With their revolutionary discovery about human origins, a pair of maverick geologists single-handedly shook the foundations of science and philosophy. Here, for the first time, is the inside story.

For much of the twentieth century, anthropologists believed in a simple, linear picture of evolution: the human family was born in Africa and remained there until Homo erectus, a relatively advanced form of human, migrated into eastern Asia about one million years ago. All later humans, these anthropologists thought, developed through a steady modernization process from Homo erectus. But when Garniss Curtis and Carl Swisher of the Berkeley Geochronology Center applied advanced potassium/argon dating techniques to previously studied -- and incorrectly dated -- fossils in Indonesia, their findings shocked the anthropological community and drastically altered our current view of human evolution.

With lucid prose and infectious enthusiasm for the subject, the authors take us on a journey to the Indonesian island of Java, where Curtis and Swisher made two important discoveries: first, that human ancestors left the Cradle of Mankind -- the African continent -- and migrated east almost two million years ago, much earlier than anthropologists had believed, and second, that Homo erectus might have survived until as late as 27,000 years ago, suggesting that Homo erectus actually coexisted with Homo sapiens and was probably not an evolutionary precursor. Their findings not only destroy the straight line of human evolution, but also call into question the inevitability of the evolution of Homo sapiens.

Eventually, politics and a lack of funding find their way into the story, providing a realistic, if unfortunate, look at the travails that accompany scientific discovery. Swisher's and Curtis's findings are often met with skepticism, and their scientific methods are called into question. But conviction and determination lead them to conclusions that not only redefine their field but raise philosophical questions about what it means to be human.