Strain dating suggests gut microbes rare in industrialized people traveled with early humans
Stanford-led researchers find the Hadza and Tsimane share over 1,200 gut bacterial species, about 60% of them rare or absent in industrial guts. For many species, strain split dates match migrations out of Africa and into the Americas, so the missing microbes look like companions handed down over millennia.
The Scientist · Science desk
What happened
- The ancestral populations of the Hadza, hunter-gatherers in Tanzania, and the Tsimane of the Bolivian Amazon separated geographically tens of thousands of years ago.
- The work is the first deep sequencing of Tsimane stool samples, which a 2020 Nature Communications study had read only at low resolution.
- A 2023 Cell study by the same Stanford group found the average Hadza person carries about 750 gut species, against 250 for the average Californian.
- The paper is due in Nature on Oct. 7 and asks whether Homo sapiens has carried a characteristic, diverse microbiome going back millennia.
Why it matters
- What's now possible capability A dated list of long-resident gut species gives researchers specific candidates for testing how losing them changes human biology.
- What it limits constraint Health claims built on this result outrun it, because whether microbiome loss contributes to autoimmune disease, type 2 diabetes or obesity is still unresolved.
- What it limits constraint Comparisons that treat industrialized microbiomes as the human baseline are measuring against communities that lack most of the species these two distant groups share.
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The design depends on distance. The Hadza are hunter-gatherers in Tanzania, and the Tsimane are forager-horticulturalists in the Bolivian Amazon whose lives have had comparatively limited exposure to industrialization [3]. A shared species list alone would not show that the microbes traveled with people. The stronger evidence is timing. The team used several complementary population-genetics methods to estimate when strains of each species diverged [6]. Strains picked up recently and separately would have no reason to split on the schedule of prehistoric human migrations.
Taken at face value, about 60% of more than 1,200 shared species comes to roughly 720 species that are rare or missing in industrialized guts [18]. Justin Sonnenburg, a professor of microbiology and immunology and the study's senior author [8], put it in stronger terms. "Our study establishes that the hundreds of bacterial species that are rare or missing in industrialized microbiomes were ancient companions of ours as we migrated around the globe, likely passed from generation to generation for millennia," he said [7].
Deep metagenomic sequencing reads all the DNA in a stool sample as millions of short fragments, joins overlapping fragments into longer sequences and matches those against databases of microbial genomes [9]. The Tsimane samples were given voluntarily and collected by the Tsimane Health and Life History Project, whose members are collaborators on the study [16]. Sequencing them deeply let the Stanford team build a census that includes hard-to-capture species [12]. The Hadza samples had been sequenced in the group's earlier work [17].
The dates measure how long the microbes have lived with humans and say nothing about why industrialized people lack them. Sonnenburg calls the removal recent. "This long-term association has implications for how such recent biodiversity loss in our microbiome may impact our biology and thus our health," he said [11]. What the study shows was handed down is the microbes themselves. The earlier evidence that lifestyle shapes microbiome composition [13] is untouched by the dating.
I think the timing result is the strongest part of the work, provided "many species" turns out to mean a large share of the 1,200 [4][6]. The Stanford account does not give that share, or the number of people sampled.
What to watch
- The full Nature paper's sample sizes and the share of the 1,200-plus species whose strain split dates actually match the migration timeline.
- Strain-level dating in other nonindustrialized populations, to test whether the co-migration pattern holds beyond two groups.
- Experiments testing whether adding or removing specific long-resident species changes immune or metabolic measures in people.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence76
- Adoption
- Not scored
- Hype gap+15
- Incentives
- Not scored
- Confidence72
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A Stanford University-led study scheduled for publication Oct. 7 in Nature attempted to answer whether Homo sapiens hosted a characteristic and diverse microbiome going back millennia.
- [2]
The ancestral human populations that gave rise to the Hadza and Tsimane became geographically separated tens of thousands of years ago.
- [3]
The researchers conducted the first deep comparison of the microbiomes of the Hadza in Tanzania, one of the world's few remaining hunter-gatherer groups, and the Tsimane, Indigenous forager-horticulturalists in the Bolivian Amazon whose lifestyles have had comparatively limited exposure to industrialization.
- [4]
The Hadza and Tsimane share over 1,200 bacterial species.
- [5]
Most of the shared species, about 60%, are rare or completely absent in industrialized populations' microbiomes.
- [6]
Using several complementary population genetics analysis techniques, the researchers estimated when microbial strains separated; for many species, those estimates correspond to the time frame of major prehistoric human migrations out of Africa and into the Americas.
- [7]
"Our study establishes that the hundreds of bacterial species that are rare or missing in industrialized microbiomes were ancient companions of ours as we migrated around the globe, likely passed from generation to generation for millennia,"
- [8]
Justin Sonnenburg is a professor of microbiology and immunology and the study's senior author.
- [9]
Deep metagenomic sequencing reads all the DNA in a sample, generating millions of small sequences; overlapping stretches indicate how they join into longer sequences, which are compared with databases of microbial genomes to identify organisms.
- [10]
The Stanford researchers did the first deep sequencing of the Tsimane samples, which had previously been sequenced only at low resolution in a 2020 Nature Communications study.
- [11]
"This long-term association has implications for how such recent biodiversity loss in our microbiome may impact our biology and thus our health."
- [12]
The sequencing enabled the researchers to build a comprehensive census of the microbes in the respective microbiomes, including hard-to-capture species.
- [13]
There is evidence that lifestyle affects microbiome composition, and people in industrialized countries show a profound loss of microbiome diversity compared with people living nonindustrialized lifestyles.
- [14]
People in industrialized countries suffer from autoimmune diseases, type 2 diabetes, obesity and other chronic conditions that are rare among nonindustrialized groups; whether microbiome loss contributes to these diseases is still unresolved.
- [15]
Gaining insight into which long-term residents of the microbiome coevolved with humans could point to ways to investigate how the loss of microbial diversity through industrialization affects human biology.
- [16]
The Tsimane Health and Life History Project team, whose members are collaborators on the study, had obtained voluntarily provided stool samples from the Tsimane.
- [17]
Sonnenburg and colleagues previously completed metagenomic sequencing on Hadza samples, reported in a 2023 Cell study, showing that the average Hadza individual has about 750 species in their microbiome while the average Californian has 250.
- [18]
About 60% of the more than 1,200 shared species is roughly 720 species rare or absent in industrialized microbiomes.
Sources
2 independent publishers whose own reporting we read for this story.
- nature.comGut microbes that trace ancient human journeys
2 articles · October 6, 2026
- phys.orgGut bacteria reveal ancient ties to human migrations across continents, genetic analysis suggests
1 article · October 7, 2026
Topics and entities
Topics
- Gut Microbiome and Protein Fermentation
- Metagenomics
- Prehistoric human migration
Entities
- Justin Sonnenburg
- Tsimane Health and Life History Project
- Nature
- Stanford University