Abstract
How do new infectious diseases emerge? Why do some antibiotics cease to be effective? What consequences can lifestyle changes or public health policies have on the virulence of pathogens? The pandemic caused by the new human coronavirus, following those caused by HIV or multi-drug-resistant bacteria, is a striking illustration of the importance and speed of the evolution of microbes.In addition to the Pasteurian approach, which deconstructs cellular mechanisms to provide answers at the individual level, it is necessary to combine a Darwinian approach which studies the dynamics of populations within their environments: only by integrating both approaches will it be possible to control infectious agents and find both original and sustainable treatments.