I voted "other" because humans are weird. We're one of the few animals that can consciously override our natural impulses on a grand scale (a society level), and we're also social creatures.
I don't think there's a "natural" state for humans unless you consider having sex with anything that moves "natural". Because, seriously, I think it's pretty safe to say that humans will have sex with anything that moves. And a lot of things that don't.