This book investigates the evolutionary origins and biological mechanisms of emerging infectious diseases that pose significant threats to human populations. Christopher Wills, an evolutionary biologist, utilizes a framework of coadaptation and mutation to explain how pathogens transition between species. By analyzing the historical trajectory of viruses and bacteria, the author argues that understanding the secret lives of these organisms is the primary requirement for developing effective medical interventions and long-term control strategies.

Experts in the field of evolutionary biology recognize this work as a clear synthesis of complex epidemiological concepts for a general audience. Readers frequently note the accessible prose style, which effectively bridges the gap between technical biological research and public health history.