This book focuses on the biomedical aspects, while not ignoring other life-changing influences of space living. For example, what happens to people physiologically in the microgravity of space, where weight and the direction "up" become meaningless? Adapting to microgravity represents the greatest environmental challenge that life will have encountered since our ancestors moved from the seas to solid Earth. Away from Earth the human body will begin almost immediately to adapt and change, to be able to function in these strange environments. As a person adapts in space he or she will become less fit to live on earth.