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Human couples usually have sex in private, hidden not only from predators, but also - other humans. It is unlike behavior of most species, including our relatives: bonobos, chimpanzees and gorillas.

Is private sex mostly a biological or cultural behavior? What is the advantage (if any) of such behavior?

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Interesting question. I'm not an expert on this, but maybe it is a kind of non-dominant mating strategy. In social animals, the dominant "alpha" males typically control reproductive access to females and non-dominant males sometimes develop strategies to circumvent this control. Maybe limiting sex to private is one of those strategies -- if it's in private the alpha male has less chance to stop it. Is there any evidence that any other species do this? –  Dan M. Aug 21 '12 at 17:40
Another possibility (but I don't dare propose an answer): humans try to avoid competition in physical terms, so as to focus on intellectual and cultural features. We don't show our sexual endowment in public, so as sexual partners are chosen with other criteria, which are more relevant to the long-term evolution of the species. –  Javier Rodriguez Laguna Aug 22 '12 at 17:46
The BBC has a nice show called What’s the Problem with Nudity?. It has some very interesting hypothesis on why people don't like being nude, and it is difficult to have sex with out being nude. –  Allen Morris Aug 23 '12 at 5:09
@Tiberiu-IonuțStan: Are you saying that people don't have sex in public merely because there are laws for it? Do you think that general unwillingness of majority of population to not have sex in public is driven entirely by this factor? If that would be the case, we would live in an utopian paradise, where nobody steals, kills and rapes, because we have laws for it. I think you are missing the point here big time. Those laws are there because over time some factors caused us to create them. Here we are trying to hypothesise what were those factors. –  Geek On Acid Aug 23 '12 at 11:30

5 Answers 5


It is interesting and quite under-researched topic in psychology. What has been studied and definied extensively are different abnormal sexual behaviours, and exhibitionism is one of them. In the DSM-IV exhibitionism is defined as sexual arousal by revealing one's body or performing sexual acts in public and it's a form of paraphilia. Attraction to being watched by others during sexual intercourse is a form of exhibitionism called martymachlia. Presence of such sexual behaviours in DSM-IV is a clear indication that majority our society have deeply enrooted social and moral norms regarding inhibition sexual behaviour in public. If you think about it, majority of countries bans public sex and limits exhibitionism to designated places (nudist beaches and nudist colonies).


Following valid and constructive comments by @Piotr and @Preece I removed speculative part of my answer about cultural factors and expanded my answer arguing for evolutionary explanation.

Territorial mating behaviour in animals

Initially I should point out that you are not exactly right in saying that 'most species don't practice private sex'. It's true that many primates do that. But we can argue that some territorial behaviours in animal kingdom are a form of providing security during mating. Those behaviours are very common in animal world including lizards (Davis, 1980), birds (Brown, 1969; Greenwood, 1980) and mammals (Greenwood, 1980).

Evolutionary development of shame

@PiotrMigdal specified that he is mainly interested in the issue of "unwillingness to have sex in public". We can trace the origin of such 'unwillingness' to the sense of shame that could be explained from evolutionary standpoint. Darwin (1872) argued that shame represents what would be at the primitive level an instinctive seeking for cover, but his elaboration on this wasn't clear. MacCurdy (1930) took this idea further. He argued that prehistoric man sought concealment for activities which expose him to danger in a hostile environment, e.g., eating, sleeping, sexual intercourse and excretion (Maccurdy, 1930). Concealment was sought prior to the fulfilment of any act that would limit or prevent rapid self-defence. For example, Maccurdy (1930) boldly pointed out that postures during both sexual intercourse and excretion prevents people from rapid self-defence.

Malinowski (1927) writes that:

it is characteristic that sexual activities, sleep and excretion are surrounded by protective taboos and mechanisms of concealment and isolation in almost every society.

In this context, the sense of shame could have developed as a response to natural drive for self-protection (Dawrin, 1872; Maccurdy, 1930). Therefore, evolutionarily this would form the basis of unwillingness of having sexual intercourse in public.

Because personal security increased with the development of civilisation, the sense of shame has also transformed and became more sophisticated (Maccurdy, 1930). The shame exists only for specific situations (e.g. public sex), but it doesn't apply in other social conditions. Maccurdy (1930) gives examples with excretion, where it isn't uncommon for partners to urinate in each others presence or in the presence of other friends. We can also put nudist beach in this 'shame-exclusion' category. Overall, evolutionary account would highlight that out need for private sex is related with growth for security, the extension of shame, and the evolution of modesty. Along the same line, Malinowski (1927) also points out that sexual intercourse in public could excite jealousy and would be an indicator to invite rivals to seize that which is being enjoyed.


  • American Psychiatric Association. (2000). "Diagnostic and statistical manual of mental disorders" (4th ed., text rev.).
  • Davis, J. (1980) "The times of mating and oviposition of the Western fence lizard S.o.occidentalis", J. Herpetol. 14:102
  • Brown, J. (1969) "Territorial behavior and population regulation in birds: a review and re-evaluation". Wilson Bull. 81:293-329.
  • Greenwood, P. J. (1980) "Mating systems, philopatry and dispersal in birds and mammals." Anim. Beha. 28, 1140-1162.
  • Darwin, C. (1872) "The Expression of the Emotions in Man and Animals." London: John Murray.
  • MacCurdy, J. (1930) "The Biological Significance of Blushing and Shame." British Journal of Psychology, 21, 174-182.
  • Malinowski, B. (1927) "Sex and Repression in Savage Society." London: Kegan Paul, Trench, Trubner & Co.
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Thanks, you rise a few good points. However, my question is not on sexual norms, but unwillingness to have sex in public. –  Piotr Migdal Aug 21 '12 at 19:57
Yet, private sex seems to transcend individual cultures. Not in an absolute way, but there is a definite trend. I like that you go to Exhibitionism as part of your explanation, I think that could be fruitful. But your answer right now is mostly just a guess. –  Preece Aug 22 '12 at 1:03
The argument that people prefer to have sex in privat in order to protect themselves when they are helpless does not convince me. Especially the analogy to other activites limiting the possibility of self-defence like sleeping or eating is not appropriate (in my opinion), because people commonly take the latter two activities in presence of other trusted people (to feel safer?), while having sex in presence of friends and family would be even more embarrassing (correct me if it is seen different in any other culture). –  Marta Cz-C Aug 31 '12 at 18:27

This is a fascinating question. According to Donald Symons (1979) "The evolution of human sexuality", it is a species specific adaptation that seems to be universal across cultures. Symons argued that having sex in private underlines the exclusivity of the relationship between monogamous couples. This theory does assume that sexual exclusivity is a universal feature of human relations. On the other hand, Ryan & Jethá (2010) "Sex at Dawn" argues that humans are not by nature sexually exclusive, although I don't think they explained why people around the world generally have sex in private.

There are instances, of course, where people have sex more openly. For example, I think it was Captain Cook or someone like that who described scenes in Tahiti where people were having sex while their neighbours looked on. But I don't know if this was considered usual behaviour in Tahiti or if there was some special context, such as it being part of a special ceremony where the usual expectation of privacy was relaxed.

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can you dig up a reference for the Cook example? Also, the second book you cite seems to have very mixed reception among academics, do you have a more authoritative source? –  Artem Kaznatcheev Aug 22 '12 at 18:14

Just a very brief note: in some cultures, sex does not appear to have been confined to private space. One article on the subject reads:

In fact, it seems that much of Athenian love life took place in public places: many vases show how people are looking when two people are having intercourse. There is not a single written statement that people objected to public sex.

Afther this remark, the author suggests a possibility that "the vases are just as unrealistic as modern pornography" but also offers a way to counter that claim. There is a little more on that subject in the article itself. My guess is that such cultural differences would render a purely evolutionary approach rather hopeless – although I do not have enough expertise in the field to verify the cited claim.

As one might expect, there is some literature concerning similar problems in the humanities. I suppose it could be of use here. However, not being well acquainted with the subject matter, I can only point out two names: Michel Foucault and Anthony Giddens. There is probably more to be found if one digs deep enough.

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@Stanislaw could you include the relevant quote (which I assume is what Piotr quoted) in your answer to make it self-contained? Also, is there a reason to believe that the website you are linking is an authority on ancient Greek culture? There is a lot of misinformation about such things on the web, we wouldn't want to be a source of further. –  Artem Kaznatcheev Aug 22 '12 at 18:08
Thanks for the comments, I have tried to improve my note a bit (and it stopped being very brief, I presume). Like I said, I am not an expert, so I am also softening the tone of the note. (Also, Artem, thank you for bringing some order into it!). –  Stanislaw Krawczyk Aug 22 '12 at 18:29

In chimpz, we see stronger chimps beating up weaker chimps that have consensual sex.

Basically sex is not a purely consensual matter among chimps. It's to the best interest of stronger males to prohibit weaker males from entering mating market especially if the weaker males are more attractive. In gorilla, sex is not about consent at all. The stronger Gorilla beat the hell out of weaker gorilla and get all the girls.

If you are a very attractive weaker chimps, what would you do?

You do it in private.

In humans, sex is also not purely consensual. There are so many rules created by more politically powerful humans to prevent weaker humans from having sex.

In fact, it doesn't really matter what the terms are. Someone somewhere somehow will have incentive to hurt you for having sex. I mean, if you get a hot girl, for example, her ex boyfriend would want you death.

The most obvious way to avoid conflict is then to hide your success and have sex in private.

The more a society is based on consent instead of force, the less you have to worry about other seeing you getting the hot mates. Those societies will have more public sex & porn etc.

Or lets' put it this way:

What do you get for having sex in public?

  1. Other girls got impressed with your size and want you too? Not applicable for most males.
  2. You like fresh air?

There isn't much benefit.

What can go wrong?

  1. You can get mugged, robbed, raped, while naked.
  2. People know you don't have gun with you.
  3. Knowledge is power. If people know too much about you, that's usually bad.
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It sounds plausible, but do you have any reference to back it? (Also, while it is not an official requirement, slightly more formal style is being preferred. (E.g. less rhetorical questions and colloquialisms.)) –  Piotr Migdal Dec 25 '13 at 20:09
Well, ugh, common sense. Not good enough? Evolutionary psychology, which I think is common knowledge. I mean I am a mathematician. I don't refer to paper. If there is simple theory that can correctly predict stuffs in ways that make sense I say it. My answer is similar with the highest voted answer. It's based on reasoning rather than empirical studies. –  Jim Thio Dec 26 '13 at 3:54
Well, things like "we see stronger chimps beating up weaker chimps that have consensual sex" are factual statements (so referencing them would be desirable). In evolution it is easy to come up with a solution, but hard to check if it is actually correct (opposite of mathematics); plus, in empirical sciences reasoning without empiricism does not work. (But sure, there is no "no original research" policy, so of course, you are encouraged for your writing your hypotheses.) –  Piotr Migdal Dec 26 '13 at 11:20

The answer has its roots in the evolution of human morality and disgust. I'll point to Steven Pinker for this one -- "Disgust is intuitive microbiology". Sex is among the list of topics that elicit disgust, like spoiled food, bodily waste, poor hygiene, death, infection, inbreeding, etc, and these emotional reactions evolved to avoid diseases. We excrete our waste in private, we have sex in private, we keep our infections covered.

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I'm not convinced. People are not disgusted by looking at other's having sex (unless they are their parents, which is a different story). –  Piotr Migdal Aug 22 '12 at 16:18
@DavidWiner if it is obvious, then humor us by providing a reference. Also, tone is hard to judge from comments, so try to avoid potentially rude statements. –  Artem Kaznatcheev Aug 22 '12 at 18:15
To those who grow up in a nudist colony, nudity does not elicit disgust or shame. Even in ugly people. –  Preece Aug 22 '12 at 18:42
Anyway, why so downvoted? While I'm not convinced, the answer is far from from being "not useful". (Perhaps a long time ago sex was dirty.) –  Piotr Migdal Aug 23 '12 at 8:09
This doesn't explain why humans behave differently than other species on the topic. –  Christian Dec 18 '13 at 0:44

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