The existence of the individual family as a social unit, based upon the physiological facts of maternity, the social factor of marriage and other social factors, are thus chosen as the basis upon which we may proceed to analyze more in detail the individual parental relation. Whether this basis exists in all human societies and forms what was called above the constant, invariable elements of parental kinship, may remain an open question. This could only be answered correctly _a posteriori_, on the basis of a series of special researches in many societies. The existence of individual motherhood, as this word is defined here, seems to obtain in the majority of human societies (or even in all of them). Nevertheless, as pointed out above,[516] even this point cannot be treated as self-evident. This applies in still higher degree to individual marriage, which has often been denied as regards many societies.[517] In this place we have mainly to keep before our eyes the Australian society and our own society, the latter of which affords, so to say, the heuristic principle, the clue to the understanding of the former. As far as those two societies are concerned, our choice appears to be the right one, and the social-physiological basis mentioned above contains the essential common elements of kinship in both societies. [516] In reference to Dr. Rivers' article, compare pp. 6, 7. [517] In some cases, when the position of the father is very subordinate in the family and his relation to the mother and her children is a very loose one--it seems doubtful whether the existence of the individual family (in the sense here defined) can be accepted (compare, for examples of such peoples, Dr. Westermarck, _H.H.M._, p. 109, and Sir Laurence Gomme, _loc. cit._, pp. 231, 232). In these cases the necessary condition for individual _paternal_ kinship according to our theory would be lacking. The existence of individual marriage and its legal, sexual and psychological aspects have been discussed and established in the preceding chapters, as far as Australia is concerned. A discussion on individual motherhood will be given below. The existence of the individual family group in Australia, based upon individual marriage and upon individual motherhood, is the subject of the remaining chapters of this study. So that the existence of this physiological and social basis of kinship may be taken as granted.