Imagine spending half of your day chewing food like our cousins, the chimpanzees. You’d never get anything done. Strikingly, human teeth have evolved to become smaller over the past million years or so. This begs the question: how did we become such efficient eaters? There are two answers. For one, human ancestors started eating higher quality food (meat) and, secondly, they employed food processing. By applying tool use to anything outside slicing and cutting meat, these early ancestors may have opened the flood gates of innovation.

Image: Pixabay

Daniel Lieberman of Harvard University knows first hand how hard it is to eat raw meat. He and colleagues from the Human Evolutionary Biology faculty chewed raw goat meat, the closest thing they could find to game, for science!

Each volunteer  had eight electrodes attached to the face to measure the movements and force of four muscles involved in chewing. An electrode was also attached to each hand to phase out background noise. A force transducer placed in the left molar measured chewing force.

A gourmet diet of two thirds vegetables and one third raw goat meat was served. Participants had to chew the chunks until they were small enough to swallow with ease, then spit them out. “It stays like a wad in your mouth,” Lieberman told the LA Times speaking about what’s it like to eat raw meat. “It’s almost like a piece of chewing gum.”

The Harvard researchers found that just by processing the meat through slicing reduced the required number of chews by 20%. That’s 2.5 million less chews per year, the researchers say.

“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” said Katie Zink, the first author of the study, and a lecturer working in the lab of Daniel Lieberman, the Edwin M. Lerner II Professor of Biological Sciences.

“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,” Zink said.

Human teeth aren’t meant for chewing meat. Carnivores have scissor-like teeth that slice through the meat fast and efficient, while our puny molars are better at grinding. Though they’re roughly four times smaller today, our ancestors had similar functioning teeth 2.5 million years ago. Simply put, had our ancestors not thought of how to slice meat using stone tools, meat would have been a luxury they couldn’t had afford.

By processing meat, our genus was opened to new opportunities. Our jaws, teeth and chewing muscles became smaller, and behaviour changed to hunter gathering. Maybe most importantly, this paved the way for the next step culinary evolution: cooking.

The Harvard researchers found cooked meat actually takes more force to break down, but since the fibers are stiffer chewing is even easier overall. Previously, neuroscientists at  the Federal University of Rio de Janeiro in Brazil found that humans nowadays would need to eat 9 hours non-stop to get enough energy from unprocessed raw food alone to support our large brains. Cooked food is more efficiently absorbed in the body, significantly increasing the relative energy intake compared to digesting raw food. Follow-up studies at the time demonstrated that rodents or pythons grow faster and bigger when they eat cooked meat instead of raw meat, and that it takes less energy to digest cooked meat than raw meat.

It all started one chew at a time, though.

“One of the innovations that helped make us human is cutting up and pounding our food,” Lieberman said. “Extra-oral processing first by using stone tools and then by cooking played a very important role in human evolution because it released selection for big faces and big teeth, which then enabled selection for shorter faces which were important for speech, and enabled us to grow big brains and have large bodies. We are partly who we are because we chew less.”

Findings appeared in Nature.