Scientists Push Back Veil of Human History By a Million Years

ADDIS ABABA, Ethiopia, August 13, 2010 (ENS) – The first use of stone tools and consumption of meat by human ancestors occurred almost one million years earlier than previously known, an international team of researchers announced Thursday.

Working in Dikika, Ethiopia, the scientists have discovered bones that show human ancestors were using stone tools and consuming the meat and marrow of large mammals roughly 3.4 million years ago.

Dr. Zeresenay Alemseged of the California Academy of Sciences in San Francisco, California and Dr. Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany say their discovery provides the first evidence that these behaviors can be attributed to Lucy’s species – Australopithecus afarensis.

“This discovery dramatically shifts the known time frame of a game-changing behavior for our ancestors,” says Alemseged. “Tool use fundamentally altered the way our earliest ancestors interacted with nature, allowing them to eat new types of food and exploit new territories. It also led to tool making – the precursor to such advanced technologies as aeroplanes, MRI machines, and iPhones.”

On both the bones found in Dikika, Ethiopia, unambiguous evidence of stone tool use in the form of cut marks and percussion marks were found. (Photo courtesy Dikika Research Project)

Although the butchered bones may not look like noteworthy fossils to the lay person, Alemseged describes them with excitement. “This find will definitely force us to revise our text books on human evolution, since it pushes the evidence for tool use and meat eating in our family back by nearly a million years,” he explains. “These developments had a huge impact on the story of humanity.”

The study conducted by the Dikika Research Project is reported in the August 12 issue of the journal “Nature.”

The Dikika Research Project was founded in 1999 by Alemseged, an Ethiopian paleoanthropologist who chairs the Anthropology Department at the California Academy of Sciences.

While working in the Afar region of Ethiopia, the Dikika Research Project scientists found bones bearing unambiguous evidence of stone tool use – cut marks made while carving meat off the bone and percussion marks created while breaking the bones open to extract marrow.

Until now, the oldest known evidence of butchering animals with stone tools came from Bouri, Ethiopia, where several cut-marked bones date to about 2.5 million years ago.

The oldest previously known stone tools, dated to between 2.6 and 2.5 million years ago, were found at nearby Gona, Ethiopia.

The new stone tool-marked fossil animal bones from Dikika have been dated to approximately 3.4 million years ago. They were found a few hundred meters away from where Alemseged’s team previously discovered “Selam,” the name assigned to “Lucy’s baby,” a young Australopithecus afarensis girl who lived about 3.3 million years ago.

The Dikika bones were found in the Andedo drainage, a natural gully system. The location and age of the stone tool-marked bones indicate that members of the A. afarensis species made the cut marks.

The Dikika bones were found in the Andedo drainage, a natural gully system. (Photo courtesy Dikika Research Project)

“The only hominin species we have in this part of Africa at this time period is A. afarensis, and so we think this species inflicted these cut marks on the bones we discovered,” said Alemseged.

Both of the marked bones came from large mammals. One fossil is a rib fragment, the other a femur shaft fragment. Both are marred by cut, scrape, and percussion marks.

“Most of the marks have features that indicate without doubt that they were inflicted by stone tools,” explains Dr. Curtis Marean from the Institute of Human Origins at Arizona State University, who performed the mark identifications. “And the range of actions includes cutting and scraping for the removal of flesh, and percussion on the femur for breaking it to access marrow.”

“The bones come from two animals, one (a femur) the size of a goat and the other (a rib) at least the size of a cow,” observes Marean. “Our closest living relatives, the chimps and bonobos, don’t hunt or scavenge animals this size, so this suggests that the Dikika australopithecines had already begun to engage in hunting or scavenging larger mammals. This places them in competitive and risky contexts.”

“Now, when we imagine Lucy walking around the east African landscape looking for food, we can for the first time imagine her with a stone tool in hand and looking for meat,” says Dr. McPherron, archaeologist with the Dikika Research Project.

“With stone tools in hand to quickly pull off flesh and break open bones; animal carcasses would have become a more attractive source for food,” she said. “This type of behavior sent us down a path that later would lead to two of the defining features of our species – carnivory and tool manufacture and use.”

“We can very securely say that the cut-marked bones date to between 3.42 and 3.24 million years ago, and that within this range, the date of the bones is most likely 3.4 million years ago,” says project geologist Dr. Jonathan Wynn from the University of South Florida.

To determine the age of the bones, Wynn relied on a well documented and dated set of volcanic deposits called tuffs. These same tuffs were previously used to determine Selam’s age and are well known from nearby Hadar, where Lucy was found.

The new find site is located in a drainage that contains only deposits older than a tuff securely dated to 3.24 million years ago. Below the find site is another tuff dated to 3.42 million years ago. This makes the age of the bones between 3.42 and 3.24 million years ago, but because the cut-marked bones are much closer to the lower tuff and below several other horizons, whose date can be estimated, the bones’ estimated age can be further refined to 3.4 million years ago.

Microscope and elemental analysis using secondary electron imaging and energy dispersive x-ray spectrometry demonstrated that these marks were created before the bones fossilized, eliminating recent damage as the cause of these marks.

While it is clear that the australopithecines at Dikika were using sharp-edged stones to carve meat from bones, it is impossible to tell from the marks alone whether they were making their tools or simply finding and using naturally sharp rocks.

So far, the research team has not found evidence of stone tool manufacture at Dikika from this early time period.

“For the most part, the only stones we see coming from these ancient sediments at Dikika are pebbles too small for making tools,” says McPherron. “The hominins at this site probably carried their stone tools with them from better raw material sources elsewhere. One of our goals is to go back and see if we can find these locations and evidence that at this early date they were actually making, not just using, stone tools.”

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