Has modern life made us sicker, or healthier? On one hand, so-called “diseases of civilization,” such as diabetes or hypertension, are more prevalent than ever, while at the same time we have dramatically reduced mortality from many infectious diseases. It is easy to assume that our health, as with other parts of our lives, is adapted to a hunter-gatherer existence, and that, with a few notable exceptions, we would be better off emulating simpler times. It turns out, however, that rapid evolution is nowhere more evident than in the genes that are associated with sickness and immunity. The signature of selection is often best seen in genes related to disease. We were never in perfect harmony with our environment, and evolutionary medicine is the ideal place to explore the complex of tradeoffs and compromises that our bodies have always represented.  And contrary to popular belief, cancer is ancient, not modern. Its origin may lie in the evolution of multicellularity itself.