External Fermentation and the Evolution of the Human Brain
Researchers from the University of Marseille in France have explored how outward fermentation processes may have influenced brain growth in early humans. Their work, reported in the journal Communication Biology, suggests that products of external fermentation could have played a role in explaining the rapid expansion of the human brain across evolutionary time.
Across the course of evolution, the brain’s size tripled, yet scientists have long debated the forces driving this substantial change. Traditional hypotheses fall short of fully accounting for the surge in neural volume. The new proposal, known as the external fermentation hypothesis, offers a complementary angle by focusing on how fermentation outside the body might have altered energy availability for the brain and shaped cognitive development.
Inside the digestive system, especially in the colon, friendly gut bacteria break down carbohydrates and other substances into readily usable nutrients through a process that can be described as internal fermentation. This microbial activity generates short chain fatty acids and helps liberate energy from dietary fiber, while also supporting the absorption of essential vitamins and minerals. The researchers argue that external fermentation could provide similar advantages, broadening the perspective on how energy resources were accessed by early hominins.
Notably, the study points to a significant shift in gut anatomy over time. The large intestine shows evidence of a considerable reduction, roughly seventy four percent, implying a decreased reliance on plant matter breakdown that occurred in earlier stages of hominin evolution. This anatomical change may reflect a broader shift toward relying on fermentation processes outside the body and a corresponding reallocation of energy toward brain development.
In early hominins, food could have been transported and stored in ways that inadvertently triggered external fermentation. Over generations, these practices might have become culturally ingrained, aiding cognitive growth and social complexity. The evolving use of fermentation tools and techniques could have been a driving force behind both brain expansion and shifts in digestive strategy, illustrating a deep link between diet, culture, and neural architecture.
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Attribution: This synthesis draws on research conducted at the University of Marseille and reported in Communication Biology, with interpretation grounded in recent reviews of human evolution and gut-brain interactions.