Gut Bacteria Traveled With Humans Out of Africa, New Study Suggests

Keypoints:

• A Stanford University-led Nature study compared the gut microbes of the Hadza of Tanzania and the Tsimane of Bolivia
• The two groups share 1,231 microbial species, about 87% of the Tsimane's species
• About 60% of the shared species are rare or absent in industrialized populations
• Genetic split times for many shared species roughly match human migration out of Africa and into the Americas
• The groups' ancestors were separated for tens of thousands of years

Two communities on different continents carry nearly the same gut bacteria. That is the finding of a Nature study published on 7 October and led by researchers at Stanford University. The groups are the Hadza, hunter-gatherers in Tanzania, and the Tsimane, forager-horticulturalists in the Bolivian Amazon. Their ancestors separated tens of thousands of years ago.

Researchers recovered about 1,400 species from the Tsimane and found 1,231 of them in the Hadza too. That is roughly 87%. Stanford's Justin Sonnenburg said the overlap was startling. The shared species also differ sharply from those in industrialized people, even city dwellers living nearby.

Sharing a species proves little by itself. A bacterium found on two continents could have been picked up recently from the environment. So the team analyzed 636 abundant shared species in detail. Most showed no recent strain sharing. Split times between the two populations roughly match human migration out of Africa and into the Americas.

The health angle is notable. About 60% of the shared species, 848 in all, are rare or absent in industrialized guts. Sonnenburg noted that the microbes in a typical modern gut are unlikely to be those handed down from great-great-grandparents. Benjamin Good, a co-author in Stanford's Department of Applied Physics, said the bacteria were presumably present in the ancestors of everyone.

What the loss of these microbes means for health is still unknown. The authors flag it as a target for future study. The study also shows what migration leaves behind in a body. People carried more than genes and stories across continents.