海角大神

The Tibetan Plateau doesn鈥檛 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 鈥撀爌erhaps 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鈥檛 found any sites older than 15,000 years old 鈥撀爑ntil 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鈥檚 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, 鈥渋f you take a look at the terrestrial environment, we can live anywhere,鈥� 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)聽for new places to make a living. But the Tibetan Plateau probably wasn鈥檛 a day鈥檚 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. 鈥淚t鈥檚 still not a lovely place,鈥� 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鈥檝e followed those familiar food resources up, and realized the high-elevation flat land wasn鈥檛 so bad. At the time, grasslands and other vegetation up there would have supported a range of animals.

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

That鈥檚 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鈥檛 have. Scientists aren鈥檛 sure how that evolved, but previous genetic research suggests that it may be the result of interbreeding with archaic humans: Neanderthals鈥� Siberian cousins, Denisovans.

Human adaptability

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

There seems to be something uniquely human 鈥� Homo sapiens at least 鈥撀燼bout such colonization of the extremes.

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鈥檙e 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鈥檛 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鈥檙e specialists. But Homo sapiens are different.

And that might be why we now reign.

鈥淲e鈥檙e not just making use of the most rationally optimal environments,鈥� 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, 鈥淚t鈥檚 very clear that we were specializing at the same time as other species were generalizing. And that鈥檚 what allows us to exploit all these environments.鈥�

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鈥檚 evidence that Homo erectus used fire, Homo sapiens have been particularly adept at altering our environments.

鈥淗uman beings have developed this response, the sort of 鈥榥ecessity is the mother of invention鈥� quality of human behavior that says, 鈥榳ell, yeah we have a challenge here in this environment. But how do we overcome it, technologically?鈥� 鈥� 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鈥檚 natural selection at work. And that, in turn, helped us out-compete other hominids.

But that鈥檚 a 鈥渄ouble-edged sword,鈥� 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鈥檚 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鈥檛 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.