We’re always hearing about how the U.S. is experiencing an “epidemic” of multiple births. Triplets are the new twins, twins are the new singleton, singletons are the new, uh, red-headed stepchild? I don’t know. What I’m trying to say is there are lots of twins in the U.S.

The rate of fraternal twins in Europe and the U.S. is somewhere around 1.2 percent and .8 percent in Japan. But in western Africa, the rate is much higher, especially among the Yoruba, who live mainly in the southwestern part of Nigeria. There, the rate of twin births is an astounding 5 percent!

Nobody knows why the rate of twins there is so high, though many experts attribute it to yam consumption. Apparently, the indigenous meal staple contains a natural hormone called “phytoestrogen,” which some experts believe may stimulate the ovaries to produce an egg from each side in a single ovulation cycle.

Others say it’s all genetics, though it’s amazing that any twin DNA survived to get passed along. In pre-colonial times, the Yoruba tribes thought twins were evil and routinely killed them. This practice ended when a Scottish missionary convinced them bad things happened for other reasons. Now, twins are revered in the culture and nearly everybody is related to one or more sets of twins.