Hot on the heel of the news Denisovans were living on the Tibetan Plateau 160,000 years ago, researchers have now discovered the earliest signs of high-altitude human living in Africa in an Ethiopian rock shelter 3,350 meters (11,000 feet) above sea level. Writing in American Association for the Advancement of Science, they reveal radiocarbon dating shows its earliest residents would have been Middle Stone Age foragers living 31,000 to 47,000 years ago.
Excavations of the site, Fincha Habera in Ethiopia's Bale Mountains, unearthed thousands of artifacts from the Middle Stone Age, from locally sourced stones to burnt animal bones, human feces, and the hearths of former fires. The evidence suggests the foragers would have exploited the nearby resources while dining on the area's abundance of giant mole-rats – the latter apparently from a sizable collection of bones dug up at the site.
The researchers are hesitant to draw too many conclusions and say it is not possible to confirm whether or not the settlement was inhabited on a permanent basis or if it was a case of human settlers coming and going over the years. Still, the discovery is important because it adds to the small but growing research that suggests high-altitude living was occurring quite a bit earlier in our species history than previously thought.
Living so far above sea level requires certain adaptions to cope with the limitations and stresses it puts on the body – including high-altitude hypoxia, low and fluctuating temperatures, water shortages, and higher levels of ultraviolet radiation. For this reason, communities that have spent thousands of years surviving in these extreme environments often show genetic adaptions to cope with their surroundings.
People living in the Tibetan Plateau – 4,500 meters (15,000 feet) above sea level – for example, have at least five different gene variants associated with living in places with low levels of oxygen, a high altitude, and food scarcity. While people living in the Bale Mountains today have several genes that promote cardiac tolerance to hypoxia.
These genetic variations – like those for blue eyes and lactose-tolerance – can take thousands of years to evolve and take hold in a population. And so, the traditional line of thought goes, living in locations of more than 2,500 meters or 8,200 feet above sea level must be a relatively recent turn of events in terms of our evolutionary history.
A growing number of archaeological sites from the Andean altiplano to the Tibetan Plateau, however, shows this was not necessarily the case.
As for the prehistoric inhabitants of Fincha Habera, the researchers say they benefited from plentiful resources and a year-round supply of prey (giant mole-rats), which was both abundant and easy to catch. A local supply of volcanic obsidian offered material for tools to hunt the critters with.
It is likely the stability of mountains provided a refuge for plants and animals – including humans – at points in history when the lowland climates were arid and less hospitable, they say.
According to The New York Times, the researchers are planning another trip to the site to excavate deeper in the hope that this time, they'll be able to find the bones of the settlers.