By taking a wrong turn in a dry riverbed in Kenya, scientists discovered a trove of stone tools far older than any ever found before. Nobody knows who made them – or why. At 3.3 million years old, they push back the record of stone tools by about 700,000 years. More significantly, they are half-a-million years older than any known trace of our own branch of the evolutionary tree. Scientists have long thought that sharp-edged stone tools were made only by members of our branch, whose members are designated “Homo,” like our own species, Homo sapiens. That idea has been questioned, and the new finding is a big boost to the argument that tool-making may have begun with smaller-brained forerunners instead.