In a village high in the Andes, Dr Iain Stewart discovers just how critical oxygen is for our own survival. When Spanish settlers first arrived, they found they couldn't have babies as the altitude caused miscarriages. How did they eventually reproduce in an environment set on the very limits of human adapatation? Watch more high quality videos on the Explore YouTube channel from BBC Worldwide here: http://www.youtube.com/bbcexplore
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