9 Biology Of Sexual Orientation

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Part 9 of "Science & Sexuality." What determines sexual orientation? Is it learned or inborn? How does culture affect the expression, perception, and treatment of sexually different people?

Published in: Health & Medicine, Spiritual

9 Biology Of Sexual Orientation

  1. 1. <ul><li>“ Gay people have a different sensibility.” Sandra Witelson, PhD </li></ul><ul><li>Homosexuality & other sexually variant behaviors in animals Bagemihl, Bruce. BIOLOGICAL EXHUBERANCE. (1999) </li></ul><ul><li>Anthropological evidence </li></ul>Biology of Sexual Orientation
  2. 2. Sexual Orientation & INAH-3 <ul><li>Simon LeVay’s work – compared brains of cadavers of gay men versus straight men </li></ul><ul><ul><li>Third interstitial nucleus of anterior hypothalamus </li></ul></ul><ul><ul><li>Was 2+X larger in straight men than in gay men or women </li></ul></ul><ul><li>Thus, INAH-3 is dimorphic with sexual orientation rather than genetically determined sex </li></ul><ul><li>Lends support to idea that sexual orientation has biological basis </li></ul><ul><li>LeVay, S. A Difference In Hypothalamic Structure Between Heterosexual And Homosexual Men. SCIENCE, 253: 1034–1037 (1991) </li></ul>
  3. 3. Sexual Orientation & INAH3
  4. 4. 2 nd Study of INAH3 & Sexual Orientation <ul><li>Confirmed earlier findings </li></ul><ul><ul><li>INAH3 contained significantly more neurons and occupied a greater volume in presumed heterosexual males than females </li></ul></ul><ul><ul><li>No sex difference in volume was detected for any other INAH </li></ul></ul><ul><ul><li>Trend for INAH3 to occupy a smaller volume in homosexual men than in heterosexual men </li></ul></ul><ul><ul><li>AIDS does not affect INAH3 </li></ul></ul><ul><li>NEW FINDING: no difference in the number of neurons within the INAH3 based on sexual orientation </li></ul><ul><li>Byne, William, Tobel, Stuart, Mattiace, Linda A., Lasco, Mitchell S., Kemether, Eileen, Edgar, Mark A., Morgello, Susan, Buchsbaum, Monte S., and Jones, Liesl B. The Interstitial Nuclei of the Human Anterior Hypothalamus: An Investigation of Variation with Sex, Sexual Orientation, and HIV Status. HORMONES AND BEHAVIOR, 40: 86-92 (2001) </li></ul>
  5. 5. INAH3 Gay Vs. Straight Males <ul><li>The same number of nerve cells in the gay and straight men suggest that there is no difference between gay and straight men in the earliest phase of brain development, when nerve cells are being generated and assemble into functional groups </li></ul><ul><li>Rather, the difference may arise at some later time, when the nerve cells in INAH3 are growing and forming connections </li></ul><ul><li>LeVay, Simon. http://www.nerve.com/regulars/scienceofsex/09-05-00/ </li></ul>
  6. 6. What Could Cause Such a Difference in Growth of INAH3? <ul><li>Wide range of possibilities </li></ul><ul><ul><li>Genetic differences between individuals </li></ul></ul><ul><ul><li>Differences in the levels of hormones (especially testosterone) that regulate cell growth in the hypothalamus </li></ul></ul><ul><ul><li>Differences in pre- or postnatal environment that could impact the growth of INAH3 through a variety of means </li></ul></ul><ul><li>When does divergence of development happen? </li></ul><ul><ul><li>Before birth (based on animal experiments) </li></ul></ul><ul><ul><li>We don't yet know for a fact </li></ul></ul><ul><li>LeVay, Simon. http://www.nerve.com/regulars/scienceofsex/09-05-00/ </li></ul>
  7. 7. Differences Between Gay Versus Straight Brains Are Discrete <ul><li>“ What's surprising about the gay/straight difference in INAH3, then, is simply that it is so localized and obvious, rather than being diffusely spread through the synaptic architecture of the entire brain. </li></ul><ul><li>This offers the hope that we will eventually be able to understand the origins of sexual orientation at a cellular level.” </li></ul><ul><li>LeVay, Simon. http://www.nerve.com/regulars/scienceofsex/09-05-00/ </li></ul>
  8. 8. Sexual Identity & INAH3
  9. 9. INAH3 & BSTc: Sexual Identity Versus Sexual Orientation <ul><li>INAH3 volume may be related to sexual orientation </li></ul><ul><li>S LeVay A difference in hypothalamic structure between heterosexual and homosexual men S cience 30 August 1991:Vol. 253. no. 5023, pp. 1034 - 1037 </li></ul><ul><li>INAH3 cell number may be related to sexual identity </li></ul><ul><li>BSTc cell number and volume both related to sexual identity </li></ul><ul><li>Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008) </li></ul>
  10. 10. INAH3 in Transsexuals <ul><li>Method: Three different stainings throughout the nuclei in every 15th section, i.e. thionin, neuropeptide Y and synaptophysin </li></ul><ul><li>INAH3 volume and number of neurons of male-to-female transsexual people is similar to that of control females </li></ul><ul><li>The female-to-male transsexual subject had an INAH3 volume and number of neurons within the male control range ( even though the treatment with testosterone had been stopped three years before death) </li></ul><ul><ul><li>No difference in INAH3 between pre-and post-menopausal women, so feminization of the INAH3 of male-to-female transsexuals was not due to estrogen treatment </li></ul></ul>Garcia-Falgueras, Alicia and Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  11. 11. Copyright restrictions may apply. Garcia-Falgueras, A. et al. Brain 2008 0:awn276v1-276; doi:10.1093/brain/awn276 Representative immunocytochemical staining of the NPY innervation of the uncinate nucleus showing the three different types: (A) typical horse-shoe shape, in which fornix fibers do not completely bisect the nucleus, (B) the two subdivisions of the Un clearly divided by fornix fibers, originally called INAH3 and INAH4 and (C) the nucleus as just one part, considered to be the INAH4 (A NBB # 98031 man 33 years old, B NBB # 98006 man 50 years old, C NBB # 91009 woman 36 years old Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  12. 12. Copyright restrictions may apply. Garcia-Falgueras, A. et al. Brain 2008 0:awn276v1-276; doi:10.1093/brain/awn276 INAH3 volume in thionin staining in different groups, according to their gender identity and hormonal changes in adulthood Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  13. 13. Copyright restrictions may apply. Garcia-Falgueras, A. et al. Brain 2008 0:awn276v1-276; doi:10.1093/brain/awn276 INAH3 number of neurons Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  14. 14. Copyright restrictions may apply. Garcia-Falgueras, A. et al. Brain 2008 0:awn276v1-276; doi:10.1093/brain/awn276 Density of neurons in INAH3 in different groups: M = control male group; F = control female group; MtF = transsexual male-to-female group; CAScastrated male group; PreM = pre-menopausal women; PostM = post-menopausal women Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  15. 15. Copyright restrictions may apply. Garcia-Falgueras, A. et al. Brain 2008 0:awn276v1-276; doi:10.1093/brain/awn276 Representative photomicrographs of the uncinate nucleus in three different groups in consecutive sections (A, B and C: NBB # 00131 male 25 years old; D, E and F: NBB # 01011 female 46 years old; G, H and I: NBB # 84037 transsexual male-to-female 44 years old) Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008)
  16. 16. Adult Hormones & INAH3 <ul><li>Castrated men had values intermediate between male and female controls </li></ul><ul><li>This data and S7 cannot be fully explained by activating affect of androgens on INAH3 </li></ul><ul><li>Indicates there are also organizational effects of androgens during development of INAH3 morphology </li></ul><ul><li>Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008) </li></ul>
  17. 17. INAH3 & BSTc Involved in Sexual Identity <ul><li>Propose that the sex reversal of the INAH3 in transsexual people is at least partly a marker of an early atypical sexual differentiation of the brain </li></ul><ul><li>Appears to be a relationship of BSTc with sexual identity rather than with sexual orientation while INAH3 seems to have a relationship with both </li></ul><ul><li>Garcia-Falgueras, Alicia, Swaab, Dick F. A Sex Difference In The Hypothalamic Uncinate Nucleus: Relationship To Gender Identity. BRAIN, (Nov 2, 2008) </li></ul>
  18. 18. Is There a Genetic Basis to Sexual Orientation? <ul><li>It has been suggested that homosexuality &quot;runs in families,&quot; meaning that there may be a genetic underpinning to the development of sexual orientation </li></ul><ul><li>Studies have examined this issue by assessing one of following </li></ul><ul><ul><li>Incidence of homosexuality in families </li></ul></ul><ul><ul><li>Similarity of sexual orientation between twins </li></ul></ul><ul><ul><li>Evidence for genetic markers among gay family members </li></ul></ul>
  19. 19. Genetics of Gayness in Males <ul><li>A genetic hypothesis posits that homosexuality runs in families and that genetic markers* for sexual orientation can be found among family members </li></ul><ul><li>Evidence for genetic markers for gay men and their gay brothers in the Xq28 region on the X chromosome </li></ul><ul><li>*Markers are regions or sections of DNA that are the same among family members, suggesting the presence of a gene </li></ul><ul><li>Hamer, D. H., Hu, S., Magnuson, V. L., Hu, N., & Pattatucci, A. M. A. Linkage Between DNA Markers On The X Chromosome And Male Sexual Orientation. SCIENCE, 261: 321-327 (1993) </li></ul><ul><li>Hu, S., Pattatucci, A. M., Patterson, C., Li, L., Fulker, D. W., Cherny, S. S., Kruglyak, L., & Hamer, D. H. Linkage Between Sexual Orientation And Chromosome Xq28 In Males But Not In Females. NATURE GENETICS, 11: 248-256 (1995) </li></ul>
  20. 20. Genetics of Lesbianism <ul><li>The following findings are consistent with a genetic hypothesis: </li></ul><ul><li>Lesbians had significantly higher rates of lesbian sisters, daughters, and cousins through a paternal uncle than did heterosexual women </li></ul><ul><li>Pattatucci, A. M. L., & Hamer, D. H. Development And Familiality Of Sexual Orientation In Females. BEHAVIOR GENETICS, 25: 407-420 (1995) </li></ul><ul><li>Increasing rates of concordance of lesbianism from nonidentical twins to identical twin pairs </li></ul><ul><li>Bailey, J. M., & Benishay, D. S. Familial aggregation of female sexual orientation. AMERICAN JOURNAL OF PSYCHIATRY, 150: 272-277 (1993) </li></ul><ul><li>Bailey, J. M., Dunne. M. P., & Martin, N. G. Genetic And Environmental Influences On Sexual Orientation And Its Correlates In An Australian Twin Sample. JOURNAL OF PERSONALITY AND SOCIAL PSYCHOLOGY, 78: 524-536 (2000) </li></ul><ul><li>But lesbianism is not associated with the locus at Xq28 </li></ul><ul><li>Hu, S., Pattatucci, A. M., Patterson, C., Li, L., Fulker, D. W., Cherny, S. S., Kruglyak, L., & Hamer, D. H. Linkage Between Sexual Orientation And Chromosome Xq28 In Males But Not In Females. NATURE GENETICS, 11: 248-256 (1995) </li></ul>
  21. 21. Homosexuality – How to Explain in Darwinian Terms? <ul><li>Samoa </li></ul><ul><ul><li>South Pacific island nation </li></ul></ul><ul><ul><li>Relatively unwesternized </li></ul></ul><ul><ul><li>Traditional, tribally-based cultures </li></ul></ul><ul><ul><li>More like the setting in which humans mainly evolved </li></ul></ul><ul><ul><li>Tighter-knit families </li></ul></ul><ul><li>Fewer anti-gay biases that alienate gays </li></ul><ul><ul><li>Culture characterized by a high degree of social tolerance towards fa'afine s </li></ul></ul><ul><li>Fa'afafine s </li></ul><ul><ul><li>Men who have sex with men </li></ul></ul><ul><ul><li>Broadly accepted social class in Samoa </li></ul></ul><ul><li>Verde Prado, Jerry. (My dying mother’s CNA) Personal interview. (2006) </li></ul>
  22. 22. Kin Selection Hypothesis’ Basic Prediction <ul><li>Androphilic (“gay”) males should direct more altruistic behavior toward kin than gynephilic (“straight”) males </li></ul><ul><li>Vasey, P, Pocock, D . VanderLaan, D. Kin Selection And Male Androphilia In Samoan Fa'afafine. EVOLUTION AND HUMAN BEHAVIOR, 28: 159–167 (2007) </li></ul>
  23. 23. Fa’afafines Put “Significantly” More Effort Into Raising Nephews and Nieces <ul><li>Childcare activities </li></ul><ul><li>Babysitting </li></ul><ul><li>Buying toys </li></ul><ul><li>Tutoring </li></ul><ul><li>Exposing the children to art and music </li></ul><ul><li>Contributing to daycare, medical and education expenses </li></ul><ul><li>Vasey, P, Pocock, D . VanderLaan, D. Kin Selection And Male Androphilia In Samoan Fa'afafine. EVOLUTION AND HUMAN BEHAVIOR, 28: 159–167 (2007) </li></ul>
  24. 24. Gay Men in Samoa Reproduce Through Kin Selection <ul><li>Gay men put extra efforts into helping raise nephews and nieces (as compared to straight men) </li></ul><ul><li>This boosts the children’s chances of survival, and someday reproduction </li></ul><ul><li>These youths, even if not gay, might share with their aunt or uncle a few genes promoting homosexuality—ensuring a clutch of “gay genes” in every generation </li></ul><ul><li>Vasey, P, Pocock, D . VanderLaan, D. Kin Selection And Male Androphilia In Samoan Fa'afafine. EVOLUTION AND HUMAN BEHAVIOR, 28: 159–167 (2007) </li></ul>
  25. 25. Is Transsexuality a Mentally Distressing Disorder? <ul><li>This Samoan study afforded the “opportunity to examine whether gender-atypical behavior, gender-atypical identity, and sex-atypical identity, in and of themselves, cause distress in sex/gender variant individuals </li></ul><ul><li>Simultaneously controlling for the confounding effects of extreme societal intolerance towards such individuals </li></ul>Vasey, P, Pocock, D . VanderLaan, D. Kin Selection And Male Androphilia In Samoan Fa'afafine. EVOLUTION AND HUMAN BEHAVIOR, 28: 159–167 (2007)
  26. 26. Transsexuality Not Distressing <ul><li>Current DSM-IV TR: Transsexual diagnosis of GIDC </li></ul><ul><li>Do adult fa'afafine “recall a strong and persistent cross-gender identification in childhood, a sense of inappropriateness in the male-typical gender role, a discomfort with their sex, or distress associated with any of the above?” </li></ul><ul><li>Vasey and Bartlett concluded that “the diagnostic category of GIDC should not occur in its current form in future editions of the DSM, as there is no compelling evidence that cross-gender behaviors or identities, in and of themselves, cause distress in the individual.” </li></ul>Vasey, P, Pocock, D . VanderLaan, D. Kin Selection And Male Androphilia In Samoan Fa'afafine. EVOLUTION AND HUMAN BEHAVIOR, 28: 159–167 (2007)
  27. 27. When Is a Variation a Disorder? <ul><li>Insert milton diamond’s letter re variations of sex development </li></ul><ul><li>Homosexuality was dropped from the American Psychiatric Association's handbook, the Diagnostic and Statistical Manual of Mental Disorders, in 1973 </li></ul><ul><li>Transsexualism, or “gender identity disorder,” is still listed, though the manual says it’s only a disorder if it causes the patient significant distress </li></ul>
  28. 28. Culture Determines How Sexual Differences Are Valued! <ul><li>Click on the URL below: </li></ul><ul><li>http://www. nytimes . com/slideshow/ 2008/12/07/ weekinreview / 1207-MUXE_ index.html > </li></ul>

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