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How a fossil discovery could simplify humankind's family tree

A skull unearthed in the Republic of Georgia suggests that human fossils from about 2 million years ago could all belong to a single species and not multiple lineages as earlier research has indicated.

By Charles Q. ChoiLivescience.com Contributor / October 18, 2013

The 1.8-million-year-old skull unearthed in Dmanisi, Georgia, suggests the earliest members of the Homo genus belonged to the same species, say scientists in a paper published Oct. 18, 2013 in the journal Science.

Photo courtesy of Georgian National Museum

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The earliest, now-extinct human lineages, once thought to be multiple species, may actually have been one species, researchers now controversially suggest.

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Modern humans, Homo sapiens, are the only living member of the human lineage, Homo, which is thought to have arisen in Africa about 2 million years ago at the beginning of the ice age, also referred to as the Pleistocene Epoch. Many extinct human species were thought to once roam the Earth, such as Homo habilis, suspected to be among the first stone-tool makers; the relatively larger-brained Homo rudolfensis; the relatively slender Homo ergaster; and Homo erectus, the first to regularly keep tools it made.

To learn more about the roots of the human family tree, scientists investigated a completely intact, approximately 1.8-million-year-old skull excavated from the medieval hilltop town of Dmanisi in the Republic of Georgia. Archaeological excavations there about 30 years ago unexpectedly revealed that Dmanisi is one of the oldest-known sites for ancient human species out of Africa and the most complete collection of Homo erectus skulls and jaws found so far. The world's largest, extinct cheetah species once lived in the area, and scientists cannot rule out whether it fed on these early humans.

This fossil, the most massively built skull ever found at Dmanisi, is the best-preserved fossil of an early human species discovered yet. It probably belonged to a male, and its right cheekbone has signs that it healed from a fracture. [See Photos of the Dmanisi Skull & Excavation Site]

"We can only guess how the fracture was inflicted on the individual — it could be that it had an argument with another member of the group it lived in, or it could be that it fell down," study co-author Christoph Zollikofer, a neurobiologist at the Anthropological Institute and Museum in Zurich, Switzerland, told LiveScience.

Unique skull

This new skull, called Skull 5, was discovered alongside the remains of four other skulls of ancient humans, all of them associated with the same location and period of time, which back 1.8 million years ago was a relatively temperate mix of forest and steppe near a river. The fossil is unlike any other Homo remains on record — it combines a long face, massive jaw and large teeth with a small braincase, just about a third the size of that found in modern humans and no larger than those of much more primitive African fossils and even modern gorillas. Scientists hadn't observed such a combination of features in an early Homo fossil until now. [In Photos: Fossils Reveal Our Closest Human Ancestor]

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