Twins were historically given supernatural capabilities, for better or worse. Multiple deliveries were something hard to understand with the scientific notions of thousand of years ago, so they had to be phenomena that forewarned inauspicious or happy events. In both case, something beyond the ordinary.
Classic traditions counted numerous twins. Romulus and Remus were considered the founders of Rome; in ancient Greece Castor and Pollux had a deity status; in Egypt Shu and Tefnut controlled air and water and from them other twins spawned, like Isis and Osiris, god of agriculture.
Also outside the Mediterranean basin, twins were often honored. In India, the Ashvin, Vivasvat and Saranyu, were in charge with the alternation of day and night; in north-western America (the current Alaska and British Columbia), the Tsimshian people believed that twins had meteorological powers. And so on, from Sri Lanka to northern Europe, from America to Persia.
There were opposite visions as well. The Tlingit population, in the north Pacific area of America, killed the “less fit” twin, that means the one who weighed less or the female; in the zone of the Puget Sound, twins parents were banned from their villages until one of the babies died; the Kwakiutl prevented the parents from working, so the poorest families were forced to immediately kill the offspring, just to survive. These kinds of punishment were common all around the world, among populations convinced that twins were “the slings and arrows of outrageous fortune”, to quote Shakespeare out of context.
The rate of multiple births is around 1% on a global scale, but there are many exceptions. Linha São Pedro, a small village in Brazil, reaches an abnormal 10%, enough to give rise to conspiracy theories, based on assumed experiments performed by the Nazis… Kodinji and Mohammadpur Umri, in India, have a 4,5% rate, more or less the same of Igbo-Ora, Nigeria, which gained the epithet of “home of twins”, with a welcome sign as celebration.
The Yoruba people, south-east of Nigeria, have a genetic predisposition, probably fostered by a yam-based diet. This tuber is particularly rich of estrogen and this would help ovulation. Even if other places have an even higher rate, Igbo-Ora hosts the annual “World twins festival” the local pride.
Actually, more of a cult. When a twin died young, the Yoruba made little votive statues, called ibeji, which accurately represented the deceased with details that indicated the lineage, to mourn the dearly departed.
They believed that, somehow, the spirit survived into the ibeji and, after specific rituals with essences of palm oil and sandalwood, the family took care of the statue like it was a living being. This cultural heritage is gone, but we can still find some ibeji, industrially made though.
We might think that this kind of belief is ancestral, it was actually just two centuries old. Twins were considered a curse among the Yoruba, possessed by evil forces and capable of killing their own parents. So they had to be eliminated. Multiple births were associated to animals and depraved sexual practices.
Until, in 1820, a royal decree forbade infanticide. But it was mostly a cultural change, sometimes a law isn’t enough to eradicate millennial beliefs, at least not immediately. The first ibeji are from 1854, according the dating of British Museum. We don’t know the reasons of this sudden change. The myth talks about an occurred protection by Shango, god of thunder.
Anyway, as the American humor writer Josh Billings said, “there are two things in life for which we are never truly prepared: twins”.