* In the ancient Inca, Egyptian, and Hawaiian societies, royal marriages between brothers and sisters were common practice.
* In the Ndzundza Ndebele African tribe, marriage is not finalized until the birth of a child.
* Environment, not genetics, determines sex in some species. Researchers postulate that Osedax begin as unsexed floating larvae. If they land away from other females feeding on a whale carcass, they become female. In they land on a female worm, their development is arrested, and they live ever after as male sperm donors inside the female.