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Interpretation of fossil finds and what they imply about human evolution often mean different things to different scientists. To many, evidence shows that the sequence of species in the Homo genus followed a linear route, from Homo habilis to Homo erectus and eventually to Homo sapiens. To other scientists, the Homo fossil record points to a bushy, branching tree rather than a single stem. Two new finds from the rich deposits around Koobi Fora ridge in Kenya’s Lake Turkana basin add more conclusive evidence that our ancestral tree branched with species that often occupied the same time periods and the same regions. Some species evolved on their own paths and died out, leaving no ancestors, while others eventually developed into new forms.

The discovery team, which was led by University College London anthropologist Fred Spoor and Meave Leakey of the National Museums of Kenya, has identified the fossils—a jaw and a skullcap—as belonging to Homo habilis and Homo erectus, respectively. The fossils date to similar time periods, supporting the notion that multiple species coexisted in this lake basin, and that they did so for almost half a million years. This Human Bulletin places these fossils in context with other Homo species and the ancestral path to humans.