This is one of the books that the Biophlilium holds as Required Reading For Humans because it explains what a human is inside and out. In the first chapter Ed Yong explains symbiogenisis far more clearly and more satisfyingly than Lynn Margulis did in her seminal book on the subject. Each of our cells is descendant from a merger of bacteria and archaea. Oh.
Next he talked about biogeography. He compares the biogeographical studies by Darwin and Wallace to the micro-biome studies happening now. He talks about every body as a landscape with differing bio regions. Then he talks about the difficulty in identifying the individual. We actually use the genes of our microbes to develop our bodies and express our selfness.
The book investigates the ideas of symbiosis and dysbiosis by looking at a series of trophic cascades like coral reefs and then compares them to the human body. He presents cutting edge research on the effects of changes in our gut biomes to digestion, mental health and immune systems and suggests that more research into the microbes that live with us could lead to an entirely new approach to wellness and medicine.
This book greatly influenced how I expect the next 300 years on earth will play out and inspired me to get my gut biome sequenced. (Which was expensive and not very interesting, I think they just gave the same ambiguous results to everyone.)