Forget Xavier's School for the Gifted - marvel instead at the real life superheroes on the roof of the world. For years anecdotes circulated amongst climbers, of the superhuman ability of the Sherpa to function at high altitude, when all others succumbed to mountain sickness - or worse. Now science has shown how they have evolved to live in one of the most inhospitable environments on Earth. Thousands of years living in the thin air of the Himalayan plateau has given the Sherpa biology that differs from lowlanders from the very cellular level.