Fossil finds from 74,000 years ago indicate remarkably adaptive humans

In 2002, a group of paleoanthropologists were working in northwestern Ethiopia when they came across chipped rocks and fossilized animal bones – telltale signs of a place where humans had once lived.

After years of excavations, researchers discovered that hunter-gatherers had indeed lived there 74,000 years ago. As described in a study published Wednesday in Nature, these ancient humans were remarkably flexible. They made arrows to hunt big game. And when their world was turned upside down by a massive volcanic eruption, they adapted and survived.

That flexibility could help explain why people from the same era successfully expanded out of Africa and settled in Eurasia, even though many previous forays had failed. “This points to how sophisticated humans were during this period,” says John Kappelman, a paleoanthropologist at the University of Texas who led the new study.

At the site, known as Shinfa-Metema 1, researchers discovered thousands of bones, some covered in cuts, of gazelles, warthogs and even giraffes, suggesting that humans hunted these species.

The team also found 215 fragments of ostrich eggshells. Are possible that the people who inhabited the site ate the eggs, or used the shells as canteens to store water. The scientists were able to accurately date the garnet fragments, which contained traces of decaying uranium, to 74,000 years ago.

Around the same time, a volcano in Indonesia called Toba released massive amounts of ash and toxic gases that spread around the world and blocked out the sun for months.

Dr. Kappelman inspected Shinfa-Metema 1 for signs of the eruption. By crushing rocks and dissolving them in acid, his team found tiny pieces of glass that could only have formed in a volcano. The scientists realized that they had an extraordinary opportunity to study people who had survived this gigantic environmental shock.

After analyzing 16,000 broken rocks, the researchers concluded that they were arrowheads and not spearheads. If this is the case in future studies, it will push back the archery record by several thousand years. The invention of archery meant that hunters did not have to get close to their prey. Even children could hunt with arrows, and Dr. Kappelman suspects that they used them to kill the frogs whose bones he and his colleagues also found at the site.

When Toba erupted, conditions at Shinfa-Metema 1 immediately became severe. The short rainy season became much shorter and the rivers were low.

Many researchers have assumed that such brutal changes forced people to refuges where the environment was more forgiving and where they could continue to survive using their old practices. But that’s not what happened at Shinfa-Metema 1. The fossil record shows that humans there adapted by giving up hunting mammals as their prey went extinct and instead fishing in the new shallow waters.

Dr. Kappelman and his colleagues gathered clues about how ancient people may have fished by looking at the practices of modern Ethiopians living in the area. For example, during dry seasons, fish can become trapped in isolated waterholes. “It literally looks like a fish in a barrel,” he said. “We think it would have been very easy to catch these fish.”

At Shinfa-Metema 1, it appears that Toba’s environmental impacts lasted only a few years. The rain returned, as did the mammals, and the local people began hunting them again. Fish bones became rare.

Dr. Kappelman thinks this snapshot of a single location could help solve the mystery of how humans expanded from Africa. Scientists have long wondered how humans could have made their way through the Sahara and the deserts of the Arabian Peninsula to reach other continents. They have speculated that this could have only happened during wet periods, when these areas were covered with plants. People could then have used their old survival tactics as they traveled these so-called ‘green highways’ to reach other continents.

But Dr. Kappelman and his colleagues proposed that people survived in arid climates by quickly inventing new ways to find food, such as fishing.

During dry periods, they may have moved along seasonal rivers while fishing. Instead of traveling on green highways, the researchers reasoned, they drove on blue highways.

Michael Petraglia, the director of the Australian Research Center for Human Evolution, said the study’s combination of archaeological and environmental evidence from the time of the Toba eruption was extraordinary. “It’s incredibly rare anywhere in the world,” he said.

Although Dr. Petraglia found the site interpretation convincing, he still favors the green highway hypothesis.

He argued that between 71,000 and 54,000 years ago, hyper-arid deserts stretched across the Sahara and the Arabian Peninsula. “Blue highway corridors were virtually non-existent,” said Dr. Petraglia.

Dr. Kappelman wondered whether the deserts were so harsh, noting that the Nile brought some water through the Sahara to the Mediterranean Sea. And while he acknowledged that a single site 74,000 years ago couldn’t speak for all of humanity, it provided a point of comparison for other researchers who might find similar sites.

“It’s a testable hypothesis that we’re putting out,” he said.