Study suggests gut microbes followed migrating humans across continents

Two rural communities separated by an ocean share many of the same gut bacteria, according to a new study. The paper, in the journal Nature, suggests this microbial kinship may have taken shape long ago, before human migration split the groups' ancestors apart, NPR reported. The study relied on stool samples from both groups. The Hadza are hunter-gatherers who have roamed northern Tanzania for thousands of years; the Tsimane forage, fish and hunt in the Bolivian Amazon, some 7,000 miles away.

Researchers found around 1,200 of the same bacterial species in the two groups, a near-90% overlap, NPR reported. The comparison used genetic material in stool samples from dozens of individuals collected by the Tsimane Health and Life History Project, alongside previous analysis from the Hadza community. Justin Sonnenburg, a professor of microbiology and immunology at Stanford University and the study's senior author, said the major overlap was "startling."

The study also showed that the microbiome — the mix of bacteria living in the gut — was markedly different in both groups than in city dwellers, even those living nearby, NPR reported. Sonnenburg said: "If we were inhabited by very similar microbes over a long period of time, it suggests that our human genomes may have come to expect a certain set of microbes and functions." He said that when biodiversity in the gut is lost, there may be big issues for human biology to adjust to and accommodate.

Andrew Moeller, an associate professor of evolutionary biology at Princeton University who was not affiliated with the paper, said the hypothesis is intriguing but not yet proven. He said another possibility is that the industrialized microbiome profile may actually be adapted to an industrialized lifestyle. "From a health perspective, is it good or deleterious that industrialized humans have lost a lot of ancestral microbial taxa [groups]? We actually don't know," Moeller said.

Sonnenburg has previously contrasted the microbiomes of the Hadza with those of industrialized people, according to NPR. He said the Hadza live a lifestyle much more similar to the one human ancestors lived. He said that lifestyle is more hospitable to microbes handed down through many generations over the course of human evolution.