Man can only tolerate a limited range of environmental conditions, whereas other lifeforms thrive in the most intense conditions - in extreme heat or many, many leagues under the sea in utter darkness or deep in the middle of rocks. Why is this so? How do people survive extremes of heat, cold, depth and height? For the geneticist, inheritance is all. But for the physiologist, extremism is all. This book explores the limits to human survival and the physiological adaptations which enable us to exist under extreme conditions.