Indigenous communities thousands of miles apart share surprisingly similar gut bacteria, suggesting that some microbes have coexisted with humans for thousands of years. A study published in Nature revealed that the Hadza hunter-gatherers of Tanzania and the Tsimane people of the Bolivian Amazon—despite living 7,000 miles apart on different continents—share roughly 1,200 species of gut bacteria, representing nearly a 90% overlap in their microbial communities.
Researchers led by Stanford University microbiology professor Justin Sonnenburg believe this shared microbial profile stems from common ancestors in Africa. According to co-author Ben Good, dating techniques based on bacterial mutation rates show that these shared bacterial strains diverged around 17,000 years ago. This timeline corresponds with ancient human migrations out of Africa, through Eurasia, and across the former land bridge connecting Asia and North America before rising sea levels separated the continents.
The study also found that both the Hadza and Tsimane microbiomes differ significantly from those of urban populations, including city residents living in nearby regions. Modern lifestyles, diets, and medical practices appear to have reduced microbial diversity in industrialized societies. Sonnenburg suggests that because human biology evolved alongside these ancestral microbes, losing them could potentially present health challenges that modern bodies must adapt to.
However, independent experts emphasize that the long-term health implications remain unclear. Evolutionary biologist Andrew Moeller of Princeton University notes that industrialized microbiomes might represent an adaptation to modern living environments rather than a harmful loss. Scientists say further research is needed to determine whether losing ancestral gut bacteria negatively impacts human health or simply reflects human adaptation to modern life.