What evolved first—our brain or gut?

What if the brain evolved to serve the gut? Scientists at Flinders University are challenging a cornerstone of biology, arguing that the gut’s nervous system may be the body’s original “brain,” with the brain evolving later to support its needs.

An opinion piece published in The Journal of Physiology draws on evidence from physiology and evolutionary biology to suggest the nervous system may have originated in the gut. The paper offers a perspective on one of evolution’s fundamental questions: why did brains evolve in the first place?

Flinders researchers argue the answer may lie in a much older nervous system embedded in the gut, which helped early organisms to secure the energy necessary to survive.

Rethinking the body’s command structure

Lead author Dr. Tim Hibberd says the idea challenges the traditional view that the brain sits at the top of the body’s command structure.

“We are proposing a different way of looking at the nervous system,” says Hibberd, from Flinders’ College of Medicine and Public Health.

“The enteric nervous system in the gut can sense its environment, process information and coordinate complex responses. In many ways, it functions like a brain in its own right.”

Often referred to as the body’s “second brain,” the enteric nervous system contains hundreds of millions of neurons and can operate independently to coordinate digestion and other essential functions.

Researchers now argue it may be more accurate to think of this as the body’s first brain.

The gut’s influence extends beyond digestion

Senior author Nick Spencer says this theory helps explain why the gut remains so influential in directing functions throughout the body.

“The gut is constantly gathering information and communicating with other organs,” says Spencer, from Flinders Health and Medical Research Institute (FHMRI).

“It plays a major role in regulating digestion, metabolism and other functions essential for survival. These fundamental processes may have helped drive the evolution of the nervous system.”

A different starting point for disease research

While this theory will not change medical treatment overnight, the researchers say it could influence future studies into conditions linked to the gut and nervous system, including obesity, diabetes, Parkinson’s disease and digestive disorders.

“The way we think about the body shapes the way we investigate disease,” says Hibberd.

“If we begin to view the gut as a central player in nervous system function, it may open up new avenues for research.”

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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