Fraternal twins, also known as dizygotic twins, are twins that develop from two different eggs fertilized by two different sperm cells. This means fraternal twins are no more alike than regular siblings. Fraternal twins can be either the same sex or different sexes. The rate of fraternal twinning varies significantly across different racial and ethnic groups.
Quick Answers
The racial group with the highest rate of fraternal twinning is non-Hispanic black women. Studies have found that non-Hispanic black women have a fraternal twinning rate around 4 per 100 births. This is roughly 2-3 times higher than the fraternal twinning rate among white or Asian women. Geography also plays a role, with Central Africa having some of the highest twinning rates in the world.
Fraternal Twin Rates by Race
Here is a breakdown of fraternal twin rates by race and ethnicity in the United States:
- Non-Hispanic black women: 4 per 100 births
- Non-Hispanic white women: 1.7 per 100 births
- Hispanic women: 1.6 per 100 births
- Asian women: 1 per 100 births
- Native American women: 1.6 per 100 births
As you can see, non-Hispanic black women have a substantially higher rate of fraternal twinning compared to other groups. The rate among non-Hispanic black women is over double that of white and Hispanic women.
Why Do Non-Hispanic Black Women Have the Highest Rate?
There are a few factors that contribute to non-Hispanic black women having the highest fraternal twinning rate:
- Genetics – Certain genetic factors make non-Hispanic black women more likely to release multiple eggs during ovulation, leading to fraternal twins.
- Body composition – Higher average BMI and body fat percentage may play a role.
- Age – Non-Hispanic black women tend to have children at younger ages on average when fertility is highest.
- Geographic ancestry – Genetic links to high twinning regions of Western Africa.
The combination of these genetic, biological, and demographic factors result in non-Hispanic black women having substantially higher fraternal twinning rates compared to other racial groups in the US.
Worldwide Twinning Rates
Looking beyond the United States, countries in Central Africa have some of the highest twinning rates in the world. This table shows twinning rates in select global regions:
| Region | Twinning Rate (per 1,000 births) |
|---|---|
| Central Africa | 27.9 |
| Nigeria | 22.5 |
| United States | 7.2 |
| China | 6.9 |
| India | 4.8 |
As you can see, Central Africa and Nigeria have exceptionally high twinning rates compared to most other world regions. This is likely due to similar factors that lead to high twin rates among non-Hispanic black women in the US.
Conclusion
In summary, non-Hispanic black women have the highest fraternal twinning rate in the United States, averaging about 4 twins per 100 births. This rate is substantially higher than other racial groups due to a combination of genetic, biological, and demographic factors. More broadly, the highest twinning rates globally are found in Central Africa and Western Africa. So among both US racial groups and global regions, populations with African ancestry tend to have elevated rates of fraternal twinning.
