Even more significantly, Bonobos devised this system spontaneously: they invented the hand signals on their own and were not taught to use them by people. Attempts to teach apes various forms of human sign language or other communication systems have demonstrated that our primate relatives in many instances possess formidable linguistic capacities, but in all cases human prompting and intervention (at least initially) are involved. What is unique about the sexual gestures is that Bonobos themselves developed the hand signals and taught them to each other (or learned them from one another), in response to a communicative need that arose naturally within their own social interactions.57 Moreover, the specific social context that prompted this development is also unique: it was sexual behavior, or rather, the highly variable and plastic nature of Bonobo sexuality, that led to this development. Because of the wide variety of heterosexual and homosexual activities that characterize Bonobo sexual interactions, a supplementary communication system arose to help negotiate sexual interactions. In response to an unsurpassed sexual capacity in this species—including prominent homosexual activities—an unsurpassed animal communication system was created.
Not only is the Bonobo gestural system an outstanding example of the spontaneous development of cultural traditions in animals, it offers some clues into the origin of the human linguistic capacity. A number of theorists have suggested that the first human communication system may indeed have been a gestural language, that is, a system of hand signals.58 Why language should have evolved in the first place among human beings, however, is a subject shrouded in mystery and controversy. Of the many theories that have been put forward, a number suggest that language developed in response to social factors, such as the need to coordinate complex group activities such as hunting or farming. The Bonobo system demonstrates that another factor may also have been involved—one that is rarely, if ever, considered in discussions of the origin of language: sexuality. In particular, as sexual interactions became more variable over the course of evolution, gestural systems of greater complexity may have developed to facilitate sexual encounters.
Primate evolution has been characterized by an ever-increasing separation of sexuality from its reproductive “functions,” including the development of numerous types of homosexual and nonprocreative heterosexual activities—most prominent in human beings and Bonobos (considered by some to be the primate most similar to humans), less so in Common Chimpanzees, Gorillas, and other apes. Scientists have also identified a corresponding increase in complexity of communication systems used during sexual interactions among apes, proceeding from Gorillas to Common Chimpanzees to Bonobos (and onward, of course, to human beings).59 The progression is probably not quite as orderly as this sequence suggests, and multiple factors are surely involved in the genesis of each species’ particular communication systems. The general trend, however, is clear: as sexual interactions become more variable, sexual communication systems become more sophisticated. It is possible, therefore, that sexuality—particularly the fluidity associated with nonreproductive sexual practices—played a significant role in the origin and development of human language.
Tools
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