Chimpanzees live only in African rainforests and woodlands. Orangutans live only in the jungles of Indonesia. But humans live pretty much everywhere. Our species has spread across frozen tundras, settled on mountaintops and called other extreme environments home.
Scientists have historically seen this adaptability as one of the hallmarks of modern humans and a sign of how much our brains had evolved. But a new study hints that maybe we aren’t so special.
A million years ago, researchers have found, an extinct species of human relatives known as Homo erectus thrived in a harsh desert landscape once considered off limits before Homo sapiens came along.
“It’s a significant shift in the narrative of adaptability, expanding it beyond Homo sapiens to include their earlier relatives,” said Julio Mercader, an archaeologist at the University of Calgary and an author of the study, which was published Thursday in the journal Communications Earth and Environment.
Fossils of our early forerunners collected over many decades seemed to confirm the special adaptability of our species. Our ancestors, known as hominins, split off from other apes in Africa about six million years ago and lived for millions of years in open woodlands. They did not seem to live in extreme environments.
Dr. Mercader and his colleagues closely examined environments in East Africa, which has yielded some of the richest troves of hominin fossils. They picked a site in northern Tanzania called Engaji Nanyori where paleoanthropologists had previously found fossils of Homo erectus.
Homo erectus is believed to have evolved about 2 million years ago in Africa. They were the first to reach the stature of modern humans, and they had long slender legs to run on. Their brains were also larger than those of earlier hominins, though only about two-thirds the size of our own.
At some point, Homo erectus expanded out of Africa, getting as far as Indonesia, where they became extinct about 100,000 years ago. In Africa, many researchers suspect, they gave rise to our own species in the past several hundred thousand years before disappearing there as well.
Dr. Mercader and his colleagues set out to determine exactly what kind of environment Homo erectus lived in a million years ago at Engaji Nanyori. They looked at fossil pollen grains, analyzed the chemistry of the rocks and searched for other clues to the landscape.
“These studies are an immense amount of work,” said Elke Zeller, a climate scientist at the University of Arizona who was not involved in the project.
For hundreds of thousands of years, the researchers determined, Engaji Nanyori had been a comfortable open woodland. But around a million years ago, the climate dried up and the trees vanished. The landscape turned to a Mojave-like desert shrub land — an extremely arid place that seemed inhospitable for early hominins.
“The data led us to a pivotal question: How did Homo erectus manage to survive and even thrive under such challenging conditions?” Dr. Mercader said.
Instead of fleeing, the hominins figured out how survive in their changing home. “Their greatest asset was their adaptability,” Dr. Mercader said.
They changed the way they searched for animal carcasses to scavenge, for example. The hominins found the ponds and streams that sprang into existence after storms. They didn’t just drink at these fleeting watering holes. They hunted the animals that also showed up there, butchering their carcasses by the thousands.
The hominins also adapted by upgrading their tools. They took more care when chipping flakes from stones to give them a sharper edge. Rather than just pick up rocks wherever they were, they preferred material from particular places. And once they made a tool, they carried it with them.
“They may have had strategies where they basically say, ‘This is a good tool. I should bring it with me and be ready if we find food,’” said Paul Durkin, a geologist at the University of Manitoba who also worked on the study.
Dr. Durkin and his colleagues found that Engaji Nanyori was at the southern edge of a vast belt of desert shrub lands that stretched out of Africa, across much of the Middle East and into Asia. It’s possible that the adaptability that Homo erectus displayed at Engaji Nanyori helped them expand to other continents.
Dr. Zeller and her colleagues have taken a different approach to studying hominins: creating large-scale climate models to figure out what conditions were like during our evolution. Their models, like the new study, suggest that Homo erectus may have thrived in environments that were once thought too harsh for species other than our own.
Studies like the ones Dr. Zeller and the Engaji Nanyori team are conducting “are all starting to tell the same story,” she said. “We definitely have to look further back in time to understand our adaptability.”