The team has found that the Puna teal, which colonized the region several million years ago and has speciated from its lowland ancestors, readily copes with extreme hypoxia. Even when the researchers dial down oxygen levels to mimic conditions at the peak of Mount Everest, almost 9,000 meters up, the Puna teal deepens its breathing, but otherwise remains unaffected. In contrast, the yellow-billed pintail colonized Lake Titicaca only a few tens of thousands of years ago and has more contact, and therefore gene flow, with its lowland counterparts. Less time at altitude means less-efficient adaptations: the pintails are far more sensitive to hypoxia and breathe much deeper and faster. Even the teal’s hemoglobin has adapted to bind oxygen with greater affinity than that of other species. Individuals can acclimatize to altitude in the short-term, but long-term adaptations spread throughout populations are a function of natural selection. Over time, teals have acquired a variety of adaptations and lost their ancestral acclimatization response. “They are making the best use of every bit of air they bring in,” says Scott.