1.8-Million-Year-Old Skull Debunks Idea that Multiple Ancient Human Species Co-Existed on Earth

In a completely lucky and unexpected discovery, scientists have found a complete skull from a human ancestor believed to be 1.8 million years old, according to a press release.

Known as Skull 5, the skull is entirely intact and has a long face, large teeth and a small brain case. Its characteristics and condition make it different from other Homo genuses (habilis, rudolfensis, erectus, etc.) and also suggests those different human species did not roam the Earth at the same time nearly two million years ago.

The skull was found at a site in Dmanisi, Georgia, but the area is not fully excavated and already it has provided researchers with a rare study opportunity. Skull 5 was found along with four other human fossils, a variety of animal remains and some stone tools, all believed to be from the same timeframe.

Skull 5 has the features of an early human, but also changes a widely accepted perspective. Photo courtesy of Georgian National Museum.

David Lordkipanidze, of the Georgian National Museum in Tbilisi, Georgia, and colleagues in Switzerland, Israel and the United States, published their findings Friday in the journal Science.

"Had the braincase and the face of Skull 5 been found as separate fossils at different sites in Africa, they might have been attributed to different species," said co-author Christoph Zollikofer, of the Anthropological Institute and Museum in Zurich, Switzerland.

Skull 5's various physical traits can be linked to several Homo species, including some whose fossils found in Africa to date back 2.4 millions years ago and those found in Asia and Europe 1.2 to 1.8 millions years ago.

"[The Dmanisi finds] look quite different from one another, so it's tempting to publish them as different species," said Zollikofer. "Yet we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species."

The traits of the Dmanisi finds support what has already been accepted in human evolutionary studies. The small brain case, the large teeth, but what is special about Skull 5 is that it changes the perspective of a long-accepted theory about early humans.

"Furthermore, since we see a similar pattern and range of variation in the African fossil record... it is sensible to assume that there was a single Homo species at that time in Africa," Zollikofer said. "And since the Dmanisi hominids are so similar to the African ones, we further assume that they both represent the same species."