Why are elephants' ears so big? Why do humans get the bends when dolphins don't? Imagine being able to consume 250,000 calories (50 Christmas dinners) daily without gaining weight! If we had the metabolism of a shrew, we could, and we would have to. In this text, Eric Widmaier offers a physiologist's view of the features and abilities humans and other creatures have evolved to meet the seemingly impossible challenges of survival.