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Title: Evolutionary explanations of sexual orientation and its effect upon body odour signals involved in mate selection
Author: Sergeant, Mark J. T.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2007
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This thesis has evaluated the possible relevance of sexual orientation-related differences in male body odour hedonicity to Miller's (2000) theory of the functional origins of homosexuality. Expanding upon earlier ideas by McKnight (1997), Miller (2000) proposed that male homosexuality is maintained in human populations through a balanced polymorphism based on the simultaneous action of multiple genes (i.e., a polygenic trait). These genes are associated with variable sensitivity to the effects of prenatal hormone regimes, resulting in increased feminisation among males. Males possessing a low number of these "feminising genes" retain their heterosexual orientation but express increased feminine traits (i.e., lower levels of physical aggression and higher levels of empathy) which are advantageous during mate choice. When a male possesses a sufficient number of these genes, he crosses a liability threshold and expresses a homosexual orientation and female-typical partner preference (i.e., an attraction to males rather than females). The goal of this thesis was to establish if male body odour hedonicity was a trait associated with these "feminising genes", and whether such a trait could provide a benefit to males during female mate choice. Specifically this thesis examined whether females rate the body odour of homosexual males as more hedonically pleasing than the odours of heterosexual males, whether female perceptions of these odours vary over the menstrual cycle and whether a male's body odour hedonicity covaries with his levels of aggression and empathy. This thesis is composed of thirteen chapters. The first four chapters serve to review the extant literature relevant to the aims of this thesis: Chapter 1 reviews definitions of homosexuality and reports on its prevalence. Chapter 2 examines the ontogenetic origins of male homosexuality while Chapter 3 reviews its functional origins and finally Chapter 4 considers the relationship between male sexual orientation and olfactory function. There are two separate methodological chapters pertaining to the two distinct methodologies employed during this thesis. Chapter 5 reviews olfactory research methods relevant to the study of body odour while Chapter 9 examines online psychological research methods relevant to the online surveys conducted during this thesis. In addition to these literature review and methodological chapters, a total of six empirical studies were conducted during this thesis, with each study described in a separate chapter. Chapter 6 investigated whether heterosexual and homosexual males differ in the hedonicity of their body odour. Chapter 7 examined a range of potentially confounding variables which may be of relevance to the other empirical studies of body odour during this thesis. Chapter 8 investigated whether female perceptions of body odour vary across the menstrual cycle, and whether female perceptions vary in a similar manner for heterosexual and homosexual males. Chapter 10 examined the relative importance of male body odour hedonicity to females during mate choice. Chapter 11 replicated and expanded upon previous research into the differences in aggression and empathy levels between heterosexual and homosexual males. Chapter 12 examined whether a male's levels of aggression and empathy co-vary with hedonic ratings given to their body odour. Finally, Chapter 13 provided a general discussion and conclusion for this thesis. Findings from the empirical studies of this thesis suggest homosexual males emit more hedonically pleasing body odour than heterosexual males. However, this finding was inconsistent across studies, possibly due to olfactory desensitisation among female participants and the ethnicity of female samples. Consistent with previous research, homosexual males reported lower levels of physical aggression and higher levels of empathy than heterosexual males. A male's level of aggression and empathy also appear to co-vary with female hedonic ratings of the male's body odour, though these findings should be interpreted with caution for the moment. Overall, these finding are consistent with Miller's (2000) theory, and suggest that sexual-orientation related differences in male body odour hedonicity may be of relevance to the functional origins of male homosexuality.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available