A troublesome thigh bone might trip up the timeline of human evolution. According to research published recently in PLOS ONE, a femur found in Southwest China could mean that a species of early human — one from a lineage other than the one that resulted in humans alive today — survived as recently as 14,000 years ago.

"Our work shows that the thigh bone strongly resembles very ancient species like early Homo erectus or Homo habilis, which lived about 1.5 million years ago or more in Africa," study author  of the University of New South Wales wrote in an article for the Conversation

Curnoe admits in his commentary that a single bone does not a mysterious lineage of pre-modern humans make. But this single femur is part of a growing body of evidence: In 2012, Curnoe and his colleagues reported on unusual skulls from the same fossil site. The residents of the area, dubbed the Red Deer Cave people by the researchers, seemed to have lived in the ballpark of 10,000 years ago, but had skulls and teeth that seemed unusually archaic. The researchers suspected they might be some long-lasting lineage of early human (or a hybrid between modern humans and an older group) but they didn't have enough evidence to really make the suspicion stick.

The owner of the newly analyzed femur would have weighed just about 110 pounds, but we don't know much else about the strange men and women that might have shared stomping grounds with our own ancestors. If the dating of these bones is accurate, there are a lot of questions to be answered. For starters, how did a smaller, more primitive species survive so long in the age of modern man? Even Neanderthals, a group now known to have co-existed and bred with humans quite successfully, disappeared into our own gene pool some 40,000 years ago.

Scientists are pretty sure that at least one small, archaic human existed in recent history: Homo floresiensis may have lived as recently as 17,000 years ago, and has been aptly nicknamed "Hobbit." But these small-brained, small-bodied humans survived for obvious reasons — they were isolated on an Indonesian island. Curnoe and his colleagues argue that the region of China where the recent femur and skulls were found might have been isolated enough to give this unknown species similar protection against extinction.

The new study is far from conclusive, and scientists will have to find a whole bunch of relevant bones before this strange species — whatever it is — makes it on the books. But whether or not the Red Deer Cave people ever emerge as a uniquely resilient species of man, it's becoming more and more obvious that our ancestors weren't the only humans on the scene.

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