This book is divided into four major units. Part I, “Evolutionary Background,” provides the basic background in genetics and evolutionary theory used throughout the remainder of the book. Part II, “Our Place in Nature,” examines the biology and behavior of the primates, the group of mammals to which humans belong. The focus of this section is the questions “What are humans?” and “How are we related to other living creatures?” Part III deals with questions of “Our Origins.” Part IV, “Our Diversity,” examines human biological variation in our species today from an evolutionary perspective. The reorganization of the eighth edition provides a more logical sequence of topics in human evolutionary history from the past to the present.