Heterosexuality

Heterosexuality is romantic attraction, sexual attraction or sexual behavior between persons of opposite sex or gender in the gender binary. As a sexual orientation, heterosexuality refers to "an enduring pattern of or disposition to experience sexual, affectionate, physical or romantic attractions to persons of the opposite sex"; it also refers to "a person's sense of identity based on those attractions, related behaviors, and membership in a community of others who share those attractions". The term is usually applied to humans, but it is also observed in all mammals.

Heterosexuality is one of the three main classifications of sexual orientation along with bisexuality and homosexuality, which are each parts of the heterosexual–homosexual continuum.

The word is etymologically formed by adding the combining form of Greek έτερος heteros (meaning "different" or "other") as a prefix to "sexuality".

History and demographics
The demographics of sexual orientation are difficult to establish due to a lack of reliable data. However, the history of human sexuality shows that attitudes and behaviour have varied across cultures.

Prenatal hormonal theory
The neurobiology of the masculinization of the brain is fairly well understood. Estradiol and testosterone, which is catalyzed by the enzyme 5α-reductase into dihydrotestosterone, act upon androgen receptors in the brain to masculinize it. If there are few androgen receptors (people with androgen insensitivity syndrome) or too much androgen (females with congenital adrenal hyperplasia), there can be physical and psychological effects. It has been suggested that both male and female heterosexuality are results of variation in this process. In these studies heterosexuality in females is linked to a lower amount of masculinization than is found in lesbian females, though when dealing with male heterosexuality there are results supporting both higher and lower degrees of masculinization than homosexual males.

Natural selection
Much human behavior is considered to be ultimately explainable in terms of natural selection. From this point of view, the variation of phenotypic expression between heterosexual and homosexual desire in individuals has emerged in humans, as is the case for many species, as an apparent better adaptation as there are no documented human populations that are uniformly heterosexual.

Heterosexual behaviors in animals
Most of the reproduction in the animal world is facilitated through heterosexual sex, although there are also animals that reproduce asexually, including protozoa and lower invertebrates.

Reproductive sex does not necessarily require a heterosexual orientation, since orientation refers to a long-term enduring pattern of sexual and emotional attraction leading often to long-term social bonding, while reproductive sex requires only the basic act of vaginal intercourse, often done one time only.

Behavioral studies
At the beginning of the 20th century, early theoretical discussions in the field of psychoanalysis posited original bisexuality in human psychological development. Quantitative studies by Alfred Kinsey in the 1940s and Dr. Fritz Klein's sexual orientation grid in the 1980s find distributions similar to those postulated by their predecessors.

According to Sexual Behavior in the Human Male by Alfred Kinsey and several other modern studies, the majority of humans have had both heterosexual and homosexual experiences or sensations and are bisexual. Kinsey himself, along with current sex therapists, focused on the historicity and fluidity of sexual orientation. Kinsey's studies consistently found sexual orientation to be something that evolves in many directions over a person's lifetime; rarely, but not necessarily, including forming attractions to a new sex. Rarely do individuals radically reorient their sexualities rapidly—and still less do they do so volitionally—but often sexualities expand, shift, and absorb new elements over decades. For example, socially normative "age-appropriate" sexuality requires a shifting object of attraction (especially in the passage through adolescence). Contemporary queer theory, incorporating many ideas from social constructionism, tends to look at sexuality as something that has meaning only within a given historical framework. Sexuality, then, is seen as a participation in a larger social discourse and, though in some sense fluid, not as something strictly determinable by the individual.

Other studies have disputed Kinsey's methodology. "His figures were undermined when it was revealed that he had disproportionately interviewed homosexuals and prisoners (many sex offenders)."

Sexologists have attributed discrepancies in some findings to negative societal attitudes towards a particular sexual orientation. For example, people may state different sexual orientations depending on whether their immediate social environment is public or private. Reluctance to disclose one's actual sexual orientation is often referred to as "being in the closet." Individuals capable of enjoyable sexual relations with both sexes or one sex may feel inclined to restrict themselves to heterosexual or homosexual relations in societies that stigmatize same-sex or opposite-sex relations.

Nature versus nurture
The considerable "nature versus nurture" debate exists over whether predominantly biological or psychological factors produce sexual orientation in humans. Candidate factors include genes, the exposure of fetuses to certain hormones (or lack thereof) and environmental factors.

The APA currently officially states that "some people believe that sexual orientation is innate and fixed; however, sexual orientation develops across a person’s lifetime", a reversal from the recent past, when non-normative sexuality was considered a deviancy or mental ailment treatable through institutionalization or other means.

Critique of studies
The studies performed in order to find the origin of sexual orientation have been criticized for being too limited in scope, mostly for focusing only on heterosexuality and homosexuality as two diametrically opposite poles with no orientation in between. It is also asserted that scientific studies focus too much on the search for a biological explanation for sexual orientation, and not enough on the combined effects of both biology and psychology.

In a brief put forth by the Council for Responsible Genetics, it was stated that sexual orientation is not fixed either way, and on the discourse over sexual orientation: "Noticeably missing from this debate is the notion, championed by Kinsey, that human sexual expression is as variable among people as many other complex traits. Yet just like intelligence, sexuality is a complex human feature that modern science is attempting to explain with genetics... Rather than determining that this results from purely biological processes, a trait evolves from developmental processes that include both biological and social elements. According to the American Psychological Association (APA), there are numerous theories about the origins of a person's sexual orientation, but some believe that "sexual orientation is most likely the result of a complex interaction of environmental, cognitive and biological factors," and that genetic factors play a "significant role" in determining a person's sexuality.

Social and historical
Since the 1960s and 1970s, a large body of scholarship has provided evidence and analysis of the extent to which heterosexuality and homosexuality are socially organized and historically changing. This work challenges the assumption that heterosexuality, homosexuality, and sexualities of all varieties, can be understood as primarily biological and psychological phenomena.

A heterosexual couple, a man and woman in an intimate relationship, form the core of a nuclear family. Many societies throughout history have insisted that a marriage take place before the couple settle down, but enforcement of this rule or compliance with it has varied considerably. In some jurisdictions, when an unmarried man and woman live together long enough, they are deemed to have established a common-law marriage.

Heterosexism
Heterosexism is a form of bias or discrimination in favor of opposite-sex sexuality and relationships. It may include an assumption that everyone is heterosexual and may involve a varied level of discrimination against gays, lesbians, bisexuals, heteroflexibles, or transgenders.

Heteronormativity
Heteronormativity denotes or relates to a world view that promotes heterosexuality as the normal or preferred sexual orientation for people to have. It can assign strict gender roles to males and females. The term was popularized by Michael Warner in 1991.

Heterosexual ally
A heterosexual ally is a heterosexual person, but nonetheless supports equal civil rights for lesbians and gays. Heterosexual allies may also support LGBT social movements.

Religious aspects
The Judeo-Christian tradition has several scriptures related to heterosexuality. In Genesis 2:24, there is a commandment stating "Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh" In 1 Corinthians, Christians are advised:

"Now for the matters you wrote about: It is good for a man not to marry. But since there is so much immorality, each man should have his own wife, and each woman her own husband. The husband should fulfill his marital duty to his wife, and likewise the wife to her husband. The wife's body does not belong to her alone but also to her husband. In the same way, the husband's body does not belong to him alone but also to his wife. Do not deprive each other except by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control. I say this as a concession, not as a command. (NIV)"

For the most part, religious traditions in the world reserve marriage to heterosexual unions, but there are exceptions including certain Buddhist and Hindu traditions, Unitarian Universalist, Metropolitan Community Church and some Anglican dioceses and some Quaker, United Church of Canada and Reform Jewish congregations.

Almost all religions believe sex between a man and a woman is allowed, but there are a few that believe that it is a sin, such as The Shakers, The Harmony Society, and The Ephrata Cloister. These religions tend to view all sexual relations as sinful, and promote celibacy. Other religions view heterosexual relationships as being inferior to celibacy. Some religions require celibacy for certain roles, such as Catholic priests; however, the Catholic Church also views heterosexual marriage as sacred and necessary.

Etymology
Hetero- comes from the Greek word έτερος [héteros], meaning "other party" or "another", used in science as a prefix meaning "different"; and the Latin word for sex (that is, characteristic sex or sexual differentiation). The term "heterosexual" was first published in 1892 in C.G. Chaddock's translation of Krafft-Ebing's "Psychopathia Sexualis". The noun came into use from early 1920s, but did not enter common use until 1960s. The colloquial shortening "hetero" is attested from 1933. The abstract noun "heterosexuality" is first recorded in 1900. The word "heterosexual" was first listed in Merriam-Webster's New International Dictionary as a medical term for "morbid sexual passion for one of the opposite sex"; however, in 1934 in their Second Edition Unabridged it is defined as a "manifestation of sexual passion for one of the opposite sex; normal sexuality". (p. 92, Katz) The adjective heterosexual is used for intimate relationships or sexual relations between male and female.

Terminology
The current use of the term heterosexual has its roots in the broader 19th century tradition of personality taxonomy. It continues to influence the development of the modern concept of sexual orientation, and can be used to describe individuals' sexual orientation, sexual history, or self-identification. Some reject the term "heterosexual" as the word only refers to one's sexual behavior and does not refer to non-sexual romantic feelings. As a result, the terms straight is sometimes preferred when discussing a person of this sexual orientation. Some object to usage of the term "straight" because it implies that non-heteros are crooked. The term "heterosexual" is suggested to have come into use as a neologism after, and opposite to the word "homosexual" by Karl Maria Kertbeny in 1868. In LGBT slang, the term "breeder" has been used as a denigrating phrase to deride heterosexuals. Hyponyms of heterosexual include heteroflexible.

Slang
The word can be informally shortened to "hetero". The term "straight" originated as a mid-20th century gay slang term for heterosexuals, ultimately coming from the phrase "to go straight" (as in "straight and narrow"), or stop engaging in homosexual sex. One of the first uses of the word in this way was in 1941 by author G. W. Henry. Henry's book concerned conversations with homosexual males and used this term in connection with the reference to ex-gays. It currently simply is a colloquial term for "heterosexual" having, like many words, changed in primary meaning over time.

Symbolism


Heterosexual symbolism dates back to the earliest artifacts of humanity, with ritual fertility carvings and primitive art. This was later expressed in the symbolism of fertility rites and polytheistic worship, which often included images of human reproductive organs. Modern symbols of heterosexuality in societies derived from European traditions still reference symbols used in these ancient beliefs. One such image is a combination of the symbol for Mars, the Roman god of war, as the definitive male symbol of masculinity, and Venus, the Roman goddess of love and beauty, as the definitive female symbol of femininity. The unicode character for this combined symbol is ⚤ (U+26A4).