Chew your food well, says almost every mother. As humans, we are set apart from other mammals by our advanced abilities to communicate, reason and even to act morally. Our ability to cut a steak and smear butter on bread also puts us at an advantage, new research shows. Results from a recent Harvard-led study published in the journal Nature reveal the evolutionary significance of how cutting our food before we chew helped our jaws evolve for the better.

When humans developed the ability to cut food with tools, they no longer needed to take such large bites. That led to the evolution of smaller teeth in humans, and in turn to changes in the jaw that facilitated a new more efficient way of eating to extract calories with less muscular effort. Chewing breaks food down from large particles into smaller particles, ultimately making it easier for the intestines to absorb nutrients and energy from the food as it passes through the digestive tract.

"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 the study’s lead author Katie Zink, a lecturer at Harvard University, in a statement. "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.”

To take a closer look into the vital role chewing played in our biological advancements, Zink and her colleagues had study participants chew raw goat meat and other foods, including carrots, beets, and yams before spitting them back out. Researchers then examined and photographed the food along with the distinctive teeth marks left behind. Instead, when subjects preprocessed their food by slicing the meat and breaking up the vegetables, they were able to reduce the number of chews required a day by nearly 20 percent. Humans first started preprocessing their foods more than 2 million years ago with rudimentary tools.

"What we found was that humans cannot eat raw meat effectively with their low-crested teeth," said the study’s senior researcher Daniel Lieberman, a biological sciences professor at Harvard University, in a statement. "But humans have done something really remarkable. Once you start processing it mechanically, even just slicing it, the effects on chewing performance are dramatic.”

Food writer and historian Bee Wilson, the author of “Consider the Fork: A History of How We Cook and Eat” describes the fork as the most universal tool known to man, and it was around the same time that human teeth evolved from having an edge-to-edge bite, as seen in apes, to now having the slight modern-man overbite. It was one of the evolutionary phenomenons that resulted from creating the intricate jaw movements that were necessary to break down small bites instead of large chunks. Wilson argues in line with Harvard’s new findings that our cranial and cognitive evolution had more to do with how we ate rather than what we ate.

“The evolution of the ability to chew food into smaller particles gave mammals a big boost of extra energy because smaller particles have a higher surface area to volume ratio, allowing digestive enzymes to then break food down more efficiently,” Lieberman said. "We eat even higher-quality foods than chimpanzees, and spend less time chewing them. Cooking makes chewing even easier.”

Humans’ closest ape relatives have to invest considerable time into chewing and extracting enough energy from their foods, which are mostly fruits. Meanwhile, other mammals such as cows eat a low-quality diet primarily of grass and hay, which requires them to spend a seemingly exorbitant amount of time chewing all day just to extract enough calories to give them energy for the day. When humans began preprocessing their food sources with tools, they embarked on an evolutionary tract that diverged them from the rest of the mammal pack, and laid the foundation for several key Darwinian advancements that led to who we are today.

"One of the innovations that helped make us human is cutting up and pounding our food," Lieberman said. "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.”

Source: Lieberman D and Zink K. Impact of meat and Lower Palaeolithic food processing techniques on chewing in humans. Nature. 2016.