent cause of the life and death of societies. This, as I have said, consists in the relative worth of the different races. Logic requires me to make clear at once what I understand by the word _race_. This will be the subject of the following chapter. CHAPTER X SOME ANTHROPOLOGISTS REGARD MAN AS HAVING A MULTIPLE ORIGIN[47] We must first discuss the word _race_ in its physiological sense. A good many observers, who judge by first impressions and so take extreme views, assert that there are such radical and essential differences between human families that one must refuse them any identity of origin.[48] The writers who adhere to such a notion assume many other genealogies by the side of that from Adam. To them there is no original unity in the species, or rather there is no single species; there are three or four, or even more, which produce perfectly distinct types, and these again have united to form hybrids. The supporters of this theory easily win belief by citing the clear and striking differences between certain human groups. When we see before us a man with a yellowish skin, scanty hair and beard, a large face, a pyramidal skull, small stature, thick-set limbs, and slanting eyes with the skin of the eyelids turned so much outwards that the eye will hardly open[49]—we recognize a very well-marked type, the main features of which it is easy to bear in mind. From him we turn to another—a negro from the West Coast of Africa, tall, strong-looking, with thick-set limbs and a tendency to fat. His colour is no longer yellowish, but entirely black; his hair no longer thin and wiry, but thick, coarse, woolly, and luxuriant; his lower jaw juts out, the shape of the skull is what is known as _prognathous_. “The long bones stand out, the front of the tibia and the fibula are more convex than in a European, the calves are very high and reach above the knee; the feet are quite flat, and the heel-bone, instead of being arched, is almost in a straight line with the other bones of the foot, which is very large. The hand is similarly formed.”