Without specialist clothing, the extreme cold of the high arctic would kill a human in minutes. The temperature drops to 50 degrees centigrade below zero, and yet there are animals that live here all the time. One such is the arctic fox. These mammals have adapted to living in these extreme environments, and being a mammal is a clear advantage. Mammals use their food to heat their bodies, they're warm-blooded, and have hair (or fur) to insulate them. Warm-bloodedness is one of the key factors that have enabled mammals to conquer the Earth and to develop one of the most complex bodies in the whole of the animal kingdom.