The cultural context of biological adaptation to high elevation Tibet

Permanent, year-round occupation of high elevation, low oxygen environments is next to impossible for human populations adapted to low elevation, high oxygen environments. Sustained human habitation of high elevation environments is therefore a comparatively late development in global human history. Though we are beginning to understand the biological differences between contemporary highland and lowland populations, we do not understand how, or when, these differences evolved. This paper presents a hypothesis for the historical context of human adaptation to the Tibetan Plateau. Archaeological data suggest that Neolithic agricultural groups living on the northeast margins of the Plateau expanded to the altitudinal limits of their farming systems by 5200 cal BP, but also to the limits of human physiological capacity for high elevation (at ~ 2500 m above sea level). With the introduction of novel, exotic domesticates (namely barley, wheat, and sheep), Neolithic agriculturalists started to push these limits, and in roughly 1600 years (by 3600 cal BP) small groups of people were living at higher elevations and deeper into the Tibetan Plateau. This required and encouraged novel cultural solutions to high elevation settings, but also imposed heavy selective pressure on the physiological capacity for low oxygen environments. These new cultural capacities enabled people to move into a stronger environment of selection (above 2500 m above sea level) that favored the physiological capacities for life at high elevation, which in turn became more common across these populations. This hypothesis about bio-cultural evolution is testable with a combination of high-resolution archaeological evidence and high throughput sequencing of datable prehistoric human DNA.