Oldowan core
© Mohamed SahnouniAn Oldowan core from Ain Boucherit
To the untrained eye, the rock would have looked like any other. But when Mohamed Sahnouni pulled it out of the ground in the summer of 2006, he immediately recognized it as a chopper: a palm-size tool deliberately flaked to create a sharp cutting edge. It looked exactly like something from the so-called Oldowan culture, a style of stone tools that existed between 1.9 and 2.6 million years ago, predate Homo sapiens, and had mainly come from East Africa.

But Sahnouni wasn't in East Africa.

For years, he and his colleagues had been exploring the archaeological site of Ain Boucherit in Algeria's High Plateaus, just an hour's drive from the Mediterranean at the continent's northern edge. This part of the continent has been relatively neglected by archaeologists, and until now, the oldest artifacts from the region were 1.8 million-year-old stone tools that Sahnouni had found at nearby Ain Hanech. But what his team discovered at Ain Boucherit was much older.

After unearthing that first chopper, his team eventually dug up 252 other Oldowan-style tools. They also found 19 animal bones with long indentations that they interpret as cut marks, a sign of prehistoric butchery. The oldest of these tools and bones are 2.4 million years old. "It was a big joy to find them," Sahnouni says.

Algeria
© (M. Sahnouni)A map of Africa showing places where Oldowan tools have been found
The tools are so old that they couldn't possibly have been made by Homo sapiens, and with no hominin bones from the site, it's unclear which species created the objects. Still, "it's extremely provocative evidence," says Eleanor Scerri, an archaeologist from the University of Oxford who was not involved in the study. The artifacts suggest that hominins were in North Africa, carving up animal meat, at least 600,000 years earlier than previously thought. More importantly, they suggest that the Oldowan culture-the earliest well-accepted stone technology-either spread from East Africa to the north very quickly or originated in different parts of Africa independently.

"It highlights North Africa, and the Sahara in particular, as a major region of importance in the evolutionary processes leading to our own species," Scerri says. "Sahnouni and his colleagues have been working in that area for many years, and I really salute their persistence."

Sahnouni has been working in the Algerian High Plateaus since the 1980s, and he uncovered the tools and bones of Ain Boucherit around a decade ago. But finding artifacts is often the easiest bit of archaeology. "The real issue was how to date them in a way that would convince the scientific community," Sahnouni says.

The geology of the Algerian plateaus is such that many widely used and highly accurate dating techniques can't be utilized there. Instead, the team relied on the fact that Earth's magnetic field has repeatedly flipped throughout the planet's history. Those inversions leave telltale signals within rocks. By comparing the magnetic signals from Ain Boucherit against a well-established global calendar, the team could work out how old any part of their site was-including the layers that yielded the bones and tools.


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The animal bones also provided clues. Many of them came from species of extinct pigs, horses, and elephants that only lived within certain time frames, which the team checked against the dates from their magnetic calendar. This work, which took most of the decade to do, revealed that the two areas the team dug up were 1.92 million years old and 2.44 million years old.

There are two ways of interpreting these dates, Sahnouni says. First, it's possible that the same hominins who made the East African Oldowan tools 2.6 million years ago rapidly spread to the northwest, covering more than 3,000 miles in about 150,000 years. To Sahnouni, that seems unlikely. "It's not like they just decided to get to the north and started walking," he says. The intervening land "wasn't easy to go through, and they would have had to look for food and resources. That takes time."

The explanation he favors is that early stone tools, and perhaps even the hominins who made them, evolved independently in different parts of Africa-in the east, northwest, and perhaps elsewhere. There's other evidence for this. For example, the oldest known hominin is 7 million years old, and was found in Chad, about 1,900 miles west of the rich finds in East Africa. "That was a turning point in rethinking the origin of humans in only East Africa," says Sahnouni, who is confident that work in other parts of Africa will upend the narrative even further.

But there's an elephant in the room. In 2010, researchers working at Dikika, Ethiopia, found 3.4-million-year-old bones that, they said, had cut marks made by stone tools. It was a stunning claim, which pushed the evidence for such tools back by 800,000 years. And if it's right, it changes the narrative again, and re-centers East Africa as a site of technological industry that was up and running well before the north got involved. But many archaeologists dispute the Dikika finds, saying that the so-called cut marks could have been made by trampling hooves or biting crocodiles, instead of by hominin butchers. The controversy is so fiery that Sahnouni's team doesn't mention or cite the Dikika evidence at all in their new paper-an academic burn, if ever there was one.

By contrast, he says the cut-marked bones he found at Ain Boucherit really were cut. One of his colleagues carefully examined them under a microscope, and found signs that are supposedly distinct from marks created by trampling or biting. "The cuts are mostly on limb bones, which are the meatiest parts," Sahnouni adds.

But Jessica Thompson, an anthropologist from Emory University, isn't convinced that the "cut marks" from Dikika and Ain Boucherit are all that different. "The paper's images are not especially convincing to me, and it makes me wonder what the other, less-good examples look like," she says. "By ignoring the [Dikika] debate, they're not really acknowledging the fact that there could be a problem with their site, too."

She doesn't fault the team. They've analyzed the bones in the same way that their peers have long done. But Thompson says that many archaeologists are now reassessing those approaches in light of Dikika. "We've realized that the way we used to do things will always create this controversy if we keep persisting," she says, "so we're using new approaches, like 3-D-scanning and machine learning."

"I dearly hope [the Ain Boucherit finds] are cut-marked bones," she adds. "You could put the total number of cut-marked bones [from other sites] inside a very small shoebox. Their collection would far outstrip that."