Morgan was undoubtedly the greatest sociologist of the past century, and in his monumental work (1871) laid a solid foundation for the study of the family and kinship systems; he formulated a scheme of the evolution of the family based on a study of the classificatory system of relationships,[105] of which he was the discoverer. According to this scheme, human society has advanced, through gradual evolution, from a state of complete promiscuity to one characterised by monogamy. Dr. Rivers[106] points out that “In recent years the scheme has encountered much opposition.... The opponents of Morgan have made no attempt to distinguish between different parts of his scheme, but, having shown that certain of its features are unsatisfactory, they have condemned the whole.” The greater part of Morgan’s work is, however, of lasting value. Morgan based his conclusions on an enormous number of kinship terms collected by himself and others from every available source. Dr. Rivers has introduced[107] a new method of collecting similar data by means of recording exhaustive genealogies from a limited area. In this way not only can kinship terms be collected with accuracy, but a large number of other sociological data are obtained with a readiness and precision not hitherto possible. Indeed, it is no exaggeration to say that this method is producing a revolution in the method of sociological field work. Footnote 105: W. H. R. Rivers, “On the Origin of the Classificatory System of Relationships,” Anthropological Essays (Tylor Volume), 1907. Footnote 106: _Jour. Anth. Inst._, xxx., 1900, p. 74; _Sociological Rev._, 1910. Footnote 107: In the classificatory system most of the kin in the same generation are grouped under one general term; _e.g._, all the males of the grandfather’s generation are called by one term—another term includes father, father’s brothers, father’s male cousins, mother’s sisters’ husbands, mother’s female cousins’ husbands, and so on. In a later book (1878) Morgan summarised his earlier conclusions and proposed a classification of culture consisting of a lower, middle, and an upper Status of Savagery, a lower, middle, and an upper Status of Barbarism, and the Status of Civilisation based upon certain inventions and industries. About this time various students wrote on marriage and the family, of whom the foremost were Giraud Teulon (1867, 1874, 1884), H. Post (1875), Letourneau (1888), Von Hellwald (1889), and others, the conclusions of the earlier writers being summed up by Professor E. Westermarck in his masterly _History of Human Marriage_ (1891); but much has been written since that date on this subject of perennial interest. Professor F. H. Giddings, in his _Principles of Sociology_, sums up in the following words the trend of modern writers on ethnological sociology:—