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In the mid-2010s, when they were still postdoctoral fellows at the Massachusetts Institute of Technology, Mathilde Poyet and Mathieu Groussin kept bumping into different sides of the same obstacle. Poyet, an ecologist and a microbiologist, was trying to study rare bacterial species, the kind that had never been grown in a lab before. Groussin, a computational biologist in the same lab, wanted to understand how humans and microbes evolved together over millenniums. Each was focused on microbes that make their homes in and on the human body, what scientists collectively refer to as the human microbiome. But the only samples they could find to work with came from the same small sliver of humanity, namely populations that were wealthy, Western and white.

It was tantalizing to think about what a fuller picture might reveal. In recent years, scientists had linked the gut microbiome to a long list of conditions, including Crohn’s and irritable bowel syndrome, Parkinson’s, dementia and autism, and they were hopeful that a better understanding of those links would lead to treatments, if not cures. They were also sifting through the nearly unfathomable array of molecules that microbes produce, in search of biological treasures: not only potential medications but also compounds capable of breaking down pollutants or repairing damaged ecosystems.