The human gut microbiome is composed of thousands of different bacteria and archaea that vary widely between populations and individuals. Scientists from the Max Planck Institute for Biology in Tübingen have now discovered gut microbes that share a parallel evolutionary history with their human hosts: the microorganisms co-evolved in the human gut environment over hundreds of thousands of years. In addition, some microbes exhibit genomic and functional features making them dependent on their host. Now published in Science, the researchers present the results of their study conducted with data from 1,225 individuals out of Africa, Asia and Europe.