The biocultural, cross-cultural, and evolutionary perspective to breastfeeding adopted in this book illustrates how behavior can and does affect biology and highlights the physiological interdependence between mother and infant. Studies are beginning to show that there are physiological, metabolic, and possibly even psychological differences between a breastfeeding mother–infant pair and a non-breastfeeding mother–infant pair. The development of the artificial infant food industry, beginning in the mid-nineteenth century, has made it possible for large numbers of infants to survive without breast milk for the first time in human history. The biological anthropologist has a unique way of viewing the world: a cross-cultural and evolutionary perspective that acknowledges that there are both biological and cultural components to human behavior. Breast milk is not a magic potion, not a panacea for all human ills. It is a vital, dynamic substance that can transmit both beneficial and detrimental substances to the infant.