We work furiously to conquer heart disease and dementia, but we never think to ask: Is aging itself necessary? Nature tells us it is not: There are tortoises and salamanders who are spry into old age and whose risk of dying is the same no matter how old they are, a phenomenon known as "biological immortality." In this "entertaining and thoughtful" overview (Wall Street Journal), Andrew Steele objectively charts the astounding progress science has made in recent years to secure the same for humans: to help us become old without getting frail, to live longer without ill health or disease.