Masturbation with a Tool by an Infant Male Chimpanzee

Masturbation with a Tool by an Infant Male Chimpanzee. Michio Nakamura. Graduate School of Science, Kyoto University, Japan. http://mahale.main.jp/PAN/2018/001.html

INTRODUCTION

Here I report a case of “masturbation” with a tool by a wild infant chimpanzee. More accurately, the infant male inserted his erect penis into a wadge discarded by an adult male and performed several thrusts, as if he was copulating with the wadge. The observed “masturbation” did not involve ejaculation, because infant chimpanzees are unable to ejaculate. A similar behavior, i.e., rubbing the penis against a piece of fruit (e.g., orange peel), was reported for infant male orangutans in captivity (Harrison 1962). There are also some reported cases of captive or rehabilitant orangutans and chimpanzees stimulating their own genitals with tools (Dixson 2012).

Masturbation, or self-stimulation of one’s own sexual organs, is common among humans and nowadays is regarded as useful for healthy sexual development (Kaestle & Allen 2011). Various nonhuman primates are also known to masturbate (Thomsen et al. 2003; Dixson 2012; Thomsen & Sommer 2015); therefore, it may be a phylogenetically ancient behavior. However, there are relatively few studies that focus on masturbation among nonhuman primates in the wild (Thomsen & Soltis 2004). Male chimpanzees (Pan troglodytes) are known to stimulate their own penises. Although Goodall (1989) noted that captive chimpanzees sometimes ejaculate by stimulating their own penises, it had not been observed to result in ejaculation in the wild conspecifics at Gombe. Similarly, at Mahale, it is common for males to “fumble with penis,” but without it culminating in ejaculation (Nishida et al. 1999). Such fumbling of penis is done usually by hand (and sometimes by foot), but, thus far, I have found no reports of such penile-stimulating behaviors with tools, at least in wild chimpanzee populations.