Glenn Wilson PhD, Gresham College, London

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BORN GAY?
THE PSYCHOBIOLOGY OF SEXUAL ORIENTATION

• Glenn Wilson PhD, Gresham College, London

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PSYCHOANALYTIC WRIT

• The consensus is that (homosexuality) is
  caused psychically, through a disabling fear of
  the opposite sex. The origins of this fear lie in
  the homosexuals parents. The mother, either
  domineering or contemptuous of the father, or
  feeling rejected by him, makes her son a
  substitute for her husband, with a close-binding,
  overprotective relationship. Thus she
  unconsciously demasculinises him. If at the same
  time the father is weakly submissive to his wife
  or aloof and unconsciously competitive with his
  son, he reinforces the process.
• Time Magazine article, 1966.

Such theories have been effectively debunked.
There is no satisfactory evidence that parenting
affects sex orientation.
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THE STABILITY OF SEXUAL ORIENTATION
This New Guinea tribe removed young boys from
female company and virilised them by having
them ingest the semen of older boys. After
spending their teenage years fellating or being
fellated by other boys most took comfortably to
married life. Only about 5 continued to seek
boys for sexual pleasure in adulthood. Apparently,
sexual orientation is not easily modified by
teenage experiences.
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AGAINST NATURE?
Many animals engage in homosexual behaviour in
the wild, sometimes for reasons of play and
dominance rather than sexual preference. Bonobos
use sex to form bonds and ease social
tensions. The best animal model of homosexuality
is sheep, where around 6 of rams will only mount
other males, even when given a choice. These rams
show levels of oestrogen in the amygdala similar
to females.
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THE SEXUAL LIE DETECTOR
It is fantasies and preferences that define
sexuality, not behaviour. Erectile responses to
erotica suggest that males are polarised even
those calling themselves bisexual respond only
to male images, or female, not both. Women seem
to have innate bisexual potential. Heterosexual
women and lesbians respond equally to male and
female erotica.
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RATES OF HOMOSEXUALITY

• Proportions reporting homosexual behaviour in
  last 5 years (Johnson et al, 2001)
• London men 5.5 women 3.9
• UK men 2.1 women 2.4
• Gay people seem to gravitate towards large
  cities.
• Rates of homosexuality are fairly stable
  across time and place. Only about 1-2 of men
  shift their orientation women slightly higher
  (Dickson et al, 2003).

The only gay in the village?
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CHILDHOOD GENDER NONCONFORMITY

• Cross-gender toy and play preferences are
  strongly predictive of adult sexual orientation.
  Around 75 of sissies and tomboys (usually
  identifiable by age 3) grow up to be gay or
  lesbian.
• This places the origin of sexual preferences
  well before any episodes of teenage seduction
  or contagion.

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MIDDLE-SEX
Individuals born with inter-sexual conditions
provide clues as to the inborn origins of sexual
orientation.
Congenital adrenal hyperplasia (XX women
masculinised by excess adrenal male hormones)
show increased lesbian interests.
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THE CASE OF BRENDA

• David Reimer was born a boy but a botched
  circumcision led to his reassignment as a girl.
  Money (1975) reported that he had successfully
  adapted to female identity but by age 14 he had
  reverted to being a boy and he committed suicide
  at age 38.

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POSSIBLE EFFECTS ON SEXUAL ORIENTATION

• 1. Genes (inherited plans for brain
  construction).
• 2. Epigenetics (early environmental factors that
  switch genes on or off).
• 3. Prenatal hormones (from both mother foetus).
• 4. Other prenatal chemistry (medicines, drugs,
  plastics).
• 5 Maternal stress (war, marital strife).
• 6. Infectious agents (viruses, bacteria).
• 7. The social environment (parental treatment,
  childhood and teenage experiences).

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THE BIG BROTHER EFFECT

• Men who have older brothers are more likely
  to be gay (each older brother raises chances by
  33).
• Effect applies only to biological brothers,
  not stepbrothers, hence not due to upbringing.
• Probably due to progressive build-up of
  antibodies in mother that affect masculinisation
  of foetal brain.

• There is no big sister effect because there is
  no hormonal conflict between mother and female
  foetus.

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BIG BROTHER EFFECT AND HANDEDNESS

• The fraternal birth order effect seems to
  apply only to right-handers (Blanchard, 2008).
• Given an elevated frequency of
  left-handedness in both gay men and lesbians this
  is curious.
• It appears that older brothers cause younger
  brothers to be either gay or left-handed but not
  often both.
• The reasons for this, whether genetic or
  environmental, are not known.

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DIRECTION OF HAIR WHORL
Klar (2004) reports that 30 of gay men show an
anti-clockwise hair whorl, compared with 8 of
straight men. The genetic mechanism connects with
that responsible for handedness (hence
hemispheric brain specialisation).
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SEXUALLY DIMORPHIC NUCLEI IN THE HYPOTHALAMUS

• LeVay (1991) found differences between gay
  and straight men in certain nuclei in the
  hypothalamus that differentiate men and women and
  are concerned with sexual behaviour.
• These were primarily the interstitial nuclei
  of the anterior hypothalamus (INAH-3) and the
  suprachiasmic nucleus (SCN).
• Because many of his post-mortem subjects had
  died of AIDS he was obliged to show that this did
  not account for his results.

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WELL CONNECTED BRAINS

• Witelson et al (2008) have shown that that
  isthmus region of the corpus callosum (the
  conduit between the two halves of the brain) is
  larger in gay than straight men. This supports
  the idea that gay men (like women) have less
  structural and functional asymmetry in the brain
  than straight men.

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AMYGDALA CONNECTIONS
Using PET and MRI scans, Savic Lindstrom (2008)
showed that the amygdala is wired more for
fight-flight reactions (action) in straight men
and lesbians and more to emotional responses such
as anxiety (feelings) in gay men and straight
women (see widespread connections on left side).
They also found more rightward asymmetry in
straight men (12cc) and lesbians (5cc), whereas
the two sides were much the same volume in gay
men and straight women.
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GRAY MATTER IN THE PERIRHINAL CORTEX
Using structural MRI, Ponseti et al (2007) found
that lesbian women had less gray matter in the
left perirhinal cortex than heterosexual women In
this respect they were more like men. This area
is involved in olfactory and visual processing
but the functional meaning of the finding is not
clear. No such differences were found between gay
and straight men.
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TASK PERFORMANCE PROFILES

• Straight women and gay men excel in verbal
  fluency and memory. Lesbians are better than
  straight women at spatial tasks (Rahman, Wilson
  Abrahams, 2004).

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PREPULSE INHIBITION IN LESBIAN WOMEN
Startle reactions (strength of eye-blink) are
reduced if the startle stimulus (sudden loud
noise) is preceded by a weaker version of itself.
PPI occurs less in women, but lesbian women
respond more like men. Since this is an
involuntary reaction it suggests hard-wiring
rather than social learning.
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FINGER RATIOS
Men typically have a shorter forefinger than ring
finger. In women they are much the same or
reversed. This seems to be a marker of exposure
to prenatal testosterone.
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FINGER RATIOS AND SEX ORIENTATION
Williams et al (2000) found that gay and straight
men were similar in 2D4D but lesbians were
inclined toward the male pattern. Relationships
were stronger on the right hand compared with the
left. There was a significant tendency for men
with older brothers to have a masculinised finger
ratio regardless of their sexual orientation.
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BEHAVIOUR GENETICS
Langstrom et al (2008) studied the origins of
sexuality in 7600 twins Men 35 genetic, 1
shared (family) environment, 64 non-shared
(unique) environment. Women 18 genetic, 16
shared (family) environment, 66 non-shared
(unique) environment. This effectively rules out
parenting as a cause of male homosexuality.
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LOCI OF GAY GENES

• Much interest in X chromosome, especially
  Xq28 (Dean Hamer)
• More recent work (Risch et al) implicates
  autosomal chromosomes (7, 8, 10). Former two
  contributed equally by mother and father, latter
  of maternal origin only.
• Almost certainly, many different genes are
  involved.

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SKEWING OF X-INACTIVATION
Women have two X chromosomes (compared to one in
men) but one is inactivated early in
development. Choice of which to inactivate is
usually random, resulting in even mosaics (c.f.,
tortoiseshell cats). Bocklandt et al (2006)
found extreme skewing more common in mothers of
gay men. (0 gay sons 4, 1 gay son 13, 2 gay
sons 23). Meaning not clear but supports
involvement of X-chromosome.
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THE DARWINIAN PARADOX

• Theories as to why gay genes are not
  eliminated by natural selection (gay people
  having fewer children)
• Kin-altruism homosexuals assist family members
  in raising more children. No satisfactory
  evidence.
• Balanced polymorphism genes causing
  homosexuality confer a direct reproductive
  benefit to relatives, c.f., sickle cell anaemia.
  (e.g. male bonding empathy, female
  competitiveness may be useful traits).
• Sexually antagonistic selection genes which
  decrease fitness in one sex are maintained
  because they increase fitness in the other (some
  evidence that female relatives of gay men are
  more fecund).

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MITOCHONDRIAL DNA

• Sykes (2003) suggests that inheritance of
  homosexuality might be via mitochondrial DNA.
  This is extra-chromosomal genetic material passed
  down the maternal line only. It is selfish in
  that it would prefer a female-only species. Male
  homosexuality could be due to mDNA sabotaging
  sons (c.f. the beehive in which sterile males
  work for the queen).
• Currently little supportive evidence but
  remains an intriguing idea.

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CHANGING ATTITUDES
The last two decades have seen a dramatic
increase in acceptance of homosexuality in the
US. The UK has gone from homosexual behaviour
being a criminal offence in 1967 to homophobia
being an offence today.
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INTERNATIONAL LAWS RE HOMOSEXUALITY

• There is considerable variation around the
  world with respect to laws on homosexuality.
  These range from countries with laws against
  discrimination to those which impose the death
  penalty.