unfortunately for him, he failed to recognize the 1st rule of life.
All that's on a man's brain is sex. Anything attractive enough will do.
I'm willing to bet that during genetic bottlenecks when humans were down to a few hundred people, it was rampant. If they didn't fuck anything they could lay their hands own, we wouldn't be here. Of course now, we have the luxury of choice. Only the poor, uneducated and underprivileged need to engage in backwards choices like incest.