The American Academy of Pediatrics (2004) has stated that "sexual orientation probably
is not determined by any one factor but by a combination of genetic, hormonal, and
environmental influences." The amount that each influence plays is highly debated.
One study on Swedish twins suggested that there was a moderate, primarily genetic,
familial effect, and moderate to large effects of the non-shared environment (social
and biological) on same-sex sexual behaviour.
The American Psychological Association (2007) has stated that: "there are probably
many reasons for a person's sexual orientation and the reasons may be different for
different people." It also stated that for most people, sexual orientation is determined
at an early age.
The American Psychiatric Association (2000) has stated that, "...to date there are
no replicated scientific studies supporting any specific biological aetiology for
homosexuality. Similarly, no specific psychosocial or family dynamic cause for homosexuality
has been identified, including histories of childhood sexual abuse."
Research into how sexual orientation may be determined by genetic or other prenatal
factors plays a role in political and social debates about homosexuality, and also
raises fears about genetic profiling and prenatal testing.
Biological Explanations
In 1993 Dean Hamer, Stella Hu, Victoria Magnuson, Nan Hu & Angela Pattatucci identified
the genetic marker Xq28 on the X chromosome as having a link with homosexuality.
This caused immense controversy and the research was disputed. However, Stella Hu,
Pattatucci, Chavis Patterson, Lin Li, David Fulker, Stacey Cherny, Leonid Kruglyak
& Hamer (1995) then found that Xq28 was found in families containing 2 gay brothers
but not in families containing 2 lesbian sisters, suggesting that male homosexuality
most definitely has a genetic factor to it.
Several mutations have been identified in flies, such as changes in the fruitless
gene, cause male flies to court and attempt to mate with other males; however, when
a modified male fruit fly is isolated with only female fruit flies, then he will
attempt to mate with them.
Twin studies give indications that genes may predispose some men to seek partners
of the same sex. Hamer commented: "From twin studies, we already know that half or
more of the variability in sexual orientation is not inherited. Our studies try to
pinpoint the genetic factors, not to negate the psychosocial factors." One common
type of twin study compares the monozygotic (MZ or identical) twins of people possessing
a particular trait to the dizygotic (DZ or non-identical or fraternal) twins of people
possessing the trait. Michael Bailey & Richard Pillard (1991), in a study of gay
twins, found that 52% of MZ brothers and 22% of the DZ twins were concordant for
homosexuality. However, a later study by Bailey, Michael Dunne & Nicholas Martin
(2000) of 4,901 Australian twins found only 20% concordance in the male MZ twins
and 24% concordance for the female MZ twins. However, the much lower concordance
rates for the DZ twins in the study still suggests a genetic element. Recently Niklas
Långström, Qazi Rahman, Eva Carlström & Paul Lichtenstein (2008) reported on a study
of 3,826 twin pairs, comprising all twins between the ages of 20 and 47 in Sweden.
Their results showed that genetic factors explained about 34-39% of the variation
whereas specific environmental effects explained the remaining 61-66% in men. In
women, the genetic part of the variation was 18-19%, with 16-17% for shared environmental
and 64-66% for unique environmental factors.
Some studies have shown that homosexual men react to certain substances believed
to be human pheromones differently from heterosexual men.
Prenatal Hormonal Theory
The hormonal theory of sexuality holds that, just as exposure to certain hormones
plays a role in foetal sex differentiation, such exposure also influences the sexual
orientation that emerges later in the adult.
Prenatal maternal stress
It has been hypothesised that elevated maternal stress during pregnancy can increase
the probability that the child will be homosexual. R H Anderson, D E Fleming, R W
Rhees & E Kinghorn (1986) found that stressing female rats during pregnancy lowered
the level of sex hormones produced which in turn affected the sexual development
of the male pups.
However, Alfred Kinsey, Wardell Pomeroy & Clyde Martin in the Kinsey Report (1948)
reported that boosting the levels of androgens increased sexual desire but did affect
the sexual orientation of the recipient of the treatment.
Physiological differences in gay men and lesbians
Recent studies have found notable differences between the physiology of gay people
and non-gay people. There is evidence that:-
- The average size of the INAH-3 (part of the anterior hypothalamus) in the brains
of gay men is approximately the same size as INAH 3 in women, which is significantly
smaller, and the cells more densely packed than in heterosexual men's brains.
Simon
LeVay (1991) discovered this from studying the brain structures of deceased homosexuals.
Neil Carlson (1993) has proposed that this hints at possible prenatal influences
when the brain is still undergoing development.
- The suprachiasmatic nucleus was found by D F Swaab & M A Hoffman (1995) to be larger
in gay men than in non-gay men; the suprachiasmatic nucleus is also known to be larger
in men than in women.
- The anterior commissure is larger in women than men and was reported to be larger
in gay men than in non-gay men, but a subsequent study found no such difference.
- Gay men report, on an average, slightly longer and thicker penises than non-gay men.
- Gay men's brains respond differently to fluoxetine, a specific serotonin reuptake
inhibitor.
- The functioning of the inner ear and the central auditory system in lesbians and
bisexual women are more like the functional properties found in men than in non-gay
women. (The researchers argued this finding was consistent with the Prenatal Hormonal
Theory of sexual orientation).
- The startle response (eye blink following a loud sound) is similarly masculinised
in lesbians and bisexual women.
- 3 regions of the brain (medial prefrontal cortex, left hippocampus, and right amygdala)
are more active in gay men than non-gay men when exposed to sexually arousing material.
- Gay and non-gay people emit different armpit odours.
- Gay men are more likely to have a counter-clockwise hair whorl pattern.
- Gay and non-gay people's brains respond differently to two human sex pheromones (AND,
found in male armpit secretions, and EST, found in female urine).
- Finger length ratios between the index and ring fingers may be different between
non-gay and lesbian women.
Cognitive differences in gay men and lesbians
Recent studies suggest the presence of subtle differences in the way gay people and
non-gay people process certain kinds of information. Researchers have found that:-
- Gay men and lesbians are significantly more likely to be left-handed or ambidextrous
than are non-gay men and women. LeVay (1996) argues that because "[h]and preference
is observable before birth... [t]he observation of increased non-right-handness in
gay people is therefore consistent with the idea that sexual orientation is influenced
by prenatal processes," perhaps heredity.
- Gay men and lesbians are more verbally fluent than heterosexuals of the same sex
- but 2 other studies did not find this result.
- Gay men may receive higher scores than non-gay men on tests of object location memory
(no difference was found between lesbians and non-gay women).
Fraternal birth order
There is evidence from numerous studies that homosexual men tend to have more older
brothers than do heterosexual men, known as the ’fraternal birth order effect’. One
study reported that each older brother increases the odds of being gay by 33%. The
fraternal birth order effect is the strongest known predictor of sexual orientation.
Interestingly, this relation seems to hold only for right-handed males. There has
been no observed equivalent for women. Peter Bearman (2002) repeated the experiments
but found no correlation between older brothers and male homosexuality and questions
the sampling methods used.
The effect has been found even in males not raised with their biological brothers,
suggesting an in-utero environmental causation. To explain this finding, a maternal
immune response has been hypothesized. Male foetuses produce H-Y antigens which may
be involved in the sexual differentiation of vertebrates.
Environmental Factors
Researchers have found childhood gender nonconformity to be the largest predictor
of homosexuality in adulthood. Daryl Bem's (1996) ‘Exotic Becomes Erotic’ theory
suggests that some children will prefer activities that are typical of the other
sex and that this will make a gender-conforming child feel different from opposite-sex
children, while gender-nonconforming children will feel different from children of
their own sex, which may evoke physiological arousal when the child is near members
of the sex which it considers as being ‘different’; this will later be transformed
into sexual arousal. Researchers have suggested that this nonconformity may be a
result of genetics, prenatal hormones, personality, parental care or other environmental
factors. Bearman showed that males with a female twin are twice as likely to report
same-sex attractions, unless there was an older brother. He says that his findings
support the hypothesis that less gendered socialisation in early childhood and preadolescence
shapes subsequent same-sex romantic preferences. He suggests that parents of opposite-sex
twins are more likely to give them unisex treatment, but that an older brother establishes
gender-socialising mechanisms for the younger brother to follow.
From their research on 275 men in the Taiwanese military, Bin Ching Shu & For Wey
Lung (2006) concluded that "...paternal protection and maternal care were determined
to be the main vulnerability factors in the development of homosexual males." Key
factors in the development of homosexuals were "paternal attachment, introversion,
and neurotic characteristics." Other researchers have also provided evidence that
gay men report having had less loving and more rejecting fathers, and closer relationships
with their mothers, than non-gay men. Whether this phenomenon is a cause of homosexuality,
or whether parents behave this way in response to gender-variant traits in a child,
is unclear.
Some authorities have suggested that homosexuality may be an expression of non-sexual
problems, such as fear of adult responsibility, or may be triggered by various experiences,
such as having sexual relationships with members of one's own sex at an early age
that prove to be very satisfying. Arguments regarding the roots of lesbianism include
disappointing heterosexual love experience, a father who displays distaste for men
who express interest in his daughter, and memories of abusive relationships with
men.
Henry Gleitman, Alan J Fridlund & Daniel Reisberg (1999) have called for longitudinal
data to be gathered via studies following both parents and children over several
decades - though some might argue this would be overly intrusive for the participants.
Innate bisexuality
Innate bisexuality (or predisposition to bisexuality) is a term introduced by Sigmund
Freud (1920, based on work by his associate Wilhelm Fliess) that expounds that all
that expounds that all humans are born bisexual but through psychological development
(which includes both external and internal factors) become monosexual, while the
bisexuality remains in a latent state.
Pepper Blumenstein & Phillip Schwartz (1977) proposed 3 factors in the development
of bisexuality:-
- Experimentation within a friendship setting (particularly among female bisexuals)
- A liberal, hedonistic environment in which sexual activities and practices can be
freely tried without the fear of persecution or judgement
- A general philosophy or outlook on life that is open and embraces eroticism – with
attitudes to sex being just one element
Freudian and Freudian-derived theories of homosexuality have included the following:-
- homosexuality is a regression to the earliest (Oral) stage of development
- most families of homosexuals are characterised by an overprotective mother and an
absent father
- homosexuals fear engulfment by a dominant mother in the pre-Oedipal phase.
Irving Bieber (1962) used Freudian concepts to explain the emergence of sexual orientation.
He suggested that homosexuals were likely to have overly-protective and doting mothers
but their fathers were likely to be aggressive and unfeeling fathers. Bieber’s views
came from a study he led of maladjusted adults undergoing psychiatric treatment who
additionally recalled events from their childhood. These factors raised concerns
for some commentators about the reliability of their accounts.
Nature or Nurture?
Alan Bell, Martin Weinberg & Sue Hammersmith (1986) studied approximately 1,000 gay
men and lesbians from the large gay community in and around San Francisco recruited
via newspaper adverts and from venues popular with gays. As well as questions about
their sexual behaviour, the respondents were also asked about their past and present
relationships with members of their family, together with childhood experiences.
Although no one clear explanation of homosexuality emerged, several contributing
factors appeared to be significant. These included identification with parents, early
sexual encounters, and gender roles in childhood. It appeared that participants’
sexual preferences were not influenced by the extent to which they identified with
the opposite-sex parent as a child, nor did the participants report being more likely
than heterosexuals to have had first sexual experience with someone of the same sex.
However, gender nonconformity in childhood was significantly related to sexual orientation
in both the males and females. A major factor also seemed to be that respondents
experienced ‘sexual feelings’ some years prior to homosexual behaviour. Both males
and females reported difficult relationships with their fathers.
Bell et al concluded that sexual preference may be brought about to some extent by
biological influences, as the participants appeared to ‘resist’ cultural and social
factors. These influences may determine the way that gender and sexual development
happens.
Other recent studies, while not directly supporting biological explanations for homosexuality,
suggest that it may be a predisposition that can be detected at an early age among
children who do not appear to have traditional gender identification. Whether it
can be easily detected or not, most theorists agree that homosexual orientation tends
to arise at an early age. Substantially fewer studies of homosexuality have been
performed among lesbians, perhaps because of the greater stigma which is often attached
to male homosexuality in many Western cultures.
Malleability of sexual orientation
The American Psychiatric Association has stated: "...some people believe that sexual
orientation is innate and fixed; however, sexual orientation develops across a person’s
lifetime." In combination with other major American medical organisations, they have
put out a statement which said: "Sexual orientation develops across a person's lifetime
- different people realise at different points in their lives that they are heterosexual,
gay, lesbian, or bisexual." A report from the Centre for Addiction & Mental Health
states: "For some people, sexual orientation is continuous and fixed throughout their
lives. For others, sexual orientation may be fluid and change over time.” One study
has suggested "considerable fluidity in bisexual, unlabeled, and lesbian women's
attractions, behaviours, and identities."
However, they have said: "...most people experience little or no sense of choice
about their sexual orientation." The Centre has further stated therapy cannot change
sexual orientation, and have expressed concerns over potential harms. The director
of the APA's LGBT Concerns Office explained: "I don't think that anyone disagrees
with the idea that people can change because we know that straight people become
gays and lesbians.... the issue is whether therapy changes sexual orientation, which
is what many of these people claim." The American Psychiatric Association has stated:
"To date, there are no scientifically rigorous outcome studies to determine either
the actual efficacy or harm of ‘reparative" treatments”, and supports research to
further determines risks versus its benefits. Similarly, United States Surgeon General
David Satcher issued a report in 2001 stating that "there is no valid scientific
evidence that sexual orientation can be changed".
Pathological model of homosexuality
Homosexuality is no longer regarded as a mental illness by most of the scientific
community. In 1973 the American Psychiatric Association removed homosexuality as
a disorder from the Sexual Deviancy section of the Diagnostic and Statistical Manual
of Mental Disorders, the DSM-II. The World Health Organization's International Classification
of Diseases, ICD-9 (1977), listed homosexuality as a mental illness - though in 1990
a resolution was adopted to remove it in the ICD-10 (1993). The ICD-10 added ego-dystonic
sexual orientation to the list, which refers to people who want to change their gender
identities or sexual orientation because of a psychological or behavioural disorder
(F66.1). Groups that advocate reparative therapy, which includes both secular organizations
such as NARTH and religious organizations such as Exodus International, do not accept
the mainstream medical position.
Homosexual Behaviour in Animals
Homosexual sexual behaviour occurs in the animal kingdom, especially in social species
and particularly in marine birds and mammals, monkeys and the great apes. Homosexual
behaviour has been observed among 1,500 species, and in 500 of those it is well documented.
This discovery constitutes a major argument against those calling into question the
biological legitimacy or naturalness of homosexuality, or those regarding it as a
meditated social decision. For example, male penguin couples have been documented
to mate for life, build nests together, and to use a stone as a surrogate egg in
nesting and brooding. In a well-publicised story from 2004, the Central Park Zoo
in the United States replaced one male couple's stone with a fertile egg, which the
couple then raised as their own offspring.
The genetic basis of animal homosexuality has been studied in the fly drosophila
melanogaster. Here multiple genes have been identified that can cause homosexual
courtship and mating. These genes are thought to control behaviour through pheromones
as well as altering the structure of the animal's brains. These studies have also
investigated the influence of environment on the likelihood of flies displaying homosexual
behaviour.
Georgetown University professor Janet Mann (2000) has specifically theorised that
homosexual behaviour, at least in dolphins, is an evolutionary advantage that minimizes
intraspecies aggression, especially among males. Studies indicating prenatal homosexuality
in certain animal species have had social and political implications surrounding
the gay rights debate.
