Homosexual behavior has been reported in a diverse range of human societies. In
contemporary North America, for instance, an estimated 2 – 10% of all individuals are
exclusively homosexual, and behavioral genetics studies demonstrate a substantial degree of heritability in homosexual behavior. Despite this finding, however, extensive efforts to identify genes that might contribute to sexual orientation have largely failed. Drawing on material presented in lecture, provide a plausible explanation for the failure of these efforts given the fact that sexual orientation is substantially heritable
- So many different loci that there isn’t just one gene for homosexuality but a lot of different ones.
- Most people have the potential to be either one, but are affected by the activation of the different loci in their genes and also affected by their environment.
- There are many loci responsible for this trait. The individual affect of any one gene is so small that you can’t find just one. Which also explains why many individuals that identify as heterosexual are capable of being attracted to the same sex
- Heritability is just being calculated in terms of probability
Define sexually antagonistic selection.
• genetic factors spread in the population by giving a reproductive advantage to one sex while disadvantaging the other
Describe the evidence presented in lecture indicating that sexually antagonistic selection contributes to the maintenance of homosexuality in at least one population.
- ii) In class we were presented with evidence from Samoa, of the Fa’afafine. These men are raised as women, perform all of the women’s duties, and are attracted to other males. In these populations, the first sisters of the Fa’afafine, produce twice as many offspring as sisters of heterosexual men from the village. This can be called a good uncle theory, where the homosexual male, uses some of his resources to help raise the children of his sister. iii) However, this can only account for some homosexuallity, as many gay males do not display these normally considered traits.
- Feminity is the trait that is disadvantaged/advantaged. It’s good for women, but not for men (who dress as women)
The evidence that you described in (ii) is such that, even if the sexually antagonistic selection hypothesis is correct, it can only account for some homosexuality; explain why this is so.
• Only addresses male homosexuality, not female homosexuality; also only males with siblings/sisters
Drawing on cross-species comparisons, describe two possible functions of human same-sex sexual behavior that could have been fitness-enhancing in ancestral human societies.
- Show dominance: homosexuality can be a display of dominance. It would be fitness enhancing the same way winning a competition might be – it is intrasexual. The dominant homosexual encounter may deter transgressors and give him access to and ultimately mate with a female to perpetuate his genes. Therefore, it may have been fitness enhancing in ancestral societies for a dominate male to show it through same-sex sexual behavior.
- Create alliances: females who display homosexual behavior may create bonds with other females and establish friendship which would increase fitness because she would have the help of other women and access to them as resources. Therefore, it may have been fitness-enhancing in other societies to engage in homosexual behavior to gain favor with other females and utilize them as a resource, be it for childcare or harassment from men.
- Our evolved psychology has as a fitness maximizing trait, flexible sexuality—the ability to be aroused by both sexes for reproductive purposes and for affiliation.
- Good uncle hypothesis (?): you’d want your genes to continue, and you don’t have a chance, so you invest in the offspring of siblings.
- To assert dominance
In light of your answers to (a) and (c), provide an explanation for the existence of obligate homosexuals (men and women who are capable of feeling sexual arousal only toward members of the same sex) that does not involve sexually antagonistic selection.
• Multiple loci
