"A GENE THAT CAUSES MIDDLE AGES MEN TO MASTURBATE IN FRONT OF THEIR COMPUTER SCREENS, WHILE WATCHING PORNOGRAPHY!"

To isolate it, they would first have to find at least one middle aged man who has a computer but has never exhibited that behaviour. A quadropoligic wouldn't do, for reason that should be obvious. Then they would have to waterboard the subject a few times, to determine if he was telling the truth. Then they would have to find at least one more, and start over, to replicate the findings. Just about an exercise in futiltiy.