Unhappily, modern science has been able to provide no clue to the labyrinth of the various opinions. No likely hypothesis has succeeded in lightening this darkness, and in all probability the human races are as different from their common ancestor, if they have one, as they are from each other. I will therefore assume without discussion the principle of unity; and my only task, in the narrow and limited field to which I am confining myself, is to explain the actual deviation from the primitive type. The causes are very hard to disentangle. The theory of the unitarians attributes the deviation, as I have already said, to habits, climate, and locality. It is impossible to agree with this.[60] Changes have certainly been brought about in the constitution of races, since the dawn of history, by such external influences; but they do not seem to have been important enough to be able to explain fully the many vital divergences that exist. This will become clear in a moment. I will suppose that there are two tribes which still bear a resemblance to the primitive type, and happen to be living, the one in a mountainous country in the interior of a continent, the other on an island in the midst of the ocean. The atmosphere and the food conditions of each will be quite different. I will assume that the one has many ways of obtaining food, the other very few. Further, I will place the former in a cold climate, the second under a tropical sun. By this means the external contrast between them will be complete. The course of time will add its own weight to the action of the natural forces, and there is no doubt that the two groups will gradually accumulate some special characteristics which will distinguish them from each other. But even after many centuries no vital or organic change will have taken place in their constitution. This is proved by the fact that we find peoples of a very similar type, living on opposite sides of the world and under quite different conditions, of climate and everything else. Ethnologists are agreed on this point and some have even believed that the Hottentots are a Chinese colony—a hypothesis impossible on other grounds—on account of their likeness to the inhabitants of the Celestial Empire.[61] In the same way, some have seen a great resemblance between the portraits we have of the ancient Etruscans and the Araucans of South America. In features and general shape the Cherokees seem almost identical with many of the Italian peoples, such as the Calabrians. The usual type of face among the inhabitants of Auvergne, especially the women, is far less like the ordinary European’s than that of many Indian tribes of North America. Thus when we grant that nature can produce similar types in widely separated countries, under different conditions of life and climate, it becomes quite clear that the human races do not take their qualities from any of the external forces that are active at the present day.