Monday, August 27, 2012

Our Ancestors – A New Addition to the Family

 It has been estimated that approximately six million years ago, the ancestral lineage that would ultimately lead to human beings diverged from that which lead to our nearest relations – chimpanzees and apes.  The fossil evidence demonstrates that between two and three million years ago, our ancestors showed indications of human attributes.  These ancestors, Lucy being an excellent example, walked upright but possessed small brains and hands that were obviously designed for the climbing of trees.  Members of this group are collectively referred to as our australopithecine predecessors.

The discovery of the complete lineage to modern humans remains unfulfilled.  However, Doctor Lee Berger, a paleoanthropologist at the University of Witwatersrand in Johannesburg, South Africa, has recently made a discovery that may provide a significant piece in this puzzle.

Fossil fragments that have been dated to be some two million years old have been found in an old miner's pit at the so-called "Malapa site" northwest of Johannesburg.  These fragments include pelvis and leg bones, ribs and vertebrae, arm bones, clavicle and skull.  From these various pieces, the partial skeletons of an adult female and young male have been assembled. 

From these cumulative findings, it became apparent to Berger and his colleagues that an entirely new hominid species had been discovered.  It was called Homo sediba.  Although the fossil evidence demonstrates a relatively small brain – a skull enclosing a volume of 420 cubic centimeters that is about one-third of the size of the brain of modern humans, its pelvis is bowl shaped.  This was an unexpected discovery, since it was previously believed that this shaped pelvis evolved to accommodate a large brain.  In addition, the shape of the skull shows an expanded frontal region indicating the further development of the frontal lobes – an area of the brain associated with higher order intelligence.  Although sediba's arms were long, the fingers were short and straight probably adapted to the fashioning of tools.

This finding sheds new light upon the evolutionary progression to modern humans – Homo sapiens.  It may also suggest that Homo habilis and Australopithecus afarensis might be, in fact, side branches and not in the direct lineage.  As a result, yet another piece of the intriguing evolutionary process has been elucidated.

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