By Ed Yong
We have tens of trillions of bacteria and other microbes in our guts—at least one for each of our own human cells. Some species within this microbiome are passers-by, which we pick up from our food and our environments. But others are much older companions.
Andrew Moeller from the University of California, Berkeley, has found that there are a few groups of human gut bacteria whose history pre-dates humanity. Their ancestors lived in the guts of ancestral apes, and as those ancient animals diverged into modern species, the microbes did, too. In technical terms, they co-speciated. In simpler ones, if you drew out their family tree, you’d get ours for free; you could reconstruct the evolution of apes simply by comparing the right bacteria in their bowels.
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