Photo by Kate Wong
See the notches at the top of these two casts of ancient hominid mandibles? If you were a paleoanthropologist, you would spend your days arguing about the shape of those notches and their deeper possible meanings.
In 2010, the scientists who found these jaw bones decided that the bones represented a previously unknown hominid species — Australopithecus sediba — whose characteristics blend those of our genus, Homo, with those of a much older genus, Australopithecus.
BUT, now, writes Kate Wong, other scientists think they're wrong, arguing that the two bones don't even come from the same species. Instead, the top mandible in this picture could be straight up Homo, and the bottom classic Australopithecus, and the whole debate — which has implications for how we draw our human family tree — hinges on the shape of that, well, hinge.