18 19 20 Sexual Orientation
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- used to scale heterosexual and homosexual tendencies in four areas
sexuality stability in men
- heterosexual more stable in self ID and behavior
- homosexual more stable in fantasy and attraction
genital arousal for men and women
- men more aroused by preferred sex
- women aroused my both male-male and female female stimuli
Men and women - sexual attraction discrete or continuous?
- men - bimodal. Consistent in extremes.
- women - steadily decrease from heterosexual to homosexual.
variations in discrete traits is due to...
- a single gene
- it is monogenic
variations in continuous traits are ...
heritability for sexual orientation
lower than 1
maternal immune hypothesis
a woman develops "anti male" antibodies when she is pregnant with a male. These antibodies may attack and alter subsequent sons' brain, may mimic prenatal androgen exposure, or may attack and deteriorate tissues that produce testosterone
brain structure - heter vs homo
heterosexual men have a 2-3times larger hypothalamus than women and homosexual men
Heterozygous advantage hypothesis
heterosexual males who have one "gay gene" allele have increased fitness over heterosexual men with no gay gene.
little support for this
kin selection hypothesis towards homosexual
homosexual men altruistically increase the fitness of their close genetic relatives.
- does not explain presence in present large scale societies.
- does not explain why would homosexuals still desire to mate? its costly and hurts their altruism
gay genes are maintained because they have different effects in different bodies
genes have different affects in different bodies
4 developmental processes leading to sex orientation variation
- prenatal androgen exposure - for women too much, for men not enough androgens
- fraternal birth order
- brain structure - larger hypothalamus hetersexual males than homo and women
- polygentic trait - threshold for the many alleles making individual homosexual.
pedigree evidence of genetic differences
brothers of homosexual men are more likely to be homosexual
heritability evidence of genetic differences
twin studies show more heritability
gene-sharing evidence for genetic differences
XQ28 gene in males increases likeliness of homosexuality
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