Biological Exuberance: Animal Homosexuality and Natural Diversity

A hallmark of human cultural evolution was the development of tools, later elaborated into the full array of material technologies that we know today. But many animals, especially primates, also use inanimate objects to manipulate or affect things in their environment in ways that can be seen as precursors to similar activities in human beings. Over 20 different types of tool use have been identified in primates and other species—Common Chimpanzees, for example, employ objects as weapons, as levers, and as drinking and feeding implements of various sorts (such as the well-known example of sticks being used to capture and eat termites or ants). Tools can also be used to affect an animal’s own (or another’s) body, for example as part of a “hygiene” or grooming regimen. Chimpanzees and other primates, for example, often use leaves, twigs, straw, rags, or other objects to clean themselves and wipe away bodily secretions (such as saliva, blood, semen, feces, and urine). Chimps and Savanna Baboons have also been observed using sticks, twigs, and stones to clean their own or each other’s teeth (and even perform dental extractions). Chimps also sometimes tickle themselves with various items such as stones or sticks, and Japanese Macaques occasionally use similar items to groom one another.⁶⁰

Less well known, however, is the use of objects for purposes of sexual stimulation. A number of primates employ various implements as masturbatory aids (in both the wild and captivity), and this aspect of tool culture has not received widespread attention in discussions of the development of animal and human object manipulation. Female Orang-utans, for instance, sometimes masturbate by rubbing objects on the clitoris or inserting them into the vagina; tools used for this purpose include pieces of liana bitten off to an appropriate size or (in captivity) pieces of wire. Male Orangs also use objects to stimulate their genitals, including one individual who ingeniously fashioned an implement by pushing a hole through a leaf with his finger. He inserted his erect penis into this “orifice,” then rubbed the leaf up and down the shaft to stimulate himself. Males also sometimes hold a piece of fruit (such as an orange peel) in their hand and masturbate against it.⁶¹

A female Orang-utan in the forests of Sumatra masturbating with a tool she made from a piece of liana

Common Chimpanzees have also developed several innovative masturbation techniques using a variety of different tools. One female gathered a small collection of sticks, pebbles, and leaves, from which she would carefully select a particular item to stimulate herself with. By placing a leaf underneath her vulva, for example, and flicking the stem with her knuckle, she made the leaf vibrate and thereby externally stimulate her genitals. She also repeatedly inserted the stem into her vagina, often lubricating it with saliva and manipulating it with her hand so as to stimulate herself internally. In one instance, she rocked back and forth with the stem inserted, rubbing the leaf against a vertical surface so that the stem actually vibrated inside her. On other occasions, she repeatedly inserted and withdrew a pebble from her vagina or used a small stick to stimulate her genitals. Other female Chimps have also been observed rubbing or tickling their external genitals with items or inserting them into the vagina, including pieces of mango, twigs, and leaves, as well as man-made objects such as small boxes or balls. Similarly, several young males assembled collections of stones, fruits, or even pieces of dried dung, which they would thrust against to stimulate their genitals. Male and female Bonobos occasionally employ inanimate objects for masturbation as well, stimulating themselves with (or thrusting against) branches, wood shavings, and other items.⁶²

Like Orang-utans, one female Bonnet Macaque invented some relatively sophisticated techniques of tool manufacture, regularly employing five specific methods to create or modify natural objects for insertion into her vagina. For example, she stripped dry eucalyptus leaves of their foliage with her fingers or teeth and then broke the midrib into a piece less than an inch long. She also slit dry acacia leaves in half lengthwise (using only a single half) and fashioned short sticks by breaking longer ones into several pieces or detaching portions of a branch. Implements were also sometimes vigorously rubbed with her fingers or between her palms prior to being inserted into her vagina, and twigs, leaves, or grass blades were occasionally used unmodified.⁶³