When sex means reproduction, certain proclivities may simply not be part of cultural models of sexuality.
Barry and Bonnie Hewlett had been studying the Aka and Ngandu people of central Africa for many years before they began to specifically study the groups' sexuality. As they reported in the journal African Study Monographs, the married couple of anthropologists from Washington State University "decided to systematically study sexual behavior after several campfire discussions with married middle-aged Aka men who mentioned in passing that they had sex three or four times during the night. At first [they] thought it was just men telling their stories, but we talked to women and they verified the men's assertions."
In turning to a dedicated study of sex practices, the Hewletts formally confirmed that the campfire stories were no mere fish tales. Married Aka and Ngandu men and women consistently reported having sex multiple times in a single night. But in the process of verifying this, the Hewletts also incidentally found that homosexuality and masturbation appeared to be foreign to both groups.
A woman who is already pregnant will see having intercourse as contributing to the health of her fetus.
While the Aka and the Ngandu live in the same general region, an area in central Africa marked by tropic forest, their cultures are distinct. The Aka are foragers and, according to the Hewletts, "gender egalitarianism among the Aka is about as pronounced as human societies get." Women may hunt, even on their own, and often control distribution of resources. The Ngandu, by contrast, are slash-and-burn farmers with stable locations and significant gender inequality, with men typically dominating over women.
What the Aka and Ngandu have in common, besides geography, is this: In both cultures, men and women view sexual intercourse as a kind of "work of the night." The purpose of this work is the production of children -- a critical matter in an area with a very high infant mortality rate. Semen is understood by the Aka and Ngandu to be necessary not only to conception, but also to fetal development. A woman who is already pregnant will see having intercourse as contributing to the health of her fetus.
The Aka and Ngandu speak of sex as "searching for children." That's not to say they don't enjoy having sex. Clearly they do. The Hewletts relay a song a group of children invented after stealthily watching two lovers having sex. In the song, the man asks, "How do you want it?" and the woman answers, "Oh, I want it big." The man asks again, and the woman answers, "Oh, I want it long." The song then enters a refrain with the man thrusting and asking his partner, "Did you come?"
But while the individuals the Hewletts interviewed -- like the song -- made it clear that sex is pleasurable for these folks, and something that brings couples closer, they also made clear that babies are the goal of sex. Said one Aka woman, "It is fun to have sex, but it is to look for a child." Meanwhile, a Ngandu woman confessed, "after losing so many infants I lost courage to have sex."
Is the strong cultural focus on sex as a reproductive tool the reason masturbation and homosexual practices seem to be virtually unknown among the Aka and Ngandu? That isn't clear. But the Hewletts did find that their informants -- whom they knew well from years of field work -- "were not aware of these practices, did not have terms for them," and, in the case of the Aka, had a hard time even understanding about what the researchers were asking when they asked about homosexual behaviors.
The Ngandu "were familiar with the concept" of homosexual behavior, "but no word existed for it and they said they did not know of any such relationships in or around the village. Men who had traveled to the capital, Bangui, said it existed in the city and was called 'PD' (French for par derriere or from behind)."
Given all this, the Hewletts conclude, "Homosexuality and masturbation are rare or nonexistent [in these two cultures], not because they are frowned upon or punished, but because they are not part of the cultural models of sexuality in either ethnic group."
The finding with regard to homosexuality is perhaps not that surprising. As the Hewletts note, other researchers have documented cultures where homosexuality appears not to exist. If homosexual orientation has a genetic component to it -- and there is increasing evidence that it does, in many cases -- then it would not be surprising that this complex human trait (one that involves non-procreative efforts) would be found in some populations but not others.
Moreoever, sexual behavior -- whether homosexual, heterosexual, or any other type -- is never simply genetically determined in humans. Humans are born with sexual potentials that will manifest differently in different cultural settings. So, about heterosexuality, the Hewletts note that Western cultures' valuing of sleeping through the night probably limits Western heterosexual couples' interest in having sex multiple times between dusk and dawn. In our culture, the work we have to do by day may overtake "the work of the night."
It's also worth noting that Western science specifically distinguishes between three components of sexuality: desire, behavior, and identity. While the Hewletts' research suggests that homosexual behavior and identity are foreign to the Aka and Ngandu, it's entirely possible that homosexual desire does exist in these groups, at least for some of their members (so to speak). A culture that recognizes such desires -- and especially a culture that does not condemn them -- and especially one that involves large groups where homosexually-inclined people can find each other -- is the type where such desires will become openly apparent.
When I put this to the Hewletts, they replied that indeed, the desire may exist in some individuals in these groups, but we simply do not know. They added that although the Aka and Ngandu live in small groups, "They travel extensively and our studies suggest each person knows about 400-500 individuals," which means that, theoretically, a person with homosexual desires might find another person with the same. But in a culture in which the general idea of a desire doesn't exist, such a desire might remain unarticulated, even if two people who share it find each other.
The absence of masturbation among Aka and Ngandu men and women may be more surprising, and perhaps also harder to explain. Recall that the Hewletts did not find that masturbation is "frowned upon or punished," but rather that there is just no general conception of it. This finding recalls a much-discussed 2010 Behavioral and Brain Sciences paper called "The WEIRDest people in the world?" in which the authors argued that far too many sweeping claims about "human nature" are drawn exclusively from samples of Western, Educated, Industrialized, Rich, and Democratic (WEIRD) societies.
Studies of small-scale, rural, non-Western cultures like the Aka and Ngandu paint a more complicated picture of human variation. The Hewletts remark that, "the Western cultural emphasis on recreational sex has ... led some researchers to suggest that human sexuality is similar to bonobo apes because they have frequent non-reproductive sex, engage in sex throughout the female cycle, and use sex to reduce social tensions." But, the Hewletts suggest, "The bonobo view may apply to Euro-Americans (plural), but from an Aka or Ngandu viewpoint, sex is linked to reproduction and building a family." Where sex is work, sex may just work differently.