San Antonio de los Cobres, Puna region in the Andes in northwest Argentina, altitude 3800 m: pulse oximetry oxyhaemoglobin saturation (Spo₂) 84% and heart rate 65 beats per minute – both low for me, and certainly much lower than my level 24 h ago at sea level. I feel fine, but I do seem to be breathing at higher lung volume. My Spo₂ is at the expected level for acute homeostasis at altitude (fig 1),1 2 and over the next few days it should improve to the level I would have had, had I stayed at 1600 m.3 What surprises me, though, is my travel companion, who has lived at sea level for the last 20 years, yet has a Spo₂ of 93%. Could those Quechuan grandparents really have something to do with this response?

Man’s migration across the planet has been mainly along coastal regions, avoiding inhospitable habitats such as mountains, desert and ice.4 However, some 25 000 and 11 000 years ago human populations settled on the Himalayan and Andean plateaus, respectively. Now, 20–30 million people live at altitudes above 3000 m, with more than half of these living in the Andean region of Latin America.5 In relation to human phylogeny, the last time Caucasians, Sherpas and Quechuas shared common ancestors was over one half the age of our species ago; Himalayan and Andean highlanders share common ancestors that date back approximately one third of our species’ history.6 In the ancestral high altitude populations, centuries of …