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Although masturbation is prevalent in the animal world – especially in primates, including humans – masturbation has long been considered more of a byproduct of sexual arousal. Now, researchers have found that masturbation could also serve an evolutionary purpose. At least in males, the research suggests, it may have been an ancient trait that increased reproductive success and helped prevent sexually transmitted infections. The results were published in the journal "Proceedings of the Royal Society".

The scientists analysed almost 400 sources, including 246 published scientific papers as well as 150 questionnaires and personal communications from primatologists and zookeepers. They wanted to find out when and why masturbation developed in male – and female – primates.

The result: Masturbation has a long evolutionary history in primates, probably common ancestors of all apes and apes, including humans, masturbated. For the question of "why", the researchers provide hypotheses:

  • "Post-copulatory selection hypothesis": Masturbation could promote successful fertilization, for example by increasing arousal before sex – if there is no ejaculation. Especially for low-ranked males who could be interrupted during intercourse, it could be a useful tactic for faster ejaculation. But the researchers also see an advantage in masturbation with ejaculation: males with inferior sperm could reject it, so that fresh, higher-quality sperm could be used in mating. Male masturbation has reportedly evolved in mating systems where competition between males is fierce – which could support the hypothesis.

  • "Pathogen avoidance hypothesis": Male masturbation could reduce the likelihood of contracting sexually transmitted diseases after sexual intercourse by cleaning the urethra. The researchers found evidence for the hypothesis that male masturbation developed with a high burden of sexually transmitted diseases throughout the primates' tree of life.

Little is known about female masturbation

While there are various theories for the development of male masturbation, the meaning of female masturbation is unclear. Although it is also common, there are much less conclusive reports that allow clear conclusions to be drawn about its evolutionary purpose. Further data is needed, the researchers write.

Ani