lthough I have never practiced medical anthropology in a formal sense, my work in human biology has always bordered on medicine and medical sciences. I have worked on infant growth and development, neonatal behavioral status, and the role of nursing in the suppression of gonadal function, among other biomedical subjects. I decided to go to medical school in mid-career for a variety of reasons, including these research interests. I have completed requirements for the M.D. degree but have not pursued, and do not immediately expect to pursue, further clinical training. I am thus in the position of having been exposed to a broad spectrum of clinical settings and of having been processed through a major portion of medical training without completing that process. I believe that this in-between position, awkward though it may be, gives me an unusual perspective on the social and behavioral aspects of medicine (cf. Konner 1987). I will return to my view of medical anthropology from this perspective, but first I wish to talk as a biological anthropologist. It seems to me that medical anthropology has been underappreciated as an aid to the understanding of human evolution, including the evolution of human behavior and social systems (Dunn 1968; Inhorn and Brown 1990). There is no anthropological setting on record, and indeed no historical setting until the 19th century, in which infectious disease is not a major source of mortality. Even other major sources, such as war and famine, have often worked through infection as the final common pathway of mortality. It is inconceivable that human biology, behavior, and culture can have evolved without responding either deliberately or inadvertently to such pressures. Yet theories of human evolution, both biological and cultural, give little attention to the role of disease. Elaborate theories are constructed around such environmental demands as hunting effort, optimal foraging strategy, land tenure, alliance, and so on. I do not mean to belittle such theories, just to point out the relative lack of attention to disease processes that may be the most important forces in a human group's adaptation. For example, given the high level of infant mortality in all human groups until recently, it is likely that a major determinant of the close prolonged human mother-infant bond has been the need to deliver regular doses of macrophage- and antibody-containing breast milk. Other theories that have been advanced-including laying the foundation of emotional life (Freud), transmitting culture (Mead), or avoiding predation (Bowlby)-probably have some validity, but it does seem extraordinary that the need to protect the immunologically weak infant from microbes and parasites has been given so little attention. To take another example, it seems inconceivable that human marriage rules and sexual mores could have evolved without being in some degree a response to