[Did humans co-evolve with the gut microbiota?]

The gut microbiome plays an important role in animal physiology and development. While the molecular, cellular and ecological mechanisms that determine its diversity and impact on animal health are beginning to unfold, we still know relatively little about its evolutionary history. Fundamental questions such as "Is the microbiota evolving and at what race?", "What are its origins?", "What are the consequences of microbiota evolution for human health?" or "Did we co-evolve with our gut bacteria?" are only beginning to be explored. In the short term (from a few days to a few years, or microevolution), gut microbes can evolve and adapt very rapidly within an individual in responses to environmental changes, such as diet shifts, which can affect human health. On the longer term (ten to millions of years, or macroevolution), evolution within individuals is counterbalanced by the transfer of microbes from other people, so that human evolution is decoupled from the evolution of most gut microbes over many generations. This suggests that, while gut microbes have probably evolved rapidly within humans, most of them have a history of exchange between host populations over millennia. Whether the evolution of the microbiota over the last hundreds of thousands of years has facilitated human adaptations remains an open question and an exciting avenue for future research.