|
There are several different environmental factors which various overlapping schools of thought hypothesize influence the determination of sexual orientation.
One of the most important questions in this area (and in the larger cultural and political debate) is whether sexual orientation is a stable attribute fixed early in life, or can be changed or chosen in adolescence or adulthood. In this case, the primary aspect of sexual orientation which is of interest is whether spontaneous attractions are for members of the same, opposite, or both genders. (For discussion about whether or not there are exactly two genders and what constitutes gender, see the article on sex.) Obviously, for the purposes of sexual behavior, any person may choose to follow or resist their spontaneous feelings, and self-identification is a psychological and social phenomenon distinct from sexual behavior and attraction.
Various environmental causes have been proposed by advocates of both the "fixed attribute" and "choice" hypotheses.
Empirical studies which attempt to quantify non-genetic influence on sexual orientation (from whatever sources) are discussed in Genetics and sexual orientation.
Early fixation hypothesis
If sexual orientation is fixed early in life, when exactly does that happen, and how? The following "environmental" mechanisms (as opposed to (genetic mechanisms) have been proposed.
Fetal development
Some have theorized that events in the womb may contribute to some subset of homosexual behavior (though certain individuals may be genetically predisposed to be vulnerable to such events, and the conditions inside the mother's reproductive system are of course influenced by her genetics).
Masculinization/feminization
A popular hypothesis in this vein is that the developing brains of homosexual men are insufficiently masculinized (i.e. they are partially "feminized") and that homosexual females are "masculinized" in some way.
Supporting evidence for this hypothesis includes:
- Observed differences in three areas of the brain in homosexual vs. heterosexual men (the anterior commisure, the supra-chiasmatic nucleus the interstitial nuclei of the anterior hypothalamus,)
- Observed differences in cognitive testing showing results for homosexual men typical of heterosexual women and results for homosexual women typical of heterosexual men.
- Observed differences in the preferences that homosexual men, heterosexual men, and heterosexual women have for the age of their sexual partners.
It is unclear whether the observed anatomical and cognitive differences are signs of a (possibly genetic) mechanism that determines sexual orientation, or symptoms of the formation of an atypical sexual orientation during childhood.
One possible mechanism is differential fetal hormone exposure, especially to testosterone (and a compound it is transformed into, estradiol) and luteinizing hormone (LH) is proposed as the mechanism. The concentrations of these chemicals is thought to be influenced by fetal and maternal immune systems, maternal consumption of certain drugs, maternal stress, and direct injection.
Hormone levels may of course vary over time. Given the semi-sequential nature of fetal development, and because multiple hormones are involved, it is possible for the hypothesized "masculinization" or "feminization" process to affect only some body or brain systems. (This is necessary to explain why someone might be say, born with a male body but with a "feminized" sexual attraction.)
Prenatal hormones have been indicated both in Simon LeVay's study of the anterior hypothalamus in cadavers with homosexual contraction of AIDS as cause of death and Marc Breedlove's study of birth order and finger length ratios in living individuals. LeVay's study suggests that homosexual men are feminized, Breedlove's study suggests that both homosexual men and homosexual women are masculinized.
Birth order
Studies find that homosexual men have, on average, more older brothers than do heterosexual men. (This difference is not observed among women.)
A chemical called the histocompatibility Y-antigen (the "HY antigen") is found on the surface of the cells of male mammals. It is hypothesized that the "older brother effect" may be related to increasing levels of antibodies produced by the mother in response to the presence of this chemical. These antibodies would then somehow trigger differential brain development, either in the uterus or in early childhood through breast milk.
Imprinting/Critical period
This type of theory holds that the formation of gender identity occurs in the first few years of life after birth. Part of adopting a gender identity involves establishing the gender(s) of sexual attraction. This process is analogous to the "imprinting" process observed in animals. A baby duckling may be genetically programmed to "imprint" on a mother, but what entity it actually imprints upon depends on what objects it sees immediately after hatching. Most importantly, once this process has occurred, it cannot be reversed, any more than the duckling can hatch twice.
A sort of reverse sexual imprinting has been observed in heterosexual humans; see the section on the "Westermarck effect" in Behavioral imprinting.
Several different triggers for imprinting upon a particular sexual orientation have been proposed.
A common hypothesis, especially among non-scientists, is that something about what young children see in the gender-roles behavior of adults, or some differences (possibly unconscious) in the way adults treat young children, somehow influence or determine a child's eventual sexual orientation.
Another such theory is described in the following section.
Exotic becomes erotic
Daryl Bem, a social psychologist at Cornell University, has theorized that the influence of biological factors on sexual orientation may be mediated by experiences in childhood. A child's temperament predisposes the child to prefer certain activities over others. Because of their temperament, which is influenced by biological variables such as genetic factors, some children will be attracted to activities that are commonly enjoyed by other children of the same gender. Others will prefer activities that are typical of the other gender. This will make a gender-conforming child feel different from opposite-gender children, while gender-nonconforming children will feel different from children of their own gender. According to Bem, this feeling of difference will evoke physiological arousal when the child is near members of the gender which it considers as being 'different'. Bem theorizes that this physiological arousal will later be transformed into sexual arousal: children will become sexually attracted to the gender which they see as different ("exotic"). This theory is known as Exotic Becomes Erotic (EBE) theory.
Chance events
The human brain is a complex organ in a complex organism, and sexual attraction is a difficult feature to construct reliably each time. It is possible that more or less random events in the internal development of the brain sometimes result in atypical structures which correspond to atypical sexual orientations.
A simple analogy is the growth patterns of trees. Even genetically identical trees will have differently-shaped branches. Many factors contribute to these differences - accidents in the formation of the seed, the randomness of Brownian motion, slightly different soil, wind, water, and lighting conditions, etc. As a result, one tree may end up with 49 apples, the one next to it, with 51.
Choice hypothesis
If sexual orientation is (completely or almost completely) a conscious choice, then social and culture influences no doubt play a large role, as they do in "lifestyle" choices like what foods to eat or how to throw a birthday party.
This hypothesis predicts that in societies where (for example) homosexuality is widely discussed or accepted as "normal", more people will adopt a homosexual lifestyle. For those who believe homosexuality is immoral, this theory provokes concern that positive portrayals of homosexuality will "harm" children by influencing them in that direction.
Some advocates of the choice hypothesis believe that sexual orientation is not a choice which is necessarily made casually or easily changed. Most choice advocates also have a negative view of non-heterosexual orientations. So they might, for instance, consider homosexuality to be a personal problem not unlike a drug or alcohol addiction (including the addictive aspects). A person might not be able to change without help, but in the end, their own choices and behaviors are an integral part of their "problem".
Not all people who believe that homosexual behavior is wrong believe that (for example) a homosexual orientation is a choice. (If something is not a choice, then it usually cannot be right or wrong, it just exists). This often leads to the conclusion that people with a non-heterosexuals should be treated with respect or compassion, but that they should be discouraged from acting on their "immoral" spontaneous erotic desires.
It is an important point to realize that almost everyone agrees that whether or not to engage in a particular sexual behavior (whether driven by a spontaneous erotic desire, external suggestion, or any other influence) is in normal circumstances a conscious choice. The main disagreements are over whether a.) there is an underlying orientation which controls emotional desires and responses to events, and whether and b.) acting on same-sex or other sexual attractions is moral, immoral, or orthogonal to moral considerations.
Most gay, lesbian, and bisexual people, and many straight people, believe that sexual orientation is not a choice. Surveys and anecdotal evidence seem to show that the gender(s) toward which most people have had spontaneous erotic desires (wheter heterosexual, homosexual, both, or otherwise) has not changed since the feelings began in adolescence.
Changing sexual orientation through therapy
Most contemporary mental health professionals consider reparative therapy - trying to actually change a patient's sexual orientation from, say, homosexual to heterosexual, through therapeutic means - to be ineffective, if not psychologically harmful.
However, there is also a modern ex-gay movement that claims that homosexuals can become heterosexual or otherwise "leave homosexuality behind" through counseling, prayer, aversion, or other therapies if they choose to do so.
See Homosexuality and psychology.
Moral and religious considerations
Religious authorities regarding homosexuality as wrong or "sinful" often distinguish between immoral sexual acts and non-heterosexual feelings. Adherents to these codes of conduct are often advised to abstain from sexual acts in general, or to attempt to foster opposite-sex relationships; celibacy is an acceptable or sometimes even admirable alternative to heterosexuality. (For example, the Roman Catholic Church.) Some religions hold heterosexual marriage to be morally superior to celibacy, or mandatory for entry into a desirable form of the afterlife. (For example, the Church of Jesus Christ of Latter-day Saints.)
Not all religious sects regard non-heterosexual orientations as wrong, nor do all adherents of organized churches that do hold that view. See religion and homosexuality for a more complete discussion.
Proponents of the "choice about behavior" position point to taboo or illegal sexual acts, such as pedophilia or incest where society requires individuals not to act out their desires, as examples where choices are expected to be made whether or not orientation is a matter of choice.
External links
On the "exotic becomes erotic" theory
On the issue of choice
- Is homosexuality a choice? (http://salmon.psy.plym.ac.uk/year1/psychobiology_site_backups/homosexuality-debate/choice.html) -- Paper on Dr Paul Kenyon's Home Page, University of Plymouth, Department of Psychology
- Position paper (http://people.bu.edu/charris/homosexuality.html) - Catherine L. Harris, PhD., Psychology Department, Boston University
- Review of Queer By Choice (http://www.queernotions.org/QNI/art4.htm) - Julia Jones, Bay Area News and Letters Committees
- Will A Gay Gene Get Us Anywhere? (http://www.nickyee.com/ponder/gaygene.html) by Nicholas Yee
References
Fetal development
In progress. Please see the talk page.
| 
