<h2>Introduction</h2>
<p>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 <strong>exhibitionism</strong> is defined as <em>sexual arousal by revealing one's body or performing sexual acts in public</em> and it's a form of paraphilia. Attraction to being watched by others during  sexual intercourse is a form of exhibitionism called <strong>martymachlia</strong>. <a href="http://en.wikipedia.org/wiki/DSM-IV_Codes#Paraphilias" rel="noreferrer">Presence of such sexual behaviours in DSM-IV</a> 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).</p>
<p><strong>EDIT</strong></p>
<p><em>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.</em></p>
<h2>Territorial mating behaviour in animals</h2>
<p>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 <strong>territorial behaviours</strong> 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).</p>
<h2>Evolutionary development of shame</h2>
<p>@PiotrMigdal specified that he is mainly interested in the issue of &quot;unwillingness to have sex in public&quot;. We can trace the origin of such 'unwillingness' to the sense of <strong>shame</strong> 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 <strong>prehistoric man sought concealment for activities which expose him to danger in a hostile environment, e.g., eating, sleeping, sexual intercourse and excretion</strong> (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.</p>
<p>Malinowski (1927) writes that:</p>
<blockquote>
<p>it is characteristic that sexual activities, sleep and excretion are
surrounded by protective taboos and mechanisms of concealment and
isolation in almost every society.</p>
</blockquote>
<p>In this context, the <strong>sense of shame could have developed as a response to natural drive for self-protection</strong> (Dawrin, 1872; Maccurdy, 1930). Therefore, evolutionarily this would form the basis of unwillingness of having sexual intercourse in public.</p>
<p>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 <strong>need for private sex is related with growth for security, the extension of shame, and the evolution of modesty</strong>. Along the same line, Malinowski (1927) also points out that <strong>sexual intercourse in public could excite jealousy</strong> and would be an indicator to invite rivals to seize that which is being enjoyed.</p>
<p>References:</p>
<ul>
<li>American Psychiatric Association. (2000). &quot;Diagnostic and statistical
manual of mental  disorders&quot; (4th ed., text rev.).</li>
<li>Davis, J. (1980) &quot;The times of mating and oviposition of the Western
fence lizard <em>S.o.occidentalis</em>&quot;, J. Herpetol. 14:102</li>
<li>Brown, J. (1969) &quot;Territorial behavior and population regulation in
birds: a review  and re-evaluation&quot;. Wilson Bull. 81:293-329.</li>
<li>Greenwood, P. J. (1980) &quot;Mating systems, philopatry and dispersal in
birds and mammals.&quot;  Anim. Beha. 28, 1140-1162.</li>
<li>Darwin, C. (1872) &quot;The Expression of the Emotions in Man and
Animals.&quot; London: John  Murray.</li>
<li>MacCurdy, J. (1930) &quot;The Biological Significance of Blushing and
Shame.&quot; British Journal  of Psychology, 21, 174-182.</li>
<li>Malinowski, B. (1927) &quot;Sex and Repression in Savage Society.&quot; London:
Kegan Paul, Trench,  Trubner &amp; Co.</li>
</ul>

CC BY-SA 3.0
2015-03-27T14:32:20.460Z
It doesn't really make sense : leaving the safety of the group to mate somewhere else is not really safe, it's even a huge risk. For excretion I think the risks are balanced by the hygienic improvement of not spoiling the place where your group lives
agemO
CC BY-SA 3.0
2015-06-25T19:35:41.637Z
I think the "protection" happening in the case of sex is more to protect the couple from the group, rather than from outside predators. Its not just that it may invoke jealousy or cause others to want to join in, but it also gives onlookers the capability to disrupt or to cause harm to the relationship - (comments, teasing).
DoubleDouble
CC BY-SA 4.0
2018-09-26T05:16:38.713Z
@MartaCz-C Probably, only until you think those friends can reject you. And many people do.
rus9384
CC BY-SA 4.0
2020-11-28T13:46:32.207Z
I looked at the answers to this question and they all strike me as absolutely unsatisfactory given that they don't point out differences between humans and other primates. Seems like 1) better self-defence 2) avoiding inciting jealousy 3) support for exclusivity of monogamous relationships would make others primates also have sex in private but AFAIK this is not the case (source: Sapolsky). So maybe it's more like we have no clue why humans have sex in private?
nikkou
CC BY-SA 4.0
2020-11-29T00:23:21.910Z
@PiotrMigdal I would say the two are closely connected. I for some reason have a week sense of social obedience amd therefore don't see anything repulsive in the idea of public sex. Still from my realization that other people don't sjare the sentiment, I would not do it. But mostly I would say that's from cultural norms. For the starter, being naked in the public also is punishable, but in many tribes that's normal.
rus9384
CC BY-SA 3.0
2012-08-21T19:57:41.173Z
Thanks, you rise a few good points. However, my question is not on sexual norms, but unwillingness to have sex in public.
Piotr Migdal
CC BY-SA 3.0
2012-08-22T01:03:35.517Z
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
CC BY-SA 3.0
2012-08-31T18:27:35.680Z
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
CC BY-SA 3.0
2012-08-21T13:48:37.487Z
2012-08-23T01:49:37.063Z
2020-06-17T09:55:31.633Z
Geek On Acid
<p>This is a fascinating question. According to Donald Symons (1979) "<a href="http://en.wikipedia.org/wiki/The_Evolution_of_Human_Sexuality">The evolution of human sexuality</a>", 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 &amp; Jethá (2010) "<a href="http://en.wikipedia.org/wiki/Sex_at_Dawn">Sex at Dawn</a>" 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. </p>

<p>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. </p>

CC BY-SA 3.0
2012-08-22T18:14:07.373Z
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
CC BY-SA 3.0
2012-08-22T11:18:49.530Z
2012-08-22T18:12:18.407Z
2012-08-22T18:12:18.407Z
Scott McGreal
<p>Just a very brief note: in some cultures, sex does not appear to have been confined to private space. <a href="http://www.livius.org/ho-hz/homosexuality/homosexuality.html">One article</a> on the subject reads:</p>

<blockquote>
  <p>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.</p>
</blockquote>

<p>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.</p>

<p>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.</p>

CC BY-SA 3.0
2012-08-22T18:08:21.923Z
@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
CC BY-SA 3.0
2012-08-22T18:29:45.047Z
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
CC BY-SA 3.0
2012-08-22T17:29:39.580Z
2012-08-22T18:31:00.630Z
2012-08-22T18:31:00.630Z
Stanislaw Krawczyk
<p>In chimpz, we see stronger chimps beating up weaker chimps that have consensual sex. </p>

<p>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.</p>

<p><a href="http://www.doctornerdlove.com/2013/03/toxic-alpha-male/" rel="nofollow">http://www.doctornerdlove.com/2013/03/toxic-alpha-male/</a>
Amongst primates that live in social groups (baboons, chimpanzees, gorillas), the largest, strongest of the male apes is the alpha male; the others are betas. The alpha rules the pack by dint of his strength and furious violence; he gets the greatest amount of food and unlimited sexual access to the females. The betas subsist on the scraps that are left over once the alpha has moved on and are excluded from sex with any of the females on threat of death. The alpha alone gets to pass along his genes; many apes – chimps and gorillas especially</p>

<p>In humans, it's not much different. The more powerful sultan live in a harem and kill his peasant children by tricking them into jihad. In humans, power is more political than muscle.</p>

<p>If you are a very attractive weaker chimps, what would you do?</p>

<p>You do it in private.</p>

<p>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.</p>

<p>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.</p>

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

<p>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 &amp; porn etc.</p>

<p>Or lets' put it this way:</p>

<p>What do you get for having sex in public?</p>

<ol>
<li>Other girls got impressed with your size and want you too? Not applicable for most males.</li>
<li>You like fresh air?</li>
</ol>

<p>There isn't much benefit.</p>

<p>What can go wrong?</p>

<ol>
<li>You can get mugged, robbed, raped, while naked.</li>
<li>People know you don't have gun with you.</li>
<li>Knowledge is power. If people know too much about you, that's usually bad.</li>
</ol>

CC BY-SA 3.0
2015-03-27T14:37:01.247Z
Interesting but it doesn't really explain why most other mammal mate in public
agemO
CC BY-SA 4.0
2020-11-28T13:41:08.913Z
"If you are a very attractive weaker chimp, what would you do? You do it in private."

Never heard of this, do you have a source?
nikkou
CC BY-SA 3.0
2013-12-25T20:09:20.210Z
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
CC BY-SA 3.0
2013-12-26T03:54:25.903Z
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.
user4951
CC BY-SA 3.0
2013-12-26T11:20:38.843Z
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
CC BY-SA 3.0
2013-12-17T13:26:16.023Z
2015-03-28T04:48:22.500Z
2015-03-28T04:48:22.500Z
user4951
<p>Perhaps it's just because we are vulnerable during sex? Evolutionary speaking, an animal or other person could attack us so it makes sense to seek a safe environment.</p>

CC BY-SA 4.0
2020-11-01T20:58:50.420Z
2020-11-01T20:58:50.420Z
danijar
<p>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.</p>

CC BY-SA 3.0
2012-08-22T16:18:33.983Z
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
CC BY-SA 3.0
2012-08-22T18:15:18.417Z
@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
CC BY-SA 3.0
2012-08-22T18:38:01.410Z
@DavidWiner I'm not disgusted by pubic hair nor genitals (as long as they are clean, healthy, perhaps young - and for that traits your explanation works).
Piotr Migdal
CC BY-SA 3.0
2012-08-22T18:38:25.903Z
Right, sorry. No offense Piotr. Okay I know Pinker mentions this somewhere, I'll find it...
David Winer
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2012-08-22T18:42:47.960Z
To those who grow up in a nudist colony, nudity does not elicit disgust or shame. Even in ugly people.
Preece
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2012-08-22T19:37:08.870Z
@Preece I'm not sure what the case is for children growing up in nudist colonies -and I'll remove my comment if I can't find evidence otherwise - but just because something is a certain way now does not mean that it didn't bias evolution. What I mean is that exposing genitals might be related to spreading disease of some kind, but I haven't had time to search for a reference. I'll be back.
David Winer
CC BY-SA 3.0
2012-08-23T08:09:19.670Z
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
CC BY-SA 3.0
2012-08-23T16:51:38.023Z
@PiotrMigdal Personally, I downvoted because this answer does not cite any sources, and on this site answers are expected to cite prior research.
Josh
CC BY-SA 3.0
2013-12-18T00:44:13.770Z
This doesn't explain why humans behave differently than other species on the topic.
Christian
CC BY-SA 3.0
2012-08-22T15:57:46.747Z
2012-08-22T15:57:46.747Z
David Winer
<p>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.</p>

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

CC BY-SA 3.0
2012-08-21T17:40:32.687Z
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.
CC BY-SA 3.0
2012-08-22T12:17:02.013Z
[Interesting and possibly relevant link](http://www2.hu-berlin.de/sexology/ATLAS_EN/html/sex_and_society.html)
jokerdino
CC BY-SA 3.0
2012-08-22T17:46:03.987Z
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
CC BY-SA 3.0
2012-08-22T18:28:52.513Z
@JavierRodriguezLaguna yet, [human 'endowment' is disproportionately large in comparison to other primates](http://en.wikipedia.org/wiki/Human_penis_size#Comparison_to_other_primates) suggesting sexual selection on the trait. However, I am not sure if wikipedia can be an authoritative source on this.
Artem Kaznatcheev
CC BY-SA 3.0
2012-08-22T18:42:39.170Z
@Artem, History may play a role here. Maybe sexual endowment was an evolutionary trait, and it is not anymore... Indeed, in most historical cultures, your sexual partner is chosen by your parents, considering mostly cultural arguments... So, it's a good idea to hide the sexual endowment in that environment.
Javier Rodriguez Laguna
CC BY-SA 3.0
2012-08-22T18:45:23.290Z
@JavierRodriguezLaguna unfortunately history is incredibly short on an evolutionary time-scale. In which case I think your answer to Piotr would be "culture, not biology". I would definitely agree with this answer, and I think there are plenty of examples to back it up, it is just that none of the answers have taken the time to dig around :P.
Artem Kaznatcheev
CC BY-SA 3.0
2012-08-22T21:17:46.557Z
It could be because there are laws against sex in public. In most countries, affecting the majority of Earth's population.
oxygen
CC BY-SA 3.0
2012-08-23T05:09:54.390Z
The BBC has a nice show called [What’s the Problem with Nudity?](http://topdocumentaryfilms.com/whats-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
CC BY-SA 3.0
2012-08-23T11:02:10.637Z
@Tiberiu-IonuțStan: We know that there are laws against it, but the question is more concerned with WHY there are such laws in the first place.
Geek On Acid
CC BY-SA 3.0
2012-08-23T11:10:49.513Z
@GeekOnAcid The question asks why people have sex in private, not why there are laws in place. There could be laws in place in order to maintain a good distribution of sexual activity among all men and women, which has lots of benefits, including reduced violence and a "happier" general population. Also, as long as such laws are in place almost EVERYWHERE, all "cognitive behaviours" described on this page cannot possibly answer the question, and are flawed from a scientific point of view (by the effectiveness of such laws).
oxygen
CC BY-SA 3.0
2012-08-23T11:30:35.360Z
@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
CC BY-SA 3.0
2012-08-23T12:25:31.497Z
Oh yeah, stealing, raping and killing are comparable to having sex for pleasure (can you please explain, you are starting to sound like some religious fanatic). You are missing the point. The point I made was: there CANNOT be ANY scientific backing of a scientific "cognitive" sort BECAUSE of the artificial laws which take precedence in the list of factors preventing a course of action. You cannot have ANY valid statistical or experimental data, so there is no science to it (period, that's the point I made).
oxygen
CC BY-SA 3.0
2012-08-23T13:06:27.350Z
@Tiberiu-IonuțStan: Chill out mate, I'm not attacking you, just your flawed argument. Obviously we don't understand each other. You seem to say that laws are ultimate cause of people practicing private sex, which I disagree. Here we're arguing that there are deeper aspects of human functioning that brought us to this point in history, where we created such laws, and we are trying to give scientific account for this. I give extreme examples because it shows how laws can't define human behaviour, they just reflect some collective agreement about what the behaviour ought to be.
Geek On Acid
CC BY-SA 3.0
2012-08-23T13:31:35.907Z
@GeekOnAcid I was perfectly chill. If you insist to analyze our conversation, I was attacking your flawed argument meant to attack my argument. People do obey most laws, including this one. Mostly in fear of fines and imprisonment.
oxygen
CC BY-SA 3.0
2012-08-23T15:38:03.677Z
@Tiberiu-IonuțStan No, the question is **not** about law, obeying it etc. It is about a one or two layer deeper thing. Needless to say, there are many positive feedback loops.
Piotr Migdal
CC BY-SA 3.0
2012-08-23T16:28:47.267Z
@PiotrMigdal The question assumes too much about the human species, problably based on your personal cultural (enviroment/media) experience. I am 100% percent sure your personal experience regarding other people and yourself having sex in private is 100% affected by the laws in place.
oxygen
CC BY-SA 3.0
2012-08-23T16:49:59.243Z
OK everybody, let's please keep the comments constructive, friendly, concise and on topic... thanks! If we'd like to have extended discussions, let's take them [to chat](http://chat.stackexchange.com/rooms/2250/the-axon-terminal).
Josh
CC BY-SA 3.0
2012-08-23T16:53:49.283Z
@Tiberiu-IonuțStan First, I know a bunch of illegal things (e.g. drinking in public in my country) that popular. Second, there is not a single issue I'm 100% sure about. If you are 100% sure, please consider putting your money where your mouth is and write an well-supported answer saying it's a cultural thing, not a biological one.
Piotr Migdal
CC BY-SA 4.0
2019-01-24T08:00:12.197Z
Aren't people just afraid being insulted? If you are having sex in public almost sure there will be someone who will insult you. Except in some cases.
rus9384
CC BY-SA 4.0
2020-11-28T13:49:34.313Z
@rus9384 I'm not sure it completely checks out for me but this hypothesis at least has the advantage of explaining why _humans but not other primates_ have sex in private. Whereas all the other hypotheses that I've read do not.
nikkou
CC BY-SA 4.0
2020-11-28T13:59:51.410Z
BTW, the comment of rus9384 is much more appealing to me now once I remembered that ONLY humans and Arabian babblers usually have private sex after reading this paper https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1330#d1e1318. The Arabian babblers are unique in the sense that they have a system of prestige similar to humans (Sapolsky).
nikkou
CC BY-SA 4.0
2020-11-28T14:01:39.173Z
The paper that I linked lays out the support for a different theory though: conceal matings to prevent sexual arousal in witnesses => control over partner and cooperation with group members who are prevented from mating. The cooperation explanation looks quite interesting.
nikkou
CC BY-SA 4.0
2020-11-28T21:30:41.470Z
@nikkou, my own theorising about humans has led me to a different conclusion. Basically, that humans do not have devices that are typical for monogamous/serially monogamous species. That's a big claim, of course, but if it is correct it makes the other theory not plausible.
rus9384
<social-psychology><evolution><sexuality>
Why do humans have sex in private?
Piotr Migdal
# Why do humans have sex in private?

(Asked by: username_0 on 2012-08-20)

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?**

**Tags:** social-psychology, evolution, sexuality

> **Comments:**
> **username_1**: 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?  
> **username_2**: [Interesting and possibly relevant link](http://www2.hu-berlin.de/sexology/ATLAS_EN/html/sex_and_society.html)  
> **username_3**: 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.  
> **username_4**: @JavierRodriguezLaguna yet, [human 'endowment' is disproportionately large in comparison to other primates](http://en.wikipedia.org/wiki/Human_penis_size#Comparison_to_other_primates) suggesting sexual selection on the trait. However, I am not sure if wikipedia can be an authoritative source on this.  
> **username_3**: @Artem, History may play a role here. Maybe sexual endowment was an evolutionary trait, and it is not anymore... Indeed, in most historical cultures, your sexual partner is chosen by your parents, considering mostly cultural arguments... So, it's a good idea to hide the sexual endowment in that environment.  
> **username_4**: @JavierRodriguezLaguna unfortunately history is incredibly short on an evolutionary time-scale. In which case I think your answer to Piotr would be "culture, not biology". I would definitely agree with this answer, and I think there are plenty of examples to back it up, it is just that none of the answers have taken the time to dig around :P.  
> **username_5**: It could be because there are laws against sex in public. In most countries, affecting the majority of Earth's population.  
> **username_6**: The BBC has a nice show called [What’s the Problem with Nudity?](http://topdocumentaryfilms.com/whats-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.  
> **username_7**: @Tiberiu-IonuțStan: We know that there are laws against it, but the question is more concerned with WHY there are such laws in the first place.  
> **username_5**: @GeekOnAcid The question asks why people have sex in private, not why there are laws in place. There could be laws in place in order to maintain a good distribution of sexual activity among all men and women, which has lots of benefits, including reduced violence and a "happier" general population. Also, as long as such laws are in place almost EVERYWHERE, all "cognitive behaviours" described on this page cannot possibly answer the question, and are flawed from a scientific point of view (by the effectiveness of such laws).  
> **username_7**: @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.  
> **username_5**: Oh yeah, stealing, raping and killing are comparable to having sex for pleasure (can you please explain, you are starting to sound like some religious fanatic). You are missing the point. The point I made was: there CANNOT be ANY scientific backing of a scientific "cognitive" sort BECAUSE of the artificial laws which take precedence in the list of factors preventing a course of action. You cannot have ANY valid statistical or experimental data, so there is no science to it (period, that's the point I made).  
> **username_7**: @Tiberiu-IonuțStan: Chill out mate, I'm not attacking you, just your flawed argument. Obviously we don't understand each other. You seem to say that laws are ultimate cause of people practicing private sex, which I disagree. Here we're arguing that there are deeper aspects of human functioning that brought us to this point in history, where we created such laws, and we are trying to give scientific account for this. I give extreme examples because it shows how laws can't define human behaviour, they just reflect some collective agreement about what the behaviour ought to be.  
> **username_5**: @GeekOnAcid I was perfectly chill. If you insist to analyze our conversation, I was attacking your flawed argument meant to attack my argument. People do obey most laws, including this one. Mostly in fear of fines and imprisonment.  
> **username_0**: @Tiberiu-IonuțStan No, the question is **not** about law, obeying it etc. It is about a one or two layer deeper thing. Needless to say, there are many positive feedback loops.  
> **username_5**: @PiotrMigdal The question assumes too much about the human species, problably based on your personal cultural (enviroment/media) experience. I am 100% percent sure your personal experience regarding other people and yourself having sex in private is 100% affected by the laws in place.  
> **username_8**: OK everybody, let's please keep the comments constructive, friendly, concise and on topic... thanks! If we'd like to have extended discussions, let's take them [to chat](http://chat.stackexchange.com/rooms/2250/the-axon-terminal).  
> **username_0**: @Tiberiu-IonuțStan First, I know a bunch of illegal things (e.g. drinking in public in my country) that popular. Second, there is not a single issue I'm 100% sure about. If you are 100% sure, please consider putting your money where your mouth is and write an well-supported answer saying it's a cultural thing, not a biological one.  
> **username_9**: Aren't people just afraid being insulted? If you are having sex in public almost sure there will be someone who will insult you. Except in some cases.  
> **username_10**: @username_9 I'm not sure it completely checks out for me but this hypothesis at least has the advantage of explaining why _humans but not other primates_ have sex in private. Whereas all the other hypotheses that I've read do not.  
> **username_10**: BTW, the comment of username_9 is much more appealing to me now once I remembered that ONLY humans and Arabian babblers usually have private sex after reading this paper https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1330#d1e1318. The Arabian babblers are unique in the sense that they have a system of prestige similar to humans (Sapolsky).  
> **username_10**: The paper that I linked lays out the support for a different theory though: conceal matings to prevent sexual arousal in witnesses => control over partner and cooperation with group members who are prevented from mating. The cooperation explanation looks quite interesting.  
> **username_9**: @username_10, my own theorising about humans has led me to a different conclusion. Basically, that humans do not have devices that are typical for monogamous/serially monogamous species. That's a big claim, of course, but if it is correct it makes the other theory not plausible.  

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## 6 answers

### Answer by username_7 on 2012-08-21. Score: 53

## Introduction

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](http://en.wikipedia.org/wiki/DSM-IV_Codes#Paraphilias) 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).

**EDIT**

*Following valid and constructive comments by @Piotr and @username_13 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.

References:

* 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.

> **Comments:**
> **username_0**: Thanks, you rise a few good points. However, my question is not on sexual norms, but unwillingness to have sex in public.  
> **username_13**: 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.  
> **username_14**: 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).  
> **username_11**: It doesn't really make sense : leaving the safety of the group to mate somewhere else is not really safe, it's even a huge risk. For excretion I think the risks are balanced by the hygienic improvement of not spoiling the place where your group lives  
> **username_12**: I think the "protection" happening in the case of sex is more to protect the couple from the group, rather than from outside predators. Its not just that it may invoke jealousy or cause others to want to join in, but it also gives onlookers the capability to disrupt or to cause harm to the relationship - (comments, teasing).  
> **username_9**: @MartaCz-C Probably, only until you think those friends can reject you. And many people do.  
> **username_10**: I looked at the answers to this question and they all strike me as absolutely unsatisfactory given that they don't point out differences between humans and other primates. Seems like 1) better self-defence 2) avoiding inciting jealousy 3) support for exclusivity of monogamous relationships would make others primates also have sex in private but AFAIK this is not the case (source: Sapolsky). So maybe it's more like we have no clue why humans have sex in private?  
> **username_9**: @PiotrMigdal I would say the two are closely connected. I for some reason have a week sense of social obedience amd therefore don't see anything repulsive in the idea of public sex. Still from my realization that other people don't sjare the sentiment, I would not do it. But mostly I would say that's from cultural norms. For the starter, being naked in the public also is punishable, but in many tribes that's normal.  

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### Answer by username_15 on 2012-08-22. Score: 16

This is a fascinating question. According to Donald Symons (1979) "[The evolution of human sexuality](http://en.wikipedia.org/wiki/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](http://en.wikipedia.org/wiki/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.

> **Comments:**
> **username_4**: 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?  

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### Answer by username_16 on 2012-08-22. Score: 15

Just a very brief note: in some cultures, sex does not appear to have been confined to private space. [One article](http://www.livius.org/ho-hz/homosexuality/homosexuality.html) 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.

> **Comments:**
> **username_4**: @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.  
> **username_16**: 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!).  

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### Answer by username_17 on 2013-12-17. Score: 6

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.

<http://www.doctornerdlove.com/2013/03/toxic-alpha-male/>
Amongst primates that live in social groups (baboons, chimpanzees, gorillas), the largest, strongest of the male apes is the alpha male; the others are betas. The alpha rules the pack by dint of his strength and furious violence; he gets the greatest amount of food and unlimited sexual access to the females. The betas subsist on the scraps that are left over once the alpha has moved on and are excluded from sex with any of the females on threat of death. The alpha alone gets to pass along his genes; many apes – chimps and gorillas especially

In humans, it's not much different. The more powerful sultan live in a harem and kill his peasant children by tricking them into jihad. In humans, power is more political than muscle.

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.

> **Comments:**
> **username_0**: 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.))  
> **username_17**: 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.  
> **username_0**: 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.)  
> **username_11**: Interesting but it doesn't really explain why most other mammal mate in public  
> **username_10**: "If you are a very attractive weaker chimp, what would you do? You do it in private."  Never heard of this, do you have a source?  

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### Answer by username_18 on 2020-11-01. Score: 1

Perhaps it's just because we are vulnerable during sex? Evolutionary speaking, an animal or other person could attack us so it makes sense to seek a safe environment.


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### Answer by username_19 on 2012-08-22. Score: -1

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.

> **Comments:**
> **username_0**: 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).  
> **username_4**: @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.  
> **username_0**: @DavidWiner I'm not disgusted by pubic hair nor genitals (as long as they are clean, healthy, perhaps young - and for that traits your explanation works).  
> **username_19**: Right, sorry. No offense Piotr. Okay I know Pinker mentions this somewhere, I'll find it...  
> **username_13**: To those who grow up in a nudist colony, nudity does not elicit disgust or shame. Even in ugly people.  
> **username_19**: @username_13 I'm not sure what the case is for children growing up in nudist colonies -and I'll remove my comment if I can't find evidence otherwise - but just because something is a certain way now does not mean that it didn't bias evolution. What I mean is that exposing genitals might be related to spreading disease of some kind, but I haven't had time to search for a reference. I'll be back.  
> **username_0**: 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.)  
> **username_8**: @PiotrMigdal Personally, I downvoted because this answer does not cite any sources, and on this site answers are expected to cite prior research.  
> **username_20**: This doesn't explain why humans behave differently than other species on the topic.  

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