News Release

Chimps, dreams, and videotape

Coincidental discovery of spontaneous nocturnal erections in chimpanzees

Peer-Reviewed Publication

Kyoto University

Nocturnal erection in chimpanzees

image: Infra-red cameras caught images of nocturnal chimpanzee behavior view more 

Credit: Kyoto University

Kyoto, Japan -- KyotoU researchers have discovered a physical phenomenon that previously was only observed in human males. 

We now learn that chimpanzees are among the league of early risers. Researchers recording and analyzing the sleep patterns of captive male chimpanzees using infrared cameras noticed that some males were frequently experiencing nocturnal erections.

"Until now, spontaneous nocturnal penile tumescence, or NPT, had not been recorded in any primates. We had only assumed its occurrence," says lead author Kristin Havercamp.

When the scientists began their analysis, they realized that they had caught this physiological phenomenon on tape, sometimes followed by masturbation and the ingestion of ejaculate.

"Masturbation by primates has already been described in numerous reports because it is observable during the daytime," Havercamp adds. 

The team, including primate sexuality experts at University College London, found that eight out of a dozen observed male chimpanzees demonstrated NPT. Additionally, of these eight, half were recorded masturbating and consuming the resulting ejaculate. This latter behavior has also been observed in other primates, which scientists speculate supplement the regular diet with essential minerals and other nutrients. 

The researchers also recorded -- perhaps for the first time -- one possible case of spontaneous ejaculation in the form of a 'wet dream'. 

As to the cause of NPT, the authors posit that this physiological function may maintain sexual health, either optimizing ejaculate quality or increasing oxygenation in genital tissue, thus preventing erectile dysfunction.

"Uncovering nocturnal erections and masturbation in chimpanzees may help us better understand similar behavior in male humans," concludes Havercamp.


The paper "Spontaneous nocturnal erections and masturbation in captive male chimpanzees (Pan troglodytes)" appeared 10 May 2022 in Behaviour, with doi: 10.1163/1568539X-bja10166

About Kyoto University

Kyoto University is one of Japan and Asia's premier research institutions, founded in 1897 and responsible for producing numerous Nobel laureates and winners of other prestigious international prizes. A broad curriculum across the arts and sciences at both undergraduate and graduate levels is complemented by numerous research centers, as well as facilities and offices around Japan and the world. For more information please see:

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