It happened roughly 2-3 million years ago. Our closest relatives, chimpanzees spend half of their waking life chewing food. But humans spend much less time and energy chewing. According to a study published in the journal Nature, these energy savings were used in the development of cognitive abilities, fueling human evolution. About 2-3 million years ago, early humans began processing their food prior to consumption.
A small change made early humans more intelligent
Early man also started eating less meat. These behavioral changes allowed them to absorb calories with less effort. By altering their diet to include only 33% meat, and slicing meat and pounding vegetables before eating, early humans saved as many as 2.5 million chews per year, according to evolutionary biologists at Harvard.
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As a result, early humans evolved smaller teeth, smaller jaws, and smaller intestines. Their surplus energy was rerouted to the development of the brain, said Katie Zink, an evolutionary biologist at Harvard. Slicing meat using simple stone tools available at the time, humans could swallow easily digestible, smaller pieces. They also lost the snout possessed by their predecessors.
Daniel Lieberman, the co-author of the study, said shortening the snout proved beneficial for producing articulate speech. Though almost all mammals employ this technique, humans seem to have perfected chewing. During the study, researchers measured how much chewing effort was expended in eating the type of food our ancestors consumed.
The number of chews dropped 17%
They had volunteers chew different foods, including raw goat meat and whole vegetables, as well as processed and cooked foods. Scientists measured energy expenditures and ergonomic forces. They found that the number of chews declined by 17% and the chewing force by 20% when volunteers ate food that was processed with basic stone tools used 2-3 million years ago.
Volunteers were also able to swallow meat pieces that were 41% smaller, thus more digestible. Daniel Lieberman said these changes allowed for selection for speech and other major shifts in the head.