Fermentation May Have Driven Evolution of Ancient Humans; How Did Dietary Changes Allow Our Brain to Grow Larger?

The human brain's size and capabilities remain one of the marvels of science. Its evolution from a smaller primate brain into a complex and creative organ remains a mystery.

(Photo: Pexels/ Quang Nguyen Vinh )

Timeline Gap in History

Experts can determine when our ancestors evolved larger brains, the point in history when they roughly tripled as ancient humans progressed from the bipedal primates called Australopithecines. However, why it happened and what spurred the change has remained elusive.

The brain tissue is metabolically expensive, requiring a lot of calories to keep it running. Hence, acquiring enough energy to survive is a constant problem. Something in the ancient diet of the larger-brained human species must have altered for them to survive.

Some scientists believe that using fire and the later discovery of cooking gave prehistoric man enough nourishment for our larger-brained predecessors to become dominant. There could be changes in what they ate, or the discovery of cooking might have allowed them to obtain more calories from whatever they ate.

However, this theory contradicts the fact that the earliest evidence of the use of fire dates back to 1.5 million years ago. This timeline is significantly later than the development of the hominid brain. The cranial capacity of our ancestors began to increase 2.5 million years ago, which means there is a 1-million-year gap in the timeline between brain evolution and the possible emergence of cooking technology. This means that there could be other dietary changes that affect brain size.

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Accidental Side Effect

Human brains could not have grown larger before something had to have changed in their prehistoric diets. In previous years, experts have proposed alternative theories, such as the consumption of rotten flesh.

Erin Hecht and her colleagues suggested a different hypothesis in their study, "Fermentation technology as a driver of human brain expansion." They offer the possibility that 'pre-digested' food provides a more accessible form of nutrition. This could have fueled the bigger brain and allowed our larger-brained ancestors to survive through natural selection.

This theory is supported by the fact that our large intestine is proportionally smaller than other primates. It suggests that our predecessors adapted to food already broken down by fermentation. Aside from that, fermented foods are also found in all cultures and across different food varieties, from Europe's cheese and wine to Asia's soybeans and soy sauce.

The research team defined "external fermentation" and compared it to the internal fermentation in the gut. Then, they proposed the External Fermentation Hypothesis as a candidate mechanism for human gut reduction and brain expansion. The transformation of gut fermentation into an external cultural practice may have been an important hominin technology that provided the metabolic conditions needed for brain evolution.

The significance of fermentation in the evolution of the human diet and the reduction in the size of the human colon have already been postulated. However, the possibility that external fermentation served as the initial metabolic trigger of hominid brain expansion and gut reduction has been unnoticed.

Hecht and her team recognize the need for an additional study of brain responses to fermented and non-fermented foods, likely using ancient DNA. They believe their hypothesis can give scientists even more reasons to explore the importance of fermented foods on human health and maintaining a healthy gut microbiome.

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