[nostrademons]

1.) I think it's both. People have sex with folks of the same attractiveness, but they don't ignore intelligence. Could you imagine an MIT grad student having sex with a trailer-trash bimbo of slightly-below-average attractiveness? (Yeah, that's a bad mental picture.)

3.) They've had less time to be surrounded by people of similar intelligence and interests. The virgin rate among MIT grad students is roughly the same as the virgin rate among average high schoolers. That's consistent with the hypothesis that MIT-caliber grad students can't find anyone until they get to MIT, and then they follow the normal rules of chance & dating & random hookups that most people do in high school.