Human behavioral ecology traditionally examines ultimate questions while “black boxing” physiological mechanisms and modes of inheritance. This chapter addresses how the intersection between human biology and behavioral ecology allows researchers to open these black boxes and how an examination of mechanisms can help to answer ultimate questions. First, the chapter discusses how physiological systems are intertwined with behavioral ones through chemical messengers, such as hormones, which broadcast information throughout the organism and coordinate actions inside the body with those outside the body. Next, the chapter looks inside the “black box of inheritance” to consider how mechanisms of inheritance beyond genes and culture, such as epigenetic inheritance, are relevant for behavioral ecology. The chapter concludes by discussing how studies of biology and behavioral ecology can complement and inform one another, leading to general insights that would be missed if both biology and behavior had not been considered in concert.

This chapter introduces approaches to materiality and biology within anthropological scholarship on sex and gender. It emphasizes how biological subfield of eco-evo-devo (which emerged in dialogue with feminist studies) can contribute to anthropological debates. The authors focus on hormones, signaling molecules that regulate many physiological processes in humans, animals, and plants. Hormones are a particularly productive site for considering how anthropologists interested in sex, gender, and bodies might benefit from additional attention to biological processes and biological knowledges, as they challenge prevailing concepts and categorical oppositions of self/world, nature/culture, and mind/matter. The authors first sketch out a history of the relationship between anthropology and biology and, within that history, how feminists have confronted biologism. They then introduce eco-evo-devo and explore how its insights about hormones and development can serve as a prompt to rethink the body within anthropology. Last, they review examples of social scientific engagement with hormones, arguing that a deeper engagement with the materiality of hormones rather than only with their popular representation can help anthropologists continue their ongoing efforts to reframe the social and apprehend gender and sexuality as entangled within complex ecologies of industrial capitalism.

The physiological and mental impact of impaired fertility is recognized by the National Institute of Health, who identified fertility status as an overall marker of health. Reduced fertility is often linked with other physiological or genetic conditions, and precise alignment of physiological processes is essential to maintaining reproductive success. Reproductive function is closely linked with the circadian system, where studies in both humans and rodent research models have demonstrated that neuroendocrine mechanisms are sensitive to circadian disruption. Circadian rhythms throughout the body synchronize reproductive tissue function to the time of day by aligning hormone release with increased target tissue sensitivity to hormones. This chapter will review the current understanding of the neuroendocrine circuit regulating male and female fertility, and how light and genetic disruption of circadian rhythms impairs fertility.

Introduction to desire and how it relates to sex, including similarities and differences against other desires. Biology of desire and reward pathways in the brain. Reward transmitters such as dopamine and chemical messengers such as oxytocin.

Norms in sexual development as people get older, age of puberty and first sexual experiences, and variation in these. The role of cultural norms and parenting in sexual development norms and also biological factors.

Assisted reproductive technology (ART) is essential for transgender people’s reproductive justice and autonomy in relation to fertility preservation and family building, whether using their own bodies (eggs, sperm, or uterus), donor gametes, or a gestational carrier. The ability to form a family using one’s own gametes and/or body is necessary for transgender people to consider before medical transition is initiated (hormones/surgeries) and is part of the Informed Consent process of gender medical transition. Progressive thinking, greater cultural awareness and modern medicine have contributed to an increase in transgender people utilizing ART to create their families. Helping transgender patients navigate medically assisted fertility preservation and reproduction requires diverse knowledge, sensitivity training and cultural inclusivity for fertility counselors. Providing gender-affirmative care in reproductive endocrinology and fertility settings when working with transgender patients involves understanding terminology used in the transgender population, use of a trauma-informed care lens, knowledge of a nonbinary gender system, avoiding heteronormativity, cisnormativity and knowledge of gender dysphoria. The American Society for Reproductive Medicine (ASRM), The Endocrine Society, World Professional Association for Transgender Health (WPATH) and American College of Obstetrics and Gynecology (ACOG) have published documents addressing fertility and preservation considerations for transgender people.

Why is birth so dangerous, even today, with modern medicine? Through historical anecdote and a contemporary case history we explore this question, discussing the process of birth and what can go wrong. By thinking about who is in control of labour – is it the mother or her fetus? – we think about how a couple might prepare for birth. The challenge posed by birth makes us look to human evolution for answers, and we describe the insight it gives into birth in some low-resource settings around the world. We tackle the question of the rising numbers of caesarean sections around the world and the possible consequences. Although it may be widely believed that a smaller baby would mean a less difficult birth, we go on to explore the risks of being small for the survival of the baby alongside new research revealing how the mother’s body limits the growth of her baby inside the womb. We discuss whether the growth of the fetus is set by the genes which the mother or the father have passed on, mother’s size, or her environment. This leads to how the fetus develops and what controls this, the focus of the next chapter.

During pregnancy in humans and rats, plasma osmolality is regulated at a level about 3% lower than in nonpregnant females (or males). This may be, in part, caused by reproduction-related hormonal changes. Late in gestation, fetal sheep show acute swallowing responses to some dipsogens, and the relevant CVOs in the brain appear to have full responsiveness to those dipsogens at this time. Postnatal development of independent drinking in rats shows that responses to hypovolemia are present and vigorous very soon after birth, whereas development of osmoregulatory drinking has a considerably slower ontogenetic trajectory. Further, this trajectory seems to be slower in mice than rats and requires further study. Some aspects of osmoregulatory drinking in rats, as well as food-associated drinking, appear to have an experiential component. Hypovolemia or other circulatory challenges before birth in rats cause alterations in the ontogenetic trajectory of drinking, although the limits and mechanisms of this phenotypic plasticity have not been fully elucidated.

The uterus serves as an incubator for the fetus during pregnancy. Within this incubator, the placenta is the main connection between the mother and the fetus and is integral to the survival of the fetus as it is an important source of fetal nutrients and oxygen. The proper development of the placenta allows it to support the fetus throughout pregnancy and expulsion or removal of a normal placenta following delivery, helps prevent postpartum complications. Maintenance of uteroplacental flow during pregnancy and during fetal surgery is important for the survival of the fetus and especially for the remainder of the pregnancy following fetal surgery. Serial monitoring of umbilical artery flow, a marker for uteroplacental insufficiency, is helpful to monitor fetal well-being. Physiology of the fetus correlates with the different stages of development in different organs and in many instances changes at delivery. The prevention of pain or the effects of noxious stimuli during fetal surgery serves many benefits, which include but are not limited to, prevention of release of stress hormones which can play a role in preterm labor and also prevention of long-term neurodevelopmental effects in the fetus.

The genome encodes the information needed to make us human, but genes do not directly cause growth and development. Gene expression is regulated and mediated by several biological systems, especially the neurological and endocrine (neuroendocrine) systems. Hormones regulate and coordinate critical developmental processes, integrating across several systems, including the central nervous system, the reproductive system, and the digestive system. Hormones are influenced by nutritional status and infections. Therefore, hormones provide a mechanism by which “real-time” information about a body’s health is communicated to the brain and processed by its regulatory centers in the hypothalamus and pituitary, through which growth is affected accordingly.

The quantification of physiological and immunological functions provides fundamental information on individual state. It fosters our understanding of the costs of and constraints on life-history strategies. Research in this area on kestrels has mainly focused on immunity, energetics, hormones and antioxidants. This chapter discusses the factors that impact the immune function and describes a number of parasites and pathogens that can be detected in kestrels. It shows how the different phases of reproduction face males and females with different energetic and physiological demands. It discusses the costs associated with sibling competition, and how male and female nestlings may differ in how they optimise the trade-off between growth and self-maintenance. Finally, this chapter describes the moult phase, which represents an understudied feature of kestrel biology.