Sexual instinct. Honestly, I see it as an itch that some people need to scratch. I’ve known guys whose sexual desire seemed to be nearly non-existent. I don’t think they were flawed in any way – it wasn’t wasn’t an itch that needed scratching.
I needed to scratch mine and was kind of envious of those whom it didn’t seem to bother.
Also, I think a lot of sexual attraction is a paraphilia that happens to be condoned by society.