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How early people conquered the ‘Roof of the World’

Why We Wrote This

What does it mean to be human? Our species has set itself apart by colonizing the farthest reaches of the globe. A discovery of 30,000-year-old stone tools on the Tibetan Plateau underscores our adaptability.

Yingshuai Jin/AAAS
Workers excavate the Newa Devu archaeological site on the Tibetan Plateau in China. Newa Devu is the highest Paleolithic archaeological site yet identified. It provides new insight into high-altitude adaptation.

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It’s rare that a single species can make its home almost anywhere on the planet. But Homo sapiens has done just that. Our species has colonized everything from the tropics to the Arctic, mountains to valleys, islands to plateaus. “If you take a look at the terrestrial environment, we can live anywhere,” says Mark Aldenderfer, an archaeologist at the University of California, Merced. Except, perhaps, he adds, someplace like the inside of a volcano. One of the most extreme environments for humans to live is on the Tibetan Plateau. At nearly three miles above sea level, the air is thin, the temperatures are frigid, and there’s minimal vegetation. And yet people have made this highland home – perhaps for 30,000 years, according to new archaeological evidence. There’s still a lot to learn about how humans came to colonize such a seemingly hostile environment during the last ice age. But the tale is one that highlights the adaptability and resourcefulness of early people. And our ability to migrate so readily may just explain why our species now reigns.

The Tibetan Plateau doesn’t seem like a very inviting place to live. At nearly three miles above sea level, the air is extremely thin. And yet, despite minimal vegetation and frigid temperatures, people have made this highland home – perhaps for tens of thousands of years.

Stone tools newly unearthed on the plateau could be the first hard evidence that people made a living at those high elevations some 30,000 years ago. Genetics had hinted at that timeline, but archaeologists hadn’t found any sites older than 15,000 years old – until now. The new find was published Thursday in the journal Science.

The peopling of such a seemingly hostile environment is a story of human ingenuity, adaptability, and migration. And it’s not a unique one. Our species has colonized almost the entire planet, from the Arctic to savannas, tropical rainforests to deserts. This highland chapter in the human history book highlights the overall flexibility and resourcefulness of early people.

Unlike other animals, “if you take a look at the terrestrial environment, we can live anywhere,” says Mark Aldenderfer, an archaeologist specializing in high-elevation sites at the University of California, Merced. Except perhaps, he adds, someplace like the inside of a volcano.

But high-elevation places like the Tibetan Plateau have long been thought to be one of the last and most challenging places for humans to live, Dr. Aldenderfer says. So how, then, could ice-age humans possibly have come to live up there?

At the time, there was no high-tech way to know whether the landscape over the next hill was barren or plentiful with resources without going there to check it out.

That might have been part of what happened, with scouts looking around (on foot) for new places to make a living. But the Tibetan Plateau probably wasn’t a day’s jog from most populations. This migration likely happened over a long period of time, as populations perhaps followed resources or moved away from overcrowded or warring groups.

Aldenderfer is partial to the idea that people were pulled to new places by following resources, not pushed there. “It’s still not a lovely place,” he says of the Tibetan Plateau. But 30,000 years ago, he explains, the climate was improving. It was a warmer period during the last ice age, the last one before the Last Glacial Maximum, and plants and animals moved up to higher elevations. Humans at lower elevations near the Tibetan Plateau would’ve followed those familiar food resources up, and realized the high-elevation flat land wasn’t so bad. At the time, grasslands and other vegetation up there would have supported a range of animals.

But it’s not all about food at such high elevations, Aldenderfer says. “Deserts are hard [to occupy] and poles are hard, but the high-plateaus are hard in a different way. There’s the whole hypoxia problem,” he explains, referring to the added challenge of breathing at high altitudes.

That’s where biology comes in. Tibetan highlanders today have a genetic trait that helps them breathe in enough oxygen at high-elevation that other humans don’t have. Scientists aren’t sure how that evolved, but previous genetic research suggests that it may be the result of interbreeding with archaic humans: Neanderthals’ Siberian cousins, Denisovans.

Human adaptability

But some scientists think there might be something more than need and genetics behind human migrations into extremes. “From a logically intuitive point of view you might say, ‘stay low, just avoid the plateau, walk around the edges,’ ” says John Olsen, a co-author on the new paper and regents’ professor emeritus at the University of Arizona and a researcher with the Russian Academy of Sciences. But “maybe part of the human story involves … a philosophy that something interesting is over the next horizon.”

There seems to be something uniquely human – Homo sapiens at least – about such colonization of the extremes.

Xing Gao/AAAS
Artifacts found at the Newa Devu archaeological site suggest that the Tibetan Plateau was occupied at least 30,000 years ago.

A team of researchers analyzed the environments in which fossils from other members of the genus Homo (such as Neanderthals, Homo erectus, etc.) have been found. Those other human species resided largely in mixed forest and grassland environments, whereas our species, even prehistorically, has lived in everything from tropical forests to the Arctic Circle to deserts and more.

Homo sapiens, it turns out, can acclimate to pretty much any environment, but once we’re in it, we can become highly specialized to that environment, developing tools and adaptations to exploit the specific resources offered there.

That combination of being adaptable generalists who also specialize is unusual. Animals are usually one or the other, explains Patrick Roberts, an archaeologist at the Max Planck Institute for the Science of Human History who led that study. Raccoons, for example, are generalists. They can eat anything, and aren’t too picky about their environment. Giant pandas, on the other hand, live only in humid bamboo forests on mountains in China, and only munch on those bamboo forests. They’re specialists. But Homo sapiens are different.

And that might be why we now reign.

“We’re not just making use of the most rationally optimal environments,” Dr. Roberts explains. And so, during periods of challenging climate, humans are able to survive more readily off the resources available. During the last ice age, when the other members of the genus Homo went extinct, he says, “It’s very clear that we were specializing at the same time as other species were generalizing. And that’s what allows us to exploit all these environments.”

Secret of our success

But what is it about our species that allows us to do that? Some researchers have suggested human intelligence and creativity are part of the answer. Although Neanderthal artwork has been found, and there’s evidence that Homo erectus used fire, Homo sapiens have been particularly adept at altering our environments.

“Human beings have developed this response, the sort of ‘necessity is the mother of invention’ quality of human behavior that says, ‘well, yeah we have a challenge here in this environment. But how do we overcome it, technologically?’ ” Olsen says.

Roberts says because Homo sapiens evolved out of a period of climate fluctuations (during the last ice age), our species probably inherited traits to make us particularly successful at adapting to varying environments. It’s natural selection at work. And that, in turn, helped us out-compete other hominids.

But that’s a “double-edged sword,” Roberts says. During the last ice age, such a voracious ability to exploit the environment was advantageous. But now, he says, with a disconnect from knowledge of how the environment responds, that capability is seeming more dangerous.

There’s still a lot to learn about what makes our species unique. But our view of our own ancestors has already changed. It used to be that scientists wouldn’t look in extreme environments for prehistoric human remains. But now, Roberts says, scientists believe our species has long been capable of living in the extremes.

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