Researchers propose that a taste for fermented morsels may have triggered a surprising jump in our ancestors’ brain growth rate.
In fact, a switch from a raw diet to one that included foods already partially broken down by microbes may have been a crucial event in the evolution of our brain, according to a perspective study by evolutionary neuroscientist Katherine Bryant of Aix-University. 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 approximately 74 percent, suggesting a reduced need to internally break down plant foods.
We know the timeline and extent of human brain expansion, but the mechanisms that allow energy to be directed into this expansion are more complex and somewhat debated.
The study’s authors lay out their “external fermentation hypothesis,” which shows that our ancestors’ metabolic circumstances for selective brain expansion may have been set in motion by shifting gut fermentation to an external process, perhaps even undergoing . with preserved foods similar to wine, kimchi, yogurt, sauerkraut and other pickles that we still eat today..
The human gut microbiome acts as an internal fermentation machine, increasing 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, such as the colon.
Fermentation is an anaerobic process, meaning it does not require oxygen, so, similar to the process 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 drives our metabolism.
The researchers argue that it is possible that culturally transmitted ways of handling or storing food encouraged the externalization of this function.
Externally fermented foods are easier to digest and contain more available nutrients than their raw counterparts. And since the colon has less to do if food is already fermented, the organ’s size could shrink over time while potentially leaving energy available for brain growth.
The brain size of our ancestors, the australopithecinesThey were similar to those of chimpanzees (Troglodyte bread) and bonobos (paniscus bread). 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, 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 long before proposed alternative explanations for this redirection of energy from the gut to the brain, such as animal hunting and cooking. of fire.
Fermentation has many advantages associated with cooked foods, such as softer textures, higher calorie content, better nutrient absorption, and defense against harmful microorganisms.
You only need simple storage spaces like a hollow, a cave, or even a hole in the ground, and it’s basically a low-stress, low-entry ticket to nutritional goodness. As the researchers note, “it can be stumbled upon rather than requiring planning and tool use.
“Hunting, scavenging large carnivores, and using fire carry their own risks”; Bryant and his colleagues write that “perhaps the risks of fermentation were more predictable and therefore more reliably mitigated through individual and cultural learning.”
In addition to increasing the bioavailability of nutrients, external fermentation can also make poisonous foods edible, for example by removing cyanide from cassava, a common staple.Manihot esculenta).
“Foresight and mechanistic understanding are No requirements for the initial emergence of external fermentation,” the researchers write. “It is possible that our early ancestors simply took food to a common place, left it there, and intermittently ate a little and added more.”
Microbes from previous foods may have inoculated new foods, leading to fermentation. As brains grew, humans may have developed a better understanding of fermentation.
The team emphasizes the need for empirical research to support or refute their hypotheses, 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 hominin innovation,” the authors conclude, “that established the metabolic conditions necessary for selection for brain expansion to take place.”
The study has been published in Communications Biology.