Damaraland mole-rats are relatives of naked mole-rats. In their clans, too nonbreeding individuals of both sexes cooperatively assist one breeding par. Even so, breeding individuals in wild Damaraland mole-rat colonies usually are unrelated, and few suboordianes move up in the hierarchy to breeding status. Researches suspect that ecological factors, not genetic ones, were the more important selective forces in Damaraland mole-rat altruism. Explain why.