558 THE AMERICAN JOURNAL OF SOCIOLOGY
tains and the forests. Thus in every province of Constantine and upon every path from the Atlas to Algeria, and from the Ural Mountains to Morocco, are found a crowd of blonds whose presence dates back four or five thousand years and who are primarily Germanic.
However, while climate in a certain measure determines the zones of habitation of the varieties of human species, it does not, in the matter of extension of the species, constitute an impass- able barrier. On the contrary, this barrier is crossed, thanks to the human variations through adaptation and acclimatization. The truth is between the old theories of Herodotus, Hippocrates, Bodin, Goguet, Montesquieu, and of almost all writers of the eighteenth century, and the equally absolute and false negation of its effect upon populations. A reaction has set in against the first conception a vigorous reaction expressed by Darwin in the following passage from a letter to A. R. Wallace: "I am com- pletely in accord with you upon the subject of the limited effects of climatic conditions which are mentioned ad nauseam in all books."
The influence of climates varies according to the different civilizations. The frontiers which climates tend to set up give way before the advances of civilization, and the superior adapta- tions which civilization gives rise to and renders realizable. In this connection, the picture presented to us of the situation of the several regions where the great ancient and modern civiliza- tions have developed, is suggestive and decisive.
We now see from the facts that the present distribution of the human species has been naturally brought about through the general laws of variability, selection, spontaneous as well as sys- tematic, adaptation, and heredity. What we commonly call acclimatization in reality comprehends all of the factors of adaptation. It comprehends notably the alimentary environ- ment, either natural or rational or scientific.
Upon the whole, the varieties of the human species in con- nection with the climatic and other zones, and with the natural frontier, far from being obstacles to its unity, are the means conformable to all of the ordinary processes by which nature is
