The Psychology of Sexual Orientation

1. The Psychology of Sexual Orientation Bill Altermatt

2. Why is this important? • Homosexuality is so stigmatized in our culture that homosexuals are often singled out for harassment, intimidation, and even murder. • Hate groups blame homosexuals for “choosing” their orientation. • If orientation is not a choice, individuals are not responsible for it. Matthew Shepard, brutally killed in Laramie, Wyoming, in 1998 Picketing outside Matthew’s funeral

3. 0Exclusively Heterosexual 1 2 3Bisexual 4 5 Kinsey Scale Members of the other gender Members of both genders equally Members of the same gender 6Exclusively Homosexual What is sexual orientation? • Enduring emotional, romantic, sexual, or affectional attraction toward...

4. How common is homosexuality? • Rates of homosexuality across many studies, involving thousands of respondents from many countries: • 3-4% of men • 1-2% of women

5. What causes sexual orientation? • Personal choice? • Environmental influences (e.g., childrearing practices, sexual abuse, etc.)? • Genetic or biological influence?

6. Personal choice? No. • Why would it be chosen? • High costs of homosexuality in our culture • When would it be chosen? • Orientation emerges prior to sexual experience, so how would you know what you were choosing? • Changeable through willpower? No. • Research indicates you can control behavior but not orientation (desire)

7. Environment? No evidence. • Kinsey Institute survey (Bell et al., 1981; Hammersmith, 1982) • Compared 1,000 homosexuals and 500 heterosexuals on every imagined possible cause of homosexuality • Parental relationships, childhood sexual experiences, peer relationships, dating experiences • No differences found between heterosexuals and homosexuals.

8. Biological? Probably. • Critics of homosexuality regard it as “unnatural,” “against biology,” and the product of human culture. • But Bruce Bagermihl (1999) reports that sexual behavior has been documented by biologists in over 450 species

9. Bagermihl (1999) • 6-10% of rams are not interested in ewes and seek to mount other males (Perkins & Fitzgerald, 1997)

10. Bagermihl (1999) • Every homosexual behavior performed by humans has been documented in non-human animals

11. Bagermihl (1999) • In many species, same-sex attraction leads to long-term bonds between partners, who sometimes raise offspring together. A homosexual pair of male Flamingos raising their foster chick.

12. Unnatural? • If the definition of “natural” is “occurring in nature,” then homosexuality appears to be very natural. • Given the widespread prevalence of homosexuality among non-humans, it is unlikely that homosexuality is the product of human culture and more likely that there is a biological cause of homosexuality.

13. Evidence that sexual orientation is biological • Family studies: • 9% of brothers of gay men are gay (compared to 3-4% on average) • 6% of sisters of lesbian women are lesbian (compared to 1-2% on average) • Adopted twin studies: rule out same-house effects • Bailey et al. (2000) studied 1,538 twin pairs and estimated h2 = .51 for males, .23 for females • 51% of the similarity in homosexuality between two males can be explained by the genes they share.

14. Evidence that sexual orientation is biological • Fraternal birth order effect • Each older brother increases the probability of male homosexuality by approximately 1% • Likely cause: maternal immune response to male fetuses, which increases with each pregnancy • Probably explains 15% of male homosexuality • No birth order effect for lesbians

15. Major theories for biological origins of sexual orientation • Neurohormonal hypothesis: sexual orientation is determined by hormones acting on the brain during prenatal development • Neuroanatomical hypothesis: sexual orientation is determined by structural differences in the brains of homosexuals and heterosexuals

16. Neurohormonal hypothesis • Hypothesis: • prenatal androgen activity in the brain  attraction to females • absence of such activity  attraction to males • Evidence: • Female infants with CAH (high prenatal androgen exposure) • 48% reported arousal imagery for females (compared to 7% in control condition) • 22% reported sexual contact with females (compared to 4%)

17. More neurohormonal evidence • Males with AIS (androgen insensitivity syndrome): brains do not respond to androgen • Externally female, no ovaries • 100% reported attraction to males • Male infants with cloacal exstrophy (ambiguous genitalia) reassigned female (with surgery & hormones). • By age 14, 100% reported sexual attraction to females (Reiner, 2002).

18. Neurohormonal conclusions • Sexual orientation is probably influenced by exposure to hormones before birth: • Exposure to androgens (and sensitive to androgens)  attracted to females • Normal males, reassigned males, CAH females • Not exposed to androgens (or insensitive to androgens)  attracted to males • Normal females, AIS males

19. Neuroanatomical hypothesis • One structure in the brain that corresponds to attraction to males or females is INAH-3

20. INAH-3 • Sex differences • Three studies found that INAH-3 is 2x larger in men than in women • Sexual orientation • Three studies found that INAH-3 is 2-3x larger in heterosexual men than in homosexual men • Similar differences observed in rams exhibiting same-sex preferences

21. INAH-3 Conclusions • Evidence suggests larger INAH-3 predicts attraction to females, smaller INAH-3 predicts attraction to males • Problems with INAH-3 research • Cause or effect unclear • Studies have not included lesbians

22. General conclusions • No evidence that sexual orientation is caused by personal choice or by a particular environmental factor. • Strong evidence that sexual orientation has a biological/genetic component. • Evidence for the effects of genes, prenatal hormones, and brain structure