The writer and doctor considers the transformations in mind and body that continue across the arc of human life. Some of these changes we have little choice about. We can’t avoid puberty, the menopause or our hair turning grey. Others may be welcome milestones along our path – a much-wanted pregnancy, a cancer cured or a long-awaited transition to another gender. We may find ourselves turning down dark paths, towards the cruel distortions of anorexia, or the shifting sands of memory loss. New technologies and medicine have unprecedented power to alter our lives, but that power has limitations.