Artifacts reveal that early humans adapted to very high elevations

Some 370 miles south-southeast of the Peruvian capital of Lima as the condor flies, lies a small valley nestled between two volcanoes high in the Andes Mountains.

The valley sports wetlands and a small alpine lake, sustained by snow and rain during a six-month wet season. Two hamlets share the valley, where residents farm, raise alpaca and sheep for wool and meat, and work in local mines.

Far above tree line, this small oasis in the midst of barren rock and lava floes has a new distinction: It hosts two sites where scientists have uncovered 12,000-year-old remains of human occupation. Perched more than 14,200 feet above sea level, these sites are higher than any human settlement from the same period anywhere in the world.

Until now, the oldest evidence above 13,000 feet for settlement in the region appeared roughly 1,000-2,000 years later, with full-time occupation appearing about 7,000 years ago, according to an international team of researchers reporting the find in Friday's issue of the journal Science.

This latest discovery implies that humans during the late Pleistocene had a greater ability to adapt to the harsh conditions of high-altitude living in the Stone Age than some researchers had previously thought, the team posits.

“We don't know if people were living there year round,” said University of Calgary researcher Sonia Zarillo, a member of the research team, in a prepared statement. “But we strongly suspect they were not just going there to hunt for a few days, then leaving.”

Researchers working in Bolivia, Chile, and Argentina have uncovered hints that people there were living at high altitudes, notes Tom Dillehay, an anthropologist at Vanderbilt University in Nashville, Tenn., who was not a member of the research team.

By 14,000 years ago, he writes in an e-mail, Ice Age glaciers in the area had retreated, leaving behind a landscape above 13,000 feet that was dotted with lakes and grasslands.

Indeed, the Pucuncho Basin, home to the two newly reported sites, shows no evidence that glaciers had ever reached it to leave behind remnants that would thwart early human settlement.

These latest finds represent an example of researchers in effect looking under a rock no one else was inspired to lift, he explains.

So what prompted the researchers, led by University of Maine anthropologist Kurt Rademaker, to explore the Pucuncho Basin? Call it the Mystery of the Missing Outcrops.

“You've heard the term 'follow the money?' In archeology, we follow the obsidian,” says Katherine Moore, an anthropologist at the University of Pennsylvania and a member of the research team.

Obsidian is a volcanic glass that can be readily formed into arrowheads, spear points, blades, and scrapers of various types – tools whose value to Pleistocene hunter-gatherers was enormous. The Andes include a long string of volcanoes along mountainous terrain pushed up by the action of the Pacific Plate as it grinds its way underneath the South American plate and back into Earth's mantle.

Using a portable X-ray device, researchers can analyze a sliver of obsidian and match its chemical makeup with those of known outcroppings of obsidian in the wider region to identify the deposits the ancients exploited.

In this case, Dr. Rademaker was hunting for the source of a variant of the region's obsidian, known generically as Alca obsidian. Researchers led by University of Maine colleague Daniel Sandweiss had uncovered artifacts made from this variant at Quebrada Jaguay, a settlement site on the Peruvian coast dating to some 13,000 years ago. Samples from these obsidian artifacts were thoroughly analyzed and their composition is now well known. But the composition didn't match that of any known Alca obsidian source, Dr. Moore explains.

So Rademaker and colleagues went out and mapped the distribution of Alca obsidian and its six variants – in the process discovering that the region hosting Alca outcroppings was nearly seven times larger than previous mapping efforts had revealed.

Armed with its map, some modeling results, and some old-fashioned boots-on-the-ground work, the team found the remains of two open-air workshops in the tiny valley, nestled between the Solimana and Coropuna volcanoes.

One site, dubbed the Pucuncho open-air workshop, was located near outcroppings of two forms of Alca obsidian. There the researchers found more than 260 tools, including projectile points, as well as works in progress and chips off the finished tools. This workshop appears to have supplied Quebrada Jaguay, about 90 miles to the south.

The team found a second workshop, Cuncaicha four miles east of Pucuncho. The shelter is 14,700 feet above sea level.

This site was at a slightly higher elevation with a rock shelter some 100 feet upslope of the workshop. There the team found rock art, ceilings covered with soot, as well as tools. They also found planet and animal remains, well preserved by the cold, dry climate. Some of the animal remains indicated that the occupants butchered the animals and ate them there, suggesting that it was a kind of base camp rather than a hunting site. Among the comestibles were tubers that occupants would have had to hike to lower elevations to find.

Finding such industry so early and at such high elevations – especially as more sites at comparable elevations are uncovered – will help answer some fundamental questions about these early occupants of coastal South America, the researchers say.

“One of the big controversies is: How big a settlement pattern, how big a series of occupations do you have to have to make a living in these very demanding environments?” Moore says.

High altitudes are challenging. They expose people to high levels of ultraviolet radiation from the sun, low oxygen levels, relatively little fuel for fires, and a need for more calories than would be the case at lower elevations. But the coast of Peru is no Riviera either. The coastline is characterized by small areas of vegetation separated by “trackless deserts that never experience any rainfall," Moore explains.

Working eastward and up the slopes, people would have climbed up through steep canyons that only occasionally saw rain, continued up along steep, dangerous pathways cut by glaciers, only to have a vista open of lush wetlands teeming with wildlife, plenty of water, and, after poking around, valuable obsidian deposits.

“Putting that all together gives us a chance to look at how varied and skilled those guys were, how much of a single chunk of Peru would be occupied by one social and cultural group, how far they had to go to make a living, how connected they were to other groups, and how stressed they were by this very demanding environment,” Moore says.