While the sub-Arctic and the Sahara are very different environments, both present extreme challenges to large mammals that live there.Martha Foley and Curt Stager compare the camel and the caribou, which, while not closely related, have made similar evolutionary adaptations to survive in barren terrain.Both need coats that can insulate against temperature extremes, complex nasal equipment to preserve hydration, and digestive tracts adapted to handle a wide range of coarse and nutrient-poor foods.