Although human DNA is 98% similar to that of the chimpanzee, the infections we catch are ~80% different. Some pathogens have co-evolved with the host since chimpanzees and hominids diverged, but most are serendipitous acquisitions that we have picked up as humans spread across the world. In fact, pandemic infections like smallpox and influenza only date from the last 12,000 years or so after we adopted settled farming communities and later developed large colonies known as cities. Does the history of infectious diseases help to predict future epidemics? I shall illustrate my story with examples of HIV and ectoparasites.