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Food preservation technique may have triggered human brain growth, scientists say: ScienceAlert


Researchers suggest that the taste of the fermented morsels may have triggered a surprising increase in the growth rate of our ancestors’ brains.

In fact, the shift from a raw food diet to one that included foods already partially broken down by microbes may have been a crucial event in the evolution of our brains, according to a prospective study led by evolutionary neuroscientist Katherine Bryant of the University of Aix-Marseille in France and two American colleagues.

The size of the human brain has tripled over the past two million years of evolution, while the human colon has shrunk by about 74 percent, suggesting a reduction in the need to break down original foods internally. plant.

We know the timing and extent of human brain expansion, but the mechanisms for directing energy toward this expansion are more complex and somewhat debated.

The study authors outline their “external fermentation hypothesis” which shows that our ancestors’ metabolic circumstances for selective brain expansion may have been triggered by shifting intestinal fermentation to an external process, perhaps even by experimenting with preserves that are reminiscent of wine, kimchi, yogurt, sauerkraut and other pickles that we still eat today.

A schematic representation of the external fermentation hypothesis. (Bryant et al., Communication biology2023)

The human gut microbiome acts as an internal fermentation machine, which stimulates nutrient absorption during digestion. Organic compounds are fermented into alcohol and acids by enzymes, usually produced by bacteria and yeast that live in parts of our digestive system like our colon.

Fermentation is an anaerobic process, meaning it does not require oxygen. So, similar to the process that takes place in our intestines, it can occur in a sealed container. The process produces energy in the form of adenosine triphosphate (ATP), which is an essential source of chemical energy that fuels our metabolism.

The researchers argue that it is possible that culturally transmitted methods of handling or storing food may have encouraged the outsourcing of this function.

Externally fermented foods are easier to digest and contain more available nutrients than their raw counterparts. And because the colon has less to do if the food is already fermented, the size of the organ could shrink over time while potentially leaving energy available for brain growth.

The size of the brains of our ancestors, Australopithswere similar to those of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). The brain expansion of the human lineage accelerated with Homoemergence and continued throughout Homo sapiens And Homo neanderthalensis.

How did our ancestors, with brains the size of chimpanzees, manage to harness the power of external fermentation?

Bryant and his team suggest that hominids with lower cognitive abilities and smaller brains may have adapted to fermentation much earlier than alternative explanations proposed for this redirection of energy from the gut to the brain , such as hunting animals and cooking over a fire.

a comparison of expected and actual organ sizes
Estimated mass proportions of major organs in a typical 65 kg modern Western human. Left: expected ratios if humans were like other great apes. Right: actual ratios. (Bryant et al., Communication biology2023)

Fermentation has many benefits associated with cooked foods, such as softer textures, increased caloric content, better nutrient absorption, and defense against harmful microorganisms.

It only needs simple storage spaces like a hollow, cave, or even a hole in the ground, and is basically an easy, stress-free entry ticket to nutritional benefits. As the researchers point out, “it can be stumbled upon rather than requiring planning and the use of tools.”

“Hunting, scavenging large carnivores, and using fire carry their own risks; Bryant and colleagues write, “perhaps fermentation risks were more predictable and therefore more reliable through individual and cultural learning.”

In addition to increasing the bioavailability of nutrients, external fermentation can also make toxic foods edible, for example by removing cyanide from cassava, a common staple food (Manihot esculenta).

“Foresight and mechanistic understanding are not “The conditions required for the initial emergence of external fermentation,” the researchers write. “Our early ancestors may have simply brought food to a common location, left it there, ate some intermittently, and added more.”

Microbes from previous foods may have inoculated new foods, leading to fermentation. As the brain grew, humans might have developed a better understanding of fermentation.

The team emphasizes the need for empirical research to support or refute their hypothesis, such as microbiological studies, comparative analyses, and genetic and genomic investigations.

“The transfer of intestinal fermentation to an external cultural practice may have been an important innovation among hominids,” the authors conclude, “which established the metabolic conditions necessary for selection for brain expansion to take hold. “

The study was published in Communication biology.

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