We live in the golden age of masturbation. Self-pleasuring is celebrated, not demonized, and even science is on board with a little self-lovin’, pointing to a wealth of beneficial biological side effects: happier genitalia, greater intimacy in relationships, excellent siring abilities — and a solid thumbs-up from evolution.

What is masturbation if not a natural way of life? Our closest relatives — the great apes — have never once questioned their manual capabilities, with bonobos practically building an entire society around self-pleasure. Enos, who went by his moniker “the Penis,” was the first chimp to orbit the Earth, earning his nickname by masturbating a ton in space. The same goes for humping dogs, humping dolphins, and self-fellating walruses. They are just doing what thousands of generations of evolution had likely programmed them to do — play the brain’s reward game by fiddling with their joysticks. Humans do the same, but we get a curiously unique reproductive benefit out of it — one that no other animal seems to have.

There’s a big difference between self-pleasuring in the animal kingdom and what’s taking place in the halo of laptop screen light: Humans, more than any other animal, masturbate to completion, as Scientific American’s Jesse Bering points out, noting that our ability to conjure up arousing mind-porn is likely the reason we’re so good at it. Having sex with oneself, he writes, can actually help humans be better at making babies in the long run.

Model: Myself Proberbly one of my most successful self-portraits. I have a thing for using my laptop as a strobe :)
Masturbation in men may improve their chances of fathering children.

This may seem counterintuitive: If the biological objective of any individual is to have kids, shouldn’t self-pleasuring from start to sticky finish be avoided? At first, it seems that it makes more sense for dudes to save up their sperm for when it counts rather than sentencing it to a fruitless sock-bottom doom. (We’ll get to female masturbation later.) Scientists were torn on this question until 1992, when British evolutionary biologists Robin Baker and Mark Bellis came up with a hypothesis explaining why masturbation is actually good for men. Their thesis rested on a single biological fact: Sperm get old.

In their study, published in Animal Behavior, they determined that masturbation gets rid of old sperm cells — they’re only viable up to a week after they’re made — to make room for new, more vigorous ones that are better at making babies. After all, with 3 million new sperm being produced each day, the testes are going to feel a bit crowded very quickly.

To test their theory, Baker and Bellis had 30 heterosexual couples collect the “flow-through” — that is, the excess sperm that spills out of the female body after sex — and subsequently measured the amount of sperm still present. In couples where the man had recently masturbated before sex, they counted low numbers, concluding that the majority of the ejaculated sperm, being new and healthy swimmers, resisted being rejected by the woman’s body. It follows that those men were more likely to father children, especially considering that early Homo sapiens females were likely to have hooked up with several males at any given time.

www.wendynelsonphotography.com
In women, masturbation appears to play a more holistic role in overall health.

The “sperm competition” theory is one compelling argument for the evolutionary survival of masturbation in humans, but it doesn’t take into account the female side of the story. Women, contrary to social stereotypes and despite social stigma, actually masturbate a lot; one nationally representative study of Americans, published in the Journal of Sexual Medicine in 2010, found that 85 percent of women masturbate (compared to 94 percent of men). Doing so, public health researchers report in The Conversation, gets cervical fluid flowing through the female genitalia, thereby flushing out bacteria and other infection-causing, pregnancy-preventing substances. In addition, they report that orgasms reduce stress, blood pressure, and pain, and it increases self-esteem.

While the physiological benefits of masturbation for women may seem less specific than they are for men, they’re no less important in an evolutionary context: Males only have to worry about getting their sperm to their intended destination, but mothers-to-be have to stay holistically healthy for at least the next nine months.

Reproductive advantages to self-pleasuring aside, science often neglects the most crucial element of self-play: Masturbation just feels good. While the physiological benefits of improved well-being — less stress, a stronger immune system, and better interpersonal skills — are great on their own, there’s no biological reason why gaming the brain’s reward system to occasionally dole out higher returns isn’t good for you. Sure, too much and it could turn into a full-blown addiction, like any other brain dopamine hack, but that’s why evolution equipped most of us with a sense of discipline.

Photos via Flickr / simonlesleyphoto, Flickr / Wendy Nelson Photography.

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.