We think of disease as our enemy, something we try to eradicate; germs and infections are things we battle.But in this witty, engaging book, evolutionary biologist Marlene Zuk reveals that, in fact, disease is our partner, not our foe, and is responsible for everything from how we look to how we have sex.Since the earliest days of life on earth, disease has evolved alongside us. Drawing on the latest research and studies, Zuk explains the role of disease in answering a fascinating range of questions such as: Why do men die younger than women? Why does the average male bird not have a penis? Why do we-and lots of other animals-get STDs? How is our obsession with cleanliness making us sicker? And how can parasites sometimes make us well?Using her own work on sexual selection as well as a sampling of stories from the natural world, Zuk makes us reconsider the fearsome parasite.