Mouthful of clues
Did a shift in the way infants were weaned give early humans an evolutionary advantage over their Neanderthal cousins? Scientists have long speculated that a change to earlier weaning played a key role in human development, but they have been stymied in efforts to prove such theories by the lack of an accurate record for comparing weaning ages in both species. Now, Harvard scientists say they’ve discovered such a record, and that it was right in front of researchers all along — in teeth. Tanya Smith, an associate professor of human evolutionary biology, and Katie Hinde, an assistant professor of human evolutionary biology, worked with colleagues at the Icahn School of Medicine at Mount Sinai in New York and Westmead Hospital in Australia to demonstrate that the levels of barium in teeth correspond with increases in breast-feeding, and fall as infants are weaned. Importantly, the researchers say, the barium levels survive in...