Gut microbes may have traveled with humans out of Africa
Hunter-gatherers in Tanzania and forest farmers in Bolivia share more than 1,200 kinds of gut bacteria, a new study found. Many of these microbes are rare or gone in people in rich, industrial countries. The Stanford-led team says the bugs likely traveled with humans as they spread out of Africa.
Two groups of people live about 7,000 miles apart, with an ocean between them. Yet their guts are home to many of the same bacteria. A new study says those microbes may have traveled with our ancestors as they spread across the globe.
The study, led by Stanford University researchers, was published Oct. 7 in Nature. It compared the gut microbiomes of the Hadza, hunter-gatherers in Tanzania, and the Tsimane, Indigenous forager-farmers in the Bolivian Amazon.
The two groups share more than 1,200 bacterial species, Stanford said. About 60% of those species are rare or completely missing in people living in industrialized countries. Both groups' gut bacteria were also very different from those of people in cities, even nearby ones, NPR reported. The research used stool samples collected from both groups.
The team then estimated when different strains of the microbes split apart. For many species, the timing lined up with major human migrations out of Africa and into the Americas.
"Our study establishes that the hundreds of bacterial species that are rare or missing in industrialized microbiomes were ancient companions of ours," said Justin Sonnenburg, a Stanford microbiologist and the study's senior author.
Why it matters: Gut microbes help us digest fiber, make vitamins and train the immune system. People in rich, industrial countries have far fewer kinds of gut bacteria. They also get more Type 2 diabetes, obesity and autoimmune disease. Scientists have not proven that losing microbes causes those diseases.
"When you start to lose biodiversity in your gut, there may be big issues for your human biology to adjust to," Sonnenburg told NPR.
Not everyone agrees on what the loss means. Andrew Moeller, an evolutionary biologist at Princeton University who was not part of the study, said the industrialized microbiome may be adapted to modern life. "Is it good or deleterious that industrialized humans have lost a lot of ancestral microbial taxa? We actually don't know," he said.
What we know: The Hadza and Tsimane share hundreds of ancient gut microbes that many city dwellers lack.
What we don't: Whether losing those microbes harms health.
Where outlets agree Stanford and NPR both report that the Hadza and Tsimane share about 1,200 gut bacterial species, many of them rare in industrialized people.
Where they differ Sonnenburg says losing these microbes may cause problems, while Princeton's Andrew Moeller says modern microbiomes may simply be adapted to modern life.