Nothing reveals an animal鈥檚 nature quite as well as its sexual practices, and humans certainly have some strange ones 鈥� even from a biological point of view. Woman are continually receptive and have concealed ovulation 鈥� that is, there is no external sign that they are in a position to conceive. We are the only monogamous primate to live in large mixed-sex groups 鈥� more about these later. But surely nothing is quite as puzzling as our predilection for clandestine copulation. Why do humans have sex in private?
This coyness is not just the consequence of particular cultural or moral views. 鈥淚t is the rule across all kinds of human societies,鈥� says cultural anthropologist Frank Marlowe of the University of Cambridge. There is the odd case of public ritual sex, such as orgies among the Canela of Brazil. But where there is no alcohol 鈥� as would have been the case in the past before agriculture 鈥� sexual privacy is the norm. What is going on?
鈥淚n the context of other primates it鈥檚 very interesting,鈥� says Clive Wynne of the University of Florida, Gainesville. Sneaky mating occurs in species where there is a lot of inter-male competition and males control sex by controlling females, he says. Among orang-utans, alpha males copulate openly but subordinates are so discreet that nobody realised they mated at all until the advent of genetic paternity testing. The situation is similar for gorillas. In bonobos, by contrast, females control the show and sex is a free-for-all. 鈥淚鈥檝e never seen anything that resembles privacy in bonobos,鈥� says Frans de Waal of Emory University in Atlanta, Georgia. 鈥淚 think the origin of privacy [in humans] has to do with competition.鈥�
Advertisement
Nevertheless, human sexual politics has become a lot more complicated since then. For a start, women won some control from men by evolving concealed ovulation and continual sexual receptivity to confuse paternity (). Then our ancestors did something completely different from other great apes 鈥� males and females started sharing parental care. Monogamy was born. Now, infidelity among pairs living in large groups became more risky than ever, with infanticide by males the ultimate price, says Robin Dunbar of the University of Oxford. So there was a need to strengthen the pair bond. 鈥淲e have this odd thing called love,鈥� he notes, adding that privacy may also have emerged as a way to increase intimacy.
Dunbar sees clandestine copulation as a trade-off, because as well as strengthening relationships it makes infidelity easier. David Buss of the University of Texas at Austin thinks that could actually be a benefit. 鈥淗umans are socially monogamous, not sexually monogamous,鈥� he says. Infidelity is widespread in all traditional cultures and private sex allows it to occur without loss of reputation. Another very human trait, envy, may also play a part. In his landmark book, The Evolution of Human Sexuality (Oxford University Press, 1981), anthropologist Donald Symons suggests that since men can never get enough of it, sex is a precious commodity and therefore best enjoyed covertly to avoid inciting covetousness.
鈥淚nfidelity is widespread and private sex allows it to occur without loss of reputation鈥�
鈥淭his is for the same reason that during a famine anyone with food is likely to consume it in private,鈥� says Steven Pinker of Harvard University. 鈥淎 sexual act, even among consenting adults, has a high probability of upsetting someone,鈥� he adds. Parents or community members may disapprove and for children it can lead to the creation of rival siblings. So perhaps clandestine copulation simply follows the precautionary principle. 鈥淵ou can鈥檛 be too careful,鈥� Pinker says.
