A pioneering study provides new evidence that gut microbes vary across primate species and can shape physiology in ways associated with differences in brain size and cognitive function
A new study suggests that altering the community of microbes living in the gut can influence how the brain functions.
Humans have the largest brain size relative to body size among primates, yet scientists still do not fully understand how species with bigger brains evolved ways to meet the high energy costs needed for brain development and upkeep.
Researchers at Northwestern University now provide the first direct evidence that the gut microbiome helps shape differences in brain function across primate species.
“Our study shows that microbes are acting on traits that are relevant to our understanding of evolution, and particularly the evolution of human brains,” said Katie Amato, associate professor of biological anthropology and principal investigator of the study.
The research builds on earlier work from Amato’s lab showing that gut microbes from larger-brained primates, when transferred into mice, increased the amount of metabolic energy available in the host’s microbiome, a key requirement for supporting large, energy-demanding brains. In the new study, the team focused on the brain itself, testing whether microbes from primates with different relative brain sizes could directly alter how the brains of host mice function.
What they found
In a tightly controlled laboratory experiment, scientists introduced gut microbes from two large-brained primate species (human and squirrel monkey) and one small-brained primate species (macaque) into mice that had no microbes of their own.
After eight weeks, clear differences emerged. Mice carrying microbes from smaller-brained primates showed distinct patterns of brain activity compared with mice that received microbes from larger-brained primates.
The brains of mice colonized with large-brain primate microbes showed higher activity in genes linked to energy production and synaptic plasticity, the physical process of learning in the brain. Mice that received microbes from smaller-brained primates showed lower levels of activity in these same pathways.
“What was super interesting is we were able to compare data we had from the brains of the host mice with data from actual macaque and human brains, and to our surprise, many of the patterns we saw in brain gene expression of the mice were the same patterns seen in the actual primates themselves,” Amato said. “In other words, we were able to make the brains of mice look like the brains of the actual primates the microbes came from.”
Another surprising discovery the researchers made was a pattern of gene expression associated with ADHD, schizophrenia, bipolar disorder, and autism in the genes of the mice with the microbes from smaller-brained primates.
While there is existing evidence showing correlations between conditions like autism and the composition of the gut microbiome, there is a lack of data showing that the gut microbes contribute to these conditions.
“This study provides more evidence that microbes may causally contribute to these disorders —specifically, the gut microbiome is shaping brain function during development,” Amato said. “Based on our findings, we can speculate that if the human brain is exposed to the actions of the ‘wrong’ microbes, its development will change, and we will see symptoms of these disorders, i.e., if you don’t get exposed to the ‘right’ human microbes in early life, your brain will work differently, and this may lead to symptoms of these conditions.”
Implications and next steps
Amato sees clinical implications for further exploration of the origins of some psychological disorders and for taking an evolutionary perspective on the way microbes affect brain physiology.
“It’s interesting to think about brain development in species and individuals and investigating whether we can look at cross-sectional, cross-species differences in patterns and discover rules for the way microbes are interacting with the brain, and whether the rules can be translated into development as well.
Reference: “Primate gut microbiota induce evolutionarily salient changes in mouse neurodevelopment” by Alex R. DeCasien, Jacob E. Aronoff, Elizabeth K. Mallott, Sahana Kuthyar, Sriram Chitta, Brian T. Layden, Maria L. Savo Sardaro, Stanton Gray, Lawrence E. Williams, Emma R. Liechty, Hyo M. Lee, Won Lee, James P. Curley, Christopher W. Kuzawa and Katherine R. Amato, 5 January 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2426232122
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2 Comments
This yet another proven case where biochemistry alters how brain works.
Gut mycrobiome can do it; viruses can do it; drugs can do it… why is it so hard to admit that the vaccines could do it, too?
That is such a wonderful argument, the logic is self sustaining.