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.