A newly discovered 1.8 million-year-old skull offers evidence that humanity's early ancestors emerged from Africa as a single adventurous species, not several species as believed, drastically simplifying human evolution, an international research team said Thursday.



A newly discovered 1.8 million-year-old skull offers evidence that humanity's early ancestors emerged from Africa as a single adventurous species, not several, as believed. Robert Lee Hotz reports on the News Hub. Photo: Georgian National Museum.

The skull—the most complete of its kind ever discovered—is "a really extraordinary find," said paleoanthropologist Marcia Ponce de Leon at the University of Zurich's Anthropological Institute and Museum, who helped analyze it. "It is in a perfectly preserved state."

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A 1.8-million-year-old hominid skull -- the most complete of its kind ever found – was unearthed at Dmanisi in Georgia. Georgian National Museum

Unearthed at Dmanisi in Georgia—an ancient route in the Caucasus for the first human migrations out of Africa—the skull was found at a spot where partial fossils of four other similar individuals and a scattering of crude stone tools had been found several years ago. They all date from a time when the area was a humid forest where saber-tooth tigers and giant cheetahs prowled. Preserved in siltstone beneath the hilltop ruins of a medieval fortress, the remains are the earliest known human fossils outside Africa, experts said.

David Lordkipanidze, director of the Georgian National Museum, who led the team, reported the discovery in Science. The primitive skull was first uncovered on Aug. 5, 2005—his birthday. "It was a very nice present," he said.

Taken together, the finds at Dmanisi are especially important because experts in evolution could analyze the physical differences between individuals living in the same place at the same time almost 2 million years ago, when humankind first emerged from Africa to people the world, according to Yale University anthropologist Andrew Hill.

"It gives you a chance to look at variation for the first time," said Dr. Hill, who was not involved in the discovery.

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By comparing these five extinct creatures at Dmanisi to each other, and to other specimens from the same era in Africa, the researchers concluded that all of the primordial peoples of the Homo genus—the root-stock of the modern human family tree—likely belonged to just one species spreading out across the continents, not three or more as many experts have argued.



Their conclusion breaks with recent practice in the scholarly search for human origins. Typically, researchers have highlighted the differences between various human fossils—often assigning each new discovery to a separate species—and not grouping them by physical traits they had in common.

In this analysis, researchers concluded that the fossil remains most likely belonged to a tool-using species called Homo erectus, which existed from about 2 million years ago to about 143,000 years ago. Its fossilized remains have been found in Africa, Spain, Indonesia, India, China and Java.

"They nailed it," said paleoanthropologist Tim D. White at the University of California at Berkeley, who was not involved in the project. "This will cut a lot of dead wood that has accumulated in the family tree that paleontologists love to draw."

Known simply as Skull #5, the fossilized head bones likely belonged to a male, whose brain was about one-third the size of a modern human brain. The skull has a "strange combination of features," Dr. Ponce de Leon said. The face was relatively flat and long, with massive brows, a projecting jaw and big teeth.

The creature had a healed cheek fracture, a touch of arthritis and, by the evidence of wear, used his teeth for gripping things. He stood upright, with relatively modern arms and legs, the researchers said.

The other four fossilized individuals unearthed earlier at Dmanisi included skull fragments belonging to an elderly toothless male, a young female, a second adult male and an adolescent whose gender wasn't known.

Using Skull #5 as a benchmark, the researchers compared the five specimens. They examined the variations in skull bones, jaws and teeth traditionally used to sort such fossils into different species.

Through a computer analysis, the researchers determined that the variations among these five early humans were no greater than the differences normally found between members of any single primate species, including chimpanzees, bonobos or modern humankind.

If their analysis proves true, experts will have to reconsider the pattern of early human evolution.

"There are these jaw-dropping moments in the life of a scientist," said neurobiologist Christoph Zollikofer at the University of Zurich, who analyzed the skull and the other Dmanisi fossils. "You can feel in your brain how all these preconceived ideas you had start falling to pieces."

Write to Robert Lee Hotz at sciencejournal@wsj.com

istahil: I thought this was scientific fact. Didn't know people were arguing about this.