The first South Americans: Extreme living

After humans arrived in South America, they quickly spread into some of its most remote corners

Barbara Fraser

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1 cuncaicha arrival

The Cuncaicha rock shelter high is located high in the Peruvian Andes. As humans populated South America at the end of the last Ice Age, some settled at this site. Barbara Fraser

From the mouth of a cave high in the Andes, Kurt Rademaker surveys the plateau below. At an altitude of 4,500 metres, there are no trees in sight, just beige soil dotted with tufts of dry grass, green cushion plants and a few clusters of vicuñas and other camel relatives grazing near a stream.

The landscape looks bleak, but Rademaker views it through the eyes of the people who built a fire in the rock shelter, named Cuncaicha, about 12,400 years ago. These hunter-gatherers were some of the earliest known residents of South America and they chose to live at this extreme altitude — higher than any Ice Age encampment found thus far in the New World. Despite the thin air and sub-freezing night-time temperatures, this plain would have seemed a hospitable neighbourhood to those people, says Rademaker, an archaeologist at the University of Maine in Orono.

2 rademaker cuncaicha clean

Kurt Rademaker has found evidence of toolmaking and other signs of human habitation at Cuncaicha that date back 12,400 years.

The basin has fresh water, camelids, stone for toolmaking, combustible fuel for fires and rock shelters for living in,” he says. “Basically, everything you need to live is here. This is one of the richest basins I've seen, and it probably was then, too.”

Rademaker is one of a growing number of young archaeologists investigating how hunter-gatherers first colonized South America at the close of the Pleistocene epoch, when the last Ice Age was waning. Casting aside old dogmas, these researchers are finding that people arrived significantly earlier than previously believed, and adapted rapidly to environments from the arid western coastline to the Amazon jungle and the frosty heights of the Andes.

By teaming up with geologists, climate scientists and other researchers, archaeologists are gaining a clearer picture of what the ancient environments were like and how people migrated across the landscape — clues that are leading them to other ancient occupation sites.

Hidden ancestry

The archaeology that's being done in South America is becoming more scientific with the development of new methodologies, and there's a level of collegiality developing among younger researchers,” says Rademaker. “We're all really excited about the new developments that are coming faster and faster.” But researchers are racing against time as South American countries rapidly expand mining, road building and other activities that threaten to obliterate evidence from promising sites.

For decades, a fractious attitude prevailed over research on the earliest people in the Americas. One of the most acrimonious disputes concerned a site in southern Chile called Monte Verde, which Tom Dillehay, an anthropologist now at Vanderbilt University in Nashville, Tennessee, excavated in the 1970s and 1980s. He found evidence of human occupation1 that he dated to about 14,500 years ago. Dillehay's conclusions regarding Monte Verde put him in direct conflict with the accepted wisdom among leading archaeologists that people from Siberia did not spread across North America and venture south before around 13,000 years ago. That is the age of the Clovis culture, a group of big-game hunters who used distinctive spear points that are found littered across the United States. The Clovis people were thought to be the pioneers in North America, and many archaeologists there dismissed Dillehay's claim that Monte Verde was older.

But antagonism has faded over the past six years, as convincing evidence of pre-Clovis sites has emerged in North America (see Nature 485, 30–32; 2012). Meanwhile, South American archaeologists, who were never as sceptical as their northern colleagues, have found more sites dated between 14,000 and 12,000 years ago, indicating that hunter-gatherers had spread through South America before and during the rise of the Clovis culture in the north.

Now that researchers have moved beyond that debate, they are making greater headway in studying when people reached South America and what they did when they got there.

Rademaker's finds in the Andes are helping to answer those questions — and pose new ones. His journey began 150 kilometres away from the Andes cave, on Peru's arid coast at Quebrada Jaguay, where Daniel Sandweiss, an anthropologist at the University of Maine and Rademaker's graduate adviser, was excavating a site that dated to the end of the last Ice Age, between 13,000 and 11,000 years ago. Sandweiss had uncovered the remains of seafood meals, as well as flakes of obsidian produced as people chipped at the glassy mineral to make stone tools2. There are no obsidian deposits along that coastline, so the material must have come from formations high in the Andes.

Rademaker travelled into the mountains and found a large outcrop of the obsidian known as Alca3at Mount Condorsayana in 2004. Over the next three years, he studied the obsidian deposits and evidence of past glaciation in the area with geologist Gordon Bromley of the University of Maine.

Those field trips gave Rademaker his first glimpse of the Pucuncho Basin, an alpine wetland with a stream, numerous vicuñas, llamas and alpacas, and a ready supply of cushion plants, which the researchers discovered are rich in resin and can burn easily. The basin was also littered with points and shards left by early toolmakers. Hiking down the stream, he glanced up the hill to his left and saw a yawning gap — the Cuncaicha rock shelter, which he began excavating in 2007.

This is the first time we've found a site this old in the high Andes,” Rademaker says. On a day in August, he wraps a bandana over his mouth and nose and shovels dirt into buckets to fill in an excavation pit that is no longer needed. As he works, his shirt sleeve pulls up, revealing a glimpse of meticulously detailed hominin skulls tattooed up his right arm — from Australopithecus afarensisnear his wrist to Homo sapiens on his shoulder. This late in the field season, his field trousers are frayed and he has had to bind his left hiking boot with several strata of duct tape.

A chilly breeze whips across the Pucuncho plateau as some of Rademaker's companions struggle with the thin air. As well as cautioning his team members to prepare for the cold, Rademaker ensures that they acclimate gradually to the lack of oxygen.

Even while battling the extremes, the team has gathered evidence contradicting the conventional wisdom that the mountains were too high, cold and inhospitable for early human habitation. Bromley's data show that at the end of the last Ice Age, glaciers were mainly confined to some alpine valleys, and Pucuncho and other areas were not glaciated. Palaeoclimate data indicate that the environment was probably wetter then, so there might have been more plants and animals available for the early residents, says Rademaker.

These Palaeo-Indians were able to live in one of the most extreme environments on Earth, at the end of an ice age, and they seem to have done so quite successfully,” he says. “This tells us that Palaeo-Indians were capable of living just about anywhere.”

There are large numbers of animal bones, mainly from deer and vicuñas, in the earliest layers of sediment in the Cuncaicha rock shelter, showing that the inhabitants found abundant game on the plateau. And some of the tools were made of stone not available in the area, indicating that residents of the cave either travelled outside the region or exchanged materials with other groups that did. Some tools show traces of plant starch, which the researchers hope to analyse to work out what the cave-dwellers ate, and whether they domesticated tubers or other plants.

The researchers have also found a fragment from a human skull at the site. It has not yielded DNA and its age is uncertain, but it hints that the cave could contain early human remains, says Rademaker.