"Survival of the fittest." - Raw competition? Or, a level of cooperation indispensable to life? Evolution tells us that both are important. This program explores the spiraling arms race humans have with microorganisms, the only entities that pose a threat to human existence. The program follows the struggles of medical detectives uncovering the roots of epidemics and traces the alarming spread of resistance among pathogens that cause disease, like the new virulent tuberculosis - nicknamed "Ebola with wings." Interactions between species are among the most powerful evolutionary forces on Earth, and understanding them may be key to human survival.