Study finds gut bacteria shared between Hadza and Tsimane peoples may trace back to common ancestors before human migration split the groups
A new study published in the journal Nature found that the Hadza people of Tanzania and the Tsimane people of Bolivia share roughly 90% of the same gut bacterial species — approximately 1,200 overlapping strains. Researchers, led by Stanford microbiologist Justin Sonnenburg, used bacterial dating techniques and stool sample analysis to estimate these shared microbial strains last shared a common ancestor around 17,000 years ago. About 60% of those shared microbes are rare or absent in people living industrialized, urban lifestyles.
A new study in Nature compared stool samples from dozens of Hadza individuals in northern Tanzania with samples gathered by the Tsimane Health and Life History Project in the Bolivian Amazon — two communities separated by roughly 7,000 miles and an ocean. Researchers found the two groups share approximately 1,200 bacterial species in their gut microbiomes, a near-90% overlap that the study's authors described as "startling."
The research team, led by senior author Justin Sonnenburg, a professor of microbiology and immunology at Stanford University, and co-author Ben Good, a theoretical biophysicist also at Stanford, concluded that the overlap most likely reflects a shared microbial inheritance from common ancestors in Africa. According to the paper, before some of those ancestors migrated out of Africa, through Eurasia, and across a land bridge connecting Russia and Alaska into the Americas, they carried these gut microbes with them. Once sea levels rose and the land bridge closed, exchange of gut bacteria through human contact became largely impossible. Using rates of bacterial mutation, the team dated the average shared microbial lineage to roughly 17,000 years ago, with some strains dating further back.
Babies are born with a near-blank microbial slate and acquire gut bacteria first from their mothers and then from others in their household and community, primarily through what researchers describe as the fecal-oral route — the ingestion of microscopic particles via air, dust, food, soil, and water. Sonnenburg and his colleagues argue this generational, human-to-human transmission is what allowed specific microbial strains to travel alongside migrating human populations over millennia, rather than being picked up independently from local environments.