In order properly to estimate the sociological significance of DeVries’ theory it will be necessary to go back more than a century, and observe the sociological import of the leading biological ideas of that period. And here let us remark, that nobody knows better than we do the danger of transplanting, without criticism, biological theories into the field of sociology. Nevertheless, our opponents have never lost an opportunity to twist and distort science, if perchance by any possibility it could be made to contradict anything that had so much as the semblance of Socialism. We, however, have always insisted on the weakness of reasoning by mere analogy and have kept to those general laws which have been worked out separately in sociology. The principle now about to be applied belongs to this latter class. It is the most luminous principle ever employed in the interpretation of the phenomena of society. This principle is that the intellectual life of a people is determined by its mode of wealth production and the social classes arising therefrom. Jean Lamarck, the first great modern apostle of evolution, died in poverty because he advocated a theory that appeared to contradict the interests of the ruling class of his time. He had against him all that survived of feudal interests, which was intensely theological, and although his theory really favored the bourgeoisie, that class was not yet aware of it. Cuvier was the lion of that day, for he managed the remarkable feat of adapting science to the ideas, not only of the increasing bourgeoisie, but also of the diminishing feudal power. He pleased the feudal regime, such of it as remained, by denying evolution, and endorsing its theology. This made his theories welcome also among those shrewd early capitalists, as the English, who realized more quickly than their fellows, that religious belief might constitute as great a prop for one ruling class at it had already been for another. But in his capacity of scientific reflection of the class interest of his masters, Cuvier’s masterpiece was his “cataclysmic theory.” According to this theory, organisms were not the result of evolution, but they were now just as when they issued from the hands of the Creator. The difference between existing forms, and those creatures whose story is preserved in the rocks, was explained by a series of cataclysms or catastrophes by which, at certain widely separated periods, all living forms were destroyed, and a completely new stock was created to take their places.