Q. What's the highest altitude at which humans can habitate?
A. The threshold for permanent residence is around 17,000 feet—any higher and dwellers would likely suffer from the ailments well known to Himalayan climbers: hypoxia, an oxygen deficiency that damages cells, and pulmonary and cerebral edema, potentially deadly fluid buildup in the lungs and brain. People have lived higher and survived—most notably, a small community of gold miners in northern Chile, who resided at 19,500 feet for nearly two years, starting in 1984. These men were never studied for mountain sickness, but John B. West, a professor of physiology and medicine at the University of California at San Diego, met the miners and described them as "a little blue."
These days, the highest city on earth is Peru's La Rinconada, elevation 16,732 feet. Like Himalayan Sherpas, La Rinconada's residents tend to be compactly built, with genetically adapted hearts and lungs. Still, they wouldn't want to live at higher ground, for reasons both physiological and economic. "When you go above about 16,700 feet, you can't grow crops, because it's too cold," says West. "You can't raise animals, you can't get any food. So there's no point in living there."