Humans living at high altitudes — such as in Tibet or highland regions of Africa — often have specific adaptations, both genetic and cultural, that allow them to live in oxygen-starved environments.
But archaeologists and anthropologists are still uncertain on how long those adaptations took to develop, said Randy Haas, a post-doctoral research associate in University of Wyoming’s Department of Anthropology.
This month, the journal Royal Society Open Science published research conducted by Haas — and other researchers from UW and elsewhere — showing some early humans in the Andes lived permanently at elevations roughly 12,500 feet above sea level, as early as 8,000 years ago.
“We know generally that the Andean and Tibetan highlands were among the last places of human colonization on the planet,” Haas said. “These are really challenging places for human survival, and an important part of understanding how people solved those challenges is understanding when they first began to live there on a year-round basis.”
Haas’ team tested human remains from 16 individuals, found at Soro Mik’aya Patjxa, who represented all age classes and were living without the benefit of agriculture or industrial goods. Haas said these brave souls were mobile hunter-gatherers.
“They are a testament to the human spirit and an ability to persist in extremely challenging environments,” Haas said. “ … And they were so successful that they paved the way for domestication of alpacas, potatoes, and quinoa and ultimately for the emergence of state-organized societies such as Tiwanaku and the Inca.”
Human bones, from individuals adapted to permanently living at high elevations, have low oxygen and carbon isotope values. These isotope values can give one an idea of how much time the individuals spent at high elevations, Haas said.
“Oxygen isotopes in human bones reflect the elevation of the water you drink, and carbon isotopes reflect the elevation of the foods you eat,” he said. “They are long-term averages. In all cases, the values in the human bone fell in the range of high-elevation water, plants, and animals.”
The bone samples were first sent to UW Bioarchaeologist Melissa Murphy’s lab. Murphy, an associate professor of anthropology, is familiar with the specific challenges of working with ancient human bones, Haas said.
In the lab, graduate student Ioana Stefanescu, of the Department of Geology and Geophysics, and doctoral student Alex Garcia-Putnam of the Department of Anthropology, prepared the bones for the UW Stable Isotope Facility, which determined the carbon and oxygen isotope signatures.
“I have to say that going into this project, I did not expect to find the isotopic values of oxygen and carbon to have a high altitude signature for the 16 individuals, knowing that they lived between 6,800-8,000 years ago,” Stefanescu said.
She added everyone involved in the project was also surprised to find the isotopes they did, though the team was enthusiastic about the findings.
Discovering hunter-gatherer and forager skeletal remains at all is rare, given their mobility, Murphy said.
“It’s rare to find these skeletal remains in general and it’s rare to get 16 from one site,” she said. “So you’re really talking about 16 people who are probably — over the span of hundreds or thousands of years — related to one another in some way, because they keep returning to this archeological site and they keep burying their dead there.”
Isotopes alone are not definitive proof, however, so the team used other evidence from the site to back up the bone findings.
For example, the remains found at Soro Mik’aya Patjxa were both male and female and ranged in age from 4 years old to older than 50 years old.
“This tells us that site did not simply represent a short-term camp of prime-aged individuals visiting from the lowlands,” Haas said. “We also calculated that a round-trip between the site and the lowlands would have minimally required a round-trip journey of 80 hours over 250 miles of mountainous terrain — far too long for a temporary stay, especially for children and elders.”
Tools found with the human remains were carved from stone local to the site, further suggesting long-term high-elevation stays, according to the paper.
“Unfortunately, scientists can’t simply observe humans of the distant past, so we have to rely on the archaeological record to ‘see’ past events and human behaviors,” Haas said. “ … If multiple archaeological observations using different methods all point to the same conclusion, then the probability of arriving at the correct answer significantly increases.”
Murphy said the findings give researchers a better understanding of how high elevation adaptations developed by giving researchers a timeline for those adaptations and that finding early humans living permanently in such harsh conditions was astonishing.
“Laramie is at 7,200 feet, and that’s hard enough,” she said. “You have all sorts of transitions to make if you’re not from Laramie. You have to acclimate, and it takes a while. But (Haas’) site is over 12,000 feet, so this is really high. Imagine living there full time. It’s incredible.”
The paper — titled “Humans permanently occupied the Andean highlands by seven ka” — is gives archeologists a better idea of how long it took Andean populations to develop biological and cultural adaptations, Haas said.
“Again, this is just a small but important part of advancing a larger picture of human adaptation,” he said. “Going forward, the next challenges are to figure out how exactly hunter-gatherers of the Andean highlands solved the challenges of high elevation living.”
Mark Clementz, associate professor in the Department of Geology and Geophysics, and researchers from the University of California-Davis, the University of California-Merced, the University of Arizona and some Peruvian institutions contributed to the study as well.