Chewing may have played a vital role in the evolution of our face

We do it every day but barely give it a thought.

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Chewing is the simple process of masticating. The net energy gain from food will change if the energetic cost of mammalian mastication changes. The associated metabolic costs of chewing various objects are unknown at this time, even though understanding the energetic efficiency of masticatory effort is crucial to understanding the evolution of the human masticatory system.

A team of researchers from Leiden University published a new study- measuring the energy cost of human chewing. Using respirometry and electromyography of the masseter muscle, scientists found that chewing by human subjects represents a measurable energy sink. Moreover, it elevates metabolic rate above basal levels by 10 to 15%.

Six males and fifteen females between 18 and 45 participated in the study. While the subjects sucked on soft or stiff chewing gum, the researchers took various measurements. The volunteers’ oxygen consumption, carbon dioxide production, and the activity of their masseter muscles were all measured using a customized hood and electrodes, respectively.

Paleoanthropologist Amanda Henry said, “When chewing the softer gum, the volunteers increased their energetic expenditure by an average of 10.2% relative to their basal metabolic rate (BMR). This rose to 15.1% above for the stiffer gum. BMR is the amount of energy that the body burns at rest each day.”

“What we discovered was that chewing food takes a lot of energy. And more importantly: the harder the food, the more energy it takes.”

Most modern foods are processed and generally soft, while early humans would have eaten more challenging things, including seeds, nuts, tubers, and fibrous leaves. It would have required more energy to chew their food because they did not prepare it the way we do today. Early humans had a limited supply of food, therefore, it was crucial from an evolutionary standpoint to use as little energy as possible to consume them.

Henry said“We assume that natural selection produced jaws, facial muscles, and teeth that make the chewing system as efficient as possible, thus minimizing the energy spent chewing food. We, therefore, think that how we humans chew today has been optimized by evolution.”

This discovery is expected to help better understand the unique morphology we see in human ancestors.

Journal Reference:

  1. Adam Van Casteren et al. The cost of chewing: Mastication’s energetics and evolutionary significance in humans. Science Advances. 17 Aug 2022. Vol 8, Issue 33. DOI: 10.1126/sciadv.abn835