November 29, 2011 | 9
In the spring of 2010, the world met Australopithecus sediba, a nearly two-million-year-old human relative whose remains were found at a site just a short drive from Johannesburg, South Africa. By all accounts, it was an extraordinary discovery: two beautifully preserved partial skeletons–a juvenile male and an adult female–with the promise of more individuals to come. The fossils exhibit a striking mix of traits combining features of the primitive australopithecines (Lucy’s ilk), such as a small brain, with features associated with our own genus, Homo—small teeth, for instance. The anatomical mash-up led the discovery team to place them in a new species and to propose that it could be the ancestor of Homo. Spirited debate ensued.
Fast forward to this past September, when the team published a second round of papers on the fossils, this time delving deeper into details of A. sediba’s anatomy. The mosaic theme continued. In that tiny brain, for example, the researchers spotted signs of a more Homo-like reorganization of gray matter; in its hand they observed gracile digits (an australopithecine-like trait) paired with a long thumb that would have enabled a humanlike precision grip; in its foot they found an apelike heel bone accompanying a humanlike ankle bone. The list goes on and on.
The A. sediba fossils cut to the very heart of a burning question about human evolution: namely, where did Homo come from? Paleoanthropologists have lots of australopithecine fossils, and a wealth of later Homo fossils. But they have precious few clues about the origin of our genus. Could A. sediba be our long-lost ancestor? If discoverer Lee Berger of the University of the Witwatersrand and his team are right, their fossils could topple some cherished ideas about how we became human.
I’ve come to Johannesburg to get a better handle on this incredibly exciting and complex story. I’ve been visiting with Berger and his colleagues at the University of the Witwatersrand to learn about the A. sediba fossils and how the team is teasing information out of them. I’ll be hanging out with the researchers all week, checking out the fossils, interviewing team members, and visiting the discovery site (where more fossils are waiting to be unearthed). And I’ll be posting updates here in the Scientific American Observations blog. So please follow along and ask any questions in the comments section below. I’ll do my best to get you answers—and your feedback will help me write a feature article on this game-changing discovery.