Species-wise, you probably identify as human. But based on the number of cells in and on your body, you are actually more microbe, because trillions of them call you home. Your human genes are outnumbered by microbial genes and, as the scientists exploring our microbial ecosystems (known as our microbiomes) are discovering, the armies of tiny freeloaders our bodies host are quietly controlling us. Together, they can govern mood, appetite and immune responses, as well as helping to digest and metabolise foods.

Read more at Science Focus.