How do people survive extremes of heat, cold, depth, speed and altitude? This book explores the limits to human survival and the physiological adaptations which enable us to exist under extreme conditions. In man's battle for survival in the harshest of environments, the knowledge imparted by physiology, the 'logic of life', is crucial. What causes mountain sickness? Why is it possible to reach the top of Everest without supplementary oxygen, yet if your plane depressurises suddenly at the same altitude, you're dead? Why are astronauts unable to stand without fainting when they return to Earth? Why do human divers get the Bends but sperm whales don't? Will men always be able to run faster than women? Why don't penguins get frostbite?