This unit is designed to acquaint the student with both the origin of humans and how evolution has shaped human behavioral patterns, and to help the student to better understand how recent population changes have affected behaviors and customs in societies worldwide. The students will learn how humans evolved, how they established primitive social groups and how the influences of population growth have affected the relationships of humans to their environment and to each other. The unit reviews characteristics of mammals and primates and discusses early hominid evolution. Physical evolution of man is linked to behavioral evolution. The concept of Reciprocal Altruism is explained and it is proposed that this became a genetic behavioral trait. This concept is further considered as one of the main reasons for the success of human evolution. The effects of civilization upon human behavior are also considered. Increases in population density, cultural differences and technology are all related to changes in behaviors. Problems of modern-day high-technology cultures are considered in terms of reciprocal altruism. Finally there are two classroom exercises. The first demonstrates some of the problems of scavenging on the savanna of Africa. The second shows how population density affects the rates of murder, rape, assault, armed robbery, breaking and entering, drug arrests and teen-aged pregnancies.