Sexual intercourse, also known as copulation orcoitus, commonly denotes the insertion and thrusting of amale's penis into a female'svagina for the purposesof sexual pleasure or reproduction.^[3][4][5][6]The term can also describe other sexualpenetrative acts, such as anal sex, oralsex, fingering,or use of a strap-ondildo.^[3][6][7]

Sexual intercourse often plays a strong role in human bonding,usually being used solely for pleasure and commonly leading tostronger emotional bonds,^[8]and there are a variety of views concerning what constitutes sexualintercourse or other sexual activity.^[9][10]For example, non-penetrativesex (such as non-penetrative cunnilingus) hasbeen referred to as "outercourse",^[11][12][13]but may also be among the sexualacts contributing to human bonding and considered intercourse.The term sex, often a shorthand for sexualintercourse, can be taken to mean any form of sexual activity(i.e. all forms of intercourse and outercourse).^{[6][9][14][15]}Because individuals can be at risk of contracting sexuallytransmitted infections during these activities,^[16][17]although the transmission risk is significantly reduced duringnon-penetrative sex,^[12][18]safe sex practices areadvised.^[16]

In human societies, some jurisdictions have placed variousrestrictive laws against certain sexual activities, such as sexwith minors, incest,extramaritalsex, position-of-trustsex, prostitution,sodomy, public lewdness,rape,and bestiality. Religiousbeliefs can play a role in decisions about sex, or its purpose, aswell; for example, beliefs about what sexual acts constitutevirginity loss or thedecision to make a virginitypledge.^[19][20][21]Some sections of Christianitycommonly view sex between a married couple for the purpose ofreproduction as holy, while other sections may not.^[22]Modern Judaism and Islam viewsexual intercourse between husband and wife as a spiritual andedifying action. Hinduism and Buddhism views onsexuality have differing interpretations.

Sexualintercourse between non-human animals is more often referred toas copulation; for most non-human animals, mating and copulationoccurs at the point of estrus (the mostfertile period of time in the female's reproductive cycle),^[23][24]which increases the chances of successfulimpregnation. However, bonobos,^[25]dolphins,^[26]and chimpanzees are knownto engage in sexual intercourse even when the female is not inestrus, and to engage in sex acts with same-sex partners.^[26][27]Like humans engaging in sex primarily for pleasure,^[8]this behavior in the aforementioned animals is also presumed to befor pleasure,^[28]and a contributing factor to strengthening their socialbonds.^[8]

Practices

Definitions and stimulation factors

Sexual intercourse is also known as copulation, coitus orcoition; coitus is derived from the Latin word coitioor coire, meaning "a coming together or joining together" or"to go together" and is usually defined as penile-vaginalpenetration.^{[3][29][30][31]}Penetration by the hardened, erect penis is additionally known asintromission, or by the Latin name immissiopenis (Latinfor "insertion of the penis").^[32]Copulation, although usually used to describe the matingprocess of non-human animals, is defined as "the transfer of thesperm from male tofemale" or "the act of sexual procreation between a man and awoman".^[33][34]As such, common vernacular and research often limit sexualintercourse to penile-vaginal penetration, with virginity loss beingpredicated on the activity,^{[9][10][19][20]}while the term sex and the phrase "having sex" commonly meanany sexual activity – penetrativeand non-penetrative.^[9][14][35]The WorldHealth Organization states that non-English languages andcultures use different terms for sexual activity, with slightlydifferent meanings.^[14]

Anal and oralsex may be regarded as sexual intercourse,^[3][6][9]but they, as well as non-penetrative sex acts, may also be regardedas maintaining "technicalvirginity" or as "outercourse," regardless of any penetrativeaspects.^[20][36]Heterosexual couples often engage in these practices not only forsexual pleasure, but as a way of avoiding pregnancy andmaintaining that they are virgins because they have not yet engagedin penile-vaginal sex.^{[10][20][37][38]}Likewise, some gay men view frotting or oral sexas maintaining their virginity, with anal penetration regarded asvirginity loss, while other gay men consider frotting or oral sexto be their main forms of intercourse.^{[39][40][41][42]}Lesbians may regard oralsex or fingeringas loss of virginity,^[43][44]and may also regard tribadism as a primaryform of sexual activity.^[2][45]

In 1999, a study by the Kinsey Institute, published in JAMA(the Journal of the American Medical Association), examinedthe definition of sex based on a 1991 random sample of 599 collegestudents from 29 U.S. states; it reported that 60% saidoral-genital contact (fellatio, cunnilingus) did notconstitute having sex.^[35][46]Similarly, a 2003 study published in the CanadianJournal of Human Sexuality focusing on definitions ofhaving sex and noting studies concerning university students fromthe United States, the United Kingdom, and Australia reported that"[w]hile the vast majority of respondents (more than 97%) in thesethree studies included penile-vaginal intercourse in theirdefinition of sex, fewer (between 70% and 90%) respondentsconsidered penile-anal intercourse to constitute having sex" andthat "oral-genital behaviours were defined as sex by between 32%and 58% of respondents".^[9]A different study by the Kinsey Institute sampled 484 people,ranging in ages 18–96. "Nearly 95 percent of people in the studyagreed that penile-vaginal intercourse meant 'had sex.' But thenumbers changed as the questions got more specific." 11 percent ofrespondents based "had sex" on whether the man had achieved anorgasm, concluding thatabsence of an orgasm does not constitute "having had" sex. "About80 percent of respondents said penile-anal intercourse meant 'hadsex.' About 70 percent of people believed oral sex wassex."^[35]

Sexual activity can encompass a number of sexual behaviors,including different sexpositions^[2][3][9]or the use of sex toys. Foreplay may precedeparticular sexual activities, and often leads to sexual arousal ofthe partners, resulting in the erection of thepenis or (usually)natural lubricationof the vagina.^[47]

During coitus, the partners move their hips to move the penisbackward and forward inside the vagina to cause friction, typicallywithout fully removing the penis. In this way, they stimulatethemselves and each other, often continuing until orgasm in eitheror both partners is achieved.^[29]For human females, stimulation of the clitoris plays asignificant role in sexual activity; 70–80% require direct clitoralstimulation to achieve orgasm,^{[48][49][50][51]}though indirect clitoral stimulation (for example, via vaginalintercourse) may also be sufficient (see orgasm infemales).^[52][53]As such, some couples may engage in the woman ontop position or the coitalalignment technique, a technique combining the "riding high"variation of the missionaryposition with pressure-counterpressure movements performed byeach partner in rhythm with sexual penetration, to maximizeclitoral stimulation.^{[1][3][54][55]}

Anal sex involves stimulation of the anus, anal cavity,sphincter valve or rectum, mostly commonlyemploying the insertion of a man's penis into another person'srectum.^[56][57]Oral sex consists of all the sexual activities that involve the useof the tongue, rest of the mouth and throat to stimulate genitalia. It issometimes performed to the exclusion of all other forms of sexualactivity, and may include the ingestion or absorption of semen orvaginal fluids.^[11][58]Fingering is the manual (genital) manipulation of the clitoris,vulva, vagina, or anus for the purpose of sexual arousal and sexualstimulation. It may constitute the entire sexual encounter or itmay be part of mutual masturbation, foreplay or other sexualactivities.^[58][59]

Bondingand affection

In animals, copulation ranges from a purely reproductiveactivity to one of emotional bonding between mated pairs. Sexualintercourse and other sexual activity typically plays a powerfulrole in human bonding. Forexample, in many societies, it is normal for couples to havefrequent intercourse while using some method of birth control(contraception), sharing pleasure and strengthening their emotionalbond through sexual activity even though they are deliberatelyavoiding pregnancy.^[8]

In humans and bonobos, the femaleundergoes relatively concealedovulation so that both male and female partners commonly do notknow whether she is fertile at any given moment. One possiblereason for this distinct biological feature may be formation ofstrong emotional bonds between sexual partners important for socialinteractions and, in the case of humans, long-term partnershiprather than immediate sexual reproduction.^[8]

Humans, bonobos, dolphins, and chimpanzees are allintelligent social animals, whose cooperative behavior provessignificantly more successful than that of any individual alone. Inthese animals, the use of sex has evolved beyond reproduction, toapparently serve additional social functions.^[25][26][27]Sex reinforces intimate social bonds between individuals to formlarger social structures. The resulting cooperation encouragescollective tasks that promote the survival of each member of thegroup.^[8]

Duration and sexual difficulties

Sexual intercourse often ends when the man has ejaculated, andthus the partner might not have time to reach orgasm. In addition,prematureejaculation (PE) is common, and women often require asubstantially longer duration of stimulation with a sexual partnerthan men do before reaching an orgasm.^[47][60][61]Masters andJohnson found that men took about 4 minutes to reach orgasmwith their partners; women took about 10–20 minutes to reach orgasmwith their partners, but 4 minutes to reach orgasm when theymasturbated.^[47]Scholars Weiten, Dunn and Hammer have reasoned, "Unfortunately,many couples are locked into the idea that orgasms should beachieved only through intercourse [penetrative vaginal sex]. Eventhe word foreplay suggeststhat any other form of sexual stimulation is merely preparation forthe 'main event.'... ...Because women reach orgasm throughintercourse less consistently than men, they are more likely thanmen to have faked an orgasm."^[47]

In 1991, scholars June M. Reinisch and Ruth Beasley of theKinsey Institute stated, "The truth is that the time betweenpenetration and ejaculation varies not only from man to man, butfrom one time to the next for the same man." They added that theappropriate length for intercourse is the length of time it takesfor both partners to be mutually satisfied, emphasizing that Kinsey"found that 75 percent of men ejaculated within two minutes ofpenetration. But he didn't ask if the men or their partnersconsidered two minutes mutually satisfying" and "more recentresearch reports slightly longer times for intercourse".^[62]A 2008 survey of Canadian and American sex therapistsstated that the average time for intromission was 7 minutes andthat 1 to 2 minutes was too short, 3 to 7 minutes was adequate and7 to 13 minutes desirable, while 10 to 30 minutes was toolong.^[63][64]

Anorgasmia is regulardifficulty reaching orgasm after ample sexual stimulation, causingpersonal distress. This is much more common in women than inmen.^[61][65]The physical structure of the act of coitus favors penilestimulation over clitoral stimulation.The location of the clitoris then usually necessitates manualstimulation in order for the female to achieve orgasm.^[47]About 15% of women report difficulties with orgasm, 10% have neverclimaxed, and 40–50% have either complained about sexualdissatisfaction or experienced difficulty becoming sexually arousedat some point in their lives. A 1994 Laumann study reported that75% of men and 29% of women always have orgasms with theirpartner.^[66]

Vaginismus is theinvoluntary tensing of the pelvic floor musculature, making coitusdistressing, painful, and sometimes impossible for women.^[65][67][68]It is a conditioned reflex of the pubococcygeus muscle, sometimesreferred to as the "PC muscle". Vaginismus can be a vicious cyclefor women; they expect to experience pain during intercourse, whichthen causes a muscle spasm, which leads to painful intercourse.Treatment of vaginismus often includes both psychological andbehavioral techniques, including the use of vaginaldilators. A new medical treatment using Botoxis in the testing phase.^[65][69]Some women also experience dyspareunia, amedical term for painful or uncomfortable intercourse, of unknowncause.^[70][71]

About 40% of males suffer from some form of erectiledysfunction (ED) or impotence, atleast occasionally.^[72]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 drugsbecause they are accompanied by serious risks such as increasedchance of heart attack. Moreover, using a drug to counteract thesymptom—impotence—can mask the underlying problem causing theimpotence and does not resolve it. A serious medical conditionmight be aggravated if left untreated.^[73]

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."^[60]"Masters and Johnson speculated that premature ejaculation is themost common sexual dysfunction, even though more men seek therapyfor erectile difficulties." This is because, "although an estimated15 percent to 20 percent of men experience difficulty controllingrapid ejaculation, most do not consider it a problem requiringhelp, and many women have difficulty expressing their sexualneeds".^[62]The AmericanUrological Association (AUA) estimates that prematureejaculation could affect 21 percent of men in the UnitedStates.^[74]The Foodand Drug Administration (FDA or USFDA) is examining the drugdapoxetine to treatpremature ejaculation. In clinical trials, those with PE who tookdapoxetine experienced intercourse three to four times longerbefore orgasm than without the drug. Another ejaculation-relateddisorder is delayedejaculation, which can be caused as an unwanted side effect ofantidepressant medications such as Fluvoxamine.^[75][76]

Although disability-relatedpain and mobility impairment can hamper intercourse, in many casesthe most significant impediments to intercourse for individualswith a disability are psychological.^[77]In particular, people who have a disability can find intercoursedaunting due to issues involving their self-conceptas a sexual being,^[78][79]or partner's discomfort or perceived discomfort.^[77]Temporary difficulties can arise with alcohol andsex, as alcohol initially increases interest (throughdisinhibition) but decreases capacity with greater intake.^[80]

Reproduction, reproductive methods andpregnancy

Reproduction among humans usually occurs with penile-vaginalpenetration.^[81]Male orgasm usually includes ejaculation, aseries of muscular contractionsthat deliver semen containing malegametes known as sperm cells orspermatozoa from the penis into the vagina. The subsequent route ofthe sperm from the vault of the vagina is through the cervix andinto the uterus, and then into thefallopian tubes.Millions of sperm are present in each ejaculation, to increase thechances of one fertilizing an egg or ovum (see spermcompetition). When a fertile ovum from the female is present inthe fallopian tubes, the male gamete joins with the ovum, resultingin fertilization andthe formation of a new embryo. When a fertilizedovum reaches the uterus, it becomes implanted in the lining of theuterus – known as the endometrium – and apregnancybegins.^[81]Unlike most species, human sexual activity is not linked to periodsof estrus and can take placeat any time during the reproductive cycle, even duringpregnancy.^[82]Where a sperm donor hassexual intercourse with a woman who is not his partner, for thesole purpose of impregnating the woman, this may be known asnatural insemination, asopposed to artificialinsemination. However, most sperm donors donate their spermthrough a sperm bank andpregnancy is achieved through artificial insemination.^[83]Artificial insemination is performed with the express intention ofattempting to impregnate the female, and, to this extent, itspurpose is the medical equivalent of sexual intercourse.

In 2005, the WorldHealth Organization (WHO) estimated that 123 million womenbecome pregnant world-wide each year, and around 87 million ofthose pregnancies or 70.7% are unintentional. About 46 millionpregnancies per year reportedly end in induced abortion.^[84]About 6 million U.S. women become pregnant per year. Out of knownpregnancies, two-thirds result in live births and roughly 25% inabortions; the remainder end in miscarriage. However, many morewomen become pregnant and miscarry without even realizing it,instead mistaking the miscarriage for an unusually heavy menstruation.^[85]The U.S. teenagepregnancy rate fell by 27 percent between 1990 and 2000, from116.3 pregnancies per 1,000 girls aged 15–19 to 84.5. This dataincludes live births, abortions, and fetal losses. Almost 1 millionAmerican teenage women, 10% of all women aged 15–19 and 19% ofthose who report having had intercourse, become pregnant eachyear.^[86]Britain has been stated to have a teenage pregnancy rate similar toAmerica's.^[87]

Reproductive methods and pregnancy also extend to gay andlesbian couples. For gay male pairings, there is the option ofsurrogate pregnancy;for lesbian couples, there is donor insemination in addition tochoosing surrogate pregnancy.^[88][89]Further, developmental biologists have been researching anddeveloping techniques to facilitate biological same-sexreproduction, though this has yet to be demonstrated in humans (seesame-sexreproduction).^[90][91]Surrogacy and donor insemination remain the primary methods.Surrogacy is an arrangement in which a woman carries and delivers achild for another couple or person. The woman may be the child'sgenetic mother (traditional surrogacy) or she may carry a pregnancyto delivery after having another woman's eggs transferred to heruterus (gestational surrogacy). Gay or lesbian pairings who wantthe host to have no genetic connection to the child may choosegestational surrogacy and enter into a contract with an eggdonor. Gay male couples might decide that they should bothcontribute semen for the in vitrofertilisation (IVF) process, which further establishes thecouple's joint intention to become parents.^[89]Lesbian couples often have contracts drafted to extinguish thelegal rights of the sperm donor, while creating legal rights forthe parent who is not biologically related to the child.^[92]

Safesex and contraception

There are a variety of safe sex practices,including non-penetrative sex acts,^[12][18]and heterosexual couples may use oral or anal sex (or both) as ameans of birth control(contraception).^{[36][37][38][93]}Safe sex is a relevant harm reductionphilosophy.^[16][94]Condoms are used as aform of safe sex and as a form of contraception. Condoms anddental dams arewidely recommended for the prevention of sexuallytransmitted infections (STIs). According to reports by theNationalInstitutes of Health (NIH) and WorldHealth Organization (WHO), correct and consistent use of latexcondoms reduces the risk of HIV/AIDS transmissionby approximately 85–99% relative to risk when unprotected.^[95][96]

In 2004, the GuttmacherInstitute indicated in 2002 that 62% of the 62 million womenaged 15–44 are currently using a contraceptive method, that amongU.S. women who practice contraception, thePill is the most popular choice (30.6%), followed by tubalsterilization (27.0%) and the male condom (18.0%), and that 27% ofteenage women using contraceptives choose condoms as their primarymethod.^[97]A 2006 KaiserFamily Foundation report stated that among sexually active 15-to 19-year-olds in the U.S., 83% of females and 91% of malesreported using at least one method of birth control during lastintercourse.^[98]

The National Survey of Sexual Health and Behavior (NSSHB) indicatedin 2010 that 1 of 4 acts of vaginal intercourse arecondom-protected in the U.S. (1 in 3 among singles), condom use ishigher among black and Hispanic Americans than among whiteAmericans and those from other racial groups, and adults using acondom for intercourse were just as likely to rate the sexualextent positively in terms of arousal, pleasure and orgasm thanwhen having intercourse without one.^[99]

Prevalence of sexual activity

In 2003, Michael Bozon of the French Institut national d'études démographiques conducted across-cultural study titled At what age do women and men havetheir first sexual intercourse?. In the first group of thecontemporary cultures he studied, which included sub-SaharanAfrica (listing Mali, Senegal andEthiopia), the dataindicated that the age of men at sexual initiation in thesesocieties is at later ages than that of women, but is oftenextra-marital; the study considered the Indiansubcontinent also fell into this group, although data was onlyavailable from Nepal.^[100]In the second group, the data indicated families encourageddaughters to delay marriage, and to abstain from sexual activityprior to it. However, sons are encouraged to gain experience witholder women or prostitutes prior to marriage. Age of men at sexualinitiation in these societies is at lower ages than that of women;this group includes Latin cultures, both from southern Europe(Portugal, Greece andRomania are noted) andfrom Latin America(Brazil, Chile, DominicanRepublic). The study considered many Asian societies also fellinto this group, although matching data were only available fromThailand.^[100]In the third group, age of men and women at sexual initiation wasmore closely matched; there were two sub-groups, however. Innon-Latin, Catholic countries (Poland and Lithuania arementioned), age at sexual initiation was higher, suggesting latermarriage and reciprocal valuing of male and female virginity. Thesame pattern of late marriage and reciprocal valuing of virginitywas reflected in Singapore andSri Lanka. The studyconsidered China and Vietnamalso fell into this group, although data were notavailable.^[100]In northern and eastern European countries, age at sexualinitiation was lower, with both men and women involved in sexualactivity prior to any union formation; the study listed Switzerland, Germanyand the Czech Republic asmembers of this group.^[100]

According to a national survey conducted in the United States in1995, at least 3/4 of all men and women in the U.S. engaged insexual intercourse by their late teenage years, and more than 2/3of all sexually experienced teens had 2 or more partners.^[101]Based on the 2002 National Survey of Family Growth, published bythe U.S. Department of Health and Human Services, the average ageof first vaginal intercourse in U.S. participants aged 15 to 44 was17.4 years for females and 17.0 years for males.^[102][103]Special tabulations by the National Center for Health Statistics suggest that this figurehas changed between 2006 and 2010 to 17.1 years for both males andfemales.^[104]The Centers for Disease Control and Prevention (CDC) stated that45.5 percent of girls and 45.7 percent of boys had engaged insexual activity by 19 in 2002; in 2011, reporting their researchfrom 2006–2010, the CDC stated that 43% of American unmarriedteenage girls and 42% of American unmarried teenage boys have everengaged in sexual intercourse.^[105]The CDC also reports that American girls will most likely losetheir virginity to a boy who is 1 to 3 years older than theyare.^[105]

According to the U.S. Department of Health and Human Services,teenagers are delaying sex until older ages.^[106]Between 1988 and 2002, the percentage of people in the U.S. whohave had intercourse between the ages of 15 to 19 fell from 60 to46 percent for males, and from 51 to 46 percent forfemales.^[106]Additionally, a 2006 survey conducted by TheObserver suggested that most adolescents in Britain werewaiting longer to have sexual intercourse than they were only a fewyears earlier.^[107]In 2002, it was reported that 32% of British teenagers were havingsex before the age of 16, while, in 2006, it was only 20%. Theaverage age a British teenager lost his/her virginity wasreportedly 17.13 years in 2002; in 2006, it was 17.44 years onaverage for girls and 18.06 for boys. The most notable drop amongteens who reported having sex was 14- and 15-year-olds.^[107]A 2008 survey conducted by YouGov for Channel4 suggested that 40% of all 14- to 17-year-olds are sexuallyactive, 74% of sexually active 14- to 17-year-olds have had asexual experience under the age of consent, and 6% of teens wouldwait until marriage before having sex.^[108]

Healtheffects

Benefits

In humans, sexual activity has been reported to produce healthbenefits as varied as improved sense of smell,^[109]stress andblood pressure reduction,^[110][111]increased immunity,^[112]and decreased risk of prostatecancer.^{[113][114][115]}Sexual intimacy, as well as orgasms, increases levels of thehormone oxytocin, also known as"the love hormone", which helps people bond and buildtrust.^{[116][117][118]}Sex is also known as one of many moodrepair strategies, which means it can be used to help dissipatefeelings of sadness or depression.^[119]A long-term study of 3,500 people between 30 and 101 by clinicalneuropsychologistDavid Weeks, MD, head of old age psychology at the Royal EdinburghHospital in Scotland, found that "sex helps you look between fourand seven years younger", according to impartial ratings of thesubjects' photos. Exclusive causation, however, is unclear, and thebenefits may be indirectly related to sex and directly related tosignificant reductions in stress, greater contentment, and bettersleep that sex promotes.^{[120][121][122]}

Risks

Sexuallytransmitted infections (STIs) can be spread by person-to-personsexual contact, including sexual intercourse. There are 19 millionnew cases of sexually transmitted diseases every year in theU.S.,^[123]and, in 2005, the World Health Organization estimated that 448million people aged 15–49 were being infected a year with curableSTIs such as syphilis, gonorrhoea andchlamydia.^[124]In 2006, TheIndependent newspaper reported that the biggest rise insexually transmitted infections was in syphilis, which rose by morethan 20%, while increases were also seen in cases of genital warts andherpes.^[125]

STIs are caused by bacteria, viruses andparasites, which arepassed from person to person during sexualcontact. Some, in particular HIV and syphilis, can alsobe passed in other ways including from mother to child duringpregnancy and childbirth, throughblood products,and by shared hypodermicneedles.^[124]Gonococcalor chlamydial infections often produce no symptoms at all.Untreated chlamydial infection can lead to female infertility andectopicpregnancy. Humanpapillomavirus can lead to genital and cervicalcancers. Syphilis can result instillbirths andneonatal deaths. Untreated gonococcal infections result inmiscarriages,preterm births,and perinataldeaths. Infants born to mothers with untreated gonorrhoea orchlamydia can develop serious eyeinfections, which can lead to blindness.^[124]Hepatitis B can alsobe transmitted through sexual contact.^[126]Globally, there are about 350 million chronic carriers of hepatitisB.^[127]

Some STIs can cause ulceration, buteven if they do not, they increase the risk of both acquiring andpassing on HIV up to ten-fold.^[124]HIV is one of the world's leading infectious killers, and, in 2010,approximately 30 million people were estimated to have died becauseof it since the beginning of the epidemic. Of the 2.7 million newHIVinfections estimated to occur worldwide in 2010, 1.9 million(70%) were in Africa. "Theestimated 1.2 million Africans who died of HIV-related illnesses in2010 comprised 69% of the global total of 1.8 million deathsattributable to the epidemic."^[128]It is diagnosed by bloodtests, and while no cure has been found, it can be controlledwith antiretroviraldrugs, and patients can enjoy healthy and productivelives.^[129]

The most effective way to avoid sexually transmitted infectionsis to abstain from sexual intercourse, including oral,vaginal, and analsex, or to have sexual intercourse only with one long-term,uninfected partner, who also remains entirely monogamous. TheWorld Health Organization says that "Male latex condoms, when usedconsistently and correctly, are highly effective in reducing thetransmission of HIV and other sexually transmitted infections,including gonorrhoea, chlamydial infection and trichomoniasis."^[124]In cases where infection is suspected, early medical interventionis highly beneficial in all cases.

People, especially those who get little or no physical exercise,have a slightly increased risk of triggering heartattack or sudden cardiacdeath when they engage in sexual intercourse, or any othervigorous physical exercise which is engaged in on a sporadic basis.Increased risk is temporary with incidents occurring within a fewhours of the activity. Regular exercise reduces but does noteliminate the increased risk.^[130]

Socialeffects

Adults

Alex Comfort andothers posit three potential advantages of intercourse in humans,which are not mutually exclusive: reproductive, relational, andrecreational.^[8][131]While the development of thePill and other highly effective forms of contraception inthe mid- and late 20th century increased people's ability tosegregate these three functions, they still overlap a great dealand in complex patterns. For example: A fertile couple may haveintercourse while contracepting not only to experience sexualpleasure (recreational), but also as a means of emotional intimacy(relational), thus deepening their bonding, making theirrelationship more stable and more capable of sustaining children inthe future (deferred reproductive). This same couple may emphasizedifferent aspects of intercourse on different occasions, beingplayful during one episode of intercourse (recreational),experiencing deep emotional connection on another occasion(relational), and later, after discontinuing contraception, seekingto achieve pregnancy (reproductive, or more likely reproductive andrelational).^[131]

Nearly all Americans marry during their lifetime; yet close tohalf of all first marriages are expected to end in separation ordivorce, many within a few years,^[132]and subsequent marriages are even more likely to end.^[133]Sexual dissatisfaction is associated with increased risk of divorceand relationship dissolution.^[133]

According to the National Survey of Sexual Health and Behavior (NSSHB), in 2010,men whose most recent sexual encounter was with a relationshippartner reported greater arousal, greater pleasure, fewer problemswith erectile function, orgasm, and less painduring the event than men whose last sexual encounter was with anon-relationship partner.^[99]According to the Journal of Counseling & Development,many women express that their most satisfying sexual experiencesentail being connected to someone, rather than solely basingsatisfaction on orgasm.^[134]

Adolescents

With regard to adolescentsexuality, sexual intercourse is often for relational andrecreational purposes as well. However, teenagepregnancy is usually disparaged, and research suggests that theearlier onset ofpuberty for children puts pressure on children and teenagers toact like adults before they are emotionally or cognitivelyready,^[135][136]and thus are at risk to suffer from emotionaldistress as a result of their sexual activities.^{[136][137][138][139][140]}Some studies have concluded that engaging in sex leavesadolescents, and especially girls, with higher levels of stress anddepression.^[141]A majority of adolescents in the United States havebeen provided with some information regarding sexuality,^[142]though there have been efforts among social conservatives in theUnited States government to limit sex education inpublic schools to abstinence-onlysex education curricula.^[143]

One group of Canadian researchersfound a relationship between self-esteem and sexual activity. Theyfound that students, especially girls, who were verbally abused byteachers or rejected by their peers were more likely than otherstudents to engage in sex by the end of the Grade 7. Theresearchers speculate that low self-esteem increases the likelihoodof sexual activity: "low self-esteem seemed to explain the linkbetween peer rejection and early sex. Girls with a poor self-imagemay see sex as a way to become 'popular', according to theresearchers".^[144]

In India, there is growingevidence that adolescents are becoming more sexually active outsideof marriage, which is feared to lead to an increase in the spreadof HIV/AIDS among adolescents,as well as the number of unwanted pregnancies and abortions, and add tothe conflict between contemporary social values. In India,adolescents have relatively poor access to health care andeducation, and with cultural norms opposing extramarital sexualbehavior, "these implications may acquire threatening dimensionsfor the society and the nation".^[145]

Not all views on adolescent sexual behavior are negative,however. Psychiatrist Lynn Ponton writes,"All adolescents have sex lives, whether they are sexually activewith others, with themselves, or seemingly not at all," and thatviewing adolescent sexuality as a potentially positive experience,rather than as something inherently dangerous, may help youngpeople develop healthier patterns and make more positive choicesregarding sex.^[135]Likewise, others state that long-term romantic relationships allowadolescents to gain the skills necessary for high-qualityrelationships later in life^[146]and develop feelings of self-worth. Overall, positive romanticrelationships among adolescents can result in long-term benefits.High-quality romantic relationships are associated with highercommitment in early adulthood^[147]and are positively associated with self-esteem, self-confidence,and social competence.^[148][149]

Ethical, religious, and legal views

While sexual intercourse is the natural mode of reproduction forthe human species, humans have intricate moral and ethicalguidelines which regulate the practice of sexual intercourse andvary according to religiousand governmental laws. Some governments and religions also havestrict designations of "appropriate" and "inappropriate" sexualbehavior, which include restrictions on the types of sex acts whichare permissible. A historically prohibited or regulated sex act isanal sex.^[150][151]

Consent and sexual offenses

Sexual intercourse with a person against their will, or withouttheir informed legalconsent, is rape, and is considered aserious crime in mostcountries.^[152]More than 90% of rape victims are female, 99% of rapists male, andonly about 5% of rapists are strangers to the victims.^[153]

Most developed countries have age of consentlaws specifying the minimum legal age a person may engage in sexualintercourse with substantially older persons, usually set at about16–18, while the legal age of consent ranges from 12–20 years ofage or is not a matter of law in other countries.^[154]Sex with a person under the age of consent, regardless of theirstated consent, is often considered to be sexualassault or statutory rapedepending on differences in ages of the participants. Somecountries treat any sex with a person of diminished or insufficientmental capacity to give consent, regardless of age, asrape.^[155]

The expression "sexual intercourse" has been used as a term ofart in England andWales and New York State.In England and Wales, from its enactment to its repeal on the 1 May2004,^[156]section44 of the SexualOffences Act 1956 read:

Where, on the trial of any offence under thisAct, it is necessary to prove sexual intercourse (whether naturalor unnatural), it shall not be necessary to prove the completion ofthe intercourse by the emission of seed, but the intercourse shallbe deemed complete upon proof of penetration only.

Unnatural

This expression refers to buggery, including bothbuggery with a person and buggery with an animal.^[157]Zoophilia (bestiality)is sexual activity between humans and non-human animals or apreference for or fixation on such practice. People who practicezoophilia are known as zoophiles,^[158]zoosexuals, or simply "zoos".^[159]Zoophilia may also be known as zoosexuality.^[159]Zoophilia is a paraphilia.^{[160][161][162][163]}Sex with animals is not outlawed in some jurisdictions, but, inmost countries, it is illegal under animalabuse laws or laws dealing with crimesagainst nature.

Penetration

According to cases decided on the meaning of the statutorydefinition of carnalknowledge under the Offences against the Person Act 1828, which was in identicalterms to this definition, the slightest penetration wassufficient.^[164]The book "Archbold" said that it "submitted" that this continued tobe the law under the new enactment.^[165]

Continuing act

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

Section 7(2) of the Sexual Offences (Amendment) Act 1976 contained the followingwords: "In this Act . . . references to sexual intercourse shall beconstrued in accordance with section 44 of the Sexual Offences Act1956 so far as it relates to natural intercourse (under which suchintercourse is deemed complete on proof of penetration only)". TheAct made provision, in relation to rape and related offences, forEngland and Wales, and for courts-martial elsewhere.

From 3 November 1994 to 1 May 2004, section 1(2)(a) of theSexual Offences Act 1956 (as substituted by section 142 of theCriminal Justice and Public Order Act 1994) referred to "sexualintercourse with a person (whether vaginal or anal)". This sectioncreated the offence of rape inEngland and Wales.

The penal code in New York State provides: § 130.00 Sexoffenses; definitions of terms: 1. "Sexual intercourse" has itsordinary meaning and occurs upon any penetration, howeverslight.^[166]

Romanticrelationships

Sexual orientation and gender

There are various legal positions regarding the definition andlegality of sexual intercourse between persons of the same sex orgender. For example, in the 2003 NewHampshire Supreme Court case Blanchflowerv. Blanchflower, it was held that femalesame-sex sexual relations did not constitute sexualintercourse, based on a 1961 definition from Webster's Third New International Dictionary; and thereby anaccused wife in a divorce case was found not guilty of adultery. Somecountries, such as Islamiccountries, consider homosexual behavior to be an offensepunishable by imprisonment or execution.^[167]

Marriage and relationships

Sexual intercourse has traditionally been considered anessential part of a marriage; manyreligious customs required consummation of themarriage by sexual intercourse, and the failure for any reason toconsummate the marriage was a ground for annulment, which didnot require a divorce process. Annulment declaration implied thatthe marriage was void from the start – i.e. there was in law nomarriage. Furthermore, continuing sexual relations between themarriage partners is commonly considered a 'marital right' by manyreligions, permissible to married couples, generally for thepurpose of reproduction. Today, there is wide variation in theopinions and teachings about sexual intercourse relative tomarriage and other intimate relationships by the world's religions.Examples:

In some cases, the sexual intercourse between two people is seenas counter to religious law or doctrine. In many religiouscommunities, including the Catholic Churchand Mahayana Buddhists,religious leaders are expected to refrain from sexual intercoursein order to devote their full attention, energy, and loyalty totheir religious duties.^[185]

Opposition to same-sexmarriage is largely based on the belief that sexual intercourseand sexual orientation should be of a heterosexual nature.^{[186][187][188][189]}The recognition of such marriages is a civil rights, political,social, moral, and religious issue in many nations, and theconflicts arise over whether same-sex couples should be allowed toenter into marriage, be required to use a different status (such asa civil union, which either grant equal rights as marriage orlimited rights in comparison to marriage), or not have any suchrights. A related issue is whether the term marriage shouldbe applied.^{[171][190][191]}

Otheranimals

In zoology, copulation is often termed as the process inwhich a male introduces sperm into the female'sbody. Spiders have separatemale and female sexes. Before mating and copulation, a male spins asmall web and ejaculates on to it.He then stores the sperm in reservoirs on his large pedipalps, from whichhe transfers sperm to the female's genitals. Females can storesperm indefinitely.^[192]

Many animals which live in the water use externalfertilization, whereas internalfertilization may have developed from a need to maintaingametes in a liquidmedium in the Late Ordovicianepoch. Internal fertilization with many vertebrates (such asreptiles, some fish, and mostbirds)occur via cloacal copulation (seealso hemipenis), whilemammals copulatevaginally, and manybasalvertebrates reproducesexually with external fertilization.

However, some terrestrialarthropods do useexternal fertilization. For primitive insects, the maledeposits spermatozoa on thesubstrate, sometimes stored within a special structure; courtship involvesinducing the female to take up the sperm package into her genitalopening; there is no actual copulation. In groups such as dragonflies andspiders, males extrude sperm into secondary copulatory structuresremoved from their genital opening, which are then used toinseminate the female. In dragonflies, it is a set of modifiedsternites on the secondabdominal segment; in spiders, it is the male pedipalps. Inadvanced groups of insects, the male uses its aedeagus, astructure formed from the terminal segments of the abdomen, todeposit sperm directly (though sometimes in a capsule called a"spermatophore")into the female's reproductive tract.

Humans, bonobos,^[25]chimpanzees and dolphins^[26]are species known to engage in heterosexual behaviors even when thefemale is not in estrus, which is a point in her reproductive cyclesuitable for successful impregnation. These species, and others,are also known to engage in homosexual behaviors.^[27]Humans, bonobos and dolphins are all intelligent social animals,whose cooperative behavior proves far more successful than that ofany individual alone. In these animals, the use of sex has evolvedbeyond reproduction, to apparently serve additional socialfunctions. Sex reinforces intimate social bonds between individualsto form larger social structures. The resulting cooperationencourages collective tasks that promote the survival of eachmember of the group.^[8]

See also

Externallinks

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