The fossil record shows that a major shift in hominid anatomy occurred around 2 million years ago, when hominids developed a smaller rib cage and larger skull. At the same time, another major change took place in their intestines. Compared to our closest relatives, humans have a digestive tract that is 40 percent shorter. This decrease was thought to be driven by the external processing of our food, which reduced the time and energy involved in chewing and digesting. Anthropologist Richard Wrangham argues that the technological innovations of controlling fire and cooking food led to this major change, and that the excess energy we got from cooked food, in turn, supported the evolution of a larger brain.
However, two recent studies, by biological anthropologist Katie Amato in 2021 and evolutionary biologist Erin Hecht in 2023, suggest that these anatomical changes may have been driven by human use of fermentation even before humans began to cook. By allowing microbial species to ferment and break down complex carbohydrates and other macromolecules in foods, we may have turned over certain parts of an otherwise energy-intensive digestive process to microbes in a form of "external digestion." This use of fermentation to pre-digest food, intentional or not, may have served as a predecessor to cooking, providing the extra calories needed to support the evolution of a larger brain.
Another benefit of fermentation is that it offered access to foods which, previously, would have been toxic. As our ancestors came down from the trees and needed new ways to fill their stomachs, the tubers of many plants and grasses offered an appealing, ready source of calories. Tubers contain large deposits of starch. Root vegetables, such as potatoes, yams, and carrots, are our modern-day, highly domesticated equivalents. But the wild tubers of our ancestors' time were hard to chew, and some contained low levels of toxins. Varieties of cassava, for example, contain compounds that release cyanide when ingested. After just a few days of fermentation, however, microbes destroy these dangerous molecules and make the food safe to eat.2
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