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.

At the basis of all social organizations lie two elementary forces,—the “instinct for association” and the “sexual instinct.” The sexual instinct is primary, because it is obviously an essential condition of life. The instinct for association is secondary in so far as its expression in outward form is concerned. It is as old as the sexual instinct; but, since at the initial stage of human development the sexual instinct is so strong a force, the instinct of association had no observable influence on the actions of men.

The forms of social organization which the sexual instinct conditions are those based upon certain kinds of blood relationship. These forms are primary. To establish the priority of the forms thus imposed by blood relationship, we have but to remember that, as the relationship of individuals to one another preceded everything else, so the social forms based upon blood relationship must have preceded all other social forms. We are therefore to regard as the earliest stage of social organization that of groups bound together by blood relationship. But what has been the force differentiating these groups? Obviously not the same sexual instinct that has caused the formation of these primary groups. To explain the factors that have caused this differentiation we must call to our aid two phenomena,—first, that of sexual solidarity; and, secondly, that of the instinct for association.

Sexual solidarity has its roots in the nature of man and woman, and is possessed by them in equal intensity. The instinct for association is, however, a specifically masculine trait. It is found among women only in a minimal degree. An important corollary follows from this fact: If women societies are found anywhere, they are to be considered merely as imitations of men’s societies. If women are found as members in a society, this is to be regarded as secondary and purely adventitious. These, and some more specific points to be enumerated later, must be borne in mind continually, as Schurtz makes a far-reaching use of them.

The instinct for association, he goes on to say, expresses itself, however, between those of like interests; that is, between those who would most likely be of the same age. It is not likely, for instance, to occur between married and unmarried men. We have here two apparently organically determined classes. In the earliest stages of social development, however, when the norms of social expression conditioned by the sexual instinct were still of paramount importance, insistence was most naturally placed upon the most important stage of man’s physiological development,—the age of puberty. The strong line of demarcation between the period preceding and following sexual maturity was so ever-present a fact to the mind of primitive man, that it found expression in the multitude of initiatory rites. In these initiatory rites we have another of the specific “symptoms” with which we shall have to deal afterward.

When the instinct for association developed more strongly, the differences due to age, plus the physiological factor, conditioned the natural formation of two classes,—one of men before puberty, and one of men after puberty. This natural twofold division was also strengthened by another factor; for until the age of puberty, boys were under the influence of women, and were therefore to be reckoned as one with them.

The three groups—men before puberty, unmarried men after puberty, and married men—are thus built upon the basis of age distinction and common interest. They are the norms of primitive social organization, and, as we have seen, their origin is due to inherited instincts. By implication Schurtz has here also assumed the existence of a definite sequence; for the division into pre- and post-puberty groups is a consequence of the sexual instinct, and is therefore primary. Differentiation into the groups of married and unmarried men thereupon followed; but the initiation, which is synchronous with the age of sexual maturity, has introduced another factor, that of promiscuous sexual intercourse; and the regulation that this has demanded is found outwardly expressed in the “men’s house.” The common interests that drew men together into groups have thus far been those conditioned largely by age. In the development of society, however, interests became more and more diversified, and resulted, first, in the disappearance of the age factor as the essential element for associations, and, secondly, in the necessity for more closely organized units with specific characteristics. To obtain this close organization, one of the essential elements was secrecy, and thus developed out of the “men’s house” those innumerable clubs and secret societies which we find so common to-day.

In such manner we have constructed an ascending evolutionary series. It must not be forgotten that in such a series the highest stage is but a differentiated lower stage. It must likewise be remembered that there is a tendency for intermediate stages to leave vestigial remains wherever they developed into higher stages. We may consequently expect to find traces of “age groups” and “men’s houses” all over the world. In addition, we must remember that a number of “symptoms”—such as “the exclusion of women” from a society, the presence of “an initiation,” of “degrees,” and of “secrecy”—have always been associated with certain stages of growth. They may serve us for criteria of this growth and of the stages thereof, and they constitute proofs of historical identity. They will often appear unassociated with the definite stage assigned to them; but that is immaterial, for their almost universal presence is a sufficient guaranty of their significance. It is not necessary to inquire into their individual significance among definite societies, because a negative answer would prove nothing, as differences from the general scheme outlined can be interpreted most easily in terms of some functional change.