Gardner sorts out the subtle but significant differences between humans and their fellow primates. Historical charts show what is known of hominid lineage, geologic periods, and human cultural development. Early chapters describe eight different methods used to date fossils, Darwin's and Lamarck's evolution theories, genetic structures, functions and mutations, and how fossil bones are judged to be ape or hominid. Descriptions of significant hominid fossil finds, who made them, and where and when they were found lead to questions concerning the age of humans. Two theories of human population spread are compared. The text, though broken into small sections occasionally relieved by black-and-white illustrations and photographs, can be tedious in its detail. Yet persistence to the end leads to exciting news of another significant fossil discovery made in April of 1999. Analysis of this find may help clarify the picture, which seems to become more complicated with each bit of evidence. A generous list of books, magazine articles, and Web sites encourages additional exploration.