From this example it is clear that the boundaries of the nupa and apillia groups are not fixed in a given group of women; it is not possible to divide the women and the men into elder brothers and sisters on the one hand, younger brothers and sisters on the other.  But if this is the case, we are quite in the dark as to the meaning of the marriage regulations.

One thing however seems certain; viz., that the Urabunna regulations do not give the same result as the four-class regulations.  With them the division is within the generation.  There is no class of women, who, with their descendants, are the normal spouses of a class of men, with their descendants.  That being so, the Urabunna case can hardly throw light on the genesis of the four-class system.

Among the Urabunna, however, like the Wathi-Wathi, we find the rule that a man must marry in his own generation; and this is prima facie the meaning of the four-class rule.  It is true that the origin of the eight-class rule was not what its prima facie meaning suggests, viz., the desire to prevent the marriage of cousins, for we know that it originated in the distinction between elder and younger sisters.  But no similar theory appears to fit the case of the four-class tribes.  No division within the generation could possibly produce an alternation of generations.

The Red Indians have in many cases different names for the elder and younger sister; the Hausa impose on persons standing in these relations certain prohibitions and avoidances, which are not the same for both elder and younger; in Australia a man may speak freely to his elder sisters in blood, but only at a distance to his tribal ungaraitcha.  To his younger sisters, blood and tribal, he may not speak save at such a distance that his features are indistinguishable.  In many parts the elder brother has special rights with regard to the younger, and many similar customs might be quoted[139].

The question why marriage within the generation—­the rule of four-class and two-phratry tribes alike—­should have come into existence is a complicated one and involves that of the origin of kinship terms.  If we take a crucial case of kinship terminology, we find that a child applies the same term to its actual mother as to all the women whom its father might have married, to its potential mothers in fact.  If therefore we have to choose between the gradual extension of the terms from the single family to the group or their original application to a group, this instance seems decisive in favour of the latter theory.

Now if marriage was originally not “group” but individual, a question to be fully discussed in later chapters, we can hardly doubt that parent-child marriage was forbidden or perhaps instinctively avoided.  But this would be equivalent to prohibiting marriage with one of a number of men or women embraced under a common kinship term.  In the lower culture generally and especially among the Australians there is a tendency to follow things out to their logical conclusions.  If this were done in the present case, the result would be to extend the prohibition to all the persons embraced under the kinship term.