On a global scale, the birth rate of identical twins has remained the same, about four-thousandths. The reason why twins are becoming more common for this reason is the increase in the birth of fraternal twins.
Many regions are known for their high twin birth rates, and the West African country of Benin is currently the country with the highest twin birth rate, about 24 per 1,000. Nigeria is close behind, about nine thousandths.
There are more Yoruba people in these countries, and they have always been known for their twins. Scientists believe that this may be the result of a combination of diet and genes.