the reproductive process, which has certainly been one of the aims of all social organization in the past, whether of savage peoples or of civilized peoples, evidently precludes anything like the toleration of promiscuity or even of free love. SELECT REFERENCES _For brief reading:_ WESTERMARCK, _History of Human Marriage_, Chaps. I-VI. HOWARD, _History of Matrimonial Institutions_, Vol. I, Chaps. I-III HEINEMAN, _Physical Basis of Civilization_, Chaps. IV-VII. _For more extended reading:_ CRAWLEY, _The Mystic Rose: A Study of Primitive Marriage_. GEDDES AND THOMSON, _Evolution of Sex_. LETOURNEAU, _The Evolution of Marriage_. MORGAN, _Ancient Society_. STARCKE, _The Primitive Family_. SPENCER, _Principles of Sociology_, Vol. I. CHAPTER V THE FORMS OF THE FAMILY The family as an institution has varied greatly in its forms from age to age and from people to people. This is what we should expect, seeing that all organic structures are variable. Such variations in human institutions are due partially to the influences of the environment, partially to the state of knowledge, and partially to many other causes as yet not well understood. The family illustrates in greater or less degree the working of these causes of variation and of change in human institutions. The Maternal and Paternal Families.--As regards the general form of the family we have to note first of all the two great forms which we may characterize respectively as "the maternal family" and "the paternal family." As we have already seen, Bachofen, Morgan, and others discovered a condition of human society in which relationship was traced through mothers only, and in which property or authority descended along the female line rather than along the male line. Further investigation and research have shown that up to recent times, say up to fifty years ago, one half of all the peoples of the world, if we reckon them by nations and tribes rather than by numbers, practiced this system of reckoning kinship through mothers only, and passed property and authority down along the female line. Ethnologists and sociologists have practically concluded, from the amount of evidence now collected, that this maternal or metronymic system was the primitive system of tracing relationships, and that it was succeeded among the European peoples by the paternal system so long ago that the transition from the one to the other has been forgotten, except as some trace of it has been preserved in customs, legends, and the like.