Fermentation technology as a driver of human brain expansion - Communications Biology
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As brain tissue is metabolically expensive, the evolutionary expansion of human brains required shifts in energy intake and metabolism. The External Fermentation Hypothesis proposes that a shift to consumption of externally fermented foods in human ancestors permitted a reduction in gut tissue required for internal fermentation, facilitating brain expansion.

Here, we propose the initial metabolic trigger of hominid brain expansion was the consumption of externally fermented foods. We define “external fermentation” as occurring outside the body, as opposed to the internal fermentation in the gut. External fermentation could increase the bioavailability of macro- and micronutrients while reducing digestive energy expenditure and is supported by the relative reduction of the human colon.