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Friday, September 16, 2011

Direct ancestor of genus Homo

The two million year old Australopithecus sediba has been extensively studied since its discovery in 2008.  Now a team of anthropologists at the University of Witwatersrand and colleagues from around the world have made the case that A. sediba is our direct ancestor.

Five separate papers analyze different aspects of A. sediba’s physiology and behavior. Here are some of the highlights.

Hands:  In A. sediba, anthropologists found the most complete hominin hand to date.  It retains the strong grasping muscles essential for climbing trees, but has relatively short fingers and a long thumb like humans.  The researchers speculate that it would have been capable of making and using tools.

Australopithecus sediba has a relatively long thumb. The hand suggests that he may have had the capacity to manufacture and use complex tools.
Credit: University of Zurich; Peter Schmid.

BrainA. sediba’s brain was only about the size of a chimpanzee’s brain, but was organized in a similar fashion to that of modern humans.

Pelvis:  The pelvis plays a critical role in the hominin lifestyle and physiology.  Not only does the pelvis determine the stance (bipedal or horizontal), but it also limits the brain size of newborn infants.  A. sediba had a pelvis that was broader and more vertically oriented that earlier Australopiths.  As A. sediba did not have large brains, the change was clearly not driven by increased brain size.

Foot:  The A. sediba foot and ankle was a mix of ape and human-like features, indicating that it spent time in the trees, but could also walk bipedally.

You can read more about these discoveries at The Loom.