How often did Bornbad visit that village?

My guess over 100 times!

Yams? They contain phytoestrogen.

Although that wouldn't explain the high occurance of identical twins. Maybe all the fellas have supersperm that splits the eggs in two.

Extremely possible, and actually my first guess. There is a similar phenomenon in a certain African tribe - the Yoruba, if I remember correctly - and they have an extremely high twinning rate, which has been attributed to the high amount of Yams in their diet.

I only know this because my girlfriend did an enormous project on it.

Um... well, I don't know how to put this, but what really happened is this:

Evil forces have been putting something in the water to make them have more twins so that in a few years they can send their evil robot henchman named Andy to help them steal one of each pair to suck some kind of psychic brain-juice out of their heads to feed their imprisoned "Breakers", who are all working at a compound in the middle of a nuclear wasteland to destroy all of reality for some unknown reason.

Phew. Yes, that really was one sentence.

And I didn't think that up.... comes straight from a Stephen King book called "The Wolves of the Calla".

Heh.

That was going to be my first guess. I too have read the 'formula' for having twins. The hubby is a little suspicious on why all of a sudden it's thanksgiving every day. ;)