What lives in you? It is a simple enough question. Yet, for most of history, it has been unanswerable. Finally, in just the last few years, we have begun to get a picture of the creatures on which you depend for existence, the creatures that constitute, literally, the majority of your cells, the creatures being dragged around as you cook breakfast, drive your car, shower or do anything else. It is a fuzzy picture, seen through the lenses of genes rather than through a microscope, and yet it is the best we have ever had.
What exactly do we see? [...]