The text has been revised in light of new findings in the field and comments from users of the seventh edition and reviewers. Two chapters have been merged and another split, with no change in the total number of chapters. Total text length has been reduced somewhat by deleting some extraneous material and rewriting sections to provide clearer explanation. In addition to updating material, several other changes have been made, including these:

• Sections of chapters on genetics and population genetics have been revised to increase student comprehension.
• The chapters on primate biology and behavior have been restructured to provide a more cohesive discussion of primate behavior. The first chapter on primates (5) now includes a review of primate taxonomy following the discussion of basic primate characteristics. All material on principles of primate behavioral ecology have been moved to the second chapter (6), which now also includes a number of case studies of primate behavior in selected species.
• The chapter on the evolution of the genus Homo has been split into two separate chapters. The first focuses on the origin of the genus Homo and the initial dispersion out of Africa (Homo habilis and Homo erectus). The second looks at the evolution of later humans—specifically, Homo heidelbergensis and the Neandertals.
• New sections have been added on the evolution of larger brains in the genus Homo and on the evolution of language. Additional new information has been included on a variety of subjects, including evolution of Miocene apes, diet in robust australopiths, the origin of bipedalism, new finds of Homo habilis, the new female Homoerectus pelvis, eandertal DNA, the origin of modern human cranial anatomy, geography and the population history of Ireland, and new data on lactase persistence, among others.