Judgments of others' emotional states and inclinations had recurrent fitness consequences for ancestral humans. Such judgments, made under uncertainty, can result in false positives (overestimating an emotional state or trait) or false negatives (underestimating the same). When the costs of these two errors consistently and historically differed, natural selection will have favored a bias toward making the less costly error. The perception of anger entails such asymmetry. Averaged across situations over evolutionary time, underestimation of anger was the more costly error, as the fitness decrements resulting from physical harm or death due to insufficient vigilance were greater than those resulting from lost social opportunities due to excessive caution. I therefore hypothesized that selection has favored an overestimation bias in the evaluations of others' state anger and general anger-proneness (trait anger) relative to evaluations of other traits to which this error asymmetry does not apply. Moreover, I hypothesized that additional attributes which make the actor more dangerous or make the observer more vulnerable increase the error asymmetry with regard to inferring state anger and trait anger, and should therefore correspondingly increase this overestimation bias. In the study described in Chapter 2 (N = 292), models photographed with a neutral expression and holding a potentially dangerous household object were judged to be angrier than those holding a harmless object, even though the held object provided no normative information about their emotional state. In Chapter 3, Study 1 (N = 161), a fictitious individual depicted in a vignette was judged to have higher trait anger than trait disgust even after controlling for the raters' perception of how emotionally he behaved. Moreover, trait anger ratings were more responsive than trait disgust ratings to behavioral cues of emotionality. In Chapter 3, Study 2 (N = 335), participants viewed images of angry or fearful faces. The interaction of factors indicating target's formidability (male sex), target's intent to harm (direct gaze), and perceiver's vulnerability (being female or high belief in a dangerous world) increased ratings of the target's trait anger but not trait fear. In aggregate, these results suggest a domain-specific bias in evaluating anger.

The high-fertility period of the ovulatory cycle is the only time when sex can result in conception. In nonhuman mammals, this period is often marked by dramatic changes in females' social interactions, especially with males. For example, two widespread patterns are that females exhibit increased sexual interest in certain males at high fertility relative to low fertility, and males exhibit increased sexual interest in females currently exhibiting cues of high fertility. Scientific interest in whether the ovulatory cycle has similar impacts on human social behavior has surged in the past two decades, producing a large body of published evidence that is largely supportive of this possibility. Two prominent findings in this literature are that women's sexual attraction to men possessing characteristics historically associated with high genetic quality increases at high relative to low fertility and that women's attractiveness to men also increases at this time. However, studies have varied widely in the methods they have used to examine these effects, findings have been somewhat mixed, and additional nonreplications could remain unpublished. In addition, several important questions have yet to be answered. For example, can women detect cues of high fertility in other women, and do they perceive these cues as attractive?

To address these questions, I conducted two meta-analyses and a laboratory study. The meta-analyses quantitatively evaluated and synthesized evidence across published and unpublished findings for a) changes in women's mate preferences and b) changes in women's attractiveness and other possible fertility cues across the ovulatory cycle. Both analyses revealed robust support in the extant empirical literature for the hypothesized cycle shifts. The laboratory study examined women's perceptions of other women's high- and low-fertility body scents and found that, like men, women perceive other women's high-fertility body scents as more attractive than their low-fertility scents. Taken together, these studies have potentially important implications for understanding the role of the ovulatory cycle--and psychological adaptations that evolved or have been maintained in the context of cyclic variation in human female fertility--in human social cognition, motivation, and behavior.

Democracy is new, but politics is older than the human species. In three empirical studies (Chapters 1, 2, and 4) and one theoretical paper (Chapter 3), I integrate research in evolutionary biology with research on political attitudes. The first half of the dissertation applies insights from the evolutionary biology of alternative mating strategies to research on attitudes toward gay rights and abortion policy. I argue that liberal and conservative positions on these issues stem from conflicting mating strategies interacting with specific representations about how these policies, along the groups associated with them, relate to sexual promiscuity. In Chapter 1, I test whether stereotypes of gay men as promiscuous interact with mating strategies (i.e. short-term mating orientation) to predict attitudes toward gay rights. In Chapter 2, I test whether beliefs about the effects of abortion policy on sexual promiscuity—which I refer to as “deterrence beliefs”—interact with mating strategies to predict opposition to abortion. Both hypotheses received empirical support and shed light on the psychological underpinnings of policy preferences. In Chapter 3, I apply insights from the evolutionary biology of alliances and coalitions to examine political ideologies more broadly. I argue that humans, like other social primates, possess a suite of cognitive adaptations for developing alliances with other individuals and groups based on cues of similarity (e.g. common traits), transitivity (e.g. common enemies), and instrumentality (e.g. common goals). Unlike other primates, humans form complex alliances with overlapping social groups, and apply a suite of cognitive biases designed to defend their allies in conflicts. When partisans apply biases to the demographic groups associated with their political party, they generate biased narratives that form the contents of ideologies (see Chapter 3). In Chapter 4, I test a variety of the predictions entailed by this approach—referred to as the Alliance Theory—using data from the American National Election Study (ANES). I test whether or not the Alliance Theory has better predictive power than alternative approaches—i.e. those at emphasize individual differences in egalitarianism—across a range of different policy disputes. Across all policies examined, the results supported the Alliance Theory and pose a challenge to alternative theories. Taken together, the four chapters yield insights into the origins of political disagreement, and they highlight the utility of taking an evolutionary approach to political psychology.

Most women in the United States use hormonal contraceptives at some point in their lives, yet little is known about their psychological side-effects. A number of scholars have recently argued that hormonal contraceptives might impair women's ability to choose desirable mates and cause problems in their relationship functioning. My dissertation evaluated these claims through a comprehensive review of the literature and two empirical studies. In my review of more than 30 studies examining associations between hormonal contraceptive use and variables related to mate choice and relationship functioning, I found modest support for hypotheses about the effects of hormonal contraceptive use. The most robust finding was that, unsurprisingly, hormonal contraceptive users did not experience cycle shifts in mate preferences and attractiveness that had been identified in previous research (e.g. Gildersleeve, Haselton, & Fales, 2014). I note a general weakness in the literature - none of the studies comparing hormonal contraceptive users to non-users employed experimental methods, precluding causal conclusions about the effects of hormonal contraceptives. I also report two empirical studies. In the first, I tested one particular hypothesis regarding negative effects of hormonal contraceptive use. Partners who are similar to one another in their Major Histocompatibility Complex (MHC) genes are thought to be relatively less genetically compatible than partners who are dissimilar in their MHC genes. Researchers have hypothesized that hormonal contraceptives disrupt MHC preferences. I examined whether hormonal contraceptive users are indeed more MHC-similar to their partners than non-users. Both members of 274 couples were genotyped at the MHC region; the female partner reported her hormonal contraceptive use at the time the relationship began. Contrary to predictions, I found that women who used hormonal contraceptives when they met their partner were more MHC dissimilar to their partners than non-users, although this difference was not statistically significant. Additional analyses involving many potential confounds that might be masking a true relationship did not produce the predicted effect. The results of this study are inconsistent with the hypothesis that hormonal contraceptives will cause women to choose MHC similar, and thus genetically incompatible, romantic partners. In the second study, I addressed the hypothesis that cycle shifts previously documented among naturally cycling women (reviewed in Larson, Pillsworth, & Haselton, 2012) would be absent among hormonal contraceptive users. To test this hypothesis, I recruited a sample of 56 women to complete nightly surveys assessing their current attractions toward their romantic partner and toward men other than their partner (for a total of 1,366 observations). Consistent with the hypothesis, I found that cycle shifts in attraction to other men observed among non-users were absent among hormonal contraceptive users. The results of this study therefore demonstrated a potential relationship-protective effect of hormonal contraceptive use. Overall, the results of my dissertation indicate that although hormonal contraceptive users and non-users do differ in some important ways, the differences are not as large, global, or negative as previous researchers have implied.

Genetic factors are likely involved in many aspects of human social behavior, yet influences of molecular genetic markers on aspects of human intimate relationships have only recently been documented. The present dissertation begins with a review of these recent advances which have collectively given rise to the transdisciplinary sub-field of relationship genetics (Chapter Two). Particular attention is given to candidate gene studies of intimate relationship characteristics and to the elusive but tantalizing notion of "genetic compatibility" between intimate relationship partners. The review is followed by two original studies. The first of these (Chapter Three) investigates the effects of matching at major histocompatibility complex (MHC) gene markers between existing long-term relationship partners on self-reported levels of in-pair attraction. The results provide qualified support for the hypothesis that higher levels of matching between relationship partners at MHC markers leads to reduced levels of attraction between those partners. However, this effect appears to be strong and reliable only for individuals of Asian ancestry, whereas the evidence for such an effect in individuals of non-Asian ancestry is far more equivocal. The second study (Chapter Four) applies a genetic technique known as haplotype analysis to investigate associations between variation in the oxytocin receptor gene (OXTR) and self-report measures of individual differences and relationship parameters collected from partners in long-term intimate relationships. Few effects were found for measures of relationship quality, but a number of interesting and consistent associations were uncovered between OXTR haplotypes and measures of extra-pair interest and desire. Taken as a whole, the present work documents the emergence of an exciting new subfield and presents two novel contributions to this nascent literature. Relationship genetics offers the prospect of marrying cutting edge molecular genetic techniques to the investigation of questions that have been at the center of human life and thought since time immemorial.

Social status, one’s relative rank in a social hierarchy, is a ubiquitous part of human social life. A large focus of the literature has been on subjective social status (SSS), more specifically, which is one’s psychological perception of his position within the social hierarchy. It is also one factor that accounts for variation in health. While there is abundant evidence for an association between SSS and health, there are several important gaps in this literature. First, the antecedents of SSS remain largely unknown. What developmental and contextual factors (Chapter II) and observable cues (Chapter III) predict whether an individual will experience high or low SSS? Second, there is limited research regarding how social hierarchies unfold over time in a population of young adults. How does SSS in young adults change in a new social group and affect physical and mental health (Chapter IV)? Beyond needing to clarify the antecedents and stability of SSS, the molecular mechanisms explaining the relationship between SSS and health remain unclear (Chapter V). Chapters II, III, and IV tested aims in a sample of 94 undergraduate college freshmen living in residence halls. Results of Chapter II indicated that how individuals appraised potentially negative social situations predicted SSS, whereas early life stress did not. Chapter III results suggested that other-rated attractiveness, and dominance to a lesser extent, positively predicted SSS rated by an individual and by outside observers. Together, Chapters II and III highlight contextual and observable cues that predict SSS. The findings of Chapter IV identified that SSS was stable or increased for the majority of freshmen throughout the academic year, but SSS did not reliably predict physical or mental self-rated health; this is perhaps due to the nature of the social group targeted. Chapter V, a study conducted in a population of 47 young, healthy women, revealed that lower SSS individuals have heightened pro-inflammatory gene expression. Thus, those lower in SSS likely perceive diminishing social resources and a threatening social world, which manifests as heightened inflammatory processes, and has potential downstream consequences for inflammatory-related illness.