Fossils help chart human evolution

LOS ANGELES – After examining the fossils of two hominids that lived nearly 2 million years ago, anthropologists said the anatomical features of the adult female and young male strongly suggest they could be members of a species that was a direct ancestor of modern humans.

In a series of reports being published in today’s edition of the journal Science, the researchers describe the Australopithecus sediba specimens as having a curious mix of primitive and modern features that could prompt experts to redraw the human family tree.

For instance, they had hands capable of using tools but still strong enough to grasp tree branches. They had a more curved pelvis that would have theoretically accommodated a bigger brain on its way through the birth canal, even though they still had small heads.

Perhaps the mosaic of features indicates that A. sediba was at an evolutionary transition point between the tree-climbing australopithecines and upright-walking, often tool-using members of the genus Homo, which includes Homo sapiens, the single surviving member species.

The fossil remains were discovered in 2008 by Lee Berger’s then-9-year-old son, who had accompanied him to a dig site in South Africa.

Paleoanthropologists soon found the rest of the remains, and surmised that the two must have fallen down a hole into a cave and died there.

A. sediba was soon recognized as a new species and classified with the australopithecines. (The most famous member of this group is Australopithecus afarensis, better known as Lucy, who lived 3 million years ago.) But the new studies indicate that A. sediba had begun to develop more humanlike qualities.

The age of the fossils presents a problem. The researchers’ isotopic and magnetic dating showed the fossils were 1.977 million years old, about 300,000 years younger than a Homo habilis fossil that should have been their junior.

The suggestion that A. sediba is the most recent common ancestor of all Homo species has been met with careful skepticism at best and acrimony at worst by scientists who were not part of the research. Among other concerns are the way the team raised questions about the Homo habilis in order to support their theory.

“They’re going to have to make a stronger case,” said paleoanthropologist Donald Johanson of Arizona State University, who discovered Lucy.