In animals

Many animals which live in the 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, and courtship involves inducing the female to take up the sperm package into her genital opening; there is no actual copulation. In groups such as dragonflies and many 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.
See also: Mating

A pair of lions copulating in the Maasai Mara, Kenya


Love bugs mating


Tortoises mating


Dragonflies mating




Butterflies mating


Anthomyiidae flies mating


Cockatiels mating


Herring Gulls mating




In humans
Coition of a Hemisected Man and Woman (c. 1492, by Leonardo da Vinci) is an artist's interpretation of what happens inside the body during coitus.
Main articles: Human sexual behavior and Human sexuality

Vaginal sexual intercourse, also called coitus, is the human form of copulation. While its primary purpose is reproduction, it is often performed exclusively for pleasure and/or as an expression of love and emotional intimacy. Sexual intercourse typically plays a powerful bonding role; in many societies it is normal for couples to have frequent intercourse while using birth control, sharing pleasure and strengthening their emotional bond through sex even though they are deliberately avoiding pregnancy.

Sexual intercourse is also defined as referring to any form of insertive sexual behavior, including oral sex, as well as anal intercourse. The phrase to have sex can mean any or all of these behaviors, as well as other non-penetrative acts not considered here.

Coitus may be preceded by foreplay, which leads to sexual arousal of the partners, resulting in the erection of the penis and natural lubrication of the vagina.

To engage in coitus, the erect penis is inserted into the vagina and one or both of the partners move their hips to move the penis backward and forward inside the vagina to cause friction, typically without fully removing the penis. In this way, they stimulate themselves and each other, often continuing until highly pleasurable orgasm in either or both partners is achieved. Penetration by the hardened erect penis is also known as intromission, or by the Latin name immissio penis (Latin for "insertion of the penis").

Coitus is the basic reproductive method of humans. During ejaculation, which usually accompanies male orgasm, a series of muscular contractions delivers semen containing male gametes known as sperm cells or spermatozoa from the penis into the vagina. (While this is the norm, if one is wearing a condom, the sperm will almost never reach the egg.) 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. If the woman orgasms during or after male ejaculation, the corresponding temporary reduction in the size of the vagina and the contractions of the uterus that occur can help the sperm to reach the fallopian tubes, though female orgasm is not necessary to achieve pregnancy. When a fertile ovum from the female is present in the fallopian tubes, the male gamete joins with the ovum resulting in fertilization and the formation of a new embryo. When a fertilized ovum reaches the uterus, it becomes implanted in the lining of the uterus, known as endometrium and a pregnancy begins.

Coitus difficulties

The physical structure of the act of coitus favors penile stimulation over clitoral stimulation. The location of the clitoris then often necessitates manual stimulation in order for the female to achieve orgasm. In the 1974 Hite Report studies, nearly 70 percent of female respondents [3] admitted to rarely or never achieving orgasm during coitus without simultaneous direct stimulation of the clitoris with the fingers or other implement.

Anorgasmia is the lack of orgasm during otherwise pleasurable stimulation. It is much more common in women than men. Masturbation is a well supported method for a woman to explore her body and discover what feels good for her. The absence of a partner can remove the sense of performance anxiety and allow the woman to relax and enjoy. Good communication and patience are essential in helping an anorgasmic woman achieve orgasm. Whether a woman considers anorgasmia a problem or not is highly individual, though many women find it very frustrating.

Some males suffer from erectile dysfunction (ED), or impotence, at least occasionally. For those whose impotence is caused by medical conditions, prescription drugs such as Viagra, Cialis, and Levitra are available. However, doctors caution against the unnecessary use of these drugs because they are accompanied by serious risks such as increased chance of heart attack. 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.

A more common sexual disorder in males is premature ejaculation (PE). The U.S. Food and Drug Administration is examining the drug dapoxetine to treat premature ejaculation. In clinical trials, those with PE who took dapoxetine experienced intercourse three to four times longer before orgasm than without the drug.

The American Urological Association (AUA) estimates that premature ejaculation could affect 27 to 34 percent of men in the United States. The AUA also estimates that 10 to 12 percent of men in the United States are affected by erectile dysfunction.

Vaginismus is involuntary tensing of the pelvic floor musculature, making coitus distressing, painful, and sometimes impossible.

Dyspareunia is a medical term signifying painful or uncomfortable intercourse, but does not specify the cause.

Mobility Impairment

According to the Canadian Paraplegic Association, in 2007, there were thirty six thousand Canadians living with spinal cord injuries.[4] In the US there are 11 thousands spinal cord injuries every year.[4] Sexual intercourse for these mobility impaired individuals may be a psychologically daunting experience which plays an effect on self-concept as a sexual being.[4] For example Brian Chovez, a paraplegic with some mobility loss from the waist down, has indicated that he went "from having a very active sex life before the accident, to not really having one at all... it was tremendously hard psychologically." [4] However, "Sex is not impossible" according to Alan Tholkes, a quadriplegic since 1976. Tholkes said "I had sensations in all the critical areas, but my motor function was lacking. Certain positions just weren't possible."[4] There exists some sexual devices that facilitate easy motion, rocking back and forth at the right height and position, putting all vital organs together at in the right places and making thrusting motion easy - in particular, this may includes the Love Swing, which has been on the market for years, or The IntimateRider which may permit the end-users to go for hours.[4]

Functions of sex beyond reproduction

Humans, bonobos[5] and dolphins[6] are the only species that 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 three species, and others besides, are also known to engage in homosexual behaviors.[7])

In both 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]

Humans, bonobos and dolphins are all intelligent social animals, whose cooperative behavior proves far more successful than that of any individual alone. In these animals, the use of sex has evolved beyond reproduction apparently to serve additional social functions. Sex reinforces intimate social bonds between individuals to form larger social structures. The resulting cooperation encourages collective tasks that promote the survival of each member of the group.

Alex Comfort[citation needed] and others [8] posit three potential advantages of intercourse in humans, which are not mutually exclusive: reproductive, relational, and recreational. While the development of the Pill and other highly-effective forms of contraception in the mid- and late 20th century increased peoples' ability to segregate these three functions, they still overlap a great deal and in complex patterns. For example: A fertile couple may have intercourse while contracepting not only to experience sexual pleasure (recreational), but also as a means of emotional intimacy (relational), thus making their relationship more stable and more capable of sustaining children in the future (deferred reproductive). This same couple may emphasize different aspects of 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).

Oral sex
Main article: Oral sex

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

Anal sex
Main article: Anal sex

While there are many sexual acts involving the anus, anal cavity, sphincter valve and/or rectum, the specific meaning describes the insertion of a man's penis into another person's rectum.

Sexual ethics and legality

Unlike some other sexual activities, vaginal intercourse has rarely been made taboo on religious grounds or by government authorities, as procreation is inherently essential to the continuation to the species or of any particular genetic line, which is considered to be a positive factor, and indeed, enables most societies to continue in the first place. Many of the cultures that had prohibited sexual intercourse entirely no longer exist; an exception is the Shakers, a sect of Christianity that has four adherents at current. There are, however, many communities within cultures that prohibit their members to engage in any form of sex, especially members of religious orders and the priesthood in the Roman Catholic Church and priests in Buddhist monasteries. Within some ideologies, coitus has been considered the only "acceptable" sexual activity. Relatively strict designations of "appropriate" and "inappropriate" sexual intercourse have been in human culture for hundreds of years. These have included prohibitions against specific positions, but even more often against:
Coitus among partners who are not married (this is sometimes referred to as fornication)
Coitus where a married person has sex with someone to whom they are not married. (called adultery or extramarital sex)
Coitus amongst partners who are not married for consideration (called prostitution).
Coitus amongst partners of the same sex (called sodomy).
Coitus with a close relative (called incest).
Coitus with children (a symptom of pedophilia).
Coitus with animals (called bestiality).

In some societies there are (or have been in the past) taboos (social, religious and sometimes legal) against sexual relations with persons of differing ethnic, tribal or social (e.g caste) backgrounds.

Some cultures and religions, such as Islam and Judaism, prohibit coitus during a woman's menstrual period, because sacred texts specifically forbid it. However, there is no medical reason for this.

Often a community adapts its legal definitions during case laws for settling disputes. For example, in 2003 the New Hampshire Supreme Court ruled that same-sex relations do not constitute sexual intercourse, based on a 1961 definition from Webster's Third New International Dictionary, in Blanchflower v. Blanchflower, and thereby an accused spouse in a divorce case was found not guilty of adultery based on this technicality.

Most countries have age of consent laws specifying the minimum legal age for engaging in sexual intercourse. Sexual intercourse with a person against their will, or without their informed legal consent, is referred to as rape, and is considered a serious crime in many cultures around the world, including those found in Europe, northern and eastern Asia, and the Americas. Sex, regardless of consent, with a person under the age of consent is often considered to be sexual assault or statutory rape. The age of consent varies from country to country and often by state or region; commonly, the age of consent is set anywhere between twelve and eighteen years of age, with sixteen years being the most common age the law sets. Sometimes, the age of consent is lowered for people near the same age wishing to participate in intercourse. For example, in Canada, the minimum age of consent for all couples is 14. However, the age of consent can go below 14 on the condition that the couple still aren't 2 years of age apart. Religions may also set differing ages for consent, with Islam setting the age at puberty, which can vary from around 10 to 14. There are exceptions in the case of anal sex or people in a position of trust/authority.

Religious views
Main article: Religious views on sexual intercourse

Religious views on sexual intercourse vary widely between religions, between different sects of the same religion, and even between different members of the same sect.