The caring for one’s nephews and nieces is not limited to humans. Mole rats will care for nieces and nephews but not for unrelated young, and Japanese quails show a clear preference for mating with first cousins—a way to increase the amount of their own genetic material that gets passed on (the offspring of first cousins will have 56.25% of their DNA in common with each parent rather than 50%—that is, the “family” genes have an edge of 6.25% in the offspring of first cousins than in the offspring of unrelated individuals).
