Fermentation as the key to human brain development?

A study published in November 2023 by Bryant, Hansen and Hecht turns the hypothesis of our current brain development on its head.

Our ancestors were characterized by a comparatively small brain and an extensive digestive tract. Both the brain and the gut are energetically demanding organs, but an extensive gut was necessary for processing the plant and raw food that predominated at the time. Over the centuries, the human brain evolved and the digestive tract shortened - a result of evolutionary mutations that took hold. For a long time, the discovery of fire and the transition to cooking was seen as a turning point in this development. However, the authors of this study hypothesize that it was not fire, but the intake of externally fermented foods that was decisive.

What are the reasons behind this? The mostly plant-based and raw food was difficult to digest and required many resources in the intestine, which led to the longer digestive tract that was common at the time. This in turn required energy. Mutations that led to a shortened intestine and an enlarged brain could only become established after a change in diet had taken place. Food had to be easier to digest and thus provide more energy as well as through potential storage. The authors of the study argue that external (outside the body) fermentation enabled pre-digestion of nutrients. This reduced the need for a long colon, and the energy saved could now be used for other processes.

How do the authors justify their hypothesis? Firstly, they point out that the use of fire for food processing was well after the onset of brain growth. Furthermore, they believe that the use of fire for food processing requires cognitive abilities that were questionable in times of smaller brains, comparable to those of chimpanzees. In contrast, fermentation does not require an "aha" moment; it happens daily and passively. Fire, on the other hand, is not necessarily encountered on a daily basis while roaming the savannahs and forests. The ability to link the sporadic discovery of fire to food processing and to reproduce this required much more complex skills than the passive use of fermentation. In addition, fermentation made food durable and storable, which created additional energy reserves needed for brain development.

Doesn't fermenting food also require mature cognitive skills? For the level of fermentation we have today, yes, but back then fermentation was probably purely accidental. Our ancestors transported food and its processing tools to specific locations over distances of up to 10km. Food was transported over long distances, stored, eaten and new food was added. Socially transmitted practices such as reusing the same storage locations, containers or tools for food processing would have further promoted the onset of fermentation and the stability of ongoing fermentation.

The argumentation of this study opens a new perspective on the role of fermentation in human evolution and adds an important dimension to existing theories. Click here for the full study.