How Sliced Meat Altered the Course of Human Evolution

By Nathaniel Scharping | March 9, 2016 3:41 pm

(Credit: RossHelen/Shutterstock)

Taking fewer bites during meals may have contributed to human evolution in a big way.

Researchers at the Department of Human Evolutionary Biology at Harvard University published a study suggesting human teeth and jaws started shrinking once our ancestors figured out how to use primitive tools to process their foods prior to eating. Slicing, pounding and mashing meat and vegetables allowed us to spend less energy chewing, which, researchers say, led to a gradual decline in the size of the jaw muscles and teeth that were called upon to accomplish this task.

While the decline in jaw and tooth size is well-known, this study replicated ancient diets with modern humans, and provides the first empirical evidence to support the link between a change in diet and tooth and jaw size. Researchers believe easing the burden of mastication may have triggered monumental changes in human evolution. They say smaller teeth and jaws may have altered our speech patterns, how we regulate body heat and could have even affected the size and shape of our brains.

Chewing for Science

For their experiment, the researchers asked 34 subjects to chew samples of foods that were likely part of our ancestors’ diet 500,000 years ago. Two groups of participants chewed on yams, beetroots and carrots, while a third dined on goat meat. Using electrodes attached to their jaw muscles, the researchers measured the amount of force they applied each time they chomped down.

By combining the force of each chew with the number of times they had to chew, researchers could approximate the amount of energy spent consuming their food. And, instead of swallowing, the participants spit the food back out so scientists could evaluate how well they ground it up.

As our ancestors developed tools and discovered fire, they would have had access to a broader range of food preparation techniques, and researchers attempted to simulate some of those early methods. They ran the experiment under four different conditions and fed participants food that was unprocessed, pounded or mashed, sliced and cooked. It was all in an attempt to determine if culinary advancements were tied to changes in how we ate, and more importantly, how we looked.


Microscopic views of the tiny food particles chewed up and spit back back out by participants in the study. Credit: Zink & Lieberman/Nature

When comparing the raw, untouched food to meat and vegetables that had been cut up, pounded or cooked, the researchers found that our ancestors would have chewed 17 percent less and with 26 percent less force eating a processed diet of one-third meat and two-thirds vegetables. Simply pounding vegetables and slicing meat would have improved humans’ ability to break food down into smaller particles by 41 percent. The researchers say that works out to roughly 2 million fewer chews per year, which is  a lot less work for our teeth and jaw muscles. The researchers published their work Wednesday in the journal Nature.

Looks Tied to Diet

Over time, as food processing skills improved, ancient humans didn’t need giant molars and oversized jaw muscles, and the sizes of both shrunk over the past 2 million or so years. Researchers think that the composition of our diets played a role in this change as well. Humans started consuming an increasingly meat-heavy diet as they evolved, likely a function of better hunting tools and tactics. Meat is also a richer source of calories than most plants, giving ancient hunters more bang for their buck.

Combined with cooking techniques that made the process of eating easier, hominids began consuming more calories with less effort, which may have paved the way for larger, energy-hungry brains. The researchers think that it was a combination of new food preparation techniques, helped along by the development of tools, and a shift toward a more carnivorous diet that drove these critical changes in our physiology.

Today, chewing is an afterthought for most of us — our food is processed to the point where we can swallow it with ease. Compare that to chimpanzees that spend five to 11 hours chewing on a small animal, researchers estimate. In terms of human evolution, less turned out to be more, and breaking our food down before it touched our mouths may have carried significant advantages.

Still, that’s no excuse to skip out on chewing dense food like meats and vegetables up to 30 times before swallowing, as recommended by the experts.

CATEGORIZED UNDER: Living World, top posts
  • Proteios

    Is this an example of adaptation or evolution. If the latter, it suggests evolution follows a logical course of action from environmental cues. More likely an adaptive response within a genome as were seen with the “hobbits”…small humans discovered in a limited resource environment. Either way, it’s fascinating.

    • zbecktx

      I think one could say that evolution is always adaptive. When mutations occur, those mutations which increase the likelihood of reproductive success are selected for (those lucky creatures produce more progeny that live on into the next generation, etc.). Those which decrease the likelihood of reproductive success fail to produce progeny and are effectively selected out. Of course, as the environment changes, mutations that were once beneficial may become problematic and vice versa. There is no genetic adaptation except for that those now better-suited to the environment/situation reproduce successfully and those not don’t.

  • aedgeworth

    So which is it? Random, chance, accidental mutations that just happened to be beneficial; or it adapted because it needed to? When you suggest a logical course of action are you suggested purpose and direction; which would not be random, chance, and accidental mutations? Maybe the real mechanism for evolutionary change is the power of positive thinking. That has never worked for me, but maybe it did for chimps.

    Now if we can just figure out these differences between chimps and humans: hands, arms, face, nervous system, feet, hair, neck, hips, pelvis, spine, ribs, humans are bipedal and apes walk on all fours, chimps are two to three times stronger than humans, declarative language skills, human intelligence, the human brain is three times larger than a ape brain, the control of fire, human desire to teach, technological advancement, sociability, facial expression, diet, long-term relationships, humans have white around their irises whereas chimpanzees usually have a dark brown color, etc. The differences far out-weigh the similarities by about 10 to 1.

    I think that is why they are desperately looking for those “missing links” and “common ancestors,” because they know the differences between chimps and humans are too great for them to be directly related. But I hope they keep the faith. I know they will figure it all out someday.

    • zbecktx

      I think what one could hypothesize is that food processing can be described as co-evolutionary. So smaller jaws might occur randomly, but without food processing, they would be maladaptive and therefore would not be selected for (smaller-jawed animals/people would be less likely to pass their genes into the next generation). With food processing, it would be easier for everyone to extract more nutrition from food, and in that context smaller jaws wouldn’t matter as much. And if those smaller jaws allowed the creature to devote more energy to some other project (bigger, more complex brains, bigger leg muscles, whatever), then that same random mutation (smaller jaw) might actually be more adaptive, and therefore more likely to be selected for.

      • JAFischer

        It’s also the physical stress of eating unprocessed foods that leads to the larger jaws and teeth in individuals. Our level of physical activity shows in our bones: people who do hard physical labor all their lives tend towards larger bones than people who may do little more than jog a couple of days a week.

    • JAFischer

      Please read some actual science before declaring that apes and humans can’t be related, or making statements demonstrating that you barely paid attention during the joke that was your high school biology class (and haven’t cracked a science book since).

  • Endrikh Darkvine

    I read “How Sliced Meat Altered the Course of Hitman Evolution.” xD

  • joseph2237

    Chewing few times also means more mouth fulls when completion for food was high or when stealing food from others increase chance for survival. Slow eaters didn’t survive lean times.


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