Sexual Intercourse

Sexual intercourse , also known as copulation or coitus , commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The term may also describe other sexual penetrative acts, such as anal sex, oral sex and fingering, which can be practiced by both heterosexual and homosexual pairings.

Sexual intercourse typically plays a powerful role in human bonding, often being used solely for pleasure and leading to stronger emotional bonds. Non-penetrative sex (for example, non-penetrative cunnilingus) has been referred to as "outercourse", but may also be among the sexual acts contributing to human bonding and considered intercourse. The term sex can be taken to mean any mutual genital stimulation or to mean any form of sexual activity (i.e. all forms of intercourse and "outercourse"). As with most forms of sexual interaction, individuals are at risk of contracting sexually transmitted diseases, thus, safe sex practices are advised.

Religious beliefs often play a role in societal views regarding sexual intercourse, other sexual acts, and their purpose. Some sections of Christianity commonly view sex between a married couple for the purpose of reproduction as holy, while other sections may not. Modern Judaism and Islam view sexual intercourse between husband and wife as a spiritual and edifying action. The limits of marriage and concubinage within these traditions has changed over time, along with corresponding views of acceptable sexual behavior. The teachings of Hinduism and Buddhism on sexuality have differing interpretations. Buddhism's injunction to "refrain from sexual misconduct" finds its interpretation and practical definitions at the level of the individual. However, within each of these major religious traditions exist subgroups with varying stances on acceptable sexual practices, and some religious groups prohibit monks and nuns from engaging in sexual activity altogether.

Sexual intercourse between non-human animals is more often referred to as copulation; for most, mating and copulation occurs at the point of estrus (the most fertile period of time in the female's reproductive cycle), which increases the chances of successful impregnation. However, bonobos, dolphins, and chimpanzees are known to engage in sexual intercourse even when the female is not in estrus, and to engage in sex acts with same-sex partners. Like humans engaging in sex primarily for pleasure, this behavior in the above mentioned animals is also presumed to be for pleasure, and a contributing factor to strengthening their social bonds.

Practice

See also: Human sexual activity and Human sexuality

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 plays a powerful 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, sharing pleasure and strengthening their emotional bond through sex even though they are deliberately avoiding pregnancy.

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.

Humans, bonobos, dolphins, and chimpanzees are all intelligent social animals, whose cooperative behavior proves far more successful than that of any individual alone. In these animals, the use of sex has evolved beyond reproduction, to apparently 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.

Reproduction and sexual practices

Vaginal sexual intercourse, also called coitus, is the human form of copulation. While its main natural purpose and result is reproduction, it is often performed entirely for pleasure and/or as an expression of love and emotional intimacy. Coitus is the basic reproductive method of humans, and may be preceded by foreplay, which leads to sexual arousal of the partners, resulting in the erection of the penis and (usually) 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 orgasm in either or both partners is achieved. For human females, stimulation of the clitoris plays a significant role in sexual intercourse; most women (70-80%) achieve orgasm only with direct clitoral stimulation, though indirect clitoral stimulation (for example, via vaginal intercourse) may also be sufficient (see Female orgasm).

Penetration by the hardened, erect penis is additionally known as intromission , or by the Latin name immissio penis (Latin for "insertion of the penis"). 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. 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. 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. 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.

The World Health Organization (WHO) estimated in 2005 that each year 123 million women become pregnant world-wide. A substantial number of those pregnancies – around 87 million – are unintentional. About 46 million pregnancies yearly reportedly end in induced abortion. About 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. 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. Britain has been stated to have a teenage pregnancy rate similar to America's.

Reproduction 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. 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). 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 and 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. 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.

In addition to vaginal intercourse, sexual intercourse can encompass other forms of insertive sexual behavior, such as oral sex and anal intercourse. Sexual acts, other than as a means of reproduction, are varied: 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, and may include the ingestion or absorption of semen or vaginal fluids. While there are many sexual acts involving the anus, anal cavity, sphincter valve and/or rectum, the most common meaning of anal sex is the insertion of a man's penis into another person's rectum.

Non-penetrative sex acts are also common. These acts are sometimes seen among heterosexuals as mai