"Missing Link" Human Skull Found in Africa, Scientists Say

Stefan Lovgren
for National Geographic News

March 27, 2006

ALSO SEE: "MISSING LINK" FOUND: New Fossil Links Humans, Lemurs? (May 19, 2009)

Scientists working in Africa have discovered a Stone Age skull that could be a link between the extinct Homo erectus species and modern humans (interactive guide to human evolution from National Geographic magazine).

The face and cranium of the fossil have features found in both early and modern human species. The skull is believed to be between 250,000 and 500,000 years old.

"[This skull] shows the continuity of the evolutionary record, so in that sense it is a link [between Homo erectus and modern humans]," said Scott Simpson, a paleontologist from Case Western Reserve University School of Medicine in Cleveland, Ohio.

(Related: National Geographic-funded study of human "missing links.")

Rare Find

Researchers discovered the skull five weeks ago at Gawis in Ethiopia's northeastern Afar region (map of Ethiopia). The area is rich in fossil and archaeological deposits ranging from 10,000 years to 5.6 million years in age.

An international group known as the Gona Paleoanthropological Research Project began field research in the area in 1999.

Asahmed Humet, a local Afar tribesman working with project, found the early-human cranium in a small gully at the base of a steep slope of sediments.

The skull was missing a lower jaw but had a nearly intact cranium. Most early human fossils are found in many small pieces.

The scientists believe the skull comes from the middle Pleistocene era, about 600,000 to 200,000 years ago.

Homo erectus is thought to be an ancestor of modern Homo sapiens. H. erectus first appeared in Africa and lived from about 1.9 to 0.8 million years ago. (See photos and more from a recent H. erectus discovery in the republic of Georgia.)

The face and cranium of the fossil have characteristics similar to those of an early-human species, such as Homo erectus. But there is anatomical evidence that the fossil is part of modern humans' ancestry. Simpson says, for example, that the shape of the skull's dome, or vault, is similar to that of modern humans.

"If you look at Homo erectus, their vaults tend to be low, long, and angular," Simpson said. "This vault is very spherical, like modern humans'."

(Related: Make "missing links" morph with the National Geographic Channel's interactive on extreme evolution.)

Lightly Built

The African fossil record from the Gawis skull's time period is sparse, and most of the specimens are poorly dated, scientists said.

"The evolutionary period between Homo erectus and Homo sapiens is confused," said Andrew Hill, curator of anthropology at Yale University's Peabody Museum of Natural History in New Haven, Connecticut.

"The Gawis cranium is almost certain to provide very useful information."

Between 0.8 million years ago, when Homo erectus went extinct, and about 200,000 years ago, one or more species existed in Africa that gave rise to the earliest members of Homo sapiens, our own species.

"There are at least one to three species of Homo recognized within that time period. But we don't know exactly what the relationship is of any of those to modern humans," said Eric Delson, a paleoanthropologist at Lehman College of the City University of New York. Delson was not involved in the discovery.

"This specimen doesn't seem to show any specific features like modern humans', but it's much more lightly built than Homo erectus," Delson added.

Simpson, the project paleontologist, says the anatomical change seen in the Gawis skull represents humanity's transition to anatomical modernity in Africa.

"We're on the cusp of this middle Stone Age archaeological transition … where people are beginning to have a better handle on how to create more delicate tools … and human anatomy is reflecting this with the brain being reorganized like modern humans'," he said.

"We are not modern humans yet—we really don't see that coming on until 200,000 years ago—but we're certainly on the way to making it," Simpson added.