Here's an interesting joint interview from The Believer with Steve and Mark O'Donnell, two identical twin writers who were the youngest children in a family of ten children. There's nothing flabbergasting in it, but if you want to hear two very witty and perceptive twins talk about being twins, this is it.
Steve O'Donnell invented The Top Ten List while David Letterman's headwriter, while Mark O'Donnell won a Tony for co-writing the Broadway musical Hairspray. Can you guess which one is straight and which one is gay?
Yes, you can.
By the way, using the Australian Twin Registry as a source, a survey by Northwestern University's J. Michael Bailey came up with a concordance rate of 22 percent for homosexuality among identical twins who were raised together, which is pretty low.
Also, Nancy L. Segal, one of main researchers of the famous "Minnesota Twins" project and author of the 1999 book Entwined Lives: Twins and What They Tell Us About Human Nature, told me that twins raised together rarely fall in love with the same person.
This is interesting evidence for non-determinism in life's fundamentals.