2023-06-07 11:11:36
MADRID, 7 Jun. (EUROPA PRESS) –
New research published in Proceedings of The Royal Society B finds that masturbation appears to have an evolutionary purpose in primates dating back tens of millions of years.
The findings indicate that masturbation is an ancient trait in primates and that, at least in males, increases reproductive success and helps prevent contracting sexually transmitted infections (STIs).
Dr. Matilda Brindle, an anthropologist at University College London, and her colleagues assembled the largest dataset ever conducted on primate masturbation, gathering information from nearly 400 sources, including 246 published academic articles and 150 questionnaires and personal communications from primatologists and zookeepers. From these data, the authors traced the distribution of autosexual behavior among primates, to understand when and why it evolved in both females and males.
The team found that masturbation has an evolutionary history of tens of millions of years among primates and was likely present in the common ancestor of all monkeys and apes (including humans). It was less clear whether the ancestor of the other primates — lemurs, lorises, and tarsiers — masturbated, largely because data was sparse for these groups.
To understand why evolution would produce this apparently nonfunctional trait, Brindle and his colleagues tested various hypotheses.
The “postcopulatory selection hypothesis” proposes that masturbation aids successful fertilization. This can be accomplished in several ways. First, masturbation (without ejaculation) can increase arousal before sex. This can be a particularly useful tactic for low-ranking males who are likely to be interrupted during copulation, helping them ejaculate faster. Second, masturbation (with ejaculation) allows males to expel lower-quality semen, making fresh, high-quality sperm available for mating, which is more likely to outperform that of other males. The researchers found support for this hypothesis, showing that male masturbation has evolved alongside with multi-male mating systems where competition between males is high.
The “pathogen avoidance hypothesis” proposes that male masturbation reduces the chance of contracting an STI after intercourse by cleansing the urethra (a major site of infection for many STIs) with ejaculate obtained through masturbation. The team also found evidence in support of this hypothesis, showing that male masturbation coevolved with a high burden of STIs in the primate tree of life.
The meaning of female masturbation remains less clear. Although it is common, there are fewer reports describing it, which decreases the analytical power of the statistics. The team argues that more data is needed on female sexual behavior. to better understand the evolutionary role of female masturbation.
Brindle said: “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 fact that autosexual behavior may have an adaptive function is pervasive throughout the order of primates, and is practiced by both captive and feral members of both sexes, demonstrates that masturbation is part of a repertoire of healthy sexual behaviors.”
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