Researchers Reveal the Evolutionary Origins and Benefits of Masturbation

2023-06-07 18:16:14

The true origins of masturbation in our evolutionary history are largely misunderstood, although it is particularly prevalent among primates. For good reason, the phenomenon is generally taboo and sorely lacking in data and scientific observations. One of the few to decipher it, a new study suggests that it confers an essential evolutionary advantage, in particular in the success of reproduction and in the control of sexually transmitted diseases (STDs) – at least in males.

Common in the animal kingdom, masturbation is particularly present in primates (including humans). Researchers also suggest that primates are among the only ones to extend the sexual act to a purpose other than fertilization. A large number of testimonies seem to confirm this hypothesis. For example, autosexual and singularly inventive behaviors have been observed many times in chimpanzees or macaques.

Historically, masturbation is considered abnormal behavior or a byproduct of sexual arousal. In humans, the subject is generally governed by restrictive social norms (modesty or taboo) and considered undesirable. As a result, the few observations and data collected are too fragmented to really understand its distribution in primates, its evolutionary history and its adaptive significance.

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The new study, from University College London, attempts to decipher the phenomenon by analyzing more than 400 data sources from other institutes, primatologists and zoo and park staff. This would be the largest synthesis of data to date on primate masturbation. Selon Matilda Brindlelead author of the study and an anthropologist at University College: our findings help shed light on very common, but poorly understood, sexual behavior and represent a significant advance in our understanding of the functions of masturbation ».

The summary, published in the journal Proceedings of the Royal
Society B Biological Sciences, reveals that autosexuality or masturbation would be a behavior stemming from a precise evolutionary objective. This adaptive behavior is present in both captive and wild primates and “demonstrates that masturbation is part of a repertoire of healthy sexual behaviors,” Brindle said.

The long evolutionary history of masturbation among primates indicates that it was likely practiced by the common ancestor of apes and great apes. However, it has not been clearly determined whether the ancestor of the other primates (lemurs, lorises and tarsiers) practiced the practice, the data on these clades being extremely limited.

The evolving roles of masturbation

To understand the potential roles of masturbation in our evolutionary history, the researchers analyzed nearly 246 academic papers and 150 accounts from primatologists and zoo and park officials. From these data, the authors followed its distribution in primates, in order to understand when and why it evolved as much in males as in females.

If at first glance masturbation seems non-functional, Brindle and his colleagues offer several hypotheses indicating otherwise. First, that of “poscopulatory selection” suggests that the practice favors the success of fertilization. This form of masturbation can be done in two different ways: with or without ejaculation. Like “foreplay,” the former can enhance arousal prior to intercourse and could be a particularly useful strategy for males who are susceptible to interruptions during copulation. Masturbation can thus help them to ejaculate quickly and increase the chances of successful fertilization.

Secondly, masturbation with ejaculation would make it possible to evacuate poor quality sperm, in order to reserve “fresh” and high quality sperm for mating. This strategy would also promote competition between males and the selection of the best genetic backgrounds – by trying to outperform the sperm of other males (from a qualitative point of view). According to the researchers, previous studies support this hypothesis by showing that male masturbation evolved alongside mating strategies, during which several males at once compete to impregnate a female.

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The research team also suggests potential health benefits. Masturbation would in particular reduce the risk of contracting an STD by cleaning the urethra – prone to infections –, thanks to ejaculation. This theory is supported by data revealing that male masturbation has co-evolved with a high rate of STDs, in the evolutionary tree of primates.

Furthermore, studies have previously demonstrated a strong link between masturbation and ejaculation frequency, with the incidence of prostate cancer in men. Some well-being effects have also been mentioned, such as relieving stress and improving sleep. This is probably one of the reasons why it is more frequently practiced in monkeys in captivity than in those in the wild.

However, researchers have not yet been able to determine the evolutionary significance of female masturbation. Although as frequent as that of males, too little research describes it and thus considerably reduces the opportunities for statistical analysis. More data is therefore needed to understand how the practice has evolved among women/females.