1. Sexual Orientation

2. Sexual orientation  Preference for individuals of a specific sex  Not necessarily expressed behaviourally  Appears fluid rather than taxonomic Homosexual  Same-sex sexual orientation  Although the term has a “clinical” significance to it, it remains useful for scientific areas of study Key Concepts

3. Related Information Gender atypicality is common in adolescent and adult homosexual individuals 2D:4D Differences in sexual preferences and jealousy in “butch” vs. “femme” lesbians Increased incidence of non-right handedness in homosexual individuals

4. Psychoanalytic Perspectives According to Freud, all people are bisexual Possible causes of homosexual orientation  Overly-powerful or ‘misdirected’ libido  Neurosis or perversion  Unresolved Oedipal complex “Adaptational” perspective argues that homosexual individuals are afraid of the opposite sex, and so adapt by creating relationships with same sex individuals

5. Hormonal/Neurological Influences Disruptions in rat hormonal processes affect differentiation of the hypothalamus  Lordosis & mounting Human homosexual men demonstrate estrogen-feedback similar to that of women Differences in INAH 3, anterior commissure, and suprachiasmatic nucleus in homosexual men vs. controls

6. Genetic Influences (1) Twin & family studies have demonstrated some genetic relationship  Heritabilities range from.31-.74 in men &.27-.76 in women The chromosomal region Xq28 has been linked to homosexual orientation in men, though it is hotly debated

7. Genetic Influences (2) How could genes so obviously detrimental to fitness remain in the population?  Balanced superior heterzygote fitness (e.g., sickle cell anemia)  Kin selection (e.g., “sterile” castes)  Parent-offspring conflict over sibling fitness  Sex-linked benefits in females

8. Fraternal Birth Order Effect Gualtieri & Hicks (1985) argued that fraternal birth order triggers an immunological response in the mother Cantor et al. (2002) argue that each additional older brother increases the odds of homosexual orientation by 33%  Moreover, they argue that fraternal birth order affects the sexual orientation of approximately 1 in 7 gay men

9. Sexual Strategies An interesting outcome of homosexual behaviour in groups is the removal of “strategic interference”  Homosexual men have, on average, a staggeringly large number of sexual partners, many of them strangers  Comparatively, homosexual women have very few sexual partners, and it is rare for any of them to be strangers

10. We have just reviewed some of the scientific evidence for a biological basis of sexual orientation, but what does it tell us about ourselves? What is the appropriate use of this information? Can a distinction between “learned” and “innate” orientation be used to defend or attack homosexuality? Homonegativity & Science

11. The Wrap-Up Defining sexual orientation Gender atypicality, 2D:4D, handedness Psychoanalytic perspectives Hormonal & neurological influences Genetic influences Selectionist theories Sexual strategies Homonegativity & impact of science

12. Things to Come ???