A 14,000-year-old thigh bone may upend human history. Unearthed in southwest China, this femur resembles those of an ancient species of humans thought to be long extinct by the Late Pleistocene, scientists say. The scientists compare the leg bone to ancient and modern human femurs in a paper published Thursday in the journal PLOS ONE, arguing that this specimen represents a population of ancient humans that lived surprisingly recently. If they're right, this could dramatically change the way we see human history. Today, our species, Homo sapiens, are the only humans to walk the Earth. But it hasn't always been...