Biological anthropology focuses on the study of human evolution and adaptation. Biological anthropologists are particularly interested in investigating why variation arose and how it is maintained, as well as trying to explain how people are adapted to the environments in which they live. They study the human fossil and stone tool record, primate behaviour, human material culture and the development of modern human behaviour in evolutionary and comparative perspective. Typical questions that interest biological anthropologists could be: why do people have different skin colours or facial shapes? Does the environment affect fertility? What are the best ways to assess childhood malnutrition? When and how did humans evolve? What does chimpanzee aggression say about human violence? How much can you really tell about a person from their skeleton? Why is sex fun?