The science is settled

2. Masturbation might be a form of advertising. According to this idea, males that engage in autoeroticism signal to possible mates as well as competitors how much they have to offer. “Males may advertise their high quality,” explains Waterman, “signaling that they have high quantities of sperm and can afford to waste some.” Result: more mating, more babies, more families. We hasten to add that masturbation as advertising does not apply (we really, really hope) to humans.

3. Masturbation might be a sort of victory lap. Some animals masturbate after they mate. Since other members of a group know this, then masturbation signifies that the male engaging in this behavior was the chosen partner of other females. Females who are still shopping for a mate might be inspired by that information to copy their choice, as in, “if he was good enough for her …” Result: more mating, more babies.