The marriage in whole classes, such as is in force in Australia, is no doubt a very low and primitive form of group marriage, while the Punaluan family, so far as we know, is its highest stage of development. The former seems to be corresponding to the social stage of roving savages, the latter requires relatively settled communistic bodies and leads directly to the next higher stage of development. Between these two, we shall no doubt find many an intermediate stage. Here lies a barely opened, hardly entered field of investigation.[17] 3. THE PAIRING FAMILY. A certain pairing for a longer or shorter term took place even during the group marriage or still earlier. A man had his principal wife (one can hardly call it favorite wife as yet) among many women, and he was to her the principal husband among others. This fact in no small degree contributed to the confusion among missionaries, who regarded group marriage now as a disorderly community of women, now as an arbitrary adultery. Such a habitual pairing would gain ground the more the gens developed and the more numerous the classes of "brothers" and "sisters" became who were not permitted to marry one another. The impulse to prevent marriage of consanguineous relatives started by the gens went still further. Thus we find that among the Iroquois and most of the Indians in the lower stage of barbarism marriage is prohibited between all the relatives of their system of kinship, and this comprises several hundred kinds. By this increasing complication of marriage restrictions, group marriage became more and more impossible; it was displaced by the pairing family. At this stage one man lives with one woman, but in such a manner that polygamy, and occasional adultery, remain privileges of men, although the former occurs rarely for economic reasons. Women, however, are generally expected to be strictly faithful during the time of living together, and adultery on their part is cruelly punished. But the marriage-tie may be easily broken by either party, and the children belong to the mother alone, as formerly. In this ever more extending restriction of marriage between consanguineous relations, natural selection also remains effective. As Morgan expresses it: "Marriages between gentes that were not consanguineous produced a more vigorous race, physically and mentally; two progressive tribes intermarried, and the new skulls and brains naturally expanded until they comprised the faculties of both." Thus tribes composed of gentes necessarily either gained the supremacy over the backward ones or, by their example, carried them along in their wake.