Sexual intercourse

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The missionary position, the most common human sex position,[1][2] depicted by Édouard-Henri Avril.

Sexual intercourse, as coitus or copulation, is the insertion and thrusting of a male's penis into a female's vagina for the purposes of sexual pleasure or reproduction.[3][4][5][6] Other forms of penetrative sexual intercourse include anal sex, oral sex, fingering, and use of a strap-on dildo.[5][6][7]

Sexual intercourse commonly contributes to human bonding, usually being used solely for pleasure and often leading to stronger emotional bonds.[8][9] There are a variety of views concerning what constitutes sexual intercourse or other sexual activity as well.[10][11][12] Non-penetrative sex (such as non-penetrative cunnilingus), for example, has been termed outercourse,[13][14] but may also be among the sexual acts contributing to human bonding and considered sexual intercourse. The term sex, often a shorthand for sexual intercourse, can mean any form of sexual activity.[6][11][15][16] Because individuals can be at risk of contracting sexually transmitted infections during these activities,[17][18] though the transmission risk is significantly reduced during non-penetrative sex,[14][19] safe sex practices are advised.[17]

In human societies, various jurisdictions have placed restrictive laws against certain sexual acts, such as incest, sexual activity with minors, extramarital sex, position-of-trust sex, prostitution, sodomy, indecent exposure, rape, and zoophilia. Religious beliefs can play a role in decisions about sexual intercourse or other sexual activity, or their purpose, as well; for example, beliefs about what sexual acts constitute virginity loss, or the decision to make a virginity pledge.[20][21][22] Some sections of Christianity view sexual activity between a married couple for the purpose of reproduction as holy, while other sections do not.[23] Modern Judaism and Islam view sexual intercourse between husband and wife as a spiritual and edifying action. Hinduism and Buddhism views on sexuality have differing interpretations.

Reproductive sexual intercourse between non-human animals is more often termed copulation; for most non-human mammals, mating and copulation occur at the point of estrus (the most fertile period of time in the female's reproductive cycle), which increases the chances of successful impregnation.[24][25] However, bonobos,[26] dolphins,[27] and chimpanzees are known to engage in sexual intercourse regardless of whether or not the female is in estrus, and to engage in sex acts with same-sex partners.[27][28] Like humans engaging in sexual activity primarily for pleasure,[8] this behavior in the aforementioned animals is also presumed to be for pleasure,[29] and a contributing factor to strengthening their social bonds.[8]

Behaviors

Etymology and definitions

19th-century painting of a couple engaged in vaginal intercourse in a barn, by Peter Fendi
19th-century erotic interpretation of Hadrian and Antinous engaged in anal intercourse, by Édouard-Henri Avril

Behaviors termed sexual intercourse may be described or defined by different words, including copulation, coitus or coition; the term coitus is derived from the Latin word coitio or coire, meaning "a coming together or joining together" or "to go together" and is usually defined as penile-vaginal penetration.[5][30][31][32] Penetration by the erect penis is additionally known as intromission, or by the Latin name immissio penis (Latin for "insertion of the penis").[33]

The word copulation, though usually used to describe the mating process of non-human animals, is generally defined as the sexually reproductive act of transferring sperm from a male to a female or sexual procreation between a man and a woman.[34][35] Common discourse additionally limits sexual intercourse to penile-vaginal penetration, often with virginity loss based on the activity.[10][11][12][21] By comparison, the term sex and the phrase "having sex" often mean any sexual activity – penetrative and non-penetrative.[11][15][36] The World Health Organization states that non-English languages and cultures "use different terms for sexual activity, with slightly different meanings".[15] Various vulgar or slang words and euphemisms are also used to describe sexual intercourse or other sexual activity, such as the term fuck and the phrase "sleeping together".[37][38]

Researchers commonly define sexual intercourse as penile-vaginal intercourse, while using specific terms (such as anal sex or oral sex) for other sexual activities,[10][12][39][40] but have also been cited as "rarely disclos[ing] how they define sex or even whether they resolved potential discrepancies in definitions of sex".[10] Researchers' focus on penile-vaginal intercourse has been attributed to "the larger culture's preoccupation with this form of sexual activity," and a concern is that the "widespread, unquestioned equation of penile-vaginal intercourse with sex reflects a failure to examine systematically 'whether the respondent's understanding of the question [about sexual activity] matches what the researcher had in mind'".[10] This focus also regulates other forms of mutual sexual activity to foreplay or regards them as not being "real sex" and additionally limits how rape is defined.[39][41][42] Additional concern is that the "conceptual conflation of sex, vaginal intercourse, and sexual function results in less knowledge about the range of sexual behaviors that participants engage in" and "limit[s] the generalizability of research for nonheterosexual participants and/or those individuals who are not engaging in heterosexual sexual intercourse".[39]

Anal sex, oral sex and fingering may be regarded as sexual intercourse,[5][6][11] or, along with other forms of non-coital and non-penetrative sexual activities, as maintaining "technical virginity"; they may also be regarded as outercourse regardless of any penetrative aspects.[21][43] Heterosexual couples may engage in anal or oral sex not only for sexual pleasure, but as ways of maintaining that they are virgins because they have not engaged in the reproductive act of penile-vaginal intercourse.[12][21][41][44] Similarly, some gay men consider frotting or oral sex as ways of maintaining their virginities, with anal penetration defined as sexual intercourse and resulting in virginity loss, while other gay men define frotting or oral sex as their main forms of sexual intercourse.[45][46][47][48] Lesbians may define oral sex or fingering as sexual intercourse and resulting in virginity loss,[10][49][50] and may also regard tribadism as a primary form of sexual activity.[2][51]

In 1999, a study by the Kinsey Institute examined the definition of sex based on a 1991 random sample of 599 college students from 29 U.S. states; it reported that while "virtually every college student they surveyed considered penile-vaginal intercourse to be sex," and only 19–20% said that anal intercourse was not sex, 60% said oral-genital contact (fellatio, cunnilingus) did not constitute having sex.[36][40][52][53] Similarly, a 2003 study published in the Canadian Journal of Human Sexuality focusing on definitions of having sex and noting studies concerning university students from the United States, the United Kingdom, and Australia reported that "[w]hile the vast majority of respondents (more than 97%) in these three studies included penile-vaginal intercourse in their definition of sex, fewer (between 70% and 90%) respondents considered penile-anal intercourse to constitute having sex" and that "oral-genital behaviours were defined as sex by between 32% and 58% of respondents".[11]

Another study by the Kinsey Institute sampled 484 people, ranging in ages 18–96. The study reported that nearly 95% of its participants "agreed that penile-vaginal intercourse meant 'had sex.' But the numbers changed as the questions got more specific". 11% of respondents based "had sex" on whether the man had achieved an orgasm, concluding that absence of an orgasm does not constitute "having had" sex. "About 80 percent of respondents said penile-anal intercourse meant 'had sex.' About 70 percent of people believed oral sex was sex."[36]

Variation and stimulation factors

Édouard-Henri Avril's depiction of a woman on top position, a position that is more likely to stimulate the clitoris.[1]

Sexual intercourse or other sexual activity can encompass various sexual behaviors, including different sex positions[2][5][11] or the use of sex toys. Foreplay may precede particular sexual activities, and often leads to sexual arousal of the partners, resulting in the erection of the penis or (usually) natural lubrication of the vagina.[54]

During coitus, 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, often continuing until orgasm in either or both partners is achieved.[30]

For human females, stimulation of the clitoris plays a significant role in sexual activity; 70–80% of women require direct clitoral stimulation to achieve orgasm,[55][56][57][58] though indirect clitoral stimulation (for example, via vaginal intercourse) may also be sufficient (see orgasm in females).[59][60] Because of this, some couples may engage in the woman on top position or the coital alignment technique, a technique combining the "riding high" variation of the missionary position with pressure-counterpressure movements performed by each partner in rhythm with sexual penetration, to maximize clitoral stimulation.[1][5][61]

Édouard-Henri Avril painting depicting cunnilingus in the life of Sappho

Anal sex involves stimulation of the anus, anal cavity, sphincter valve or rectum; it most commonly involves the insertion of a man's penis into another person's rectum, but pegging, use of other sex toys or fingers, to penetrate the anus, and anilingus, are also anal sex.[62][63]

Oral sex consists of all the sexual activities that involve the use of the tongue, rest of the mouth and throat to stimulate genitalia or anus. It is sometimes performed to the exclusion of all other forms of sexual activity, and may include the ingestion or absorption of semen or vaginal fluids.[13][64]

Fingering is the manual (genital) manipulation of the clitoris, rest of the vulva, vagina, or anus for the purpose of sexual arousal and sexual stimulation. It may constitute the entire sexual encounter or it may be part of mutual masturbation, foreplay or other sexual activities.[64][65]

Bonding and affection

In animals, copulation ranges from a purely reproductive activity to one of emotional bonding between mated pairs. Sexual intercourse and other sexual activity typically play a strong role in human bonding. For example, in many societies, it is normal for couples to have frequent intercourse while using some method of birth control (contraception), sharing pleasure and strengthening their emotional bond through sexual activity even though they are deliberately avoiding pregnancy.[8]

In humans and bonobos, the female undergoes relatively concealed ovulation so that both male and female partners commonly do not know whether she is fertile at any given moment. One possible reason for this distinct biological feature may be formation of strong emotional bonds between sexual partners important for social interactions and, in the case of humans, long-term partnership rather than immediate sexual reproduction.[8][9]

Humans, bonobos, dolphins, and chimpanzees are intelligent social animals, whose cooperative behavior can prove significantly more successful than an act carried out by a lone individual. In these animals, the use of sexual intercourse has evolved beyond reproduction, to apparently serve additional social functions.[26][27][28] Sexual activity 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.[8]

Duration and sexual difficulties

Sexual intercourse often ends when the man has ejaculated, and thus the partner might not have time to reach orgasm. In addition, premature ejaculation (PE) is common, and women often require a substantially longer duration of stimulation with a sexual partner than men do before reaching an orgasm.[54][66][67] Masters and Johnson found that men took approximately 4 minutes to reach orgasm with their partners; women took approximately 10–20 minutes to reach orgasm with their partners, but 4 minutes to reach orgasm when they masturbated.[54] Scholars state "many couples are locked into the idea that orgasms should be achieved only through intercourse [vaginal sex]" and that "[e]ven the word foreplay suggests that any other form of sexual stimulation is merely preparation for the 'main event.'... ...Because women reach orgasm through intercourse less consistently than men, they are more likely than men to have faked an orgasm".[54]

1790 painting of an Indian couple (a "prince and lady") prolonging sexual intercourse

In 1991, scholars from the Kinsey Institute stated, "The truth is that the time between penetration and ejaculation varies not only from man to man, but from one time to the next for the same man." They added that the appropriate length for intercourse is the length of time it takes for both partners to be mutually satisfied, emphasizing that Kinsey "found that 75 percent of men ejaculated within two minutes of penetration. But he didn't ask if the men or their partners considered two minutes mutually satisfying" and "more recent research reports slightly longer times for intercourse".[68] A 2008 survey of Canadian and American sex therapists stated that the average time for intromission was 7 minutes and that 1 to 2 minutes was too short, 3 to 7 minutes was adequate and 7 to 13 minutes desirable, while 10 to 30 minutes was too long.[69][70]

Anorgasmia is regular difficulty reaching orgasm after ample sexual stimulation, causing personal distress. This is significantly more common in women than in men.[67][71] The physical structure of the act of coitus favors penile stimulation over clitoral stimulation. The location of the clitoris then usually necessitates manual stimulation in order for the female to achieve orgasm.[54] Approximately 15% of women report difficulties with orgasm, 10% have never climaxed, and 40–50% have either complained about sexual dissatisfaction or experienced difficulty becoming sexually aroused at some point in their lives. A 1994 Laumann study reported that 75% of men and 29% of women always have orgasms with their partner.[72]

Vaginismus is the involuntary tensing of the pelvic floor musculature, making coitus, or any form of penetration of the vagina, distressing, painful, and sometimes impossible for women.[71][73][74] It is a conditioned reflex of the pubococcygeus muscle, and is sometimes referred to as the "PC muscle". Vaginismus can be a vicious cycle for women; they expect to experience pain during sexual intercourse, which then causes a muscle spasm, which leads to painful sexual intercourse. Treatment of vaginismus often includes both psychological and behavioral techniques, including the use of vaginal dilators. Additionally, the use of Botox as a medical treatment for vaginismus has been tested.[71][75] Some women also experience dyspareunia, a medical term specifically for painful or uncomfortable sexual intercourse.[76][77]

Approximately 40% of males suffer from some form of erectile dysfunction (ED) or impotence, at least occasionally.[78] 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. Moreover, using a drug to counteract the symptom—impotence—can mask the underlying problem causing the impotence and does not resolve it. A serious medical condition might be aggravated if left untreated.[79]

Premature ejaculation is more common than erectile dysfunction. "Estimates vary, but as many as 1 out of 3 men may be affected by [premature ejaculation] at some time."[66] "Masters and Johnson speculated that premature ejaculation is the most common sexual dysfunction, even though more men seek therapy for erectile difficulties." This is because "although an estimated 15 percent to 20 percent of men experience difficulty controlling rapid ejaculation, most do not consider it a problem requiring help, and many women have difficulty expressing their sexual needs".[68] The American Urological Association (AUA) estimates that premature ejaculation could affect 21 percent of men in the United States.[80] The Food and Drug Administration (FDA or USFDA) has examined the drug dapoxetine to treat premature ejaculation. In clinical trials, those with PE who took dapoxetine experienced sexual intercourse three to four times longer before orgasm than without the drug. Another ejaculation-related disorder is delayed ejaculation, which can be caused as an unwanted side effect of antidepressant medications such as Fluvoxamine.[81][82]

Though disability-related pain and mobility impairment can hamper sexual intercourse, in many cases, the most significant impediments to sexual intercourse for individuals with a disability are psychological.[83] In particular, people who have a disability can find sexual intercourse daunting due to issues involving their self-concept as a sexual being,[84][85] or a partner's discomfort or perceived discomfort.[83] Temporary difficulties can arise with alcohol and sex, as alcohol initially increases interest (through disinhibition) but decreases capacity with greater intake.[86][87]

Reproduction, reproductive methods and pregnancy

Reproduction among humans usually occurs with penile-vaginal penetration.[88] Male orgasm usually includes ejaculation, a series of muscular contractions that deliver semen containing male gametes known as sperm cells or spermatozoa from the penis into 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 (see sperm competition). 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 the endometrium – and a pregnancy begins.[88] Unlike most species, human sexual activity is not linked to periods of estrus and can take place at any time during the reproductive cycle, even during pregnancy.[89] Where a sperm donor has sexual intercourse with a woman who is not his partner, for the sole purpose of impregnating the woman, this may be known as natural insemination, as opposed to artificial insemination. However, most sperm donors donate their sperm through a sperm bank and pregnancy is achieved through artificial insemination.[90] Artificial insemination is performed with the express intention of attempting to impregnate the female, and, to this extent, its purpose is the medical equivalent of sexual intercourse.

In 2005, the World Health Organization (WHO) estimated that 123 million women become pregnant world-wide each year, and around 87 million of those pregnancies or 70.7% are unintentional. Approximately 46 million pregnancies per year reportedly end in induced abortion.[91] Approximately 6 million U.S. women become pregnant per year. Out of known pregnancies, two-thirds result in live births and roughly 25% in abortions; the remainder end in miscarriage. However, many more women become pregnant and miscarry without even realizing it, instead mistaking the miscarriage for an unusually heavy menstruation.[92] The U.S. teenage pregnancy rate fell by 27 percent between 1990 and 2000, from 116.3 pregnancies per 1,000 girls aged 15–19 to 84.5. This data includes live births, abortions, and fetal losses. Almost 1 million American teenage women, 10% of all women aged 15–19 and 19% of those who report having had intercourse, become pregnant each year.[93] Britain has been stated to have a teenage pregnancy rate similar to America's.[94]

Reproductive methods and pregnancy also extend to gay and lesbian couples. For gay male pairings, there is the option of surrogate pregnancy; for lesbian couples, there is donor insemination in addition to choosing surrogate pregnancy.[95][96] Further, developmental biologists have been researching and developing techniques to facilitate biological same-sex reproduction, though this has yet to be demonstrated in humans (see same-sex reproduction).[97][98] Surrogacy and donor insemination remain the primary methods. Surrogacy is an arrangement in which a woman carries and delivers a child for another couple or person. The woman may be the child's genetic mother (traditional surrogacy) or she may carry a pregnancy to delivery after having another woman's eggs transferred to her uterus (gestational surrogacy). Gay or lesbian pairings who want the host to have no genetic connection to the child may choose gestational surrogacy and enter into a contract with an egg donor. Gay male couples might decide that they should both contribute semen for the in vitro fertilisation (IVF) process, which further establishes the couple's joint intention to become parents.[96] Lesbian couples often have contracts drafted to extinguish the legal rights of the sperm donor, while creating legal rights for the parent who is not biologically related to the child.[99]

Safe sex and contraception

There are a variety of safe sex practices, including non-penetrative sex acts,[14][19] and heterosexual couples may use oral or anal sex (or both) as a means of birth control (contraception).[43][44][100] However, pregnancy can still occur with anal sex or other forms of penis-near-vagina sex (such as intercrural sex or other genital-genital rubbing) where sperm can be deposited near the entrance of the vagina and can travel along the vagina's lubricating fluids, and heterosexual sex in general can pose the risk of pregnancy because sperm may somehow be transported to the vaginal opening by way of fingers or other non-genital body parts.[101][102]

Safe sex is a relevant harm reduction philosophy,[17][103] and condoms are used as a form of safe sex and contraception. Condoms are widely recommended for the prevention of sexually transmitted infections (STIs).[17][103] According to reports by the National Institutes of Health (NIH) and World Health Organization (WHO), correct and consistent use of latex condoms reduces the risk of HIV/AIDS transmission by approximately 85–99% relative to risk when unprotected.[104][105]

Decisions and options concerning birth control can be affected by cultural reasons, such as religion, gender roles or folklore.[106] In the predominantly Catholic countries Ireland, Italy and the Philippines, fertility awareness and the rhythm method are emphasized while disapproval is expressed with regard to other contraceptive methods.[106] Worldwide, sterilization is a more common birth control method,[106] and use of the intrauterine device (IUD) is the most common and effective way of reversing contraception.[106][107] Conception and contraception are additionally a life-and-death situation in developing countries, where one in three women give birth before age 20; however, 90 percent of unsafe abortions in these countries could be prevented by effective contraception use.[106]

In 2004, the Guttmacher Institute indicated in 2002 that 62% of the 62 million women aged 15–44 are currently using a contraceptive method, that among U.S. women who practice contraception, the birth-control pill is the most popular choice (30.6%), followed by tubal sterilization (27.0%) and the male condom (18.0%), and that 27% of teenage women using contraceptives choose condoms as their primary method.[108] A 2006 Kaiser Family Foundation report stated that among sexually active 15- to 19-year-olds in the U.S., 83% of females and 91% of males reported using at least one method of birth control during last intercourse.[109]

The National Survey of Sexual Health and Behavior (NSSHB) indicated in 2010 that 1 of 4 acts of vaginal intercourse are condom-protected in the U.S. (1 in 3 among singles), condom use is higher among black and Hispanic Americans than among white Americans and those from other racial groups, and adults using a condom for intercourse were just as likely to rate the sexual extent positively in terms of arousal, pleasure and orgasm than when having intercourse without one.[110]

Prevalence

In 2003, Michael Bozon of the French Institut national d'études démographiques conducted a cross-cultural study titled At what age do women and men have their first sexual intercourse?. In the first group of the contemporary cultures he studied, which included sub-Saharan Africa (listing Mali, Senegal and Ethiopia), the data indicated that the age of men at sexual initiation in these societies is at later ages than that of women, but is often extra-marital; the study considered the Indian subcontinent to also fall into this group, though data was only available from Nepal.[111] In the second group, the data indicated families encouraged daughters to delay marriage, and to abstain from sexual activity before that time. However, sons are encouraged to gain experience with older women or prostitutes before marriage. Age of men at sexual initiation in these societies is at lower ages than that of women; this group includes Latin cultures, both from southern Europe (Portugal, Greece and Romania are noted) and from Latin America (Brazil, Chile, and the Dominican Republic). The study considered many Asian societies to also fall into this group, although matching data was only available from Thailand.[111] In the third group, age of men and women at sexual initiation was more closely matched; there were two sub-groups, however. In non-Latin, Catholic countries (Poland and Lithuania are mentioned), age at sexual initiation was higher, suggesting later marriage and reciprocal valuing of male and female virginity. The same pattern of late marriage and reciprocal valuing of virginity was reflected in Singapore and Sri Lanka. The study considered China and Vietnam to also fall into this group, though data were not available.[111] In northern and eastern European countries, age at sexual initiation was lower, with both men and women involved in sexual activity before any union formation; the study listed Switzerland, Germany and the Czech Republic as members of this group.[111]

According to a survey conducted in the United States by the 1995 National Survey of Adolescent Men and the 1995 National Survey of Family Growth, at least 3/4 of all men and women in the U.S. engaged in sexual intercourse by their late teenage years, and more than 2/3 of all sexually experienced teens had two or more partners.[112] Based on the 2002 National Survey of Family Growth, published by the U.S. Department of Health and Human Services, the average age of first sexual intercourse in U.S. participants aged 15 to 44 was 17.3 years for females and 17.0 years for males.[113][114][115] Special tabulations by the National Center for Health Statistics suggest that this figure has changed between 2006 and 2010 to 17.1 years for both males and females.[116] The Centers for Disease Control and Prevention (CDC) stated that 45.5 percent of girls and 45.7 percent of boys had engaged in sexual activity by 19 in 2002; in 2011, reporting their research from 2006–2010, the CDC stated that 43% of American unmarried teenage girls and 42% of American unmarried teenage boys have ever engaged in sexual intercourse.[117] The CDC also reports that American girls will most likely lose their virginity to a boy who is 1 to 3 years older than they are.[117]

According to the U.S. Department of Health and Human Services, teenagers are delaying sex until older ages.[118] Between 1988 and 2002, the percentage of people in the U.S. who have had intercourse between the ages of 15 to 19 fell from 60 to 46 percent for males, and from 51 to 46 percent for females.[118] Additionally, a 2006 survey conducted by The Observer suggested that most adolescents in Britain were waiting longer to have sexual intercourse than they were only a few years earlier.[119] In 2002, it was reported that 32% of British teenagers were having sex before the age of 16, while, in 2006, it was only 20%. The average age a British teenager lost his/her virginity was reportedly 17.13 years in 2002; in 2006, it was 17.44 years on average for girls and 18.06 for boys. The most notable drop among teens who reported having sex was 14- and 15-year-olds.[119] A 2008 survey conducted by YouGov for Channel 4 suggested that 40% of all 14- to 17-year-olds are sexually active, 74% of sexually active 14- to 17-year-olds have had a sexual experience under the age of consent, and 6% of teens would wait until marriage before having sex.[120]

Health effects

Benefits

In humans, sexual activity has been reported to produce health benefits as varied as improved sense of smell,[121] stress and blood pressure reduction,[122][123] increased immunity,[124] and decreased risk of prostate cancer.[125][126][127] Sexual intimacy, as well as orgasms, increases levels of the hormone oxytocin, also known as "the love hormone", which helps people bond and build trust.[128][129][130] Sexual activity is also known as one of many mood repair strategies, which means it can be used to help dissipate feelings of sadness or depression.[131] A long-term study of 3,500 people between 30 and 101 by clinical neuropsychologist David Weeks, head of old age psychology at the Royal Edinburgh Hospital in Scotland, found that "sex helps you look between four and seven years younger", according to impartial ratings of the subjects' photographs. Exclusive causation, however, is unclear, and the benefits may be indirectly related to sex and directly related to significant reductions in stress, greater contentment, and better sleep that sex promotes.[132][133][134]

Risks

Sexually transmitted infections (STIs) can be spread by person-to-person sexual contact, especially penetrative sexual intercourse. There are 19 million new cases of sexually transmitted infections every year in the U.S.,[135] and, in 2005, the World Health Organization estimated that 448 million people aged 15–49 were being infected a year with curable STIs such as syphilis, gonorrhea and chlamydia.[136] In 2006, The Independent newspaper reported that the biggest rise in sexually transmitted infections was in syphilis, which rose by more than 20%, while increases were also seen in cases of genital warts and herpes.[137]

STIs are caused by bacteria, viruses and parasites, which are passed from person to person during sexual contact. Some, in particular HIV and syphilis, can also be passed in other ways, including from mother to child during pregnancy and childbirth, through blood products, and by shared hypodermic needles.[136] Gonococcal or chlamydial infections often produce no symptoms. Untreated chlamydial infection can lead to female infertility and ectopic pregnancy. Human papillomavirus can lead to genital and cervical cancers. Syphilis can result in stillbirths and neonatal deaths. Untreated gonococcal infections result in miscarriages, preterm births and perinatal deaths. Infants born to mothers with untreated gonorrhoea or chlamydia can develop serious eye infections, which can lead to blindness.[136] Hepatitis B can also be transmitted through sexual contact.[138] Globally, there are about 350 million chronic carriers of hepatitis B.[139]

Some STIs can cause ulceration, and, even if they do not, they increase the risk of both acquiring and passing on HIV up to ten-fold.[136] HIV is one of the world's leading infectious killers, and, in 2010, approximately 30 million people were estimated to have died because of it since the beginning of the epidemic. Of the 2.7 million new HIV infections estimated to occur worldwide in 2010, 1.9 million (70%) were in Africa. "The estimated 1.2 million Africans who died of HIV-related illnesses in 2010 comprised 69% of the global total of 1.8 million deaths attributable to the epidemic."[140] It is diagnosed by blood tests, and while no cure has been found, it can be controlled with antiretroviral drugs, and patients can enjoy healthy and productive lives.[141]

The most effective way to avoid sexually transmitted infections is to abstain from sexual intercourse, including vaginal, anal, and oral sex, or to have sexual intercourse only with one long-term, uninfected partner who also remains entirely monogamous. The World Health Organization states, "Male latex condoms, when used consistently and correctly, are highly effective in reducing the transmission of HIV and other sexually transmitted infections, including gonorrhoea, chlamydial infection and trichomoniasis."[136] In cases where infection is suspected, early medical intervention is highly beneficial in all cases.

Sexual activity can directly cause death, particularly due to coronary circulation complications, which is sometimes termed a coital coronary;[142][143] people, especially those who get little or no physical exercise, have a slightly increased risk of triggering a heart attack or sudden cardiac death when they engage in sexual intercourse or any vigorous physical exercise that is engaged in on a sporadic basis.[143] Increased risk is temporary with incidents occurring within a few hours of the activity. Regular exercise reduces, but does not eliminate, the increased risk.[143]

Social effects

Adults

Some researchers, such as Alex Comfort, posit three potential advantages of sexual intercourse in humans, which are not mutually exclusive: reproductive, relational, and recreational.[8][144] While the development of the birth-control pill and other highly effective forms of contraception in the mid- and late 20th century increased people's ability to segregate these three functions, they still overlap a great deal and in complex patterns. For example: A fertile couple may have sexual intercourse while contracepting not only to experience sexual pleasure (recreational), but also as a means of emotional intimacy (relational), thus deepening their bonding, making their relationship more stable and more capable of sustaining children in the future (deferred reproductive). This same couple may emphasize different aspects of sexual intercourse on different occasions, being playful during one episode of intercourse (recreational), experiencing deep emotional connection on another occasion (relational), and later, after discontinuing contraception, seeking to achieve pregnancy (reproductive, or more likely reproductive and relational).[144]

Nearly all Americans marry during their lifetime; yet close to half of all first marriages are expected to end in separation or divorce, many within a few years,[145] and subsequent marriages are even more likely to end.[146] Sexual dissatisfaction is associated with increased risk of divorce and relationship dissolution.[146]

According to the National Survey of Sexual Health and Behavior (NSSHB), in 2010, men whose most recent sexual encounter was with a relationship partner reported greater arousal, greater pleasure, fewer problems with erectile function, orgasm, and less pain during the event than men whose last sexual encounter was with a non-relationship partner.[110] According to the Journal of Counseling & Development, many women express that their most satisfying sexual experiences entail being connected to someone, rather than solely basing satisfaction on orgasm.[147]

Adolescents

With regard to adolescent sexuality, sexual intercourse is often for relational and recreational purposes as well. However, teenage pregnancy is usually disparaged, and research suggests that the earlier onset of puberty for children puts pressure on children and teenagers to act like adults before they are emotionally or cognitively ready,[148][149] and thus are at risk to suffer from emotional distress as a result of their sexual activities.[149][150][151][152][153] Some studies have concluded that engaging in sex leaves adolescents, and especially girls, with higher levels of stress and depression.[154] A majority of adolescents in the United States have been provided with some information regarding sexuality,[155] though there have been efforts among social conservatives in the United States government to limit sex education in public schools to abstinence-only sex education curricula.[156]

One group of Canadian researchers found a relationship between self-esteem and sexual activity. They found that students, especially girls, who were verbally abused by teachers or rejected by their peers were more likely than other students to engage in sex by the end of the Grade 7. The researchers speculate that low self-esteem increases the likelihood of sexual activity: "low self-esteem seemed to explain the link between peer rejection and early sex. Girls with a poor self-image may see sex as a way to become 'popular', according to the researchers".[157]

In India, there is growing evidence that adolescents are becoming more sexually active outside of marriage, which is feared to lead to an increase in the spread of HIV/AIDS among adolescents, as well as the number of unwanted pregnancies and abortions, and add to the conflict between contemporary social values. In India, adolescents have relatively poor access to health care and education, and with cultural norms opposing extramarital sexual behavior, "these implications may acquire threatening dimensions for the society and the nation".[158]

Not all views on adolescent sexual behavior are negative, however. Psychiatrist Lynn Ponton writes, "All adolescents have sex lives, whether they are sexually active with others, with themselves, or seemingly not at all," and that viewing adolescent sexuality as a potentially positive experience, rather than as something inherently dangerous, may help young people develop healthier patterns and make more positive choices regarding sexual activity.[148] Similarly, others state that long-term romantic relationships allow adolescents to gain the skills necessary for high-quality relationships later in life[159] and develop feelings of self-worth. Overall, positive romantic relationships among adolescents can result in long-term benefits. High-quality romantic relationships are associated with higher commitment in early adulthood[160] and are positively associated with self-esteem, self-confidence, and social competence.[161][162]

Ethical, religious, and legal views

General

18th-century erotic painting from India
Erotic painting on ancient Greek kylix

While sexual intercourse is the natural mode of reproduction for the human species, humans have intricate moral and ethical guidelines which regulate the practice of sexual intercourse and vary according to religious and governmental laws. Some governments and religions also have strict designations of "appropriate" and "inappropriate" sexual behavior, which include restrictions on the types of sex acts which are permissible. A historically prohibited or regulated sex act is anal sex.[163][164]

Consent and sexual offenses

Sexual intercourse with a person against their will, or without their informed legal consent, is rape, and is considered a serious crime in most countries.[165] More than 90% of rape victims are female, 99% of rapists male, and only about 5% of rapists are strangers to the victims.[166]

Most developed countries have age of consent laws specifying the minimum legal age a person may engage in sexual intercourse with substantially older persons, usually set at about 16–18, while the legal age of consent ranges from 12–20 years of age or is not a matter of law in other countries.[167] Sex with a person under the age of consent, regardless of their stated consent, is often considered to be sexual assault or statutory rape depending on differences in ages of the participants. Some countries treat any sex with a person of diminished or insufficient mental capacity to give consent, regardless of age, as rape.[168]

Scholars state "[p]rior to the 1970s, rape definitions of sex often included only penile-vaginal sexual intercourse"[169] and that if "sex means penile-vaginal intercourse, then rape means forced penile-vaginal intercourse, and other sexual behaviors – such as fondling a person's genitals without her or his consent, forced oral sex, and same-sex coercion – are not considered rape"; they state that [a]lthough some other forms of forced sexual contact are included within the legal category of sodomy (e.g., anal penetration and oral-genital contact), many unwanted sexual contacts have no legal grounding as rape in some states".[42]

The expression "sexual intercourse" has been used as a term of art in England and Wales and New York State. In England and Wales, from its enactment to its repeal on the 1 May 2004,[170] section 44 of the Sexual Offences Act 1956 read:

Where, on the trial of any offence under this Act, it is necessary to prove sexual intercourse (whether natural or unnatural), it shall not be necessary to prove the completion of the intercourse by the emission of seed, but the intercourse shall be deemed complete upon proof of penetration only.
Unnatural

This expression refers to buggery, including both buggery with a person and buggery with an animal.[171] Zoophilia (bestiality) is sexual activity between humans and non-human animals or a preference for or fixation on such practice. People who practice zoophilia are known as zoophiles,[172] zoosexuals, or simply "zoos".[173] Zoophilia may also be known as zoosexuality.[173] Zoophilia is a paraphilia.[174][175][176][177] Sex with animals is not outlawed in some jurisdictions, but, in most countries, it is illegal under animal abuse laws or laws dealing with crimes against nature.

Penetration

According to cases decided on the meaning of the statutory definition of carnal knowledge under the Offences against the Person Act 1828, which was in identical terms to this definition, the slightest penetration was sufficient.[178] The book "Archbold" said that it "submitted" that this continued to be the law under the new enactment.[179]

For most definitions of rape, there is a broad "conceptualization of sex, including many kinds of sexual penetration (e.g., penile-vaginal intercourse, fellatio, cunnilingus, anal intercourse, or penetration of the genitals or rectum by an object)".[169]

Continuing act

See Kaitamaki v R [1985] AC 147, [1984] 3 WLR 137, [1984] 2 All ER 435, 79 Cr App R 251, [1984] Crim LR 564, PC (decided under equivalent legislation in New Zealand).

Section 7(2) of the Sexual Offences (Amendment) Act 1976 contained the following words: "In this Act . . . references to sexual intercourse shall be construed in accordance with section 44 of the Sexual Offences Act 1956 so far as it relates to natural intercourse (under which such intercourse is deemed complete on proof of penetration only)". The Act made provision, in relation to rape and related offences, for England and Wales, and for courts-martial elsewhere.

From 3 November 1994 to 1 May 2004, section 1(2)(a) of the Sexual Offences Act 1956 (as substituted by section 142 of the Criminal Justice and Public Order Act 1994) referred to "sexual intercourse with a person (whether vaginal or anal)". This section created the offence of rape in England and Wales.

The penal code in New York State provides: § 130.00 Sex offenses; definitions of terms: 1. "Sexual intercourse" has its ordinary meaning and occurs upon any penetration, however slight.[180]

Romantic relationships

Sexual orientation and gender

There are various legal positions regarding the definition and legality of sexual intercourse between persons of the same sex or gender. For example, in the 2003 New Hampshire Supreme Court case Blanchflower v. Blanchflower, it was held that female same-sex sexual relations did not constitute sexual intercourse, based on a 1961 definition from Webster's Third New International Dictionary; and thereby an accused wife in a divorce case was found not guilty of adultery. Some countries, such as Islamic countries, consider homosexual behavior to be an offense punishable by imprisonment or execution.[181]

Marriage and relationships

Sexual intercourse has traditionally been considered an essential part of a marriage; many religious customs required consummation of the marriage by sexual intercourse, and the failure for any reason to consummate the marriage was a ground for annulment, which did not require a divorce process. Annulment declaration implied that the marriage was void from the start – i.e. there was in law no marriage. Furthermore, continuing sexual relations between the marriage partners is commonly considered a 'marital right' by many religions, permissible to married couples, generally for the purpose of reproduction. Today, there is wide variation in the opinions and teachings about sexual intercourse relative to marriage and other intimate relationships by the world's religions. Examples:

In some cases, the sexual intercourse between two people is seen as counter to religious law or doctrine. In many religious communities, including the Catholic Church and Mahayana Buddhists, religious leaders are expected to refrain from sexual intercourse in order to devote their full attention, energy, and loyalty to their religious duties.[199]

Opposition to same-sex marriage is largely based on the belief that sexual intercourse and sexual orientation should be of a heterosexual nature.[200][201][202][203] The recognition of such marriages is a civil rights, political, social, moral, and religious issue in many nations, and the conflicts arise over whether same-sex couples should be allowed to enter into marriage, be required to use a different status (such as a civil union, which either grant equal rights as marriage or limited rights in comparison to marriage), or not have any such rights. A related issue is whether the term marriage should be applied.[185][204][205]

Other animals

Mating houseflies

With regard to zoology, copulation is often termed as the process in which a male introduces sperm into the female's body.[24][34] Spiders have separate male and female sexes. Before mating and copulation, the male spider spins a small web and ejaculates on to it. He then stores the sperm in reservoirs on his large pedipalps, from which he transfers sperm to the female's genitals. Females can store sperm indefinitely.[206]

Many animals which live in water use external fertilization, whereas internal fertilization may have developed from a need to maintain gametes in a liquid medium in the Late Ordovician epoch. Internal fertilization with many vertebrates (such as reptiles, some fish, and most birds) occur via cloacal copulation (see also hemipenis), while mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.

However, some terrestrial arthropods do use external fertilization. For primitive insects, the male deposits spermatozoa on the substrate, sometimes stored within a special structure; courtship involves inducing the female to take up the sperm package into her genital opening, but there is no actual copulation. In groups such as dragonflies and spiders, males extrude sperm into secondary copulatory structures removed from their genital opening, which are then used to inseminate the female. In dragonflies, it is a set of modified sternites on the second abdominal segment; in spiders, it is the male pedipalps. In advanced groups of insects, the male uses its aedeagus, a structure formed from the terminal segments of the abdomen, to deposit sperm directly (though sometimes in a capsule called a "spermatophore") into the female's reproductive tract.

Humans, bonobos,[26] chimpanzees and dolphins[27] are species known to engage in heterosexual behaviors even when the female is not in estrus, which is a point in her reproductive cycle suitable for successful impregnation. These species, and others, are also known to engage in homosexual behaviors.[28] 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 sexual intercourse has evolved beyond reproduction, to apparently serve additional social functions. Sexual activity 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.[8]

See also

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