In 2013, Jeffrey Gordon and colleagues published a paper in the journal Science, which reported on an experiment involving mice and fecal transplants. They took fecal samples from pairs of identical human twins in which one twin had obesity and the other did not. They transferred the feces to mice. The mice that got feces from the twin that had obesity grew fat. The others did not. --- Source: https://www.nytimes.com/2013/09/06/health/gut-bacteria-from-thin-humans-can-slim-mice-down.html