In certain of these tribes a sort of categorical promiscuity is kept up. Thus, among the tribes of Mount Gambier, of the Darling River, and of Queensland, each tribe is divided into two sub-tribes, and within each of these clans all the men are reputed brothers, and all the women are sisters, and all marriage between these brothers and these sisters is strictly forbidden.[879] This is a primordial law; the violation of it is an act of the deepest guilt, which not only stains the individual, but the group to which he belongs; it is more than incest, and the Australians, who have a very lively sentiment of duty, feel intense horror of such an act. But if every man is brother to all the women in his clan, on the other hand he is husband to all the women of the other clan of his tribe. Consequently, all the men of one group are called husbands by all the women of the other, and inversely. Marriage with these Australians is not therefore an individual act, as with us; it is a social condition, resulting from the fact of birth.[880] However, the actual communal union is not obligatory in the least. A man or woman may stop at the nominal or reputed marriage; they may merely call each other husband and wife; but in principle, the right is admitted, and the men sometimes offer temporary wives of their own class to strangers who visit them.[881] Thus in the tribe of the Kamilaroi, near Sydney, every man of the Kubi clan has the right to call “my wife” every person of feminine sex belonging to the Ipai clan, and to treat her as such. There is no need of proposals, or of contract, or of ceremony; a man is a husband by right of birth, but the intimate union does not imply association by couples; the woman passes from one to the other, or even from several to several others. On the other hand, within the limit of the clan, all the men and all the women call each other brothers and sisters, and are bound to respect each other. In uniting with the men of the other sub-tribe having conjugal right over them, the women do not on that account cease to reside in their own clan, the sub-tribe of their “brothers.”