Part front matter for Part I Relationship Initiation

Relationship initiation refers to how people find and choose a relationship partner. In chapter 1, Buss reviews the foundations of evolutionary science and its application to the study of human mating. He focuses on the processes of sexual selection and how it has shaped men’s and women’s partner preferences and selection criteria. He highlights the fundamentals and premises of sexual strategies theory, including the sex-specific challenges recurrently faced by those seeking long- and short-term partners and the adaptations that men and women have evolved to heuristically address these challenges. He considers alternative explanations for variation in men’s and women’s mate preferences (e.g., the good genes hypothesis and the mate-switching hypothesis) and strategies of contest competition. Moreover, he integrates recent evidence for how individual and environmental variations (e.g., mate value discrepancies, operational sex ratio, and parasite load) shape expression of these adaptations. He concludes with a discussion of future directions in the study of sexual coercion (i.e., behavior aimed at securing reproduction by bypassing mate choice) and men’s and women’s adaptations and counter-adaptations for enacting and resisting this type of mating.

In chapter 2, Stephen and Luoto review how humans and other animals use morphological cues (e.g., face and body condition) to assess partner qualities that are of consequence to successful mating and reproduction. Their review includes a balanced discussion of traits associated with immune functioning, health status, and desirable personality traits, including cues of developmental health (e.g., symmetry and sexual dimorphism), current health (e.g., adiposity and skin color and texture), genetic quality (e.g., major histocompatibility, height, and muscularity), and personality. They discuss the myriad strategies for augmenting these cues with nonbodily ornamentation, such as luxury items, cosmetics, and other conspicuous superstimuli that exaggerate cues of phenotypic quality. They conclude by discussing how modern technology, such as social media and online dating, has decoupled the evolved psychology underlying partner evaluation from the adaptive behavior that it has historically produced, thereby creating evolutionary mismatches.

In chapter 3, Jonason and March review the psychological traits that people assess in potential mates and argue that these qualities can be organized into three superordinate traits: competence, compassion, and compatibility. Competence includes traits that assist in goal pursuit and attainment (e.g., intelligence, education, and income), compassion reflects traits that signal a partner’s willingness to invest in a partner or shared offspring, and compatibility refers to similarity in interests and belief. They outline differences and similarities among men’s and women’s preferences for these traits and draw on sociocultural (i.e., social role theory, structural powerlessness, and social learning theory) and evolutionary models (i.e., sexual strategies theory and life history theory) to explain how and when people vary in these preferences. They conclude with the importance of studying how these preferences generalize to non-Western and sexual/gender minority populations and how researchers might begin to appraise their “three Cs” model of psychological preferences.

In chapter 4, Li and Choy review the mechanisms of mate choice, including the evolved algorithms that humans employ to weigh and prioritize competing partner traits. They assess these mechanisms within the context of sexual strategies theory, agent-based simulation models (e.g., Euclidean algorithmic mate value integration), modern platforms for courting partners (e.g., social media and online dating), and speed-dating experimental paradigms. They conclude by discussing sources of evolutionary mismatch caused by the emergence of supernormal stimuli, such as sexual technology and pornography, potential partner abundance, and anonymity, that which be altering how mate choice mechanisms guide peoples’ relationship decisions.

In chapter 5, Makhanova synthesizes the experimental and cross-species evidence for how hormones mediate sexual behavior and partnership formation. She reviews the general functional design of gonadal hormones, including testosterone, estrogen, and progesterone, and the physiological systems through which these hormones influence the development and expression of male- and female-typical mating behavior. Throughout, she emphasizes how these hormonal effects are sensitive to context (e.g., social status, ovulatory fluctuation, and presence of rivals) to produce situationally malleable adaptive responses. She concludes by discussing sources of individual difference in hormone-mediated relationship formation and identifies methodological advancements that are yet needed within this field of study.

In chapter 6, Caton, Lewis, Al-Shawaf, and Evans catalogue the diverse courtship signals and behaviors that humans and other animals employ to attract partners and promote their reproductive success. Discussion is organized around the five senses to showcase how courtship is guided by sensory input and the adapted cognition that processes each sensory mode (i.e., visual, auditory, tactile, olfactory, and gustatory). Throughout, they maintain focus on cutting-edge research on psychophysical cues of mate quality, including neck musculature, lumbar curvature, and sebum detection. They conclude by discussing future directions for studying how humans use each sensory modality to assess potential partners.

In chapter 7, Krems, Bradshaw, and Merrie provide an overview of the major theories and evidence underlying research on intrasexual competition in humans. They discuss the contributions of parental investment theory and sexual strategies theory as well as the influence of biological markets and ecological factors (e.g., sex ratios and income inequality) that shape same-sex competition within men and women. They bridge historical and recent work to identify unresolved gaps in the empirical study of contest competition and spend considerable time identifying future directions in the study competition among women, sexual and gender minorities, and parents and older adults.

In chapter 8, Valentova, Amaral, and Varella give an authoritative summary of mate preference, mate choice, and relationship initiation research among hetero- and non-heterosexuals and evaluates how evolutionary scientists have approached the study of relationship initiation among LGBTQ+ individuals. They note which sex differences appear to be robust with LGBTQ+ samples and which features of attraction and courtship diverge from findings among heterosexual individuals. They identify several current limitations, including a largely restrictive focus on Western samples, insufficiently nuanced measures of sexual orientation, and interactions between sexual attraction and gender (a)typical developmental process.

In chapter 9, Koren and Ayalon consider how relationship initiation varies across age and the unique challenges that individuals must resolve to form partnerships later in life. They consider the roles of individualistic versus collectivistic cultural values, the influence that children and grandchildren exert on mate choice and repartnering, and the barriers that later-life health and living conditions can introduce. Throughout, they reference prominent models of socioemotional functioning and successful aging to highlight the importance of studying the diversity of relationships among older adults, the intersecting effects of culture and parent–offspring interactions and expectations, and the roles of physical and emotional togetherness/apartness. They conclude with research on LGBTQ+ populations, extreme old age, and emerging technologies for helping older individuals find and achieve relational satisfaction.

In chapter 10, Karandashev concludes the first section by describing the influence of biological, ecological, and cultural selection processes on cross-cultural variation in relationship initiation. Throughout, he focuses on distinctions between traditional and modern societies’ courtship customs. In doing so, he highlights international differences in beauty standards and their relation to socioeconomic status, infant mortality rates, sex ratio, and individualism/collectivism, the importance of physical appearance versus expressive behavior, survival and self-expression values, education and reproductive rate, wealth concentration and women’s access to financial resources, social rituals and symbolic gestures of love and commitment, dating customs, and the role of parental oversight (e.g., arranged marriages). He concludes by critiquing methodological customs in cross-cultural research and provides several fruitful avenues for future directions.