Gut microbes may secretly shape how primate brains function and evolve

New research has uncovered a striking connection between gut microbes and brain function in primates, including humans. The findings suggest that these tiny organisms may play a key role in shaping how the brain works—from memory and emotions to basic movement.

Scientists have long suspected a link between the gut and the brain. Now, experiments show that transferring gut microbes between species can alter brain activity in measurable ways.

The study focused on how gut microbes from humans and other primates affect brain function in mice. When researchers transplanted microbes from large-brained species into mice, the rodents' brain activity began to mirror that of the donor species. Gene expression in their brains shifted, closely resembling the patterns seen in the original host.

Human and primate microbes produced distinct effects. Those from humans boosted cognitive functions like memory and emotional control by increasing activity in the hippocampus and calming the amygdala. In contrast, microbes from macaques mainly influenced motor skills and stress reactions, without the same cognitive benefits. The team identified three main ways gut microbes may influence the brain. Some produce compounds that act like neurotransmitters, directly affecting nerve signals. Others interact with the immune system or release substances that travel through the bloodstream to the brain. Each pathway offers a potential explanation for how these microbes shape behaviour and mental processes. Every primate species, including humans, carries a unique set of gut microbes—almost like a microbial fingerprint. This consistency hints at a long-standing evolutionary relationship between these bacteria and their host's brain development.

The results open new avenues for understanding human brain evolution and disorders linked to cognitive health. If similar microbial influences exist in people, they could help explain conditions like memory loss, anxiety, or neurodegenerative diseases. Future studies will need to confirm whether these gut-brain connections work the same way in humans as they do in mice.