The book explores the field of paleoanthropology past and present. Beginning over 65 million years ago, Welker traces the evolution of our species, the environments and selective forces that shaped our ancestors, their physical and cultural adaptations, and the people and places involved with their discovery and study. It is designed as a textbook for a course on Human Evolution.
- The Miocene epoch extends from about 23.03 to 5.333 million years ago (Ma). The Miocene was named by Charles Lyell and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene and is followed by the Pliocene epoch.
- The Pliocene Epoch is extends from 5.333 million to 2.58 million years BP and follows the Miocene Epoch and is followed by the Pleistocene Epoch.
- The Pleistocene epoch is often colloquially referred to as the Ice Age and lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations.