Some such crisis must have been reached in every group of islands that was peopled by the immigration of a single family, and the natural solution in every case would have been to prohibit the marriage of both classes of cousins-german. But, little by little, the desire for alliances among chief families, for the restoration of the claims of _vasu_, and for the restoration of an equivalent of the tillage rights given in dowry, may have chafed against the prohibitions until these were so far relaxed as to allow the marriage of cousins in the degree most effective for promoting an interchange of property. For a similar reason Moses ordered the daughters of Zelophehad to marry men of their father's tribe, in order that their property should not pass out of the tribe, and "their inheritance remained in the tribe of the family of their father" (Numbers xxxvi. 12). 3. A third solution may be found in the transition from uterine to agnatic descent, a change that came about gradually as social development prompted the sons to seize on the inheritance of their father to the exclusion of the nephew (_vasu_). With the admission of the father's relationship to his son grew the idea that he was the life-giver and the mother the mere vehicle for the gestation of the child, and the child came to be regarded as related to his father instead of to his mother.[79] Thus Orestes,[80] arraigned for the murder of his mother, Clytemnestra, asks the Erinyes why they did not punish Clytemnestra for slaying her husband Agamemnon; and, upon their answer that she was not kin to the man she slew, he founds the plea that by the same rule they cannot touch him, for he is not kin to his mother. The plea is admitted by the gods. By this rule, a man is not kin to his father's sister's daughter, she being kin to her father only; but her affinity to him would render their marriage convenient as regards the family possessions. From long usage a sense of obligation would be evolved, and such cousins come to be regarded as concubitant. The children of sisters would still be within the forbidden degrees, for, although not kin through their mothers, their fathers, being presumably the concubitant cousins of their mothers, would be near kin.