Human Jaw Size Evolved Because of Food Processing

Cutting and processing food may have led to smaller human jaws
A couple eating lunch outdoors. Getty/Image Source

You may have heard the old adage that you should chew your food, especially meat, at least 32 times before you try to swallow it. While that may be overkill for some types of soft food like ice cream or even bread, chewing, or lack thereof, may have actually contributed to the reasons human jaws became smaller and why we now have smaller numbers of teeth in those jaws.

Researchers at Harvard University in the Department of Human Evolutionary Biology now believe that the decrease in size of the human jaw was, in part, directed by the fact that human ancestors began to “process” their foods before they ate them.

This does not mean adding artificial colors or flavors or the type of processing of food we think of today, but rather mechanical changes to the food such as cutting meat into smaller pieces or mashing fruits, vegetables, and grains into bite sized, small jaw friendly amounts.

Without the large pieces of food that needed to be chewed more times to get them to pieces that could be swallowed safely, the human ancestors’ jaws did not have to be so large. Fewer teeth are needed in modern humans compared to their predecessors. For instance, wisdom teeth are now considered vestigial structures in humans when they were necessary in many of the human ancestors. Since jaw size has considerably gotten smaller throughout the evolution of humans, there is not enough room in some people’s jaws to comfortably fit the extra set of molars. Wisdom teeth were necessary when humans’ jaws were bigger and the food needed more chewing to be fully processed before being able to be swallowed safely.

Not only did the human jaw shrink in size, so did the size of our individual teeth. While our molars and even bicuspids or pre-molars are still larger and flatter than our incisors and canine teeth, they are much much smaller than the molars of our ancient ancestors. Before, they were the surface upon which grains and vegetables were ground into processed pieces that could be swallowed.

Once the early humans figured out how to use various food preparation tools, the processing of the food happened outside of the mouth. Instead of needing large, flat surfaces of teeth, they could use tools to mash these types of foods on tables or other surfaces.

While the size of the jaw and the teeth were important milestones in the evolution of humans, it created more of a change in habits besides just how many times food was chewed before swallowed. Researchers believe the smaller teeth and jaws led to changes in communication and speech patterns, may have something to do with how our body processed changes in heat, and could even have affected the evolution of the human brain in areas that controlled these other traits.

The actual experiment performed at Harvard University used 34 people in different experimental groups. One set of groups dined on vegetables early humans would have had access to, while another group got to chew on some goat meat - a type of meat that would have been plentiful and easy for those early humans to hunt and eat. The first round of the experiment involved the participants chewing completely unprocessed and uncooked foods. How much force was used with each bite was measured and the participants spit back out the fully chewed meal to see how well it was processed.

The next round “processed” the foods the participants would chew. This time, the food was mashed or ground up using tools the human ancestors may have been able to find or make for food preparation purposes. Finally, another round of experiments were performed by slicing and cooking the foods. The results showed that the study participants used less energy and were able to eat the processed foods much more easily than those that were left “as is” and unprocessed.

Once these tools and food preparation methods were widespread throughout the population, natural selection found that a larger jaw with more teeth and oversized jaw muscles were unnecessary. Individuals with smaller jaws, fewer teeth, and smaller jaw muscles became more common in the population. WIth the energy and time saved from chewing, hunting became more prevalent and more meat was incorporated into the diet.

This was important for early humans because animal meat has more Calories available, so more energy was then able to be used for life functions.

This study found the more processed the food, the easier it was for the participants to eat. Could this be why the mega-processed food we find today on our supermarket shelves are often high in caloric value? The ease of eating processed foods is often cited as a reason for the obesity epidemic. Perhaps our ancestors who were trying to survive by using less energy for more Calories have contributed to the state of modern human sizes.