Jeneen Interlandi writes:

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.

“About 90 percent of all human diversity has been completely left out of the picture,” Groussin told me recently. It was as if someone had shone a bright flashlight on one small segment of a giant canvas and left the rest shrouded in darkness. The bright spot was well defined (imagine the face of a man). But they couldn’t really tell what they were looking at (whether that man was a monk, for example, or a matador) without seeing the rest of the canvas.

Scientists refer to this vast, unexplored terrain as biology’s dark matter. Our bodies are home to more bacteria — on our skin, up our noses, in our guts and mouths and around our genitals — than there are stars in the Milky Way. These microbes have evolved not only with us but inside us, and scientists who study them closely say that hardly a biological process or system exists in which they do not play a role. They helped create our digestive systems and our immune systems. They influence the size and shape of our bodies. At least some research suggests that they also affect our brains, moods, personalities and behaviors. And yet, most of them have still not been identified, let alone studied.

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.

But the unknowns still far outweighed the knowns: No one could say for certain what counted as a healthy microbiome or whether an unhealthy one could be altered intentionally. Nor was it clear whether changes to a person’s individual microbiome were a cause of illness or a consequence.

Poyet and Groussin suspected that the answers to those questions lurked not in the 10 percent of the canvas that scientists were looking at but in the remaining 90 percent. [Continue reading…]