The initial peopling of most of the large land masses in the prehistoric era is usually explained by basic theories that appeal to reason. For example, that groups of prehistoric peoples would periodically migrate into North America via a land bridge over the shortest span of ocean separating the continent from Asia seems wholly plausible. Answering questions such as when, for how long, is more problematic. Archaeological field research occasionally yields new breakthroughs, but the work is painstaking--and site discovery can often be a matter of chance. In Europe, scientists are attacking the issue in the lab rather then in the field. By applying modern genetics to population studies, archaeology, and anthropology, a new interpretation of the settlement of Europe, and the genealogy of its current inhabitants, is forming.

Despite the density of various nations and ethnic groups...