Early humans transitioned to a diet of processed foods between two and three million years ago, as stone tools were created to slice and pound raw meet into smaller, tender chunks. Researchers say this ultimately triggered the evolution of anatomical features that made early humans look more like the Homo sapiens we known today.
Using stone tools to cut up food would have dramatically reduced the time and force needed to chew. Therefore, early humans evolved a smaller jaw and teeth, which paved the way for speech and saved early humans as many as 2.5 million chews per year.
To put this in perspective, chimpanzees - our closest relatives - spend almost half of the day chewing, and with much greater force.
"Chewing is something we take for granted - we don't do it all that often and we don't think about it much," Daniel Lieberman, one of the study authors and a Harvard University evolutionary biologist, said. "But if you're a chimpanzee, you spend half the day chewing. If you're an australopith ancestor of Homo, you probably spend half the day chewing. And later we went through some amazing transitions in our evolutionary history where we now chew so little that we barely think about it at all."
For their study, Lieberman and fellow researcher Katie Zink examined volunteers as they ate raw goat meat, yams, carrots and beets. Researchers measured the number and forcefulness of the volunteers' chews.
At first, the volunteers' teeth couldn't break down the tough goat meat. However, when it was sliced into smaller pieces, and the veggies were crushed up, they had a much easier time swallowing their food.
"What we showed is that...by processing food, especially meat, before eating it, humans not only decrease the effort needed to chew it, but also chew it much more effectively," Zink explained. "Eating meat and using stone tools to process food apparently made possible key reductions in the jaws, teeth and chewing muscles that occurred during human evolution."
Researchers also note that adding sliced meat to the diet allowed early humans to get the same amount of calories needed for daily acticities with less jaw action. Without the need for an ape-like jaw and heavy teeth, early humans were able to evolve smaller snouts, better for running, and shorter jaws, better for speech.
Previously, cooking was thought to be a key turning point in the evolution of our species; however, researchers say that cooking alone would not explain such anatomical changes. Instead, they suggest cooking evolved as a trend after our ancestors began slicing and dicing their meat.
Their study was recently published in the journal Nature.
