Sexual jealousy arises in response to a perceived threat to a valued relationship with an individual, through perceptions or suspicions of a partner’s sexual infidelity. An evolutionary psychological perspective predicts that men are more sensitive to the sexual aspects of their partner’s infidelity than women, whereas women are more sensitive to the emotional aspects of their partner’s infidelity than men. This evolutionary perspective can be referred to as the sex-specific evolved jealousy mechanism (EJM). Many studies have verified the EJM. In this chapter, findings of studies on the EJM are discussed from two perspectives –the psychometric properties and participants’ and rivals’ characteristics – focusing on the findings from a meta-analysis in our laboratory (87 articles, k = 164, N = 125,698). Findings on the EJM are discussed from a psychometric perspective, focusing on (a) the rating methods of responses to a partner’s infidelity (i.e., forced-choice paradigm vs. continuous measures), (b) the validity of hypothetical infidelity scenarios used to have participants imagine a partner’s infidelity, (c) participants’ physiological responses to their partners’ infidelity, (d) participants’ response times to their partners’ infidelity, (e) participants’ recall performance for stimuli regarding infidelity, (f) participants’ responses to their partners’ infidelity under cognitive load, (g) heritability in behavior genetics, and (h) participants’ behaviors following their partners’ infidelity (e.g., morbid jealousy, violence, sexual coercion, and forgiveness). Findings on the EJM are discussed with respect to characteristics, focusing on (a) sexual orientation of participants, (b) participants who had nonmonogamous relationships, (c) children’s or siblings’ partners’ infidelity, and (d) participants’ digit ratio instead of sex. The EJM has been examined by many studies using various methods; however, conflicting findings have been reported. These differences seem to be caused by conflicting interpretations about the EJM and the rating methods of responses to infidelity.

Sex differences in obligatory parental investment and reproductive potential cause human females to desire high-quality men as partners. For men, this means that to achieve reproductive success, they must 1) combat other men to gain access to or retain mates, and to guard the resources women need for reproduction and child care, and/or 2) attract women by displaying (sexual) ornamentations or direct provision of resources. These pressures have shaped men’s physiology, as well as mating-related and other behaviors, and result in intense male–male intrasexual competition. In this chapter, I provide an overview of men’s intrasexual competitiveness, first detailing several important concepts, before focusing on the major domains of these competitions. The research reviewed shows that physical formidability and social status are central to human male–male competition – although qualitatively different, these dimensions are intertwined, such that formidable men are more likely to excel in physical combat and competition, and as a result attain higher social status and, ultimately, increased reproductive success. Men use an array of tactics to compete with same-sex rivals, ranging from direct aggression and physical contests (e.g., in sports or fights) to (verbal) competitor derogation, and the conspicuous flaunting of possessions, leisure activities, and helping behaviors. Finally, yet importantly, research on the context-dependent fluctuations in men’s testosterone levels sheds light on the underlying processes of male intrasexual competition. Specifically, increases in testosterone are observed both in preparation for and as a result of male–male competitions, and a sharp decline in testosterone after entering in a long-term romantic relationship or during fatherhood suggest a down-regulation of these competitive tendencies.

A commitment ensures I forsake other options and allows another to make predictions about my future actions. Emotions are physiological and psychological experiences that serve a survival function by motivating our behavior. From an evolutionary psychological perspective, an emotional commitment is a mating strategy with a psychological, physiological, and behavioral milieu naturally selected to forge an ensuring partnership with short-term sacrifices for long-term gains. Using Dawkins’ concept of genesmanship, people have the predisposition to commit to another because this long-term alliance will increase the likelihood of passing on their own genetic legacy. Women and men faced differing reproductive issues over the course of human evolution, and through sexual selection, the sexes have developed competing mating strategies to solve problems of maximizing fitness. Women have far fewer reproductive opportunities and far more substantial childbearing and childrearing costs compared to men, and therefore making a an emotional commitment to a man, and securing one from him in return, would have allowed for a better chance of offspring survival in the environment of evolutionary adaptedness (EEA) by access to provisioning and protection. With our minds still operating today as they did over the course of millions of years of human existence, women world-wide still seek emotional commitment to a greater extent than men. In this chapter, I discuss the nature of emotional commitment, and the significance of love, romance, and marriage. Moreover, emotional commitment to others (nonromantic partners) also serves a survival function. I therefore also discuss emotional commitment to kin (parent-child attachment, other family) and to non-kin (friends, pets).

Over human evolutionary history, women have benefited from competing with same-sex mating rivals to acquire and retain desired mates. Winning a rivalry may lead to direct advantages, such as securing an attractive, healthy mate who has the ability and willingness to invest in a relationship, as well as possessing important resources that may help sustain future children. Simultaneously, such competition is associated with potential costs, such as jeopardizing alliances, being victimized within social networks, becoming the target of malicious gossip, or, in the case of a loss, wasting one’s time and effort that could have been allocated elsewhere. Here I first present the evolutionary framework that underpins women’s intrasexual mating competition, and then review the existing literature on the specific ways that this competition is manifested. Attention is especially paid to competition via physical attractiveness, namely women’s efforts to improve or enhance their attractiveness, given men’s universal tendency to prefer attractive mates. I focus on how this competition typically utilizes indirect aggression tactics and relies on women behaving in a strategic manner that depends on the local environment, such as the number of available mates, the mate value of potential rivals, and concerns about maintaining one’s reputation.

Evolutionary perspectives offer a comprehensive theoretical approach to parental investment, as they include not only explanations for why an individual makes such investment, but also for why an individual might withhold such investment. These explanations lay the foundation for deriving predictions concerning when an individual will be more or less likely to withhold investment. This chapter introduces evolutionary psychological perspectives on paternal filicide (i.e., child homicide perpetrated by a man in the context of paternal care). These perspectives suggest that reproductive conflicts between men and the children in their care may activate mechanisms that evolved to regulate paternal investment. These mechanisms may increase the risk of a lethal lowering of investment. Further, these perspectives suggest that reproductive conflicts between men and their current or former partner may activate mechanisms that increase the risk of both filicide and familicide (i.e., the killing of a current or former partner in addition to children). Paternal filicide is then, despite being rare in current societies, no less a result of men’s evolved psychology. This chapter presents the theoretical foundation for disaggregating paternal filicide perpetrators who are genetic fathers from those who are stepfathers of their victims, and paternal filicide perpetrators suffering from nonadaptive psychopathology (such as psychosis or suicidal ideation) from those not suffering from psychopathology. The chapter will further present the theoretical foundation for predicting a distinct pattern of characteristic traits for each of these subcategories, along with a selection of the empirical support for the predicted pattern documented cross-culturally. Although paternal filicide perpetration is reduced to historic lows in several societies, there are still certain groups of men in these societies that are more vulnerable to perpetrating paternal filicide. The chapter will identify these groups of men and suggest why their vulnerability persists, focusing on Scandinavian countries.

The imbalance of minimum obligatory parental investment between sexes has imposed distinct and often conflicting adaptive problems for males and females. One such adaptive problem faced by the less investing sex (males) is the acquisition of more reproductive opportunities with members of the more investing sex. One potential solution to this problem is the use of sexual coercion or force to nullify female mate choice. Although males of many species have been observed to employ coercion or force to achieve copulation, the extent to which human sexual coercion and rape are evolved behaviors remains an open question. The present chapter is a brief review of the comparative literature, as well as empirical research from a wide range of domains within human psychology, weighing support for both the adaptation and byproduct theories of rape in humans. The similarities in the sexually coercive behaviors of nonhuman primates, heritability of sexual offending, and the potential adaptive benefit of sexual coercion across various mating contexts provide considerable support for the evolution of rape in humans. Nevertheless, support in favor of the adaptation theory of rape is not necessarily exclusionary to the byproduct theory. Therefore, there remains a need for additional evolutionary research to contribute to this open question.

Researchers have spent decades investigating factors in attraction; biological variables, cultural norms, and social pressures have all had their time in the spotlight. Humans are complicated animals and each of these realms have shown measurable effects. However, evolutionary approaches provide a unifying theory that subsumes and explains each of these factors and how they interact to create intricate yet predictable patterns in human mating behavior. In this chapter, we give a brief summary of major factors influencing attractiveness as perceived by men, including biological factors such as age and ovulatory status but also social factors such as exposure to highly attractive, or simply novel, women. Understanding how attractiveness can vary over time and within relationships can be useful, not only to research but also in applied clinical fields such as couples’ and marital therapy.

Despite a tendency to form socially monogamous pair-bonds that carry expectations of sexual exclusivity, infidelity has been a recurrent feature of human mating across societies. The attitudes, social cognition, affect, and behavior associated with infidelity vary in patterned ways between women and men. In the current chapter, we use an evolutionary perspective to make sense of the historical and cross-cultural ubiquity of extradyadic behavior, as well the adaptative costs and benefits of men’s infidelity. Specifically, we review theory and research pertaining to men’s extra-pair mating and consider salient individual differences, romantic relationship dynamics, and social–ecological factors that influence mating strategies and extradyadic involvement. Following other scholars, we argue that men have evolved adaptations for short-term mating that facilitate opportunistic extra-pair behavior in a “quantity-over-quality” reproductive strategy. Consequently, on average, men are predicted to express a stronger desire to engage in sexual infidelity and to have more permissive attitudes toward extradyadic involvement than women. However, only particular men appear to execute a mixed mating strategy involving a long-term mate and an extra-pair partner, such as those with greater mate value. Satisfaction with and commitment to the relationship appear to be crucial in preventing men’s infidelity, and socio-ecological factors, including cultural dynamics (e.g., norms surrounding infidelity) and sex ratios that create conditions of mate scarcity, are inextricably tied to men’s extra-pair mating.

The present chapter advances the view that women’s mate preferences can be grouped into at least two overarching domains: competitiveness and fatherhood. Theoretical and empirical considerations suggest that female mate preferences evolve in contexts of male competitiveness and often amplify the effects of male–male competition. Evidence for the importance of male–male competition and female choice for competitiveness in humans is reviewed. Evidence is likewise offered for the importance of human fatherhood as an additional domain of female choice outside of male competitiveness. Implications of more inclusive mate preferences for the evolution of cognitive architecture are discussed alongside the social and ethical implications of female choice for competitiveness.

Despite the extensive empirical exploration of sexual desire, only one field explains the proper biological function of this phenomenon—evolutionary psychology. This chapter reviews women’s copulatory urgency—individual differences in the experience or intensity of sexual desire—from an evolutionary psychological perspective. An evolutionary psychological perspective of the function of sexual desire can shed light on how deficits in this motivational force may emerge, which may be useful for clinicians when helping patients understand the etiology of sexual desire concerns. An evolutionary psychological perspective of sexual desire further reveals: (1) why men and women differ in their experiences of sexual desire, (2) how natural selection produces individual differences in sexual desire, and (3) how extremes in sexual desire may be associated with hypersexuality, paraphilias, or an evolutionary mismatch between the adaptive problems faced during our species’ past and the challenges we face today. I begin the chapter by presenting a brief history of research on sexual desire and highlighting the limitations of early models of sexual responding. Next, I discuss the difficulties of measuring sexual desire, and explain how evolutionary meta-theory can be fruitful when examining context-dependent individual differences in sexual desire. I then describe the impact of several important contextual factors (e.g., age, relationship length, parental effort, partner habituation) on variation in women’s sexual desire responses and highlight avenues for future research. The chapter ends by discussing the qualities of compulsive sexual behavior and proposing that extreme variations in sexual desire as we currently understand them may be the result of an evolutionary mismatch. In sum, I suggest that scientists distinguish between sexual desire and sexual arousal, consider evolutionary meta-theory when thinking about context-dependent variation in sexual desire, and be cognizant of potential confounds when examining women’s sexual desire responses.

This chapter focuses on the behaviors employed by men in the service of attracting mates, which we discuss as having emerged to solve specific reproductive problems faced by women. We consider behaviors employed by men to attract mates in short-term mating and long-term mating contexts, given the differential valuation on certain behavioral repertoire that emerge. In short-term mating, we specifically consider behavioral displays of dominance with their dispositional and situational antecedents before discussing men’s pursuit of distinctiveness and humor use, behaviors ostensibly indicative of good genes. In long-term mating, our discussion centers around the desirability of different resource displays and benevolence. We further discuss cues ostensibly diagnostic of paternal investment ability and an interest in monogamy. Our final section addresses how modern mating markets present adaptive problems for men (e.g., online dating, appearance enhancing behaviors) and how men seek to solve the new problems that have emerged.

Extrapair sex, although not a dominant human mating strategy, has been a part of our mating landscape throughout human history. Although prevalence rates vary across studies, a conservative estimate is that at least 1 out of 5 persons have cheated on a committed partner. In this chapter I discuss theories and evidence addressing extrapair interest and behavior (i.e., cheating on a committed partner) as produced by adaptations. Topics include the costs and benefits of extrapair behavior, comparisons to nonhuman animal extrapair behavior, sex differences, and purported female cyclical variations in extrapair orientation. I briefly discuss proximate factors that predict proclivity to cheat. I also touch on infidelity advertisement, cheating detection, forgiving a partner’s infidelity, and infidelity in popular culture. I conclude with some observations about the state of the field. Regardless of causes and correlates, infidelity can be costly, yet humans remain interested in and intrigued by the phenomenon.

Unlike extensive research conducted on courtship, foreplay, and intercourse, what happens after ejaculation is one of the most neglected dimensions of human sexual behavior. As described in this chapter, postejaculatory adaptations have important and diverse implications for such things as penis hypersensitivity, the refractory period, female infidelity, sperm competition, semen displacement, self-semen displacement, spousal rape, the risk of transmitting sexually transmitted diseases for uncircumcised men, and the incidence of nonpaternity. This chapter also outlines ways to test the Bruce effect in human females and provides a novel explanation for the absence of the Coolidge effect in women.

In this chapter we summarize and discuss the literature on human female romantic jealousy from an evolutionary perspective. We first define jealousy as a complex cognitive, affective, and motivational state that occurs in response to the threatened or actual loss of a valued relationship to a rival, and that can trigger different emotions. We further discuss different dimensions of jealousy, stressing both state and trait jealousy. We outline behavioral consequences of jealousy, such as mate guarding and mate retention, and we discuss how some qualities of rivals can trigger jealousy. The most frequently studied area in research on human jealousy is sex differences in sexual versus emotional jealousy, suggesting a robust and replicated finding of higher emotional jealousy in women, and higher sexual jealousy in men. We further discuss individual differences that explain variation in jealousy, such as higher overall jealousy among women, associations between women’s jealousy and their anxiety and self-esteem, developmental factors influencing jealousy, lower jealousy among non-monogamous individuals, and high jealousy among pathologically jealous individuals. We challenge the research on sex differences in jealousy with reference to intra-sexual variation among individuals of different sexual orientations. We show that female jealousy is influenced by hormonal and genetic factors, and we discuss examples of non-human species to show analogies to human jealousy. Throughout the chapter we stress the plasticity of jealous response depending on contextual factors, including environmental and sociocultural contexts. Human diversity in the manifestations of state jealousy does not contradict the evolved nature of jealousness. We conclude by considering the distal functions of jealousy, including maintenance of a valued relationship and self-esteem, mate-poaching, and mate-switching. We note several gaps in the literature of female jealousy, and we hope this chapter integrates the literature, informs newcomers, and inspires new evolutionary research.