Most apes spend about half their day chewing—an enormous waste of time and energy.
We humans, on the other hand, spend just a few minutes per day grinding our food before we swallow. Our efficient habits are certainly a product of cooking—which softens food—but also our choice of cuisine. Specifically, meat.
By the time of Homo erectus, about two million years ago, early humans had already evolved larger brains, smaller teeth, and weaker chewing muscles, said Daniel Lieberman and Katherine Zink of Harvard University. “This introduces a paradox,” Lieberman said. Cooking didn’t become common until around 500,000 years ago, so some other aspect of our early ancestors’ dietary practices had to have changed to power our bigger brains and heftier bodies.
He and Zink wanted to know if Paleolithic food-processing technologies enabled us to be more effective at chewing, decreasing the need for strong bite force or large teeth and putting off the rise of cooking for another 1.5 million years.
They invited adult participants in their study to chew bite-sized pieces of food veggies like beets and yams as well as mildly-processed goat meat, which best mimics wild game from that time period. Instead of swallowing, they spit out the tiny food particles for Lieberman and Zink to assess. Meanwhile, electrodes attached to the participants’ mouths measured which muscles were involved in chewing.
In a paper published today in Nature, Lieberman and Zink report that a hypothetical diet composed of about one-third meat and two-thirds plants (the former sliced into pieces and the latter pounded with a stone tool before ingesting) would have enabled early Homo to chew 17% less often—equivalent to 2.5 million fewer chews per year—and 26% less forcefully compared to what a completely vegetarian diet without any processing techniques would have allowed. That’s in part because meat, cut up into small pieces, requires less masticatory force to chew per calorie than the tough plants that were available to early hominins.
Their findings represent the first study to locate the critical role of chewing among all Homo species comprising the 1- to 1.5-million period between just before Homo erectus and the popularization of cooked food.
It also suggests that meat-eating might have allowed the many beautiful languages spoken in the world today to come into existence. When early hominins stopped needing to select for big teeth, facial structures were freed up to select for other advantageous properties—like short vocal cavities relative to the vocal tract, increased turbulence in the nose, and shorter snouts. The first two characteristics would have helped early hominins produce speech, and the latter would have shifted our center of mass for increased stabilization while running.
The research may also challenge a common belief that cooking is the foremost trait that makes us human. “I would argue that what made us human was hunting and gathering,” Lieberman said. “It involves cooperation, extractive foraging, tracking. What we’re showing is that among the many things that made us human are cooking and mechanical food processing.”