In a quiet corner of southwestern Nigeria, the streets of Igbo-Ora echo with laughter twice as loud, voices doubled in harmony. This is no coincidence—Igbo-Ora is famously known as the "Twin Capital of the World". Within the Yoruba ethnic group that populates this region, an interesting biological phenomenon unfolds: spontaneous dizygotic (fraternal) twinning rates that far surpass global norms. This unique genetic signature, deeply rooted in ancestry, diet, and possibly even spirituality, continues to mystify scientists and anthropologists alike.

Across Yoruba communities such as Igbo-Ora, Ekiti, and Ilesha, the twinning rate has been historically documented at 45 to 50 twin births per 1,000 births, a staggering figure when compared to the global average of approximately 12 per 1,000. Even with modern demographic shifts and the slight decline recorded in more recent studies—rates falling to about 20.7 to 23.8 per 1,000—Yoruba twinning remains among the highest documented anywhere in the world.

This phenomenon is neither replicated across Nigeria nor mirrored in neighboring countries. Twinning rates in eastern and northern Nigeria and nearby Ghana are significantly lower, signaling a distinct ethnic and regional pattern rather than a purely geographic one.

Countries like Benin, which also hosts a large Yoruba population, report high national twinning rates (up to 27 per 1,000 births). While Yoruba communities appear to lead the world in twin births, the lack of comprehensive ethnicity-specific data globally prevents researchers from definitively declaring them the absolute leaders.

The question remains: why the Yoruba? The answer lies in an intricate blend of nature and nurture. Genetic predisposition is a leading theory. Yoruba women, and others in genetically related groups, are found to have higher levels of follicle-stimulating hormone (FSH), which promotes the release of multiple eggs during ovulation—key for dizygotic twinning. High fertility rates in sub-Saharan Africa, where women commonly have multiple children, compound this effect. Birth order, more than maternal age, plays a vital role; studies suggest that the more births a woman has had, the higher the chances of delivering twins.

But beyond biology, cultural and environmental factors swirl around the mystery. The Yoruba diet, rich in yams—especially a specific variety believed to contain phytoestrogens and hormone-like compounds—has drawn attention. While the hypothesis that yam consumption stimulates FSH production and multiple ovulations remains unproven, its persistence reflects the cultural curiosity that surrounds this phenomenon. In Yoruba folklore, twins (known as Ibeji) are revered, often believed to bring luck or spiritual power. Perhaps, in a beautiful twist of nature and belief, culture has shaped biology—or vice versa.

This intersection of genetics, environment, and culture makes Yoruba twinning not merely a biological event but a living cultural legacy, with implications for medical research, fertility studies, and even anthropological exploration.

While the scientific world continues to probe the exact causes, the streets of Igbo-Ora and beyond carry on their legacy—one double blessing at a time.

In summary:

• Yoruba twinning rates reach 45–50 per 1,000 births, compared to a global average of ~12 per 1,000.
  
  

• These rates are four times higher than most populations, and far exceed those of other Nigerian ethnic groups and global averages.
  
  

• The likely causes include a genetic predisposition, particularly elevated FSH levels, high fertility and birth order, and possibly dietary influences (yam consumption), though the latter remains unproven.
  
  

• While Africa overall shows high twinning rates, ethnicity-specific comparisons are limited, leaving room for more research but making the Yoruba a great case study in natural twinning.
  
  

Image Credit: Jessica Felicio of Unsplash