Science is a collective effort; individuals around the world contribute their findings and debate their significance. In this way, science advances in fits and starts, with occasional reversals when new discoveries overwrite old understandings.
In no field is this more apparent than anthropology. A generation ago, human evolution was presented as a clear linear progression from archaic to modern species. Today, the picture of human evolution is understood to be much more complicated. With many hominid species coexisting at once, and many “dead-end” species falling into extinction throughout history, the family tree of human evolution is a matter of ongoing debate.