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  1. 1. www.ThePsychFile Sexual Orientation Summary of Current Research Michael A. Britt, Ph.D. Fall, 2009 The Psych Files podcast www.thepsychfiles.com
  2. 2. www.ThePsychFile Background Info • Demographics: 3% of males and 2% of females 5% of US population self identify as gay (260 million x .05 = 13 million) • Sexual Behavior vs. Sexual Orientation – An important distinction – People can engage in homosexual behavior (ex: experimentation in adolescence, homosexual behavior in prison), but not have a homosexual orientation - Don Allen • Sexual orientation is considered by many researchers to be on a continuum – On one end: those who are exclusively heterosexual and on the other, those who consider themselves to be exclusively homosexual with all degrees in between
  3. 3. www.ThePsychFile Homosexuality among animals • Necking and rubbing to sexual excitement is common among male giraffes • Common among pygmy chimpanzees • Greylag geese can have homosexual unions that last up to 15 years
  4. 4. www.ThePsychFile Physiological differences between gays and straights • Simon LeVay (1991) – Neurobiologist at the Salk Institute in La Jolla California – The third interstitial nucleus (located in the hypothalamus) • is normally larger in men than in women • in his sample of gay men, the third interstitial nucleus was about the same size as in women – Hypothalamus plays a role in sexual motivation – Published in the Journal Science – Critics: it can't be as black/white as this because of the idea of a continuum
  5. 5. www.ThePsychFile Physiological differences between gays and straights • Handedness – Lesbians are 91% more likely to be left handed than heterosexual women – Gay men are 34% more likely
  6. 6. www.ThePsychFile Hormones • index (pointer) and ring finger – Women: the length is more similar than in men (men: bigger difference in the length of these two fingers) – caused by exposure to male hormones in utero – you can see this difference at age 2 – Lesbians: the difference is more similar to men – suggests that lesbians may have had a greater exposure to male hormones in the womb
  7. 7. www.ThePsychFile Hormones • ”Fraternal Birth Order Effect" - James Cantor, et. al • the more older brothers you have, the more likely a male is to be gay • doesn't matter what the sexual orientation of the older brother • not true if your older brothers are step brothers or adopted • confirmed across cultures • no relationship found for lesbians • explanation: a change in the hormonal balance in the mother's uterus with each additional child
  8. 8. www.ThePsychFile Hormones • Testosterone – no difference in testosterone levels between adult male hetero and homosexuals • Spatial Abilities – Mental Rotations task – homosexual men perform more similarly to women – "...these spatial ability data suggest possible biological and neuropsychological factors co- related to the development of sexual orientation" - Brian Gladue – lesbians not sig different from heterosexual women
  9. 9. www.ThePsychFile Hormones • Adrenal Glands • Age 10 (4th grade) – The mean age of your first sexual attraction • Between 6 and 8 the adrenal cortex begins to secrete DHEA (dehydro-piandrosterone) • Well before puberty • same for hetero as for homo-sexual adults – the time of your adrenal glands mature • "...the biggest nongonadal source of sex steroids” • "This biological process, distinctly different from gonadarche, may underlie the development not only of sexual attraction, but of cognition, emotions, motivations and social behavior as well”
  10. 10. www.ThePsychFile Genes: Twin Studies • Types – Dizygotic twins • “fraternal twins” - two eggs, so they don't look alike • 22% of twins of gay males were also gay • 16% for lesbians – Monozigotic twins • "identical twins" (one egg) • 52% of the identical twins of gay males were also gay” • 48% for lesbians – remember: this is not a perfect correlation, so environment must play some part
  11. 11. www.ThePsychFile Genes: Twin Studies • focus: identical twins raised apart – same genes, different environment – so: if identical twins raised apart are both gay, that argues for a genetic influence – when one twin is gay, the chances that the other one is gay are much higher than would be expected – Results: Roger Hock: results are "quite consistent” – higher, for example, than if the twins were dizygotic – but: even twins raised apart are not likely to be raised in very different family environments
  12. 12. www.ThePsychFile Nurture/Environment • Childhood Experiences – Research by Bell, Weinberg & Hammersmith (1981) – "..conducted face-to-face interviews with 979 homosexual participants (293 women and 686 men) and 477 heterosexual controls. The researchers found no single condition of family life or childhood experience that in and of itself appeared to be a factor in either homosexual or heterosexual development."
  13. 13. www.ThePsychFile Nurture/Environment • Influence of Gay Parents – Patterson, C.J. (2000). Family Relationships of Lesbians and Gay Men, Journal of Marriage and Family, 62, 1052-1069 – Mikach interviewed 75 gay fathers - only 7 of their sons identified themselves as gay – ... no significant problems in the development of sexual identity among children of lesbian mothers have yet been identified" - p. 1060 – "...gay men are no more likely than heterosexual men to perpetrate child abuse (Jenny, Roesler, & Poyer, 1994). Fears that children in custody of gay or lesbian parents might be at heightened risk for sexual abuse are without empirical foundation" - 1060-1061
  14. 14. www.ThePsychFile Nurture/Environment • Myths: Roger Hock: "resoundingly rejected" as explanations for homosexuality: – homosexual men have overly protective mothers and distant fathers and homosexual women had overly protective fathers and distant mothers • If you know 1-3 gays who have a protective mother and distant father - that's too small a sample size for confident conclusions • Possible confirmation bias: how many heterosexual men do you know who have a distant father and protective mother? We often don't even think about looking at this • The weakness of doing a survey on this issue: even if you find support - which one is the causal factor? Did the parents cause the child to be gay, or did the child's homosexuality cause the parents to act this way? – homosexuals were molested as children by a same sex adult (The so-called "seduction hypothesis") – homosexuals are more likely to have had a gay mother or father - no evidence that homosexuality is more likely when children have gay parents
  15. 15. www.ThePsychFile Nature AND Nurture • EBE: "Exotic Becomes Erotic" theory – Sandra Bem: Sexual orientation is a combination of in-born temperament and experiences with other children – Temperament • male typical: aggressive, activity focused • Female typical: relationship-oriented, non-aggressive • temperament guides children toward "Gender conforming behaviors” – Experiences • boys playing sports, "rough and tumble" play, girls play with dolls, pretend activities – Homosexuality results when: • children with a temperament that doesn't match gender-typical activities are drawn toward opposite sex activities and same sex children are seen as "exotic” • In adolescence, these feelings of the same sex being different, naturally turn to feelings of attraction – Critics: not much empirical support
  16. 16. www.ThePsychFile Conclusions • Wood, Wood & Boyd: The World of Psychology – "Clearly there are no certain predictors of homosexuality” • Brian Gladue – "The presence of biological factors in the development of homosexuality (and heterosexuality) is becoming increasingly obvious. Already we have a set of reliable findings, from many laboratories, demonstrating that human sexual orientation has a genetic basis....” – "...not all men and women arrive at their sexual orientation following the same path.” • The continuum: back to where we started – The danger of black/white, gay/straight thinking. We're all along that continuum somewhere. – For some, their orientation was influenced by hormones in the womb, others by events in their childhood. – That's what's fascinating about the study of psychology.
  17. 17. www.ThePsychFile Conclusions • William Byne: The Biological Evidence Challenged (1994, Scientific American) – "While attempts to replicate these preliminary finding continue, researchers and the public must resist the temptation to consider them in any but the most tentative fashion. Perhaps more important, we should also be asking ourselves why we as a society are so emotionally invested in this research. Will it- or should it - make any difference in the way we perceive ourselves and others or how we live our lives and allow others to live theirs? Perhaps the answers to the most salient questions in this debate lie not within the biology of human brains but rather in the cultures those brains have created."
  18. 18. www.ThePsychFile References • Bailey, J.M., Bobrow, D., Wolfe, M., & Mikach, S. (1995). Sexual Orientation of Adult Sons of Gay Fathers. Developmental Psychology, 31 (1), 124-129. • Bell, A., Weinberg, M., & Hammersmith, S. (1981). Sexual preference: Its development in men and women. Bloomington: Indiana University Press. • Bem, D.J. (1886). Exotic becomes erotic: A Developmental theory of sexual attraction. Psychological Review, 103, 320-335. • Byne, W. (1994). The Biological Evidence Challenged. Scientific American, May. • Ciccarelli, S. & Meyer, G.F. (2006). Psychology. Prentice Hall. • Cantor, J.M., Blanchard, R., Paterson, A.D. & Bogaert, A.F. (2002). How many gay men owe their sexual orientation to fraternal birth order? Archives of Sexual Behavior, 31, 1; Psychology Module.
  19. 19. www.ThePsychFile References • Carroll, M.P. (1998). But fingerprints don’t lie, eh?. Psychology of Women Quarterly, 22, 739-749. • Gladue, B.A, The BioPsychology of Sexual Orientation. in Current Directions in Human Sexuality and Intimate Relationships, Fisher, T.D. & McNulty, J. eds. Allyn and Bacon. • Hock, R. (2010). Human Sexuality, 2e. Prentice Hall. • Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (2000). Sexual orientation in a U.S. national sample of twin and nontwin sibling pairs. The American Journal of Psychiatry, 157; 11; Health Module. • King, B.M. (2005). Human Sexuality Today. Prentice Hall, 5e. • Levay, S. (1991). A difference in hypothalamic structure between heterosexual and homosexual men. Science, 253, 1034-1037.
  20. 20. www.ThePsychFile References • McClintock, M.K. & Herdt, G., Rethinking Puberty: The Development of Sexual Attraction in Current Directions in Human Sexuality and Intimate Relationships, Fisher, T.D. & McNulty, J. eds. Allyn and Bacon. • Patterson, C.J. (2000). Family Relationships of Lesbians and Gay Men, Journal of Marriage and Family, 62, 1052-1069 • Rind, B. (2001). Gay and bisexual adolescent boys' sexual experiences with men: an empirical examination of psychological correlates in a nonclinical sample. Archives of Sexual Behavior, 30 (4). • Selekman, S. (2007). Homosexuality in children and their parents. Pediatric Nursing, 33(5). • Smith, B. (2007). The Psychology of Sex and Gender. Allyn and Bacon. • Toates, F. (2007). Biological Psychology. Prentice Hall. • Wood, S.E., Wood, E. G., & Boyd, D. (2005). The World of Psychology, 5e. Allyn and Bacon.

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