Sleep is one of the most important aspects of our life, health and longevity and yet it is increasingly neglected in twenty-first-century society, with devastating consequences: every major disease in the developed world - Alzheimer's, cancer, obesity, diabetes - has very strong causal links to deficient sleep.Until very recently, science had no answer to the question of why we sleep, or what good it served, or why its absence is so damaging to our health. Compared to the other basic drives i...