The main entry's closing observation that real twin births are treated with unusual attention almost everywhere, as either especially auspicious or especially dangerous, is illustrated with unusual clarity by two neighboring West African traditions that reached opposite conclusions about which twins actually are.
The Yoruba, who have among the highest documented twinning rates in the world, developed an elaborate and wholly positive ritual response: twins, ibeji, are believed to share a single soul between two bodies, and if one twin dies, a small carved wooden figure, also called an ibeji, is made to house the surviving soul's other half, cared for, fed and dressed as a living family member, sometimes for the rest of the surviving twin's life. Twin births are occasions for specific celebratory ritual, and the mother of twins receives a distinct honorific title, reflecting the belief that twins bring particular blessing to their family.
Traditional Igbo communities in pre-colonial and early colonial Nigeria, by sharp contrast, in some areas held twin birth to be an abomination associated with evil spirits, and infant twins were in some documented cases killed or abandoned shortly after birth, a practice that became a target of Christian missionary intervention, most famously associated with Mary Slessor, a Scottish Presbyterian missionary active from the 1870s who worked to end the practice and to rescue abandoned twin infants herself, and whose efforts are still commemorated in parts of southeastern Nigeria today. The contrast between two geographically proximate traditions holding opposite beliefs about the same biological event demonstrates that neither reading of twin birth follows automatically from the event itself.