Scientists Ponder When Our Ancestors First Started Cranking the Hog

"It's not that some species woke up one day and started doing it. This is an ancient, evolved trait."

Old Habits

Thanks to science, we may now have a good idea of when our ancestors first started pleasuring themselves — and it could help answer why they would develop such a practice when, on its face, it seems to provide no evolutionary benefit.

The findings of a new study, published Wednesday in the journal Proceedings of the Royal Society B, suggest that masturbation is actually a long-possessed trait of humanity's primate predecessors, predating us by at least tens of millions of years.

"What we can say is this behavior was present around 40 million years ago, in the common ancestor of all monkeys and apes," study lead author Matilda Brindle, an evolutionary biologist at the University College London, told The Guardian.

"It's not that some species woke up one day and started doing it," she added. "This is an ancient, evolved trait."

Helping Hand

According to the researchers, masturbation is actually pretty common in the animal kingdom, but primates are especially prolific.

Yet the old way of thinking brushed off this "autosexual" behavior as aberrant, arising mostly as a stress response in monkeys and apes held in captivity. This hypothesis, though, failed to explain why primatologists would go on to frequently observe this behavior in the wild.

So to blow the lid on this mystery, Brindle and her team drew from nearly 400 papers and records documenting the masturbation habits of these creatures, both wild and captive. The raw data showed that 73 percent of wild male primates masturbated, but females lagged behind at 35 percent.

From there, the researchers used mathematical modeling to construct an evolutionary history of the behavior across primate species, which is how they discovered that, not only have primates been cranking it for tens of millions of years, but that the behavior has remained ubiquitous throughout the ages.

Load Bearing

Exactly why this behavior emerged in the first place eludes scientists, but they have a few strong theories — for males at least.

One is that masturbating before mating helps get rid of potential sexually transmitted infections from the genital tract.

Or, similarly, this same principle could also flush out old and expiring sperm. But the most amusing explanation, in our opinion, is that masturbating could help a weaker male finish the job more quickly with a partner before a dominant male could stop him. Both of these theories, the researchers say, would help boost a male's chance of impregnating a partner, granting them an evolutionary advantage.

However, why females also masturbate remains even more mysterious, largely because primate studies have neglected them. But overall, Brindle says that all of this is surprisingly uncharted territory.

"This is such a common behavior across the animal kingdom, I find it absolutely baffling that nobody has researched it before," Brindle said, adding that it's "perfectly natural behavior."

More on primates: Gene Therapy Gives Primates Young Eyes Again