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Saturday, December 19, 2009

Ardi is named Breakthrough of the Year

The discovery of Ardipithecus ramidus, or "Ardi," was named ‘Breakthrough of the Year’ by Science and by its publisher, the American Association for the Advancement of Science (AAAS), the world's largest science society.  The announcement was made in the Dec. 18th issue.

Although Ardi was discovered and named in the early 90’s, it took over a decade of research before it was unveiled to the public. Why the long delay?  Ardi changed many previously held notions about human evolution.  The scientists wanted to be sure of their data before going public.  They now have a reasonably complete picture of where and how Ardi lived.
Ardi was a hominid who lived 4.4 million years ago.  In comparison, we diverged from chimpanzees about 6 million years ago, and Lucy (Australopithecus afarensis) appeared on the scene 3.2 million years ago.  So Ardi is on our branch of the family tree, but not on the chimp branch.
It had been assumed that hominids came down from the trees first, moved onto the savannah, and then began to walk erect.  However, Ardi clearly walked upright, based on skeletal features such as its pelvis and limbs, yet it had chimp-like grasping feet.  This new data suggests that our hominid ancestors began to walk upright on tree branches, rather than on the ground. The analysis of fossils found near Ardi confirms that it lived in woodland areas, not savannah.
If not to negotiate the newly conquered savannah, why did upright walking evolve?  The new theory is that males had to have their arms free to bring presents to females.  Unlike the other great apes, but like modern humans, male and female Ardipithecus ramidus did not differ greatly in size.  Males probably did not fight each other for control of mates, but instead may have wooed them with food gifts, an enterprise made much easier if you have your hands free.
The study of human evolution is a particular favorite of mine.  I think Science made an excellent choice.

Ardipithecus ramidus specimen, uploaded by FunkMonk, Nov. 14, 2009.