Weekend Feature: Has the Long-Sought Link to Modern Humans Been Found?

  Cranium-australopithecus-sediba_custom

Scientists say a pair of fossils from a South African cave— an adult female and a juvenile — which display a small brain, but a brain that's beginning to reorganize in some ways that resemble our brain–could be the long-sought transition between ape-like ancestors and the first humans.


It's surmised that Australopithecus sediba still used his hands for climbing in trees, but it was likely also capable of making the precision grips believed necessary to make stone tools, according to Tracy Kivell, paleoanthropologist, with the Max Planck Institute

The "mix-and-match" anatomy, with traits of both primitive and modern animals,make the
South African fossils, dated at 1.9 million years ago is  "probably the best candidate ancestor for giving rise to our immediate ancestor."

According tp Berger, just before the earliest humans appeared, Africa was thick with all sorts of ape-but-not-ape creatures. The evolution of big-brained, walking, tool-making primates was like a river splitting into numerous streams.

Berger says his two sediba fossils look like a real transition between Lucy's "people" and something pretty human-like. "It shows a small brain," he says, "but a brain that's beginning to reorganize in some ways that resemble our brain. You have things like a heel bone that's as primitive as a chimpanzee, attached to the ankle bone that's as evolved as ours is."

Sediba's hand is unusually complete and also shows a "mix-and-match" anatomy. "Sediba likely still used his hands for climbing in trees, but it was likely also capable of making the precision grips that we believe are necessary to make stone tools," says Tracy Kivell of the Max Planck Institute in Germany and a member of Berger's team.

Berger assembled a team of experts to examine these fossils and allowed many others to look at them. One reason is that proving you've found the "last ancestor before humans" requires extraordinay evidence.

Because there are fossils with human-like traits that are older than Berger's, doubters say sediba could have been one of many evolutionary experiments at the time, one that may have just died out.

Direct ancestor or not, the weird jumble of primitive and modern traits in sediba could rewrite textbooks. Connected features, like the arm and the hand, are thought to evolve together. But sediba had an ape's arm and a more human-like hand.

The Daily Galaxy via Science.com

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