In the 1940s a Harvard paleontologist named Hallum Movius drew something called the Movius line, dividing the side with Acheulean tools from the one without. The line runs in a southeasterly direction across Europe and the Middle East to the vicinity of modern-day Calcutta and Bangladesh. Beyond the Movius line, across the whole of southeast Asia and into China, only the older, simpler Oldowan tools have been found. We know that Homo sapiens went far beyond this point, so why would they carry an advanced and treasured stone technology to the edge of the Far East and then just abandon it?

"That troubled me for a long time," recalls Alan Thorne of the Australian National University in Canberra. "The whole of modern anthropology was built round the idea that humans came out of Africa in two waves——a first wave of Homo erectus, which became Java Man and Peking Man and the like, and a later, more advanced wave of Homo sapiens, which displaced the first lot. Yet to accept that you must believe thatHomo sapiens got so far with their more modern technology and then, for whatever reason, gave it up. It was all very puzzling, to say the least."