“Each has the other’s name tattooed on his inner lip”

For [twins] raised in the same culture with the same opportunities, differences in IQ reflected largely differences in inheritance rather than in training or education. … This ran counter to the prevailing belief of behaviorists that our brains were blank slates waiting to be inscribed by experience.

The current National Geographic has an interesting article on twins, as well as twin hypnotic twin-photo galleries (one, two).

If there are any identical twins in the crowd: do you ever get jealous of your twin, and how? Or is there usually some kind of equilibrium?