Living at high-altitudes is hard for humans, and selection has tried to handle the stress caused by lifelong hypoxia (i.e. low levels of oxygen). A paper due to appear in P.N.A.S. by Cynthia Beall, demonstrates that this problem has been solved differently in the two main high-altitude regions inhabited by humans:
This paper presents evidence that Tibetan and Andean high-altitude natives have adapted differently, as indicated by large quantitative differences in numerous physiological traits comprising the oxygen delivery process. These findings suggest the hypothesis that evolutionary processes have tinkered differently on the two founding populations and their descendents, with the result that the two followed different routes to the same functional outcome of successful oxygen delivery, long-term persistence and high function.