Why Yoruba Communities Have the World's Highest Documented Twinning Rate

Twins are rare almost everywhere in the world, born naturally in something like 1 or 2 out of every 100 pregnancies across most populations. Among the Yoruba of southwestern Nigeria, they are not rare at all. Research stretching back more than half a century has found this region produces twins at a rate researchers describe as the highest documented anywhere on Earth, a statistical anomaly that arrived with its own body of biology and its own body of belief.

The foundational research came from P.P.S. Nylander, a gynecologist who studied births at hospitals in Ibadan between the early 1970s and early 1980s. His work found twinning rates of roughly 45 to 50 sets per 1,000 births among mothers of Yoruba or wider Western Nigerian origin, a figure later research has broadly reproduced. For comparison, Western European countries in the same decades recorded rates closer to 9 to 11 per 1,000, and East Asian populations in Japan, Hong Kong and Singapore recorded rates as low as 5 to 6 per 1,000. By Nylander’s numbers, a Yoruba mother was four to five times more likely to have twins than a Western European one, and roughly eight times more likely than a mother in East Asia.

One town in particular has become the public face of the phenomenon. Igbo-Ora, in Nigeria’s Oyo State, is majority Yoruba and has been studied repeatedly by researchers trying to explain why its twinning rate runs so high even by regional standards, earning it the nickname “Twin Capital of the World” in local and international press. Scientists who have worked there, including teams publishing in PLOS ONE and the journal Twin Research and Human Genetics, have pointed to genetic factors, particularly a tendency toward hyperovulation that makes releasing more than one egg per cycle more common, as the leading biological explanation, while local residents in the same studies often point instead to diet, especially a starchy yam some communities believe contains compounds that stimulate the ovaries.

The biology alone doesn’t explain why the fact is so central to Yoruba identity. Twins in Yoruba culture are known as Ibeji, and are treated as sacred from birth, believed to share a single soul split between two bodies and to bring good fortune to households that honor them properly. If one twin dies in infancy, a practice documented across generations and cataloged in detail by researchers including John Pemberton III, John Picton and George Chemeche, families historically commissioned a carved wooden ere ibeji figure to stand in for the lost child. The figure would be dressed, adorned with beads and cowrie shells, fed at mealtimes, bathed and even danced with at festivals, treated by the surviving family as a continuing presence of the child who died. That tradition, still visible in museum collections and family shrines today, grew directly out of a demographic reality: in Yorubaland, having twins was never unusual enough to go unmarked by ritual. It was common enough to need one.