Population physiology is a branch of physiological anthropology studying the physiological structure of populations under specific environmental conditions. The theoretical basis of this discipline is the theory of physiological homeostasis and, more generally, notions such as biological system and integrity. The primary task of human population physiology is the study of within- and between-population variability of separate physiological characteristics and of the physiological status a whole. The systemic approach allows assessing similarities versus dissimilarities between populations in physiological status and interpreting them in terms of ecological specificity, and adaptation versus maladaptation.