By Ann Gibbons
NEW ORLEANS, LOUISIANA—A remarkably complete skeleton introduced in 2010 as “the best candidate” for the immediate ancestor of our genus Homo may just be a pretender. Instead of belonging to the human lineage, the new species of Australopithecus sediba is more closely related to other hominins from South Africa that are on a side branch of the human family tree, according to a new analysis of the fossil presented here last week at the annual meeting of the American Association of Physical Anthropologists.
When fossils from several individuals’ skeletons were found in a collapsed cave in Malapa, South Africa, in 2008, their discoverer, paleoanthropologist Lee Berger of the University of the Witwatersrand, noted that they helped fill a key gap in the fossil record 2 million to 3 million years ago when some upright-walking australopithecine evolved into the earliest member of our genus, Homo. But the oldest Homo fossils, at 2.4 million to 2.9 million years, are scrappy, and a half dozen more primitive hominins may have been walking around Africa at roughly the right time to be the ancestor. Researchers have hotly debated whether their direct ancestor was the famous 3.2-million-year-old fossil Lucy and her kind, Australopithecus afarensis from Ethiopia, or another australopithecine.
With its fossils dated to 1.98 million years ago, Au. sediba is too young to be directly ancestral to all members of the genus Homo. But Berger and his colleagues proposed in 2010, and again in 2013 in six papers in Science, that given the many humanlike traits in Au. sediba’s face, teeth, and body, the Malapa fossils were a better candidate than Lucy or other East African fossils to be ancestral to Homo erectus, a direct human ancestor that appeared 1.8 million years ago.
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