twinism

In some parts of precolonial Yorubaland, […] twins and their parents were either banished or ritually slaughtered. This was not arbitrary as the prevailing explanation for the phenomenon of twinism found the mother culpable of an adultery with a spirit who was believed to own one of the babies. Twinism also harbored confusion of age-bracket in a society where seniority and hierarchy were valorized.