What does the Covid virus exist for? It is by wanting to answer this question that Boucar embarked on writing this book where he shows us the fascinating history of micro-organisms. Microbes are a necessary evil for the survival of humanity. Full of hope but always lucid, the biologist storyteller shows us how our destiny is linked to these very distant ancestors. And why we should have more respect for this form of life essential to biodiversity, which our species would not exist without? For Boucar, the microbes "are there to teach humility to this bipedal who claims the right of life and death over the rest of creation." This accessible book opens our eyes to the infinitely small and, with kindness, reminds us that "whoever slaughters the environment harvests viruses.