Ethiopian jawbone fossil pushes back human origins

A 2.8-million-year-old jawbone fossil with five intact teeth unearthed in an Ethiopian desert is pushing back the dawn of humanity by about half a million years.

Scientists said Wednesday the fossil represents the oldest known representative of the human genus Homo and appears to be a previously unknown species whose evolution may have been triggered by climate change.

Our species, Homo sapiens, appeared only 200,000 years ago, following a procession of others in the same genus. Until now, the oldest known remains from the human genus were about 2.3 to 2.4 million years old and from the species Homo habilis.

"Although it is probably a new species, we are awaiting more material before definitively naming a new species," said University of Nevada, Las Vegas anthropologist Brian Villmoare, who helped lead the research published in the journal Science.

The jawbone was found in 2013 in northeastern Ethiopia's Afar region about 40 miles from where the remains of "Lucy," one of the most famous fossils of a human ancestor, were discovered in 1974. Lucy's species, Australopithecus afarensis, immediately preceded the Homo genus.

The anatomy of the new fossil, encompassing the left side of the lower jaw, suggests a close relationship with later Homo species. It boasted features including tooth shape and jaw proportions that separate early Homo lineage species from the more apelike Australopithecus. 

"At 2.8 million years ago, this places the evolution of our genus very close to 3.0 million years ago, which is when we last see Lucy's species," Villmoare said.

The Homo genus developed larger brains and tool use and began eating meat after especially after 2 million years ago.

In another paper published in Nature, members of Villmoare's team suggested that climate change intensified in the area around 2.8 million years ago — transforming forests in the Afar region into more arid grasslands. 

The landscape where the individual belonging to the jawbone lived probably was more of an open habitat of mixed grasslands and shrub lands with trees lining rivers and wetlands, a Penn State press release said.

Researchers said that climate shift could have spurred evolutionary changes in many mammal lines — including one that resulted in the origin of the Homo genus. 

"There are two ways to handle that: one is to go extinct, the other is to make some sort of evolutionary adaptation," Villmoare said in a Nature press release, adding that the Homo sapiens' ancestors turned to hunting game which led to their developing larger brains and more agile bodies.

The two papers confirm significant variation among 'early Homo' species, and reveals how little scientists know about its origins.

"The question on everybody's mind is what happened at this transition to the origin of early Homo and in early Homo," Daniel Lieberman, a palaeoanthropologist at Harvard University in Cambridge, Massachusetts, said in the Nature release.

"We just don't understand what's going on."

Al Jazeera and wire services