Beginning with the immediate ancestors of humans who lived a few million years ago, anthropology traces the development of humans until the present.
Every part of the world that has ever contained a human population is of interest to anthropologists. Anthropologists have not always been as broad and comprehensive in their concerns as they are today. Traditionally, they concentrated on non-Western cultures and left the study of Western civilization and similarly complex societies, with their recorded histories, to other disciplines. In recent years, however, this general division of labour among the disciplines has begun to disappear. Now anthropologists can be found at work in cities of the industrial world as well as in remote villages of the non-Western world. What induces the anthropologist to choose so broad a subject for study? In part, he or she is motivated by the belief that any suggested generalization about human beings, any possible explanation of some characteristic of human culture or biology, should be shown to apply to many times and places of human existence.
If a generalization or explanation does not prove to apply widely, we are entitled or even obliged to be skeptical about it. The skeptical attitude in the absence of persuasive evidence is our best protection against accepting ideas about humans that are wrong. Anthropologists had known for years that in many parts of the world where milking animals are kept, people do not drink fresh milk; rather, they sour it before they drink it or they make it into cheese. Why this is so is now clear. Many people lack an enzyme, lactose that is necessary for breaking down lactose, the sugar in milk.