First and foremost among the points with which Morgan has failed to deal is that of the constitution of the primitive group.  Was it composed of parents and children only or were more than two generations represented?  If the former, why were the children expelled? if the latter, how are brother and sister marriages introduced, when ex hypothesi the father of any given child was unknown and may have been any adult male?  If Morgan and his supporters evade this difficulty by defining brother and sister as children of the same mother, they are met by the obvious objection that no revolution in a promiscuous group would result in the marriage of children of the same mother. Ex hypothesi there were several child-bearing women in the group, and their children, if a reform were introduced prohibiting marriage outside one’s own generation, would intermarry; but the children of these women are, on the definition adopted, not brothers and sisters.

If brother and sister does not mean children of the same mother, what does it mean?

By what process are these names supposed to have come into existence in a promiscuous group?  If brother in this sense is taken to imply common parentage, the name must clearly denote the relation between two males because, although a whole group of men had access to the mother, the male parent was or may have been the same person in each case, and this whether the mother was the same or not.  Now, quite apart from the fact that primitive man was unlikely to have evolved a term for such an indefinite relationship, except in so far as it involved rights or duties, it is obvious that great complications would arise which would in practice make the nomenclature unworkable.  For to call two boys brothers because they have the same group of men as possible fathers is only practicable in a society which has already evolved a system of age grades, and has established restrictions on intercourse between different generations, to use a somewhat indefinite term.  For it is clear that in a state of promiscuity the class of adults is continually being recruited and that the boy passes at puberty, in so far as restrictions in the nature of initiation ceremonies are not imposed, from the class of sons to that of fathers.  In other words, if a group consists of M_1 M_2 M_3 M_4, and they have male children of all ages N_1 N_2 N_3 N_4, as soon as N_1 reaches puberty he becomes a possible father of the children O_1 O_2 O_3 O_4, who differ in age from N_4 only by a few years at most and reckon as his brothers.  But this means that N_1 is the son of M_1, for example, but at the same time the father of O_1, who is likewise the son of M_1; in the same way O_1 is the brother of N_4, who is the brother of N_1; but O_1 is not the brother of N_1.  The extraordinary complexity of the relations that would arise is at once obvious, and it seems clear that relationship terms could never come into existence under such circumstances unless they implied something beyond mere relationship and denoted rights and duties[148].  But if they denoted rights and duties, these must have preceded the relationship term, which consequently need not be held to apply to kinship in any proper sense of the term.