Archaeologists say they’ve found the highest-known remains of Ice Age human settlements in the southern Peruvian Andes, dated to more than 12,000 years old. The two sites, described in the journal Science, sit higher than 4,000 meters (more than 13,100 feet) above sea level and indicate that humans may have adapted to the extremely harsh climate far sooner than many researchers had expected.
...Above 13,100 feet, the thin air and treeless terrain offers little protection from the high solar radiation. There’s not much fuel to make fires, there’s much less oxygen available to breathe and it takes about twice the number of calories just to "maintain normal metabolic function," the study authors wrote.
For many archaeologists, these factors explain why human settlements higher than about 13,100 feet and older than 11,500 years of age have eluded them. It probably took a good amount of time for the genetic variations to arise in the population that would favor, among other traits, higher metabolic rates and more lung capacity – traits found in certain high-altitude populations today. And yet these high-altitude settlements were set up within about 2,000 years of humans’ first arrival in South America. Whether they had developed the ideal traits or not, clearly humans didn't take that long to settle in (or, in this case, settle up).
one reason for fleeing up into the mountains is to flee from more war like tribes.
Maybe they need to check about fortifications...