[Truncated abstract] The assumption that facial attractiveness signals mate quality is central to current evolutionary theories of human sexual selection. Evidence for direct links between attractiveness and mate quality is, however, scarce, and the exact nature of mate quality remains the subject of debate. Mate quality may include genetic diversity, because genome-wide diversity has been linked to individual fitness, and diversity within the Major Histocompatibility Complex (MHC) has been associated with immunocompetence and health in many species. This thesis investigates whether individual genetic diversity plays a role in human sexual selection. The main aim is to examine whether MHC diversity, compared to genetic diversity in general, is especially important for mate preferences, health and mating success. The four studies herein are based on data collected from a large sample of heterosexual, Caucasian males and females. Participants were photographed, provided a DNA sample, and completed questionnaires regarding sexual history and health. Genetic diversity was calculated as both mean heterozygosity (H) and standardised mean-d2 (d2), separately for 12 MHC microsatellite loci and 11 nonMHC loci. The photographs were rated for various attractive features by opposite-sex raters. The first study investigated whether MHC diversity influences preferences for facial appearance in a potential mate, and if so, are they specific to the MHC and are they mediated by specific facial characteristics? I found that MHC-H, but not nonMHCH, positively predicted male facial attractiveness, and that this relationship was mediated by facial averageness. For females, nonMHC-d2 predicted facial symmetry, and potentially attractiveness. These findings indicate that faces contain visual cues to mate quality in both males and females, providing support for evolutionary theories that our preferences are adaptations for identifying mates of high quality. ... Measuring them both allowed me to tease apart their effects on mate preferences, and on health and mating success. Indeed, the MHC appears to be especially important in sexual selection as MHC diversity predicted female mate preferences after controlling for nonMHC diversity, and MHC dissimilarity predicted male mate preferences after controlling for nonMHC dissimilarity. Moreover, although MHC diversity did not appear to influence males’ preference for females, it did predict female mating success, suggesting that males also attend to MHC-related cues, although perhaps non-facial cues, when seeking mates. Additionally, nonMHC diversity predicted both male preferences for female faces and health, suggesting that such preferences are adaptive. Importantly, by providing direct links between facial attractiveness and biological markers of individual quality, genetic diversity, these results support the commonly held assumption that facial attractiveness signals mate quality.

[Truncated abstract] Early psychosocial stress is conjectured to place individuals on a developmental trajectory leading to earlier pubertal maturation, earlier initiation of sexual activity and earlier reproduction than those with less early psychosocial stress. This may have an adaptive function to minimise the chances of lineage extinction, which is more likely in environments of high risk and uncertainty. Previous studies have examined the relationship between early psychosocial stress and life history stages (e.g., age at puberty, age at first sex and age at first birth). However, these studies are limited in that they either examined only a few early psychosocial stressors, examined psychosocial stress relatively late in individuals' lives and/or were restricted to women. Thus, the first aim of the present thesis was to examine these findings in both genders using a measure of early psychosocial stress comprised of 24 categories of retrospectively assessed stressors (e.g., sexual abuse, physical abuse, parental divorce, rated quality of family life) during the first 7 years of life. It was hypothesised that individuals with high, as opposed to low, levels of early psychosocial stress would pass through life history stages earlier. The second aim was to examine how early psychosocial stress affects characteristics associated with life history traits, such as individuals? length, number and type of heterosexual relationships, number of sex partners, adult attachment styles, number of pregnancy terminations, and attitudes and behaviours towards contraceptive use. High levels of early psychosocial stress were predicted to be associated with characteristics reflecting a quantitative, as opposed to a qualitative, reproductive approach (e.g., more sex partners, more short-term relationships, insecure attachment styles). The third aim was to examine how early psychosocial stress is related to mate choice because numerous studies have identified what traits individuals' desire in a mate but not whether early psychosocial stress affects these choices. ... Early psychosocial stress generally had no effects on age at first sex, age at first birth, the number of pregnancy terminations, and mate choices. On the other hand, individuals with high, as opposed to low, levels of early psychosocial stress were more likely to be insecurely attached, had more short-term sexual relationships (men only), had more extra-pair copulations, were more likely to be divorced/separated, had a greater lifetime number of sex partners (men only), and had lower self-rated frequencies of contraception use. Overall, some of these findings are consistent with life history theory, which suggests that individuals with high levels of early psychosocial stress (i.e., those living in environments of high risk and uncertainty) should reach biological maturation earlier, engage in behaviours that facilitate earlier and more frequent reproduction to minimise the chances of lineage extinction. Implications for public health, limitations of the present study and future directions are also discussed.

The purpose of this research study was to conduct an exploration of the dating preferences of African American women and U.S. men between the ages of 30-74 years old. This research focuses on the dating preferences and desirability of African American women and if they are influential on the high unmarried rates of African American women. A weighted stratified sampling of 2,800 personal advertisements of African American, Asian, Latino and White men and women from Match.com were collected to conduct the research. The five research hypotheses of this study were tested using frequency and percentage distribution, logistic regression and cross-tabulation models. The findings partially support the hypotheses African American women are more likely to prefer a mate with a bachelor's degree or higher and African American women are more likely to prefer a mate of the same race compared to U.S. women of other races. The findings also suggested non-African American men are less likely to have an interest in dating African American women and non-African American men, who are interested in dating African American women, are less likely to prefer women with a bachelor's degree or higher or a more socially desirable body type.