Spontaneous nocturnal erections and masturbation in captive male chimpanzees (Pan troglodytes)

Abstract Nocturnal penile tumescence (NPT) has been reported for males of only a few mammalian species, including humans, albeit this scarcity might be an artefact the difficulty documenting it. We investigated NPT in 12 adult male chimpanzees living all-male group at Kumamoto Sanctuary, Japan. Recorded non-invasively with infrared video cameras across 72 nights (6 per individual), we observed two thirds individuals (8/12), events total. More than three quarters occurred during transition from sleep to wakefulness, suggesting may associated rapid eye movement sleep, similar humans. Masturbation conjunction NPT, likely consumption ejaculate, 4–6 individuals. While detailing nocturnal erections help us better understand robust physiological phenomenon further comparative research is necessary reconstruct its phylogenetic history. At present, our findings support hypothetical functional explanations such as facilitation emissions order increase ejaculate quality or tissue oxygenation prevent erectile dysfunction.