The Science of Sustainability

SF Scientist Discovers Earliest Tool Use by Human Ancestors

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Artist's rendering of A. afarensis using stone tools. By Viktor Deak, copyright California Academy of Sciences

Originally reported for KQEDnews.org.

The next time you reach for your high-carbon, stainless steel chef’s knife to trim the excess fat off a bone-in Porterhouse steak, you may want to raise a glass to your ancestors who roamed Africa millions of years ago.

A Bay Area researcher and his team made a startling discovery when they unearthed a pair of bones recently in northeastern Ethiopia: the earliest evidence of stone tool use by upright human ancestors 3.4 million years ago – nearly a million years earlier than scientists previously had believed.

“The moment that sort of primitive species, not so primitive anymore, started to use those tools, it started to open up the type of species we are today,” said Zeresenay Alemseged, chair of the anthropology department at the California Academy of Sciences in San Francisco.

“That primitive stone tool they made 3.4 million years ago is the precursor for all the technologies that we have today.”

Alemseged’s research appears in Thursday’s edition of the journal Nature.

Zeresenay Alemseged in his office at the California Academy of Sciences. Photo by Sheraz Sadiq

Meat at the ancient watering hole

The discovery could help rewrite understanding how humans evolved, because stone tool use and meat eating were key steps taken along the evolutionary path leading to the big-brained species we are today.

“Brain tissue is extremely expensive to grow and maintain, so meat provided a dense source of calories, and additional nutrients like fats and proteins that are important for growing big brains”, said Teresa Steele, a professor of anthropology at the University of California-Davis.

The species at the center of the research bore only a passing resemblance to today's Homo sapiens. Known as Australopithecus afarensis, the human forebears were long-limbed, about four feet tall, resembling chimpanzees that walked upright but also partially lived in trees. They were thought to have eaten mostly leaves and fruits. But now scientists have a more accurate picture of their diet and behavior.

“This new discovery clearly shows that the picture we had was wrong, because the species was not only using tools, but was using tools to interact with large mammals, to exploit meat from very large mammals and no other non-human species can do that,” said Alemseged.

They weren’t so much hunting their meals as scavenging them, he said, because their legs weren’t built for chasing prey. Alemseged believes they would venture into the open grasslands of East Africa to find dying or recently deceased animals, like antelope, and use their tools to obtain the nutrient-rich meat. Then, they would need to work as a team in a landscape teeming with other hostile, hungry predators.

“When some were using tools to carve the meat off the bone or break the bones to access the marrow, some maybe were watching for hyenas or lions. And that’s why I can confidently say that when we revise the textbooks for the earliest evidence for stone tool use and meat eating, we will have to revise also the picture of the species Australopithecus afarensis on the ancient landscape,” he added.

The behavior suggests a certain level of intelligence and planning, which is impressive considering that “Lucy,” a partial skeleton of Australopithecus afarensis unearthed 36 years ago, had a brain that was roughly a third the size of a human brain, which first started cogitating in modern human form about 200,000 years ago.

Humans and chimps share a common evolutionary ancestor, and chimps also use tools, such as twigs to dig for termites in mounds or rocks to break open nuts. Humans, however, are the only primate species to intentionally make sharp-edged tools to hunt or scavenge prey much larger than themselves.

Fossilized bone fragments from Dikika, Ethiopia that show evidence of stone tool use. Copyright California Academy of Sciences.

Leaving no fossil unturned

Alemseged’s latest discovery grew out of the Dikika Research Project, which he has led since 1999, looking annually for fossils in the Afar region of Ethiopia — a dry land once dotted with forests and grassy savannahs on which the earliest upright human ancestor would have taken its first two-legged steps six million years ago. In early 2009, just six miles from where Lucy was found, this “cradle of mankind” as Alemseged calls it, offered up the tantalizing find announced this week.

“We took everything back to the camp and a group of us was sitting in the camp and just everyday going through each bone. And then our paleontologist noticed something on the foot bone of an antelope, and when we looked at it, there were cut marks evidently,” Alemseged said.

Although that bone didn’t turn out to have the cut marks that were indicative of stone tool use, two bone fragments did – one from the rib bone of a cow-like animal and one from the leg of a goat-sized antelope. But the team had to be sure, because the marks could have been caused by abrasion over the years or by the teeth of another predator. So Alemseged received permission from the government of Ethiopia to send the bones out of the country to Arizona State University, where they were examined by high-tech forensic tools.

An environmental scanning electron microscope enlarged the cut marks to reveal a pattern consistent with a scraping and pounding motion from a sharp-edged stone tool. Within one of the cut marks on one of the bones was further irresistible proof of early human activity.

“We discovered a rock that has a completely different chemical composition from the bone itself. So that means that it came into the cut mark when someone was using a sharp-edged igneous rock to cut the bone or the meat. Based on chemical analysis we were able to show that that cut mark was made by stone and done before the fossil fossilized,” Alemseged said.

Since massive volcanic eruptions 3.42 and 3.24 million years ago spewed layers of volcanic ash into the basin where the cut-marked bones were found, dating the bones was relatively straightforward. The research team settled on a date of 3.4 million years because the bones were found in a sediment layer close to the layer containing the volcanic ash from 3.42 million years ago.

Under a microscope, one of the bone fragments reveals evidence of a scraping motion. Photo courtesy of Hamdallah Bearat, Arizona State University

Where are the tools?

Alemseged, a 41 year-old, Ethiopian-born paleoanthropologist, had already made a name for himself with his discovery in 2000 of “Selam,” the oldest and most complete remains of an Australopithecus afarensis child who lived more than three million years ago.

As he once more enters the world of this ancient human ancestor, a key mystery remains.

“The most obvious question is, ‘where are the tools?’”, said David Braun, a senior lecturer at the University of Cape Town in South Africa who studies fossils bearing marks of early stone tool use. “These early tools will actually represent the dawn of human culture and will likely be difficult to identify”, said Braun.

The oldest found stone tools – made of basalt, quartz and flint – were also discovered in Ethiopia, dating back some two and a half million years ago. If they still exist, it will be a challenge to find stones with sharp, flaked edges that could have been used to butcher meat more than three million years ago, now dispersed and lying hidden for millennia under layers of soil. And while these ancient human ancestors now appear to have been using tools, whether they actually made them is likely to be a subject for debate. “There is currently no evidence that they actively chipped stone to make tools. The earliest tools are most likely sharp-edged stones that were opportunistically used”, said Braun.

When they’re in the field, Alemseged and his team of scientists and graduate students works up to 12 hours a day, seven days a week for a month or more, combing an area not just for large, readily identifiable bones, but also for fragments which require further scrutiny.

“The fact that we made this discovery is because we changed the way we were collecting the fossils, so we need to continue to look for more cut-marked bones and really show that it is a standard thing to do and then find the stone tools that were used to inflict those marks on the bones,” he said.

“We’re trying to address one of the most important questions in humanity: who we are and where do we come from. This individual who carved that stone tool contributed to your genes, my genes, to every person’s genes on this planet.”

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Sheraz Sadiq

About the Author ()

Sheraz Sadiq is an Emmy Award-winning producer at San Francisco PBS affiliate KQED. In 2012, he received the AAAS Kavli Science Journalism award for a story he produced about the seismic retrofit of the Hetch Hetchy water delivery system which serves the San Francisco Bay Area. In addition to producing television content for KQED Science, he has also created online features and written news articles on scientific subjects ranging from astronomy to synthetic biology.