David Bainbridge is the Clinical Veterinary Anatomist at Cambridge University, and fellow and admissions tutor in the arts and humanities at St Catharine’s College. He trained as a veterinary surgeon and has carried out research into pregnancy in man and animals at the Institute of Zoology at Regent’s Park, the Royal Veterinary College, and Cornell, Sydney and Oxford Universities. His previous popular science books take a zoological approach to human biology, including pregnancy (A Visitor Within, 2000), genes and sexuality (The X in Sex, 2003), the brain (Beyond the Zonules of Zinn, 2008) and adolescence (Teenagers: A Natural History, 2009). He lives in Suffolk with his wife and three children. He was forty when he started to write this book, has a belly, eschews reading glasses, drives a sports car and seems not to have heard of clichés.