The comparability of the data of civilization and biology brought in its train, however, the natural corollary that the general course of their development was the same. Such an assumption fitted in admirably with the psychological presuppositions of Schurtz, and with the inferences he felt justified in drawing from the historical data. Neither Schurtz, nor, for that matter, any theoretician of his time, ever made any attempt to prove that the method of biological evolution was the same as that of the historical. It was commonly assumed to have been the same; but, quite apart from this acceptance of a fact that seemed to need no proof, the similarity in the evolution of biological and historical phenomena was by implication conditioned by his psychological assumptions. The number of norms are necessarily reduced to a minimum when inherent tendencies are acting on a “group mind,” for it would be tacitly admitting a large range for personal individuality, to assume the existence of many norms; but if there are only a few norms, or, as Schurtz concludes, one norm,—that of the age-group,—variations can only have arisen as differentiations of this norm, due to influences either from within or from without. We are consequently reduced to a condition exactly parallel to that which we find, according to the theory of evolution, in biology. Variations are the result of a differentiation of some unit. It is the object, in the classification of biological data, to demonstrate, by means of a series of ascending forms, the evolution of the most highly differentiated from the least differentiated. In thus arranging the data, it followed that the least-differentiated forms contained the simple general manifestations of life, and that at the same time the most highly-differentiated forms likewise contained all these simple general manifestations, although they were here, as a rule, so changed as to be entirely obscured, if not unrecognizable. In a manner almost exactly parallel to the above, Schurtz sought to classify the phenomena of social organization. The highest must contain within itself the simple and general phenomena of the lowest form. Having thus demonstrated to his satisfaction the existence and the necessity of an ordered sequence, he turned his attention to demonstrating that this sequence was psychologically as well as historically conditioned. His line of argument here can best be shown by analyzing the first few chapters of his book.