You may not know it, but masturbating is not an exclusive practice of the human being. Quite the contrary, it is common among animals, especially primates, our closest living relatives. Some monkeys in Indonesia even use stones for it. Beyond taboos, its health benefits are well known. It promotes relaxation, improves mood, reduces urinary tract diseases, relieves menstrual pain in the case of women, and helps overcome psychological barriers that lead to sexual dysfunction. An investigation on primates that is published this Wednesday in the magazine ‘Proceedings of The Royal Society B‘ has revealed that it also has evolutionary advantages, since it increases reproductive success and helps avoid contracting sexually transmitted diseases. “Our findings help shed light on a very common but poorly understood sexual behavior and represent a significant advance in our understanding of the functions of masturbation,” explains the study’s lead author, anthropologist Matilda Brindle, from University College. From london.
The authors of this research assembled the most comprehensive data set on primate masturbation to date, including 246 academic articles and 150 contributions from specialists and keepers of these captive animals. They discovered that sexual self-indulgence has a long evolutionary history that would go back to the common ancestor of all primates. And that, as has been said, would have evolutionary advantages.
Lack of information for females
The first would be that it increases reproductive success. It is what they call in the study ‘hypothesis of post-copulatory selection’. On the one hand, masturbation without ejaculation increases arousal before sex, which would help non-dominant males to secrete their semen faster, who would probably be interrupted by their hierarchical superiors in their encounters with females. On the other hand, masturbation with ejaculation allows inferior quality semen to be expelled, leaving the best available for intercourse.
Both aspects fit especially with species like chimpanzees, where ‘sperm competition’ occurs. Simply put, male chimpanzees compete sexually on the quality of their sperm, not their imposing physiques like gorillas. The dominant males of the latter monopolize access to females, but in chimpanzees, they have sexual encounters -every five years if they do not lose their young before- with various partners, who, as has been said, fight among themselves through their sperm. This explains why they have the largest genitalia of all primates. According to a study published in ‘Nature’ in 1981, their testicles weigh 119 grams compared to the gorilla’s 30 grams. In humans they are around 40 grams. Regarding the size of the penis, important because the larger, the closer to the uterus it deposits the sperm, chimpanzees are also the best endowed among primates -in this case the human male clearly surpasses them-.
The other big advantage would be what they call the ‘pathogen avoidance hypothesis’. From this perspective, male masturbation reduces the possibility of contracting a sexually transmitted disease by cleaning the urethra, the focus of many of these pathologies, with ejaculation.
As for female masturbation, the study’s conclusions are much less clear. As in males, it is frequent, but there is less data on it, so more information would be needed to better understand its evolutionary role. “The fact that autosexual behavior can have an adaptive function, is ubiquitous in all primates, and is practiced by members of both sexes both in the wild and in captivity, demonstrates that masturbation is part of a repertoire of healthy sexual behaviors,” conclude.
