Unlike other species, humanity has devised a whole suite of ways to make sex private, concealed, indeed clandestine.
Despite counter-currents from modern swingers parties back to Roman orgies, most human societies keep sex private. Of course many conservative societies impose moral laws on modesty which invoke severe punishments such as stoning for adultery and stipulate dress codes which cover all their feminine features, not just their sexual organs, from the fig leaves of genesis on down. But why is this? Why do married people still keep their sex private from others when as long as they remain faithful, it should't matter if they have sex with one another in public? In fact in many ways, if we insisted sex was made in public, we would have a much better idea of who was having sex with who and keep better track of assumed infidelity.
So is this something men have imposed on women as one might assume from the ways Muslims and many other conservative religions try to cover up women so no other man can see them and chaperone them with relatives so they have no personal freedoms at all, all the time threatening them with dire punishments if they transgress?
On the other hand one can see why women might want to keep sex private under these constraints too because it avoids them becoming vulnerable to accusations of infidelity, or siring an offspring with an alien man in a moment of love, passion or the allure of superior genes or exotic complementary histcompatability antigens as human pheromone tests have shown women are very sensitive to for reasons of providing their offspring with improved immunity to disease.
Named and Shamed. An adulterous couple put on public display in Japan.
So is sexual secrecy driven by men or women or both? Sexual privacy in humans is a complex process which seems to be a combined product of both male and female strategies.
In primates, where there is strong male competition, such as orangutans and gorillas, alpha males copulate openly, but subordinate males are so discrete that no one realized they did at all until genetic paternity testing came along. Female dominated bonobos by contrast have sex openly, while chimps have an overt estrus in which the dominant male clan have sex openly, but females may also go on discrete safari with select males.
Humans have a complex sexual history. Although like most apes, most human societies are female exogamous so the females 'migrate' to the male's extended family, and men have traditionally struggled zealously to control female reproduction, out of a fear of paternity uncertainty, women have won a good degree of control from men by evolving concealed ovulation and continual sexual receptivity to confuse paternity and enable female reproductive choice to operate (Ethology and Sociobiology, vol 14, p 381). Female reproductive choice, after all is the principal form of genetic selection among mammals where females have a vastly higher parenting investment in live offspring, lactation and in humans long-term child rearing, which gives the females an incentive to be very choosy about who they sire with and also to seek privacy for sex to give more freedom of choice of lovers without consequences such as infanticide, or losing the support of a husband for their children.
Paradoxically Jesus decried divorce but forgave adultery.
Humans have also evolved to engage in pair-bonded parenting, with the emotional bond of love entering into the sexual equation and the stakes becoming even higher for discovery of infidelity.One can also see reasons why males might also want to keep sex private to avoid resentment and competition from other males who they might need to be in coalition with to preserve positions of power. For human males sex becomes a precious commodity and to avoid jealousy and envy for one's own male mates it is easier to be discrete in the same way people conceal food in a time of famine.
Thus it looks like the female and male reproductive strategies, although differing vastly in terms of reproductive investment, both come together in favoring clandestine sex for paradoxical reasons.Clandestine copulation thus becomes a unique and intriguing male-female trade-off, in which relationships are strengthened, but infidelity becomes easier, enabling us to be socially monogamous but not sexually monogamous in a context where frequent social sexuality is the emotional glue of familial romantic and erotic relationships (See also: Human nature: Being clandestine New Scientist 23 April 2012 Bob Holmes and Kate Douglas).