Zoologists from the University of Lethbridge in Canada discovered that crab-eating macaques on the island of Bali rubbing their genitals and masturbating with stones. They talked about it in a magazine article. ethology.
Researchers observed 173 monkeys from the Monkey Forest in Ubud, a Balinese Hindu temple. These macaques have been known to masturbate with their hands before, and scientists have also observed monkeys hitting or rubbing their genitals with stones, but it’s unclear whether this provides sexual satisfaction.
Observations have shown that this behavior leads to erections in men. While females prefer angular and rough stones to interact with the genitals, they do not show a particular preference for stones that touch other parts of the body. Also, males who did not have the opportunity to mate with females were more likely to use stones to stimulate their genitals.
“Overall, our data partially support the ‘sex toy’ hypothesis, suggesting that hitting and rubbing the genitals and groin with stones is a sexually motivated behavior. Our study suggests that these behaviors of questionable adaptive value may have been sustained through evolution through the same mechanisms of the brain’s reward system that underlie play and sexual activity.”