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First Human Ever Possibly Discovered in Ethiopia

Mar 04, 2015 04:09 PM EST

Scientists have possibly discovered the first human ever to walk the Earth, based on an ancient jaw fossil from Ethiopia dating back 2.8 million years ago, according to new research that also reveals the conditions under which the earliest humans evolved.

For years, scientists have been searching for signs of the earliest phases of the human family, during the shift from the more ape-like Australopithecus to more human Homo- species. Until now, the earliest known record of the genus Homo dates back between about 2.3 million and 2.4 million years ago.

Now, researchers have found fossil evidence at the Ledi-Geraru research site in the Afar region of Ethiopia that's between 2.8 and 2.75 million years old, pushing back the history of humans by about 400,000 years.

"There is a big gap in the fossil record between about 2.5 million and 3 million years ago - there's virtually nothing relating to the ancestors of Homo from that time period, in spite of a lot of people looking," study co-author Brian Villmoare, a paleoanthropologist at the University of Nevada, told Live Science. "Now we have a fossil of Homo from this time, the earliest evidence of Homo yet."

The fossil, known as LD 350-1, constitutes only a jaw bone with five teeth, and while this is enough to suggest that it is the first known human, Villmoare and his colleagues cannot say much about what this individual's body looked like.

By dating volcanic ash layers above and below the fossils, the researchers can determine how old the specimen is. That's because when volcanoes, erupt, the ash they spew out contains radioisotopes that undergo radioactive decay, allowing researchers to date back the layers of rock in which the fossils are found.

"We are confident in the age of LD 350-1," Erin N. DiMaggio from Penn State, lead author on one of the papers, said in a press release. "We used multiple dating methods including radiometric analysis of volcanic ash layers, and all show that the hominin fossil is 2.8 to 2.75 million years old."

What's more, the new fossil was unearthed near the Ethiopian site of Hadar, where Australopithecus afarensis was found - a species that includes "Lucy," a famous potential ancestor of the human family. While LD 350-1 only dates to about 200,000 years after Lucy, and possess features similar to that of Australopithecus, other characteristics such as its teeth and proportions of its jaw indicate that it indeed belongs to the genus Homo.

The research team has yet to determine whether this latest find is its own species or belongs to a known extinct human species.

The fossil does not just shed light on what may be the earliest of humans, but also on the environment in which they lived.

Other fossils found in this area of Ethiopia include those of prehistoric antelope, water dependent grazers, prehistoric elephants, a type of hippopotamus and crocodiles and fish. This suggests that the region was probably similar to African locations like the Serengeti Plains or the Kalahari - mostly a mix of grasslands and shrubs, with scatterings of trees near water.

According to previous research, global climate change intensified roughly 2.8 million years ago, resulting in African climate variability and aridity that triggered evolutionary changes in many mammal lines, potentially including the first members of the genus Homo.

"We can see the 2.8 million-year-old aridity signal in the Ledi-Geraru faunal community," said study co-author Kaye Reed of Arizona State University. "But it's still too soon to say that this means climate change is responsible for the origin of Homo. We need a larger sample of hominin fossils and that's why we continue to come to the Ledi-Geraru area to search."

The findings were published in two papers in the journal Science.

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