GAINESVILLE, FLORIDA—The University of Florida reports that geologist George Kamenov has demonstrated that trace amounts of lead in human teeth can be used to figure out where people came from. The four isotopes that make up lead change according to the rocks, soil, and ores in each part of the world, and can be identified in teeth because tooth enamel, which develops during childhood, preserves the lead. “When you grow up, you record the signal of the local environment,” Kamenov explains. “If you move somewhere else, your isotope will be distinct from the local population.” Archaeologists can use the information from teeth to identify, for example, the presence of Europeans in the New World to trace human migrations.