The present thesis investigated how genetically identical twins with discordant sexual orientations differed in correlates of their sexual orientation in order to understand to what degree non-genetic factors affect the formation of sexual orientation. Because identical twins share 100% of their genes, factors other than genetics may contribute to any differences within these pairs. Chapter 1 gives an overview of the literature. Chapter 2 focuses on childhood gender nonconformity (femininity in males, masculinity in females), which predicts a non-straight (gay, lesbian, or bisexual) sexual orientation in adulthood. In order to avoid the limitations of self-report measures, gender nonconformity of these twins was assessed via observer ratings of their photographs from childhood and adulthood. In addition, although genetically identical twins can differ in their self-reported sexual orientations, it is unclear to what degree these self-assessments reflect observable differences in sexual arousal such as genital response or pupil dilation patterns while viewing sexual stimuli. Chapter 3 focuses on these responses in identical twin pairs with discordant sexual orientations. Finally, differing intrauterine environments during the early development could result in a discordant development of sexual orientation in identical twins. This includes varied prenatal hormonal exposures between twins. Chapter 4 highlights a putative biomarker of early hormonal exposure: the ratio of index to ring finger length (2D:4D), within these twin pairs In combination, findings suggested that these twins differed in many (but not in all) correlates of their sexual orientation, suggesting non-genetic influences. However, there were also subtle similarities within pairs that pointed to potential familial (e.g., genetic) influences.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:721384 |
| Date | January 2017 |
| Creators | Watts, Tuesday M. |
| Publisher | University of Essex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://repository.essex.ac.uk/20189/ |
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