Theoretically, the tribe was built up from natural increase within itself. All members, except wives from outside tribes, should show male descent from the original ancestral pair. In practice, however, many female breaks are found owing to adoptions, sharing of children, or matrilocal residence. The senior chiefly lines should show no female breaks, and some do not. In Table 3 Aiteina shows an unbroken tama tane line in Ngati-Vara, but Akaeakore is a tama va'ine to Ngata-Vara through his mother in the 13 th generation, and became a Ngati-Vara as part of the share of his mother's family.
The incessant wars that ravaged Mangaia led to the arbitrary taking up of sides by certain people. Married women were the only ones who could move freely between tribes, their own and their husband's, during a state of war. As the result of intertribal adoptions, members of the same biological family were forced to meet each other in battle. Sometimes blood overruled the law and sometimes it did not.
In a battle between the Ngati-Vari and Ngati-Tane, Poito's two sons, who had been shared to the Ngati-Tane, fought against their father's tribe. In the battle they approached an enemy who was fighting valiantly. The elder son cried out to his brother, "Let us engage elsewhere. It is our father Poito." The younger son took no notice. Poito, recognizing his opponent, made a mere pretence of striking at him and allowed, himself to be killed. The younger son, though literally obedient to custom, is not admired in Mangaia for his action.
The tribe was a closed corporation, as regards rank and status of its members, but there were certain accretions that added to its numerical strength:
1. The men of defeated tribes often sought out some powerful protector for whom they worked. A protector might be sought out by a man's wife in her own tribe, in which case the arrangement was instituted by the woman. So long as the tama va'ine tribe was not the one actively opposed to them, such an incorporation was easily arranged. The people so included usually occupied a menial position and were on probation until they proved their loyalty to the tribe by assisting it in war. After a successful battle, the outsider who had proved his valor was rewarded with a share of land and so became a free man in the tribe he served. His children became absorbed into the tribe in the course of events. It is extremely probable that some of the tribes which became extinct were not all killed off, but that the survivors, after the last disastrous defeat, sought refuge in other tribes or were enslaved by the victors and so absorbed. 2. People who were defeated and accepted a menial position forced upon them in order that they might live were also added to the tribe. The women of defeated tribes were spoils to the victors. They were often taken as supplementary wives by chiefs, and their children became tama tane in the conquering tribe. The pedigrees transmitted page 106orally are those of the leading families in the tribe and take no cognizance of the lower stratum of the tribe formed of additions from outside sources.