Biological Factors in Homosexuality:

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Biological Factors in Homosexuality

• Whats TheEvidence? The Implications?

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BEFORE WE GET STARTED

• Lets stick with the facts

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Homosexuality What do we know?

• Do we know people who are homosexual?
• Probably
• _____ of men
• _____ of women
• (Laumann others, 1994)
• Do surveys get an find accurate results?
• Social Desirability/Classification Issues
• EX _____________________________________, etc.
• How can we determine the cause?
• Hormonal studies
• Genetic Studies
• Observational studies

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A quick historical note
A quick historical note

• 1973
• The American Psychological Association removed
  homosexuality from the DSM-II as a mental
  disorder
• What does this mean?
• Homosexuality occurs in the normal range of human
  behavior
• Currently using DSM-IV-TR (4th Ed. Diagnostic
  Statistic Manual)

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But where does homosexuality come from?

• The __________________________ debate
• Are people homosexual because they are born that
  way or because of environmental factors they
  experience after birth (OR BOTH?)
• Lets take a look at some studies

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What about animals?

• Turkeys in the woods
• Mating behavior
• http//www.nwtf.org/all_about_turkeys/sounds_of_tu
  rkeys.html
• Biological Exuberance Animal Homosexuality and
  natural diversity
• Bagemihl, 1999
• 450 different species of animals including
  lizards, dolphins, flamingoes, penguins, etc.

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and then there are the pygmy chimpanzees
(Bonobos)

• _____________________
• Used to resolve conflict and form group bonds
  (particularly in females)
• Frequent sexual encounters with same sex
• Evolutionary implications
• Estimated to genetically be 99.5 related to
  humans
• Behaviors of closely related species often similar

http//www.worldwildlife.org/wildplaces/congo/imag
es/about.jpg
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Animals

• Hormonal treatments
• - Prenatal injections of
• testosterone in guinea pigs
• - Females demonstrated
• male (mounting) behavior
• Castrated males demonstrated
• female mounting behavior
• (I. L. Ward O. B. Ward, 1985)

http//cuddlycavies.homestead.com/costumes.html
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And in people?

• No hormonal differences in ________________
  hetero- and homosexual men
• Hormones like testosterone have greater affect on
  ________________________________
• (Barahal, 1940)
• Results for women have been less consistent
• Problems with these studies
• Not accounting for external factors!

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Prenatal hormonal differences

• Congenital Adrenal Hyperplasia (CAH)
• Synthesis of cortisol disrupted
• Adrenal glands secrete extra androstenedione
• Metabolized into testosterone,
  dihydrotestosterone (Zucker, 1999)
• 48 of women with CAH reported same-sex arousal
• 22 reported same-sex sexual partner contact
• (Money et al., 1984)

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Can someones orientation be CHANGED?

• Remember Nurture vs. Nature ?
• A hypothetical example of sexual reassignment
  (mad scientist stuff)
• The real thing (almost)
• ______________ (thats a big Oops!)
• Cloacal extrophy (Reiner et al., 1999)

http//www.flickr.com/photos/himike/page8/
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but I saw a story on the news about this guy and

• Case studies of people changing or discovering
  their orientation doesnt refute consistent
  evidence that biology is a factor.
• If a person has schizophrenia but recoversdoes
  this mean there is no biological influence?
• Data remains incomplete
• Media still shows stories about people changing
  orientation
• Availability Heuristic

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Does it run in the family?

• Twin study
• Monozygotic (identical) twins 58 likelihood of
  homosexuality when one twin is homosexual
• Decreases to 41 with different home environment
• (Kirk et al., 2000)
• Siblings meta-analysis
• Dizygotic (fraternal) twins 22
• Brothers 9
• Sisters 6-25 (Bailey Pillard, 1995)

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Family ties

• Big Brother is affecting you?
• Fraternal birth-order effect
• Probability of males being homosexual __________
  with the more older brothers they have
• (Blanchard, 1997)
• However, no gay gene has been isolated
• Current hypothesis Women creating antibodies
  (antigens) when foreign Y chromosome is present
  
• No measurable effect on sisters

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Brain structure differences

• ______________
• Forebrain structure thought to regulate eating,
  drinking, sexual behavior, etc.
• Autopsied brains
• Homosexual men has smaller cluster of neurons
  associated with hypothalamus
• (LeVay, 1991)
• What does it all mean??

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Brain Activity

• EEG
• Gay men differ from straight ones on minor
  ability tests
• Left visual field dot detection (Sanders
  Wright, 1997)
• Resembled heterosexual women during various
  verbal and spatial tasks (Wegesin, 1998)
• Doesnt show much
• What about fMRI?
• Well see

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What does it all mean?

• Biological differences/factors do exist
• Hormones
• Predisposed orientation
• Genetics (Twins/big brothers)
• Dont rule out the environment
• This is just the BEGINNING!