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
The use and manufacture of tools by primates is considered an important example of cultural behavior in animals, and a forerunner of the activities that are so widespread among human beings. Although many different forms and functions are evident in animal tool use, these examples show that nonreproductive sexual activities are part of the overall behavioral pattern: the primate capacity for object manipulation extends seamlessly into the sexual sphere. Apes and monkeys use a variety of objects to masturbate with and even deliberately create implements for sexual stimulation by cutting or forming materials such as leaves or twigs (often in highly creative ways). Similar types of activities occur among people, of course, and sexual implements of various sorts have a long and distinguished history in human culture. Dildos or phalli made of stone, terra-cotta, wood, or leather, for example, were used in ceremonial “deflowering” and fertility rites—as well as for masturbation and inducing sexual pleasure in a partner—in ancient Egypt, Rome, Greece, India, Japan, and Europe. Examples have been recorded from at least as far back as the Paleolithic through medieval times—including some biblical references—as well as in the ongoing traditions of many indigenous peoples throughout the world.64 However, few (if any) anthropologists have ever considered the possibility that sexual stimulation may have been a component of tool use among early humans or even played a part in the origin and elaboration of material culture. Of course, technological complexity is not the only measure of cultural development—some of the most complex linguistic and oral history traditions, for example, are to be found among the South African San peoples and the Australian Aborigines, whose material culture is relatively simple. And certainly many more “utilitarian” functions can be identified in the development of tool use among our human, protohuman, and primate ancestors. Nevertheless, the pursuit of sexual pleasure may have contributed, in some measure, to our own heritage as creatures whose tool-using practices are among the most polymorphous of any primate.
Taboo
The vast majority of human cultures prohibit sexual relations between people who are related. There is still ongoing debate among scientists as to whether this prohibition—commonly known as the incest taboo—is instinctual or learned. Regardless of the extent to which biological factors are involved, there are clearly strong social and cultural components to incest avoidance. Different human cultures and societies vary widely in how they define incestuous relations and to what extent such activities are both stigmatized and practiced. For example, although parental incest (father-daughter, mother-son) is prohibited in virtually all societies (yet still occurs, despite such prohibition, with varying frequencies), there is wider latitude regarding other blood relations. Cousin marriage is considered acceptable in some cases, unacceptable in others, while some societies make a further distinction between relations with cross cousins as opposed to parallel cousins—a biologically arbitrary distinction, since there is no evidence of any greater genetic “harm” in one form of cousin marriage than another. Brother-sister marriage was widely practiced in ancient Roman Egypt, and among the royal families of some central African and Balinese societies, ancient Incans, Hawaiians, Iranians, and Egyptians—in fact, Cleopatra is thought to have been the product of 11 generations of incestuous marriages within the Ptolemaic dynasty.65
Further evidence of a learned or cultural component to incest prohibitions relates to the role played by social familiarity as opposed to genetic relatedness in choice of partners. In our culture, sexual relations between adoptive or stepfamily members are generally frowned upon even though the individuals involved are not related by blood. Conversely, people who are genetically related but, because of social circumstance (e.g., separation at birth), are unaware of their biological connection may develop a relationship (at least until they learn of their relatedness). Other societies vary considerably in this regard: in the Israeli kibbutzim, for instance, unrelated individuals who are brought up together hardly ever marry one another. In contrast, a traditional form of Taiwanese marriage involved girls being adopted into families as children and then, on reaching adulthood, marrying their stepbrothers, although such marriages were considered less preferable than other arrangements. Among the Arapesh people of New Guinea, a similar practice of stepsister marriage was widely accepted and preferred.
The fact that homosexual relations are usually prohibited between related individuals also points to the importance of nonbiological factors in the incest taboo. In most human cultures that “permit” some form of same-sex eroticism, from contemporary America to indigenous tribes of New Guinea, the choice of homosexual partners is subject to distinctions of “kin” and “nonkin.” This is in spite of the fact that no children, and hence no potentially harmful genetic effects, can result from such unions. Typically the same restrictions are applied to homosexual as to heterosexual relations. In a number of New Guinean societies, however, slightly different kinship constraints regulate the choice of same-sex and opposite-sex partners. In fact, homosexual partners in some tribes are actually required to be more distantly related than heterosexual ones—the exact opposite of what would be expected if incest taboos were based solely on biological factors.66
This is significant, because most theories about the biological basis of the incest taboo focus on the potential for increased rates of birth defects and lower genetic variability as a result of inbreeding. Even for heterosexual relations, though, the evidence is not nearly as unequivocal as one would suppose: numerous studies of small populations that have practiced inbreeding for many generations reveal no deleterious effects, owing to the rapid elimination of genetic defects and subsequent stabilization of the gene pool.67 To adduce further evidence for a biological basis to the prohibition, scientists often point to the existence of “incest taboos” in animals. Ironically, though, many animal species actually show evidence of a “cultural” or “social” dimension to their avoidance of sexual activity between relatives that parallels the human examples—most notably among primates, and most notably involving homosexuality.
There is a great diversity of incestuous activity among animals, not only in the frequency and types of relations that occur but also in the degree to which such activity is avoided or pursued, in both heterosexual and homosexual contexts. Even among primates, many different scenarios and versions of “taboos” are found. In Rhesus Macaques, for instance, incest of any sort is not common although mother-son, brother-sister, and brother-brother relations do occur (some males actually appear to prefer mating with their mothers). In Gibbons, heterosexual incest (both parental and sibling) is sometimes practiced and homosexual relations are almost always incestuous, while both heterosexual and homosexual activity between siblings (or half-siblings) occurs in Gorillas. Most strikingly, several species appear to have developed systematic homosexual “incest taboos,” each with its own socially defined set of “acceptable” and “unacceptable” partners. In some cases, these restrictions differ significantly from those governing the corresponding heterosexual relations (as in some human populations).