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Stone Tools: Oldest Yet Discovered Challenge Early Human History

May 21, 2015 11:15 AM EDT

Stone tools recently discovered in the desert badlands of northwestern Kenya are the oldest yet discovered, dating back 3.3 million years, and now they are challenging our long-held notion of early human history.

That's at least according to new research published in the journal Nature, which details how these artifacts, which push the known date of such tools back by 700,000 years, may not have actually been created by one of our close human ancestors. Rather, this discovery provides the first evidence that an even earlier group of proto-humans may have been smart enough to bang two rocks together to create sharp-edged tools.

"The whole site's surprising, it just rewrites the book on a lot of things that we thought were true," co-author and geologist Chris Lepre, of the Lamont-Doherty Earth Observatory and Rutgers University, said in a statement.

The tools "shed light on an unexpected and previously unknown period of hominin behavior and can tell us a lot about cognitive development in our ancestors that we can't understand from fossils alone," added lead author Sonia Harmand.

Hominins are a group of species that includes modern humans (Homo sapiens) and our closest evolutionary ancestors. It has long been believed that our relatives in the genus Homo were the first to craft stone tools, but now it appears that other, earlier species of hominin - the equivalent of distant cousins - may have been the brains behind the operation.

Although the toolmakers' identity remains unknown, the researchers suspect the hominin Kenyanthropus platytops could be the culprit. Back in 1999, the skull of a 3.3-million-year-old K. platyops was found about a kilometer from the Kenyan tool site, along with a tooth and piece of skull bone only a few hundred meters away. (Scroll to read on...)

However, the family tree of modern humans is complex, and scientists have yet to figure out exactly how K. platyops relates to other hominin species. What they do know is that Kenyanthropus predates the earliest known Homo species by roughly half a million years, and could have made the tools. Also, another species from the same era, such as Australopithecus afarensis or an as-yet undiscovered early type of Homo, could be the toolmakers.

Regardless, the tools mark "a new beginning to the known archaeological record," the researchers wrote in their study.

So what were these stone tools used for anyhow?

While anthropologists thought human ancestors banged rocks together to make sharp-edged stones - better for cutting meat off animal carcasses - the size and markings of the newly discovered tools "suggest they were doing something different as well, especially if they were in a more wooded environment with access to various plant resources," said paper co-author Jason Lewis of the Turkana Basin Institute and Rutgers.

The researchers think the tools could have been used for breaking open nuts or tubers, bashing open dead logs to get at insects inside, or something else entirely.

"The capabilities of our ancestors and the environmental forces leading to early stone technology are a great scientific mystery," added Richard Potts, director of the Human Origins Program at the Smithsonian's National Museum of Natural History, who was not involved in the research. The newly dated tools "begin to lift the veil on that mystery, at an earlier time than expected," he said.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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