Sex (activity)

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This article is about the activity. For other uses, see Sex (disambiguation).

Sexual intercourse, commonly referred to simply as sex or as making love, is an activity involving prolonged genital contact, such as when the penis enters part of another person's body, most commonly the vagina, for the purposes of pleasure and sometimes reproduction. Sex can be part of homosexual (gay) as well as heterosexual (straight) relationships. Often, however, sex occurs just so the participants can experience the sensation of pleasure that accompanies the activity, including orgasm, and they may well take steps to avoid a later pregnancy by using contraceptives. Some of these methods, such as condom use, also reduce the risk of transmitting viruses that rely on sex to spread. Contraceptives, family planning and responsible attitudes to sex are three reasons that help explain why, while it is the main way of introducing sperm into a woman's body so that a man's genetic material has the opportunity to fuse with an egg to form an embryo, very often acts of sex do not eventually lead to the birth of a child.

However, even without any contraception, and even when both partners are fertile, most instances of sexual intercourse will not result in a pregnancy. The reproductive cycle (menstrual cycle) of a woman typically recurs every 28 days, but successful fertilisation can only take place on a few days of that cycle (at "mid-cycle"). However, women may be willing to engage in sexual intercourse at any time of the cycle. In this, women are unlike the females of almost all other mammallian species. For example, the rat has a four day reproductive cycle, and is receptive to males only on one of these days, the day of proestrous, when estrogen levels are high; at all other times she will reject the attentions of males, who for their part generally will show little interest anyway. Thus in rats virtually every instance of mating results in a successful pregnancy.

Thus humans are almost unique amongst mammals in engaging extensively in sexual activity when there is no possibility of it resulting in pregnancy. This unique feature raises the obvious question of what is sex for, in biological terms. A possible answer relates to another unusual feature of humans - that they are often monogamous, that they make very prolonged pair bonds that are important for ensuring the development to adulthood of their children. Sex plays an important part in forging and maintaining these bonds.

This belief comes in part from studies of the few other monogamous mammalian species. One of these the prairie vole makes lifelong pair bonds, and the male plays an active parental role. In the prairie vole, coitus is known to be instrumental in establishing this bond.

Sex is a consensual activity: though adults and adolescents have little or no control over their sense of sexual attraction, they must freely choose to have sex. When a person is forced into sex, this is rape, and for the victim it is never a sexual act but a horrific assault. Scholars have often identified the reasons for rape as social rather than biological: in this view, rape is about power over others,[1] as a rapist - in most definitions, always a man - for deviant reasons[2] seeks to violently dominate or punish another person and keep them in a state of fear.[3] More recently, controversy has erupted over evolutionary explanations that root rape not just in social conditions and the extension of violent activity, but the innate male sex drive[4] and its conflict with women's ability to choose who fathers their children.[5] This debate has also involved discussion on the irresponsibility of ignoring sex itself as a motivator for rape,[6] the rejection of the idea that all men whether rapists or not are ultimately beneficiaries of rape,[7] and the assumption that if rape is in any way a consequence of innate, evolved traits, then this sends the message that it is in some way more acceptable.[8] Of course, researchers seeking an explanation for the presence of rape in all societies have taken great care to make the obvious point that the intent behind such work is to find a way to reduce rape in society.[9]

While rape is a crime or at least proscribed in every society on earth,[10] attitudes towards consensual sex and the freedom to practice it vary more widely. Clearly, there is a great interest in sex: there are hundreds of millions of pornographic websites,[11] the sex industry in the United Kingdom alone is estimated to be worth at least £1 billion a year,[12] and in many countries mildly sexual images are used to advertise virtually any product, while books and magazines offering advice on improving one's 'sex life' fill the shelves. The interest in sex and the urge to depict it are not recent trends: for example, the destruction of the city of Pompeii in 79 AD preserved sexually explicit artworks decorating the walls of Roman houses. Most cultures have usually spent a good deal of largely unsuccessful effort attempting to control the sexual activity of their people, and therefore worldwide sex is a taboo subject to a greater or lesser degree.


  1. This is the definition given in the United Nations document 'Situation of Human Rights in the Territory of the Former Yugoslavia' (UN document e/CN.4/1993/50). Published in International Journal of Refugee Law 5: 319-333. 10th February 1993. The definition appears on p.330 of the report, which also includes descriptions of the ordeals suffered by women raped in wartime.
  2. Groth & Burgess (1977).
  3. Brownmiller (1975: 14).
  4. Brownmiller & Merhof (1992). cf. Thornhill & Palmer (2000/2001); Jones (1999); Pinker (2002: 161-162, 359-371).
  5. 'Reply to Jerry Coyne'. John Tooby and Leda Cosmides, Center for Evolutionary Psychology, University of California, Santa Barbara. 2000.
  6. Paglia (1990: 51, 57).
  7. McElroy (1996).
  8. Pinker (2002: 363).
  9. Pinker (2002: 364-365, 367).
  10. Brown (1991).
  11. Evidence suggests, however, that the overall proportion of sexually explicit websites on the internet is small compared to other sites: about 1.1%. See Stark (2008).
  12. BBC News: 'Inside Britain's sex industry'. 27th February 2005.

See also