Cause of homosexuality: hereditary, but not genetic?

Scientists may have discovered why people are gay.

It's hereditary- but not genetic- which is why homosexuality, an evolutionary dead-end, doesn't die out. It's also why identical twins of gays are straight about half the time.

There is, of course, no more and no less of a biological reason for gays to express their sexuality in behavior than straights.

HT: Drudge