The complete skull of a big-toothed, small-brained male found at the crossroads of Western Asia and Eastern Europe may erase an entire collection of named, early hominid species by showing they were all, in fact, variations of a single species.

The skull, dated to nearly 1.8 million years ago, is the earliest known human-like species outside of Africa ever found, according to a study published in the latest issue of Science.

It belonged to an adult male of the species Homo erectus, a.k.a. "Upright Man" and is called "Skull 5" because it was the fifth set of hominid remains recovered at the archeological site, Dmanisi, located in the Caucausus of the Republic of Georgia.

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"All the Dmanisi individuals are around 1.77 million years old," co-author Christoph Zollikofer from the Anthropological Institute and Museum in Zurich, Switzerland, told Discovery News. "What is very special about Dmanisi Skull 5 is that it is the only known completely preserved and undeformed skull of an adult individual from these remote times."

Tim White, a professor of Integrative Biology at the University of California at Berkeley, told Discovery that these early members of our genus were fairly short in stature with large, projecting faces, big teeth and small brains. The latter confirms that big brains weren't needed to get humans out of Africa.

"They walked on two legs, and if you could look in on them, you might see them using primitive tech- stone tools- to remove meat and marrow from animal bones," said White. "You might also see them being killed and hauled off by a carnivore." (All five were found in underground dens where carnivores appear to have dragged their carcasses.)

Zollikofer, lead author David Lordkipanidze from the Georgian National Museum, and colleagues noted that the remains for the five Dmanisi individuals were very different. They attribute that to just normal variation within a single population. Moreover, they extended their comparisons to other documented Homo genus species and concluded that the variation was again reasonable for a single species.

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They propose that Homo habilis, Homo rudolfensis, Homo ergaster and other early hominids from the same time were all misnamed and were really just members of the species Homo erectus. This bold theory would nearly wipe clean many early hominids.

Discovery News contacted multiple experts in early human history for their views, and received an earful of passionate, mixed opinions.

White and Dean Falk, an anthropologist at Florida State University, support the paper's conclusions. As Falk said, "I see no reason not to accept the authors' claim that the specimens all belong to one highly variable and highly sexually dimorphic species."

He further thinks that, although the Dmanisi individuals' brains were small, they were still in the process of slowly evolving into larger brains. That is significant, as some earlier studies have proposed that brain size suddenly took off around 2 million years ago.

"Skull 5" -- the world's first completely preserved adult hominid skull -- seen in situ.Photo courtesy of Georgian National Museum

Caley Orr, an assistant professor in the Department of Anatomy at Midwestern University, and Eric Delson, a paleoanthropologist at Lehman College/CUNY and the American Museum of Natural History, both think that the new theory erasing the other Homo species is intriguing, but believe that more specimens and additional research are needed to fully validate it.

Darren Curnoe, an associate professor in the School of Biological, Earth & Environmental Sciences at the University of New South Wales; Chris Stringer of the Natural History Museum, London; and Ian Tattersall of the American Museum of Natural History support the broader significance of the Dmanisi fossils, but doubt that all of the early Homo fossils can reasonably be lumped into an evolving Homo erectus lineage.

Tattersall said, "Paleoanthropologists are having a hard time letting go of the old idea that human evolution was a linear process, but fossils like this one from Dmanisi are making it ever clearer that hominid history has been one of diversity and evolutionary experimentation with the hominid potential."

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Clive Gamble, professor of archaeology at the University of Southampton, pointed out another intriguing possibility -- that the early human homeland wasn't just in Africa or Asia, but instead encompassed both regions and possibly more.

"Rather than seeing the Dmanisi skulls as the first excursion of the earliest Homo outside Africa, what they suggest is that the homeland of small-brained Homo was always bigger than Africa," Gamble told Discovery News.

"…The time has come for paleoanthropologists to broaden their idea of what evolutionary landscapes looked like almost 2 million years ago. To call them Africa or Asia and draw arrows between them misses the significance of Dmanisi for understanding our earliest evolution."