Yes, I'm posting before I read all of the responses...THEREFORE, I'm sure that I'm simply REstating the obvious. Somehow, I'm compelled:
For civilization to survive there must be HETEROsexual relationships.
Well, I did hear about one situation where a turkey baster did the deed for a lesbian couple.
Seems like there was a male or a transgendered or something like that somewhere in the equation, though.