The Psychology of Sexual Orientation

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The Psychology of Sexual Orientation

• Bill Altermatt

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Why is this important?

• Homosexuality is so stigmatized in our culture
  that homosexuals are often singled out for
  harassment, intimidation, and even murder.
• Hate groups blame homosexuals for choosing
  their orientation.
• If orientation is not a choice, individuals are
  not responsible for it.

Matthew Shepard, brutally killed in Laramie,
Wyoming, in 1998
Picketing outside Matthews funeral
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What is sexual orientation?

• Enduring emotional, romantic, sexual, or
  affectional attraction toward...

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How common is homosexuality?

• Rates of homosexuality across many studies,
  involving thousands of respondents from many
  countries
• 3-4 of men
• 1-2 of women

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What causes sexual orientation?

• Personal choice?
• Environmental influences (e.g., childrearing
  practices, sexual abuse, etc.)?
• Genetic or biological influence?

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Personal choice? No.

• Why would it be chosen?
• High costs of homosexuality in our culture
• When would it be chosen?
• Orientation emerges prior to sexual experience,
  so how would you know what you were choosing?
• Changeable through willpower? No.
• Research indicates you can control behavior but
  not orientation (desire)

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Environment? No evidence.

• Kinsey Institute survey (Bell et al., 1981
  Hammersmith, 1982)
• Compared 1,000 homosexuals and 500 heterosexuals
  on every imagined possible cause of homosexuality
• Parental relationships, childhood sexual
  experiences, peer relationships, dating
  experiences
• No differences found between heterosexuals and
  homosexuals.

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Biological? Probably.

• Critics of homosexuality regard it as
  unnatural, against biology, and the product
  of human culture.
• But Bruce Bagermihl (1999) reports that sexual
  behavior has been documented by biologists in
  over 450 species

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Bagermihl (1999)

• 6-10 of rams are not interested in ewes and seek
  to mount other males (Perkins Fitzgerald, 1997)

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Bagermihl (1999)

• Every homosexual behavior performed by humans has
  been documented in non-human animals

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Bagermihl (1999)

• In many species, same-sex attraction leads to
  long-term bonds between partners, who sometimes
  raise offspring together.

A homosexual pair of male Flamingos raising their
foster chick.
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Unnatural?

• If the definition of natural is occurring in
  nature, then homosexuality appears to be very
  natural.
• Given the widespread prevalence of homosexuality
  among non-humans, it is unlikely that
  homosexuality is the product of human culture and
  more likely that there is a biological cause of
  homosexuality.

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Evidence that sexual orientation is biological

• Family studies
• 9 of brothers of gay men are gay (compared to
  3-4 on average)
• 6 of sisters of lesbian women are lesbian
  (compared to 1-2 on average)
• Adopted twin studies rule out same-house
  effects
• Bailey et al. (2000) studied 1,538 twin pairs and
  estimated h2 .51 for males, .23 for females
• 51 of the similarity in homosexuality between
  two males can be explained by the genes they
  share.

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Evidence that sexual orientation is biological

• Fraternal birth order effect
• Each older brother increases the probability of
  male homosexuality by approximately 1
• Likely cause maternal immune response to male
  fetuses, which increases with each pregnancy
• Probably explains 15 of male homosexuality
• No birth order effect for lesbians

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Major theories for biological origins of sexual
orientation

• Neurohormonal hypothesis sexual orientation is
  determined by hormones acting on the brain during
  prenatal development
• Neuroanatomical hypothesis sexual orientation
  is determined by structural differences in the
  brains of homosexuals and heterosexuals

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Neurohormonal hypothesis

• Hypothesis
• prenatal androgen activity in the brain ?
  attraction to females
• absence of such activity ? attraction to males
• Evidence
• Female infants with CAH (high prenatal androgen
  exposure)
• 48 reported arousal imagery for females
  (compared to 7 in control condition)
• 22 reported sexual contact with females
  (compared to 4)

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More neurohormonal evidence

• Males with AIS (androgen insensitivity syndrome)
  brains do not respond to androgen
• Externally female, no ovaries
• 100 reported attraction to males
• Male infants with cloacal exstrophy (ambiguous
  genitalia) reassigned female (with surgery
  hormones).
• By age 14, 100 reported sexual attraction to
  females (Reiner, 2002).

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Neurohormonal conclusions

• Sexual orientation is probably influenced by
  exposure to hormones before birth
• Exposure to androgens (and sensitive to
  androgens) ? attracted to females
• Normal males, reassigned males, CAH females
• Not exposed to androgens (or insensitive to
  androgens) ? attracted to males
• Normal females, AIS males

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Neuroanatomical hypothesis

• One structure in the brain that corresponds to
  attraction to males or females is INAH-3

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INAH-3

• Sex differences
• Three studies found that INAH-3 is 2x larger in
  men than in women
• Sexual orientation
• Three studies found that INAH-3 is 2-3x larger in
  heterosexual men than in homosexual men
• Similar differences observed in rams exhibiting
  same-sex preferences

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INAH-3 Conclusions

• Evidence suggests larger INAH-3 predicts
  attraction to females, smaller INAH-3 predicts
  attraction to males
• Problems with INAH-3 research
• Cause or effect unclear
• Studies have not included lesbians

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General conclusions

• No evidence that sexual orientation is caused by
  personal choice or by a particular environmental
  factor.
• Strong evidence that sexual orientation has a
  biological/genetic component.
• Evidence for the effects of genes, prenatal
  hormones, and brain structure