- The term "act of union" is used as a euphemism for sexual intercourse
- This article is about sexual intercourse in humans and its societal implications. For biological copulation in general, see copulation.
Sexual intercourse, specifically coitus, is the human form of copulation. The term sexual intercourse refers to a wider range of sexual activities than the term coitus, which only refers to male-female genital sex. See Human sexual behavior for a discussion of the broader sense of sexual intercourse and list of sexual positions for the wide variety of sexual activities that exist. See the terms frot for male-male genital sex and tribadism for female-female genital sex. "Genital sex" as used here refers to genito-genital sex, among BDSM/fetish practitioners the term "genital sex" can mean any sex involving the genitals including anal, oral, manual, etc., as opposed to those based on toys, costumes or fantasies.
To engage in sexual intercourse, the erect penis is inserted into the vagina and one or both of the partners move their hips to move the penis backward and forward inside the vagina to cause friction, typically without fully removing the penis. In this way, they stimulate themselves and each other until orgasm and ejaculation are achieved. Penetration with the penis is also known as intromission, or by the Latin name immissio penis.
A detailed description of the physiology of sexual arousal and orgasm can be found in the article Human sexual response cycle.
Coitus is the basic reproductive method of humans. During ejaculation, which normally accompanies male orgasm, a series of muscular contractions delivers semen containing male gametes known as sperm cells or spermatozoa into the vault of the vagina. The subsequent route of the sperm from the vault of the vagina, is through the cervix and into the uterus, and then into the fallopian tubes. Millions of sperm are present in each ejaculation, to increase the chances of one fertilizing an egg or ovum. When a fertile ovum from the female is present in the fallopian tubes, the male gamete joins with the ovum resulting in fertilization and the formation of a new embryo. When a fertilized ovum reaches the uterus, it becomes implanted in the lining of the uterus, known as endometrium and a pregnancy begins.
Heterosexual intercourse (coitus), where both participants are believed to be fertile, should always be considered likely to result in pregnancy, unless adequate contraceptive (birth control) measures are taken.
Functions of sex beyond reproduction
Humans, bonobos and notably dolphins are all species known to have non-reproductive sex, apparently for the sake of pleasure. All three engage in heterosexual behaviors even when the female is not in estrus, that is, at a point in her reproductive cycle suitable for successful impregnation. Likewise, all three sometimes engage in homosexual behaviors. That is not to say that homosexuality and non-reproductive heterosexuality are limited to these three species; rather, they are unusual for female receptivity to sex independent of estrus.
In both humans and bonobos the female undergoes relatively concealed ovulation, so that males generally do not know whether she is fertile at any given moment. There is said to be a functional advantage to sex anytime for social reasons rather than reproductive ones. The emotional attachment between the partners, encouraging them to stay together over a long term, often allows them to support each other in cooperative tasks, such as raising their offspring.
Humans, bonobos and dolphins are all intelligent social animals, whose cooperative behavior proves far more successful than that of any individual alone. In these animals, the use of sex has evolved beyond reproduction to serve additional social functions. It may be that sex reinforces intimate social bonds between individuals to form larger social structures. The resulting cooperation encourages collective tasks that promote the survival of each member of the group.
At an emotional level sexual intercourse is often, though not always, seen as the ultimate physical expression of feelings of romantic love between two humans. In many cultures, mutual romantic love often forms a formalized or informal partnership, a full sexual relationship within this partnership, procreation or adoption of children, and subsequent parenting. Romantic love is not limited to those of opposite sexes, and also occurs among those of the same sex.
On a biological level, an increasing amount of research is demonstrating that a man's sex drive (and sexual attractiveness to women) is closely linked with hormones such as testosterone. A man can boost his testosterone naturally through reducing (or eliminating) smoking, alcohol, certain drugs such as most anti-depressants, emotional stress, simple carbohydrates such as white sugar, and dietary sources of estrogen such as soy. He should also avoid exposing his testicles to too much heat such as from a hot tub. Conversely, eating a diet of 70% fruits and vegetables and 25% to 30% meat boosts a man's testosterone, as does drinking more water, lifting weights, sunbathing, and meditation. 
Sexual intercourse is also often decoupled from romantic love and/or from a wish for procreation. Casual sex, often used to satisfy a physiological need, is common although it is censured by some as being promiscuous and morally questionable. The sex industry is the commercialization of sex, usually casual and including prostitution.
While being well suited for effective stimulation of the penis, intercourse is less well suited for effective stimulation of the clitoris. Many women, up to 70 percent rarely or never have orgasms during intercourse without simultaneous direct stimulation of the clitoris. Disregard of this fact is seen as the most common cause of female anorgasmia.
Anorgasmia is the inability to achieve orgasm. It is much more common in women than men and usually needs attention from both partners over a long time span to solve. Many women, especially younger women with little sexual experience, have difficulty achieving orgasm. Whether a woman considers anorgasmia a problem or not is highly individual; the popular notion that both partners should achieve orgasm in "normal" intercourse may contribute to a woman's concern over anorgasmia.
Some males suffer from erectile dysfunction (ED), or impotence, at least occasionally. For those whose impotence is caused by medical conditions, prescription drugs such as Viagra, Cialis, and Levitra are available. However, doctors caution against the unnecessary use of these drugs because they are accompanied by serious risks such as increased chance of heart attack. Also, using a drug to counteract the symptom—impotence—can mask the underlying problem causing the impotence, and does not fix the problem. A serious condition might be aggravated if left untreated.
A more common sexual disorder in males is premature ejaculation (PE). The U.S. Food and Drug Administration (Food and Drug Administration) is examining the drug dapoxetine to treat premature ejaculation. In clinical trials, those with PE who took dapoxetine experienced intercourse three to four times longer before orgasm than without the drug.
The American Urological Association (AUA) estimates that premature ejaculation could affect 27 to 34 percent of men in the United States. The AUA also estimates that 10 to 12 percent of men in the United States are affected by erectile dysfunction.
Vaginismus is involuntary tensing of the pelvic floor musculature, making coitus distressing or impossible.
Dyspareunia is painful or uncomfortable intercourse; it can be due to a variety of causes.
Sexual morality and legality
Unlike some other sexual activities, sexual intercourse has rarely been made taboo on religious grounds or by government authorities, as procreation is inherently essential to the continuation to the species or of any particular genetic line, which is considered to be a positive factor, and indeed, enables most societies to continue in the first place. Many of the cultures that had prohibited sexual intercourse entirely no longer exist; an exception is the Shakers, a sect of Christianity that has very few adherents at current. There are, however, many communities within cultures that prohibit their members to engage in any form of sex, especially members of religious orders and the priesthood in the Roman Catholic Church and lamas in Buddhist monasteries. Within some ideologies, coitus has been considered the only "acceptable" sexual activity. Relatively strict designations of "appropriate" and "inappropriate" sexual intercourse have been almost universal in human culture for thousands of years. These have included prohibitions against specific positions, but even more often against:
- Intercourse between two people wherein at least one of them is married, but where neither is married to the other (called adultery)
- Sexual intercourse with a close relative (called incest). This may also be called inbreeding in slang terms, the term applies more towards animals.
Some cultures and religions also prohibit or at one point prohibited sexual intercourse during a woman's menstrual period; one such religion is Judaism, wherein the main sacred text laid specific instructions for behavior during and after this period, including explicitly forbidding sexual contact.
Often a community adapts its legal definitions during case laws for settling disputes. For example, in 2003 the New Hampshire Supreme Court ruled that same-sex relations do not constitute sexual intercourse, based on a 1961 definition from Webster's Third New International Dictionary, in Blanchflower v. Blanchflower, and thereby an accused spouse in a divorce case was found not guilty of adultery based on this technicality.
Most countries have age of consent laws specifying the minimum legal age for engaging in sexual intercourse. Sexual intercourse with a person against his or her will, or without their informed legal consent, is referred to as rape, and is considered a serious crime in many cultures around the world, including those found in Europe, northern and eastern Asia, and the Americas. A consequence of this is that it may be illegal to have sex with someone who is intoxicated, because that person cannot give his or her informed consent. Sex, regardless of consent, with a minor (a person under the age of consent) is often considered a comparable or equivalent crime to rape or sexual assault, especially in instances where the older partner is not him- or herself a minor. The age of consent varies from country to country and sometimes even within the same country; generally, the age of consent is set anywhere between thirteen and eighteen years of age.
In Judaism, sex is seen as a natural act, similar to eating and drinking. It is said that if it is done properly - as with the eating of a meal on Purim, or the drinking of four cups of wine on Passover - it can be considered a holy act. Likewise, it is also seen as illicit and sinful if the sexual acts do not follow the guidelines of Jewish Law. The Torah states, "...it is not good for man to be alone"(Gen 2:18) which implies to many the importance of intimacy, love, and healthy sexual companionship. Judaism regards adultery as forbidden by God, with the Torah prescribing death for those caught engaging in it; over the centuries, Jewish religious scholars (see Rabbi) have derived and interpreted additional restrictions, laws and endorsements from the basic ones established in the Torah.
In the Christian faith, sex outside marriage is officially condemned with varying degrees of severity. This has often been interpreted by Christian denominations as forming part of a prohibition against sex acts committed solely for pleasure, and has led to the Roman Catholic Church’s highly controversial condemnation of artificial forms of contraception. See (for example) .
Many Christian denominations have, over time, developed and changed their approaches to sex and sexuality. Within the modern Catholic Church, for example, the disallowance of sexual intercourse between non-married people is generally seen as stemming not from a belief in the inherent sinfulness or negativity of sex itself, but rather from a belief that sexual intercourse is the most sacred act a man and a woman can physically share. Thus, in order to fully experience this sacred bond, it is believed that one's sexuality should be saved for the person with whom one intends to spend the rest of one's mortal life. However centuries of advocating celibacy among Catholic clergymen as a "higher way" of life have led many throughout the church's existence to associate clerical asceticism with a general religious disapproval of sex, though it is also of note that Catholic clergymen are also prohibited from marrying. By contrast, the Shakers continue to advocate absolute celibacy, both in and outside of the clergy, which has played no small part in the diminution of their ranks over the years.
In Islamic societies, open or public sexuality is generally forbidden due to Qu'ranic or hadith-related prohibitions. In Shia Islam, there is a practice of Mut'a or Misyar, a temporary marriage that can be as short as a day or as long as several years. The term "Mut'a" is derived from the Arabic word for pleasure, and is often used in sexual courtship amongst the youth in such regions as Iran. With rising levels of sexual freedom in Islamic societies, there has been a corresponding rise in temporary marriages within the greater Sunni world amongst the youth; although not accepted by the wider society, known as 'Arfi marriage. In Islamic theology, sex is seen as a need similar to that of eating. In the holy month of Ramadan, Muslims must abstain from both eating and having sex from dawn until sunset.
There is, and always has been, a good deal of controversy about the kind of relationship one should have with someone else before engaging in sexual intercourse. This controversy is somewhat beyond the scope of this article; interested readers are encouraged to read the articles on chastity, evolutionary psychology, and sexual morality for further detail on the matter.
- Synonyms for sexual intercourse – the WikiSaurus list of synonyms and slang words for sexual intercourse in many languages
- Safe sex
- Sexual slang
- ↑ Frans de Waal, "Bonobo Sex and Society", Scientific American (March 1995): 82-86. Available online at: http://songweaver.com/info/bonobos.html.
- ↑ Dinitia Smith, "Central Park Zoo's gay penguins ignite debate", San Francisco Chronicle (February 7, 2004). Available online at http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/07/MNG3N4RAV41.DTL.
- ↑ Bruce Bagemihl, Biological Exuberance: Animal Homosexuality and Natural Diversity (St. Martin's Press, 1999). ISBN 0312192398
- ↑ John Alexander, How to Be Her Best Lover Ever (Lulu Press, 2005). ISBN 1411637739
- ↑ Sexual Honesty, by Women, For Women, by Shere Hite (1974)
- The International Encyclopedia of Sexuality
- Janssen, D. F., Growing Up Sexually. Volume I. World Reference Atlas
- Biology of sexual intercourse
- Dutch Society for Sexual Reform article on "sex without intercourse"
- UK legal guidance for prosecutors concerning sexual acts
- Resources for parents to talk about sexual intercourse to their children
- Planned Parenthood information on sexual intercourse
- Medical Resources related to sexual intercourse
- W. W. Schultz, P. van Andel, I. Sabelis, E. Mooyaart. Magnetic resonance imaging of male and female genitals during coitus and female sexual arousal. BMJ 1999;319:1596-1600 (18 December).
- Social Determinants of Attitudes Towards Women's Premarital Sexuality Among Female Turkish University Studentsbg:Пол
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