New Fossil Fits as 'Missing Link,' Scientists Argue

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"If you lay out all specimens of Australopithecus africanus on one side of a table and specimens for Homo erectus on the other side, Australopithecus sediba (shown here) serves as a nice morphological intermediate between those two," says Steven Churchill.
Brett Eloff courtesy of Lee Berger and the University of the Witwatersrand

THE GIST:

- Fossils for a new human ancestor suggest it's the transitional species that gave rise to humans.

- Remains previously attributed to the genus Homo may actually belong to australopithecines.

- A remnant of the new human ancestor's dried brain may exist, and could yield DNA.

A new human ancestor recently found in South Africa is poised to forever change the human family tree and what it means to be human, with some scientists arguing the 1.9-million-year-old species represents the so-called missing link between modern humans and ape-like beings.

At the same time, the news that the fossil contains remnants of brain matter poses the possibility of recovering DNA of an ancient ancestor, leading to unprecedented information about the early hominid and our own human lineage.

Scientists working on the project told Discovery News that they have discovered even more fossils at the same Malapa cave site. All of the hominid remains come from the new ancestor, Australopithecus sediba, which lived around 1.9 million years ago. Some scientists believe that it's the transitional species between more ape-like beings and our closer relatives in the genus Homo.

For more stories and interactives on the discovery of Australopithecus sediba and on human evolution, click here.

The discovery of "Sediba," which means wellspring, appears in the latest issue of the journal Science.

Co-author Steven Churchill and his colleagues now think it's likely that an even earlier, more ape-like human ancestor, Australopithecus africanus, gave rise to A. sediba, which they suspect evolved into Homo erectus.

"If you lay out all specimens of Australopithecus africanus on one side of a table and specimens for Homo erectus on the other side, Australopithecus sediba serves as a nice morphological intermediate between those two," Churchill, associate professor of evolutionary anthropology at Duke University, told Discovery News.

Project leader Lee Berger of the University of Witwatersrand added, "Sediba shows a strange mix of primitive australopithecine traits and derived Homo traits."

He explained that parts of its face, its long orangutan-like arms, and its feet and ankles are more primitive features, but its pelvis, lower limbs, and back teeth are more human.

Dissenting Views

Not everyone, however, believes A. sediba gave rise to humans.

Richard Potts, director of the Smithsonian's Human Origins Program, has pointed out that there is evidence for the genus Homo that predates A. sediba, such as an upper jawbone previously attributed to Homo habilis that dates to 2.3 million years ago.

Anthropologist Fred Grine of Stony Brook University echoed Potts' concerns.

Berger and his team, however, think that many fossils currently identified as being in the genus Homo are actually australopithecines. Churchill suggested that all fossils for Homo habilis and Homo rudolfensis might actually fall within the genus Australopithecus.

"Australopithecus sediba raises the bar on what it takes to determine if something is in the genus Homo," explained Berger, who added that many claims for early humans were just based on fragmentary evidence, such as a handful of jawbones that were dated based on surrounding fauna.

"If we only had the mandible for sediba, we would probably be calling it something else entirely, maybe Homo habilis," he said. "We learn from sediba that you need more than just one part of the anatomy, more than fragments, and that context is everything."

Intact DNA?

One sediba individual, a male juvenile who died at about the age of 13 after plunging down a cave, is so well preserved that high-powered X-rays recently suggested part of his brain might still exist. An extended low-density area was detected in the individual's skull where the brain is located.

"It is our colleague Paul Tafforeau, a specialist in imaging at the European Synchrotron Radiation Facility in Grenoble, France, who feels it is organic in shape and may be the remnant of the 'dried' brain," Berger said. "We shall wait and see."

The X-ray process also showed what could be fossilized eggs whose larvae may have fed on the flesh of the young male shortly after death. If the brain yields soft tissue, or if these insects or other matter is well enough preserved, there is a slim chance they could yield DNA that might unlock the genetic code for A. sediba.

If this happened, unprecedented details about an early hominid would shed light on its history and overall make-up. It could also open the door to bringing such an individual back to life through cloning, but that possibility is extremely remote and controversial.

"We are looking to see if any proteins are preserved in any possible organics at Malapa," Berger concluded. "Again, time will tell."