Sexual Orientation-is it Nature or Nurture?

1. Sexual Orientation-is it Nature or Nurture? Ela Lutwak

2. Homosexuality in animals Great apes Penguins Sheeps 98% bisexual (Zuk, 2002)

3. Homosexuality in humans • 2% of the general population in the United States are gay, lesbian or bisexual. • 1.7% of the general population of Canada identified as gay, lesbian or bisexual. • Determining an actual number is complicated by problems defining these terms and by the fact that some people are reluctant to admit their sexual feelings to those doing surveys.

4. From antiquity Historical Perspectives • Concept of inborn homosexual orientation dates from 1860s • Psychiatric illness needing a cure • Sigmund Freud's basic theory of human sexuality

5. Current Theories Many existing and differing theories, most of which can be categorized into one of two generalized categories: Non-biological theories ( environment) Biological theories • Genes • Hormones • Anatomy • Brain studies—anatomy • Cognitive studies • Birth order • Psychoanalytic • Behaviorism/socialization

6. Non-biological theories (environment) Psychoanalytic theories • close-binding mother • absent or distant father • unconscious hatred of their mothers • envy of a brother’s penis Homosexuality resulted from pathological family relationships during the oedipal period (around 4-5 years of age( (Bieber et al., 1962). homosexuals who were seeking treatment or therapy. "double blind" procedures have not been used in clinical psychoanalytic studies of homosexuality.

7. Behaviorism/socialization • parents, teachers, peers, and society Effect of sexual experiences • There are significant cultural and historical differences in the manifestation of sexual behavior • Psychoanalytic studies suffer from small and unrepresentative samples

8. Gay genes and evolution • kin-selection • balanced polymorphism • reciprocal altruism - same sex alliances • The analogy is to the sickle-cell gene (Miller, 2000) The evolutionary value of gay genes may become clearer if and when such genes are identified and their mechanism of action determined.

9. Genes In the fly Drosophila melanogaster the gene called fruitless, nicknamed fru, influences sexual development and behavior. Males with fru gene mutations behave as bisexual ­ they cannot tell other males from female flies when courting.. Manoli et al., 2005; Stockinger et al., 2005 • In insects, sex differentiation is largely cell-autonomous • In humans sexual differentiation is not cell-autonomous but depends in large part on circulating sex hormones.

10. Twins and sibling Studies brothers of gay men 22% brothers of heterosexual men 4% Pillard & Weinrich, 1986 J.M. Bailey and R.C.. Pillard 1991

11. Are Genes involved in Sexual Orientation?

12. Family studies (pedigree): More male homosexuality on maternal side X

13. These were “genes” or “DNA sequences” of unknown function (the only thing known was where on the X-chromosome they were located). • The concordance patterns of each gene was examined and compared to the degree of relationship to the self-identified gay male. • Conclusion: higher concordance with close relatives. An “association” of some gene or genes on the tip of the X-chromosome with something the group of gay males shared in common. Schematic X-chromosome

14. Genetic Evidence- Linkage studies • Xq28region (Hamer et al., Science 1993 (

15. Genetics and Male Sexual Orientation 82% 67% 46% 64% 66% D. H. Hamer; et al., Science 285, 803a (1999)

16. New Study Proves that “Gay Gene” Theory Is Totally Dead By MassNews StaffPosted 2-1-2005 Brian S. Mustanski March 2005 Human Genetics • The presumption was that at least one “doctor” or gay gene would be found.  • They found several identical stretches of DNA that were shared among gay siblings on chromosomes other than the female X. • About 60% of these brothers shared identical DNA on three chromosomes - chromosome 7, 8 and 10. • Multiple genes - and not just the sex chromosomes - are important in sexual orientation

17. Hormone & Prenatal Evidence • Adult hormone levels –no significant differences • Prenatal hormone level organize the brain in a male/female-specific fashion • Maternal stress -The reason is that the stress activates the fetuses’ stress hormones which in turn lead to a diminution in the levels of testosterone during a critical period of brain development.

18. Birth Order-How many gay men owe their sexual orientation to fraternal birth order? • Latter born sons more likely to be gay • Mothers develop immunity to H-Y Antigen • The transfer of anti-male antibodies across the placenta from the maternal into the fetal compartment • The transfer of maternal cytokines across the placenta • Maternal immune reactions affecting the placenta itself. (Blanchard and Klassen 1997, Blanchard 2001, Cantor 2002).

19. Prenatal hormones Brain function Auditory system Sexual arousal Neurotransmitter function Odor responses Cognitive and personality traits Visuospatial tasks Object location memory Verbal fluency Aggressiveness Handedness Body anatomy penis size finger length ratios fingerprints Brain anatomy Suprachiasmatic nucleus INAH1

20. Finger-length ratios Penis size Fingerprints Our erotic personalities are as unique as our fingerprints? Williams, T. J. et al (2000) Nature

21. Human Brain Anatomy and Sexual Orientation INAH1-4 regions (interstitial nuclei of the anterior hypothalamus) • examined homosexual men, heterosexual men and women • area INAH3 differentiated groups (Simon LeVay, 1991)

22. LeVay found structural differences in the size of the hypothalamus of gay and straight men (1991). • LeVay used HIV patients in study. HIV impacts brain negatively. • Byne, et al (2001) failed to replicate LeVay’s findings and said “sexual orientation cannot be reliably predicted on the basis of INAH3 volume alone.”

23. Does IHAH-3 have more cells in the brains of straight males?

24. Critique of Brain Studies Selection of samples: • All from autopsies • Retrospective assignment of sexual orientation • Confounding variable of HIV infections Analysis • Microscopic measurements • Very tiny differences • Wide statistical variations Comparisons: gay males = females Lack of replication by other scientists

25. LeVay said about his research: • "It's important to stress what I didn't find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn't show that gay men are born that way, the most common mistake people make in interpreting my work. Nor did I locate a gay center in the brain. ...Since I look at adult brains, we don't know if the differences I found were there at birth or if they appeared later.“ Nimmons, D. (1994). Sexual brain. Discover, 5, 3.

26. a close-binding mother facial beauty Non-biological theories vs biological theories hormonal changes

27. Some scientists believe sexual attractions are primarily determined by genetics and/or prenatal factors • Others believe that people mainly develop their sexual attractions throughout their life via a combination of life experiences and personal traits. • No gay gene has been discovered • Environmental circumstances have not been identified that always lead to same sex attractions for all people.

28. ? ? ? ? Evidence exists to support both points of view, but there is not enough evidence to be conclusive about either viewpoint. ? ? ? ? ? ?

29. Thank you for listening

30. References • Bailey, J. M., M. P. Dunne, and N. G. Martin. 2000. Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. J. Personality SocialPsychology 78:524-536. • Blanchard, R. 2001. Fraternal birth order and the maternal immune hypothesis of male homosexuality. Hormones and Behavior 40: 105-114. • Blanchard, R. and P. Klassen. 1997. H-Y antigen and homosexuality in men. J. Theor. Biol.185: 373-378. • Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brother and homosexuality in men. Journal of Theoretical Biology, 230:173-187. • Byne, W., M. S. Lasco, E. Kemether, A. Shinwari, M. A. Edgar, S. Morgello, L. B. Jones, and S. Tobet. 2000. The interstitial nuclei of the human anterior hypothalamus: An investigation of sexual variation in volume and cell size, number and density. Brain Research 856: 254-258. • Cantor, J. M., R. Blanchard, A. D. Paterson, and A. F. Bogaert. 2002. How many gay men owe their sexual orientation to fraternal birth order? Arch. Sexual Behav. 31: 63-71. • Hall, J. A. Y., & Kimura, D. (1995). Sexual orientation and performance on sexually dimorphic motor tasks. Archives of Sexual Behavior,24, 395-407. • Keener, C. S. and D. E. Swartzendruber. 2001. Does homosexuality have a biological basis? pp. 17-48. In Ruth Conrad Liechty (ed.), Biological and psychological perspectives. Booklet #5 in the "Welcome to Dialogue Series," Goshen, IN. • LeVay, S. 1991. A difference in hypothalamic structure between heterosexual and homosexual men. Science253: 1034-1037.

31. LeVay, S. 2003b. The biology of sexual orientation. Available from LeVay's web site: http://members.aol.com/slevay • Morris, J. A., K. L. Gobrogge, C. L. Jordan, and M. Breedlove. 2004. Brain aromatase: Dyed-in-the-wool homosexuality. Endocrinology 145: 475-477. • Mustanski, B. S., Dupree, M. G., Nievergelt, C. M., Bocklandt, S., Schork, N. J., & Hamer, D. H. (2005). A genomewide scan of male sexual orientation. Human Genetics. • Pillard, R. C. and J. M. Bailey. 1998. Human sexual orientation has a heritable component. Human Biology70: 347-365. • Roselli, C. E., K. Larkin, J. A. Resko, J. N. Stellflug, and F. Stormshak. 2004. The volume of a sexually dimorphic nucleus in the ovine medial preoptic area/anterior hypothalamus varies with sexual partner preference. Endocrinology 145: 478-483. • Roselli, C. E., J. A. Resko, and F. Stormshak. 2002. Hormonal influences on sexual partner preference in rams. Arch. Sexual Behav. 31: 43-49. • Swaab, D., W. C. J. Chung, F. P. M. Kruijver, M. A. Hoffman, and T. A. Ishunina. 2001. Structural and functional sex differences in the human hypothalamus. Hormones andBehavior 40: 93-98. \ • Williams, T. J., Pepitone, M. E., Christensen, S. E., Cooke, B. M., Huberman, A. D., Breedlove, N. J., Breedlove, T. J., Jordan, C. L., & Breedlove, S. M. (2000). Finger-length ratios and sexual orientation. Nature,404, 455-456.