Missing Link Found?


New Fossils May Redraw Human History

Four apelike individuals with human features died when they fell into a 100 to 150 foot funnel-shaped shaft into a deep cave 1.977 million years ago in present day South Africa. Their bodies were swept away in an underground river and exquisitely preserved in a quiet pool of rapidly forming sedimentary rock.

Three years ago, 9-year-old Matthew Berger made a major archaeological discovery when he stumbled over a log while chasing his dog Tau through some tall grass in a hilly area north of Johannesburg called the Cradle of Humankind and discovered the fossilized remains of one of those individuals, a 4-foot-2 boy who was only a few years older than Matthew when he fell into the cave and died.

Matthew is not just any Berger. His father is Dr. Lee R. Berger, an American paleoanthropologist with the Institute for Human Evolution at the University of the Witwatersrand in Johannesburg. For the past twenty years, Dr. Berger has been searching for hominid bones in a nearby area of the the Cradle of Humankind.

The New York Times reported on April 8, 2010:

Dr. Berger said the path to the discovery began over the Christmas holidays in 2007 when he began using Google Earth to map caves in the Cradle of Humankind. On a recent visit to his office, he rotated Google Earth images of the dun landscape on his desktop, showing how he spotted the shadows and distortions of the earth that gave clues to the location of caves, often topped with wild olive and white stinkwood trees.

On Aug. 15, 2008, when Matthew called his father to look at the bones he had found, Dr. Berger began cursing wildly as he neared his son. The boy mistook his father’s profanity for anger. But from 15 feet, Dr. Berger, who had done his Ph.D. thesis on hominid shoulder bones, among them the clavicle, was astounded to see that his son had in his hands a clavicle with the unmistakable shape of a hominid.

“I couldn’t believe it,” Dr. Berger giddily recalled. “I took the rock, and I turned it” and “sticking out of the back of the rock was a mandible with a tooth, a canine, sticking out. And I almost died,” he said, adding, “What are the odds?”

Since Matthew’s discovery, Dr. Berger and his fellow researchers from the institute have discovered much more of the boy’s skeleton, including his extraordinarily well-preserved skull, and three other individuals, including a woman.

The New York Times article reported that the fossils from the boy and a woman are a surprising and distinctive mixture of primitive and advanced anatomy and thus qualify as a new species of hominid and have been named Australopithecus sediba.

The species sediba, which means fountain or wellspring in Sotho, strode upright on long legs, with human-shaped hips and pelvis, but still climbed through trees on apelike arms. It had the small teeth and more modern face of Homo, the genus that includes modern humans, but the relatively primitive feet and “tiny brain” of Australopithecus, Dr. Berger said.

In an update dated September 8, 2011 the New York Times reports:

The discoverer of the fossils, Lee Berger of the University of Witwatersrand in Johannesburg, says the new species, known as Australopithecus sediba, is the most plausible known ancestor of archaic and modern humans. Several other paleoanthropologists, while disagreeing with that interpretation, say the fossils are of great importance anyway, because they elucidate the mix-and-match process by which human evolution was shaped.

Dr. Berger’s claim, if accepted, would radically redraw the present version of the human family tree, placing the new fossils in the center. The new species, in his view, should dislodge Homo habilis, the famous tool-making fossil found by Louis and Mary Leakey, as the most likely bridge between the australopithecenes and the human lineage. Australopithecenes were apelike creatures that walked upright, like people, but had still not forsaken the trees.

Dr. Berger and his colleagues present this claim in five articles in the current issue of Science that describe various aspects of the new fossils. As is common in the field of paleoanthropology, the discoverer of a new fossil is seeking to place it as close as possible to the direct line of human descent, while others are resisting that interpretation.

In this particular case, there are many uncertainties regarding the fossil record from that time, including when the human lineage first emerged and how Homo habilis fits in the picture.

The principal significance of the new fossils is not that Australopithecus sediba is necessarily the direct ancestor of the human genus, other scientists said, but rather that the fossils emphasize the richness of evolutionary experimentation within the australopithecine group.

“This is really exciting new material,” said Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York. “I think it holds the possibility of flinging wide open the question of what Homo is.”

* * *

In the articles in Science, Dr. Berger’s team describes novel combinations of apelike and humanlike features in the hand, foot and pelvis of the new species. The hand, for instance, is apelike because it has long, strong fingers suitable for climbing trees, yet is also humanlike in having a long thumb that in combination with the fingers could have held tools in a precision grip. A cast of the inside of the skull shows an apelike brain, but one that had taken the first step toward being reorganized on human lines.

This mixture of apelike and humanlike features suggests that the new species was transitional between the australopithecines and humans, the researchers said at a news conference on Wednesday. Given its age, Australopithecus sediba is just old enough to be the ancestor of Homo erectus, the first species that paleoanthropologists agree belonged to the human ancestry and which existed 1.9 million years ago.

But the fossils are significant even if sediba is not a direct human ancestor. They are evidence that a ferment of evolutionary experimentation was going on at the time, out of which the human lineage somehow emerged. “If you take sediba as a metaphor for evolutionary change, it is a whole lot more powerful than the claim for direct ancestry,” Dr. Tattersall said.

Here is an exciting video of Dr, Berger describing the discovery.

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