This aspect of the problem, which has been neglected or put on one side by the followers of McLennan, was not so treated by McLennan himself. As we should expect from the general character of his work, McLennan clearly recognised that the classificatory system must have been determined by social conditions, and he tried to show how it might have arisen as the result of the change from the Nair to the Tibetan form of polyandry.[3] He even went so far as to formulate varieties of this process by means of which there might have been produced the chief varieties of the classificatory system, the existence of which had been demonstrated by Morgan. It is quite clear that McLennan had no doubts about the necessity of tracing back the social institution of the classificatory system of relationship to social causes, a necessity which has been ignored or even explicitly denied by those who have followed him in rejecting the views of Morgan. It is one of the many unfortunate consequences of McLennan’s belief in the importance of polyandry in the history of human society that it has helped to prevent his followers from seeing the social importance of the classificatory system. They have failed to see that the classificatory system may be the result neither of promiscuity nor of polyandry, and yet have been determined, both in its general character and in its details, by forms of social organisation. [3] _Op. cit._, p. 373. Since the time of Morgan and McLennan few have attempted to deal with the question in any comprehensive manner. The problem has inevitably been involved in the controversy which has raged between the advocates of the original promiscuity or the primitive monogamy of mankind, but most of the former have been ready to accept Morgan’s views blindly, while the latter have been content to try to explain away the importance of conclusions derived from the classificatory system without attempting any real study of the evidence. On the side of Morgan there has been one exception in the person of Professor J. Kohler,[4] who has recognised the lines on which the problem must be studied, while on the other side there has been, so far as I am aware, only one writer who has recognised that the evidence from the nature of the classificatory system of relationship cannot be ignored or belittled, but must be faced and some explanation alternative to that of Morgan provided. [4] _Zur Urgeschichte der Ehe_, Stuttgart, 1897 (reprinted from _Zeitsch. f. vergleich. Rechtswiss._, 1897, xii., 187).