Twins in West African Culture and Society of the Iron Age
African Festivals honouring twins
I can't find the source I really wanted, but I know I've read how in some tribes the mother of twins are given a special title as an honor, in others they and/or their babies are actually killed as the epitome of evil.
IIRC it was something written by somebody who took a dim view of Joseph Campbell and the way Campbell tried to universalize myths and legends. I think the author's point was that tribal groups a few hundred miles away, even in the same language group, could have a radically different take on stuff like this, with a whole bunch of myths and legends with radically different lessons.