Metaphors that scientists use to talk about the microbiome influence scientific understanding and can shape medical treatment. For example, viewing the microbiome as an "organ" or a "part of the immune system."

Some physicians support fecal microbiota transplantation (FMT) - treating the malfunction of the gut microbiome by swallowing a pill full of someone else's poo. It follows the same basic principles as an organ transplant, and the treatment is probably a consequence of understanding the microbiome as an organ.

To think of a microbiome as an organ creates a limited perspective because organs are relatively set. Generally, a heart will develop and remain the same in each person. But a microbiome is not one thing. It's trillions of things and responds to small changes in our diet, environment, and...