A disturbing report of the current global crisis of new and resurgent diseases. This account investigates how and why diseases such as AIDS, legionnaires' disease, ebola, TB, and new forms of cholera and malaria occur. Karlen charts humanity's relationship with microbes, from the earliest hominids' probable encounters with bubonic plague, to the spread of infections through trade, conquest and empire, to the problems awaiting the human race in the near future. Using research from the fields of genetics, virology and epidemiology, he concludes that today's epidemics are part of an ancient pattern: whenever people make radical changes in their lifestyle and environment, disease flourishes.