Brain tissue requires significant energy, especially in larger-brained mammals. A new study from Northwestern University suggests that gut microbes may have played a role in the evolution of larger brains by influencing energy production and usage. Researchers found that mice with gut microbes from large-brain primates produced and used more energy compared to those with microbes from small-brain species, which stored more energy as fat.

This research, published in Microbial Genomics, provides evidence that gut microbes can influence biological variations across species. Katherine Amato, first author of the study and associate professor of anthropology at Northwestern, stated, “We know the community of microbes living in the large intestine can produce compounds that affect aspects of human biology — for example, causing changes to metabolism that can lead to insulin resistance and weight gain.”

In their experiment, researchers introduced microbes from two large-brain primate species (human and squirrel monkey) and one small-brain species (macaque) into microbe-free mice. They observed physiological changes such as weight gain and liver function over time. The findings showed similarities between mice with human and squirrel monkey microbes despite these species not being closely related.

Amato explained, “These findings suggest that when humans and squirrel monkeys both separately evolved larger brains, their microbial communities changed in similar ways to help provide the necessary energy.” Future studies aim to include more primate species with varying brain sizes to further explore these microbial influences on metabolism.