Sex Differences in Cognition

Organizational and activational effects of sex steroids were first discovered in laboratory animals, but these concepts extend to hormonal actions in the human central nervous system. This chapter begins with a brief overview of how sex steroids act in the brain and how the organizational-activational hypothesis originated in the field of endocrinology. It then reviews common methods used to study these effects in humans. Interestingly, certain cognitive functions appear to be subject to modification by sex steroids, and these endocrine influences may help explain the sex differences often seen in these functions. The chapter considers spatial cognition as a representative example because the spatial family of functions has received the most study by researchers interested in the biological roots of sex differences in cognition. The chapter reviews evidence that supports an influence of both androgens and estrogens on spatial functions, and concludes with a glimpse of where the field is headed.

Sex Differences in Anxiety Disorders

Women are more likely than men to meet lifetime criteria for an anxiety disorder. Moreover, anxiety is a risk factor for the development of other psychiatric conditions, including major depression. Numerous studies have identified evidence of sex differences in anxiety disorders, and there is considerable research concerning factors that may contribute to vulnerability for anxiety in females. In addition to psychosocial influences, biological components such as the female reproductive hormone cycle have also been implicated. Although psychotropic medication is more likely to be prescribed to women, there is little controlled data available concerning sex differences in the efficacy and/or tolerability of pharmacotherapy in anxiety disorders. This chapter provides an overview of the impact of gender in the epidemiology, phenomenology, course, and treatment response in generalized anxiety disorder (GAD), social anxiety disorder (SAD), posttraumatic stress disorder (PTSD), panic disorder (PD), and obsessive-compulsive disorder (OCD).

Hormones and Behavior

Hormones mediate the expression of life history traits—phenotypic traits that contribute to lifetime fitness (i.e., reproductive timing, growth rate, number and size of offspring). The endocrine system shapes phenotype by organizing tissues during developmental periods and by activating changes in behavior, physiology, and morphology in response to varying physical and social environments. Because hormones can simultaneously regulate many traits (hormonal pleiotropy), they are important mediators of life history trade-offs among growth, reproduction, and survival. This chapter reviews the role of hormones in shaping life histories with an emphasis on developmental plasticity and reversible flexibility in endocrine and life history traits. It also discusses the advantages of studying hormone–behavior interactions from an evolutionary perspective. Recent research in evolutionary endocrinology has provided insight into the heritability of endocrine traits, how selection on hormone systems may influence the evolution of life histories, and the role of hormonal pleiotropy in driving or constraining evolution.

Intersexual and Intrasexual Competition and Their Relation to Jealousy

This chapter discusses sex differences in intersexual competition and describes particularly the consequences of such competition for conflict between the sexes, as well as for sex differences in mate guarding and, relatedly, in the types of infidelity that evoke jealousy, including online infidelity. It also discusses individual differences in jealousy as related to attachment styles and describes the effects of height, hormones, and the menstrual cycle on jealousy. Next, the chapter moves on to intrasexual competition and discusses, among other topics, intrasexual competition among men and among women, the role of sex differences in rival characteristics in evoking jealousy, the role of attachment styles and hormones, and individual differences in intrasexual competitiveness.

Integrating Mechanisms and Functions to Understand Behavior

Evolutionary psychology and behavioral endocrinology provide complementary perspectives on interpreting human behavior and psychology. Hormones can function as underlying mechanisms that influence behavior in functional ways. Understanding these proximate mechanisms can inform ultimate explanations of human psychology. This chapter introduces this edited volume by first discussing evolutionary perspectives in behavioral endocrinology. It then briefly addresses three broad topic areas of behavioral endocrinology: (1) development and survival, (2) reproductive behavior, and (3) social and affective behavior. It provides examples of research within each of these areas and describes potential adaptations. The chapter concludes with a discussion on the importance of integrating mechanisms with function when investigating human behavior and psychology.

Reproductive Behavior in the Human Male

Given the pivotal role of differential reproduction to the evolutionary success of ancestral men, evolution has produced a plethora of reproductive strategies aimed at solving the complexities of intramale competition and satisfying and/or thwarting the reproductive desires of women. Life history theory recognizes that an organism has limited resources and must invest energy appropriately. Broadly, reproductive strategies can be dichotomized into short-term (emphasizing mating over parental effort) versus long-term (emphasizing parenting over mating effort) strategies. Increasingly, the neuroendocrine system—especially testosterone—has been recognized as the proximate mechanism orchestrating adoption of one strategy over the other. This chapter reviews behaviors geared toward solving problems associated with both long-term and short-term reproductive strategies and discusses the neuroendocrine correlates. The adoption of one strategy over another is conceptualized as conditional or facultative adaptations in which strategic switching points are tuned over evolutionary time to produce optimal fitness responses to men’s social and physical conditions.

Endocrine Disruptors and Other Environmental Influences on Hormone Action

Endocrine-disrupting chemicals (EDCs) interfere with hormone action by altering hormone synthesis, secretion, transport in the blood, binding to receptors, metabolism, or excretion. This chapter reviews the history of EDCs and other environmental chemicals, methods used to identify EDCs, and common uses for these chemicals in consumer products. It also describes major principles of endocrinology and how these features influence the actions of EDCs. This chapter will also evaluate controversies in the study and regulation of EDCs, including the concept of “low dose effects,” the question of whether humans are exposed to EDCs at levels that can cause harm, and the determination of “safe” doses of exposure. Finally, this chapter reviews other environmental factors that can influence the health of laboratory animals and interfere with the study of EDCs.

Hormones and Major Depressive Disorder

Hormonal influences figure prominently in the development of major depressive disorder (MD). The chapter addresses the hypothalamic-pituitary-adrenal (HPA) axis and gonadal (i.e., estrogen and testosterone) hormones that are most relevant to MD. There is substantial evidence of HPA dysfunction in persons with MD, including adrenal hypersensitivity leading to elevated cortisol levels and deficient negative feedback control of the axis. These abnormalities may represent a marker of vulnerability for MD, as they are observed in high-risk populations prior to the development of the disorder. Gonadal hormones are related to specific presentations of MD. Estrogen sensitivity appears to underlie a “reproductive” form of MD in women, as seen during the menstrual cycle, postpartum period, and perimenopausal transition. Low testosterone, as occurs during normal aging, is associated with an increased risk for MD in men. These hormonal changes may be important in defining subtypes of MD that might be treated with targeted interventions.

Stress Hormones, Physiology, and Behavior

Stress, be it physical or psychological, can have a devastating long-term impact on an individual’s development, health, and well-being, and yet can be adaptive in the short term (e.g., promoting immediate survival, triggering the desire to remedy social conflict). The stress response system involves physiological processes in reaction to a real or perceived threat, which serve a variety of purposes. This chapter reviews pertinent topics and research within the social neuroendocrine study of stress, including acute versus chronic stress, and how stress influences social behavior and status. Where appropriate, it offers critiques of current theoretical models and includes suggestions for future directions within this research area.

Evolution and Human Fatherhood

This chapter reviews research on the evolution of paternal care in humans. It examines human fatherhood within the phylogenetic distribution of paternal care in vertebrates, especially mammals. Phylogenetic comparisons draw out several correlates of paternal care across species, with the most important being social monogamy. Research on the evolution of paternal care in humans has also focused on the relationship between social monogamy and the evolution of paternal care. The chapter reviews this research and major debates around whether male provisioning was a key adaptation in the evolution of pair-bonds and human life history. It discusses evidence for direct male care and summarizes a possible evolutionary sequence of its evolution in humans. It considers studies on the neuroendocrinology of male care in humans, drawing from comparative studies where appropriate. Lastly, this chapter outlines several major biocultural frameworks for understanding population-level patterns of paternal care as integrated, developmental responses to specific socioecological factors.