Most yaks are domesticated, but wild populations still exist – this animal is in Nepal.
The yak is a strong contender for this title (as long as we’re talking about earthbound animals, rather than any that have been sent into orbit). These large, shaggy, mainly domesticated bovines live in the Himalaya at altitudes as extreme as 6,000m. The animals are superbly adapted for such high lives – the combination of a dense, furry undercoat and a long, shaggy overcoat keeps out the bitter mountain chill; their limited sweat glands conserve heat; and their large lungs, together with a particularly high red-blood-cell count, retain oxygen. Other enthusiasts for elevation include the snow leopard, which lives as high as 5,400m, also in the Himalaya; and the vicuña, the wild ancestor of the alpaca, which survives up to 5,800m in the Andes.