Processing food before eating likely played key role in human evolution, study finds

Credit: Jm Verastigue/public domain

How much time and effort do you spend chewing? Although you probably enjoy a few leisurely meals every day, chances are that you spend very little time and muscular effort chewing your food. That kind of easy eating is very unusual. For perspective, our closest relatives, chimpanzees, spend almost half their day chewing, and with much greater force.

When and how did eating become so easy? And what were its consequences?

According to a new Harvard study, our ancestors between 2 and 3 million years ago started to spend far less time and effort by adding meat to their diet and by using to process their food. The researchers estimate that such a diet would have saved as many as 2.5 million chews per year, and made possible further changes that helped make us human. The study is described in a March 9 paper published in Nature.

One of the biggest puzzles in human evolution is how species such as Homo erectus evolved smaller teeth, smaller faces, and smaller guts, and yet managed to get more energy from food to pay for their bigger brains and bodies before cooking was invented. "What we showed is 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.

By changing their diets to include just 33 percent meat, and processing their food - slicing meat and pounding vegetables - before eating, Zink and Lieberman found that the muscular effort required per chew and the number of chews required per day was reduced by almost 20 percent. They also found that by simply slicing meat with the sorts of simple tools available more than 2 million years ago, humans were able to swallow smaller, more easily digestible pieces than would have been possible without using tools.

"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.

But testing a process as basic as chewing isn't as easy - or as attractive - as it might sound.

"What Katie did was creative but sometimes, frankly, a little stomach-churning," Lieberman said. "Not only did she have people come into the lab, chew raw meat and other foods, and spit them out, but then she had to analyze the stuff."

It wasn't just any food - or any meat - that subjects noshed on.

To approximate the toughness and texture of the game that early humans ate, Zink and Lieberman (after much experimentation) settled on using goat - which subjects chewed raw while Zink used instruments attached to their jaw to measure the effort involved.

In each trial, volunteers were given, in random order, a selection of foods prepared in several ways - raw, sliced, pounded and cooked goat, as well as several vegetables, including carrots, beets and yams. After chewing each morsel until they would normally swallow, subjects spit out the food. Zink then spread the individual food particles out onto a tray, photographed them, and digitally measured their sizes.

"What we found was that humans cannot eat effectively with their low-crested teeth. When you give people raw goat, they chew and chew and chew, and most of the goat is still one big clump - it's like chewing gum," Lieberman said. "But once you start processing it mechanically, even just slicing it, the effects on chewing performance are dramatic."

But why study chewing at all?

"Chewing is one of the key characteristics of being a mammal," Lieberman explained. "Most other animals, like reptiles, barely chew their food—they just swallow it whole. 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."

Most mammals, however, eat a relatively low-quality diet- think of cows eating grass and hay - that they need to spend most of the day chewing. Even humans' closest ape relatives, with a diet that consists mainly of fruit, must spend nearly half their day chewing to extract enough energy from their food, Lieberman said.

"But we humans have done something really remarkable," he said. "We eat even higher-quality foods than chimpanzees, and spend an order of magnitude less time chewing them."

Making that change, however, presented early humans with a new challenge.

One of the critical components of that higher-quality diet is meat, which - despite being calorically dense - is very difficult for humans to chew effectively.

"Meat has a lot of nutrients, but it is also very elastic. You can think of it as being like a rubber band," Zink said. "So the problem is that we can't break it down with our flat, low-cusped teeth. But if you slice it up, then you do not need to use your teeth to break it down as much, and you swallow much smaller particles. Cooking makes chewing even easier."

That pre-processing, and the reductions in chewing effort that came with it, Zink and Lieberman said, may have opened the door to one of the most important lifestyle changes in human evolution - the emergence of hunting and gathering.

"With the origin of the genus Homo...we went from having snouts and big teeth and large chewing muscles to having smaller teeth, smaller chewing muscles, and snoutless faces" Lieberman said. "Those changes, and others, allowed for selection for speech and other shifts in the head, like bigger brains. Underlying that, to some extent, is the simplest technology of all: slicing into smaller pieces, and pounding vegetables before you chew them."

The impact that higher-quality diets and easier chewing could have on early humans is clear if you imagine what day-to-day life might have been like millions of years ago.

"Suppose you go out hunting for antelopes like impala or kudu, but at the end of the day you come back empty-handed, which happened fairly often for early humans," Lieberman said. "Chimps couldn't survive that way - they would then have to spend all night eating.

"Following the invention of hunting and gathering, though, humans can benefit from a division of labor," he continued. "Someone else may have come back with an impala, or some tubers you could eat. And instead of spending all night eating it, you'd spend a lot less time, energy and effort to chew it by pounding it or cutting it with just a few stone stone tools. What a dramatic shift!"

Though many aspects of our biology changed when the genus Homo evolved, Zink and Lieberman said that processing food before eating almost surely played a significant role.

"One of the innovations that helped make us human is cutting up and pounding our ," Lieberman said. "Extra-oral processing first by using stone tools and then by cooking played a very important role in 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."

Explore further

Chewing over the aging process

More information: Impact of meat and Lower Paleolithic food processing techniques on chewing in humans,
Journal information: Nature

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User comments

Mar 09, 2016
Nice work, but I'll have to chew on the result.

Mar 09, 2016
Nice work, but I'll have to chew on the result.

You'll need to figure out how to chew with tongue-in-cheek. : )

Mar 09, 2016
That is some delicious looking curry.
I would think that fire i.e. cooking, would have played an even bigger role in our evolution. We owe a lot to the human, who instead of running away in fear, chose to stick his meat in fire.

Mar 09, 2016
Of course, there is another, easier way to make meat easier to chew and digest - let it rot. All meat and game is left to hang now to make it more tender. Pheasant, it is reputed, is best left to hang until it is green.

Another way, which seems very unpleasant to us, is to catch a predator and eat its gut contents. A dog or cat would have no trouble with that. Why would proto-humans?

Oysters, seafood, insects, grubs, some fish, all easy to chew and great sources of protein.

Mar 10, 2016
not rated yet 4 hours ago
Of course, there is another, easier way to make meat easier to chew and digest - let it rot.

Letting meat hang, slicing it, cooking it....whatever: It's all a form of external (pre) digestion to get at the interior of cell matter.
A more extreme form is what spiders do: Externally dissociate their prey with enzymes and then slurp up the goo.

The idea behindal this is the same. Have some external mechanism crack the tough cell mebranes instead of having to do it yourself (which requires either large teeth or a very aggressive/extensive digestive system)

Mar 10, 2016
Еvolutionists can not answer to the fundamental question how life emerged on the planet Earth by chance. Also can not answer to the question how fictional evolution can be passible when there is only negative effects from random changes in genetic information (mutations) in the living organisms that insert only dиsinformation noice in the system. How can emerge new genes and functionality and its control mechanisms simultaniuosly in the living organisms without the ideas, the will and the know how of intelligent being, that is compatible with old functionality. Life is very complex thing. The simplest bacterias on Earthwhich live in the external environment have about one milion base pears in their DNA, which ensuring the very base functionality for the living organism.

Mar 10, 2016
They can not answer to de question haw this basic functionality can emerge uddenly like a magic. Can not answe to thе questions how complex multicelled organism can separate in two sexes within one generation to be passible next generation. This requires too complex functionality, which should be fully compatible between both sexes. They know that this theory is not scientific and is full with logical and factologiocal contadictions, so not even trying to answer to this fundamental questions. Just trying to earn time.

Mar 10, 2016
If I'm reading this correctly, we evolved by beating our vegetables and not our meat.

Mar 10, 2016

A 100 star comment!

Mar 10, 2016
"Processing food before eating likely played key role in human evolution"

-and devolution as well. The lack of fiber and nutrients in our diets from the domesticated foods we've created is killing us.

Our jaws atrophy and our gums recede because of all the pap we eat.

Mar 11, 2016
"That's abiogenesis. Evolution deals with the diversity and complexity of life. You would know that if you weren't so willfully ignorant."

I do not by this. Fictional abiogenesis is invention of evolutionists and is part of the theory of evolution. Nothing can evolve theoretically if it does not exist. If one person defend the idea that the living organisms can evolve which is in contradiction with the physical laws and the creation event, it must defend the idea that life can emerge by chance without the intervention of intelligent being. When evolutionst can not answer to fundamental questions for life emergence and complexity, they find convenient lay to to no answer to thi squestions by declaration that this is not their speciality despite that is part of the theory of evolution support.

Mar 11, 2016
" It is not a random process, but evolution doesn't know what the end result of what its "making" and has no end goal other than the passing of genes. But your brain cant get around this because of your Creationist bias."

Explain in details how works this non random process that have no ideas an goal and must obey physical laws like everithing else in the physical reality. How and why this unonsciousness fictional procces should have the goal to transffer genes after all? Obviously to be working such kind of process without consciousness, intelligence, ideas and purpose it should be passible to cause the increasing of information (order) in the physical systems. But it does not existing such proceses in nature.

Mar 11, 2016
Еxplain what is the point of emergence and existence of different structures and elements of the living cells if they are not organised in the living cell? When these are not part of the cell, their existance is pointless.
A machine to work and have certain functionality, it has to be assembled from all its necessary elements. The existence of a each element separately outside the context of this machine is pointless. The needed functionality determines the structure and organization of physical systems and embedded information which renders them functional.
What makes science viable are the scientific facts and not the declarations and philosophizing.

Mar 11, 2016
Viko everything has been explained to you.....many times by many posters on many articles. YOU just refuse to accept ANY evidence that YOU ask for because of your creation bias
ALSO for the nooB's!

not only is 13 being completely accurate, but as you can see- viko has no evidence to support ANY conclusion

Here are the arguments she uses
1- because i/the bible/my deity says so

2- Nuh-uh, and you can't prove it

(when presented evidence of something)
3- *fingers in ears or head up *ss) LALALALALALALA - I CAN'T HEAR YOU!

4- nuh-uh, and you can't prove that is real

5- (typical of all religious idiots) that study is pseudoscience (repeat ad nauseum)


it doesn't matter WHAT evidence you bring, it will be ignored and she will spout one of the above arguments

Mar 13, 2016
explain... explain... explain...
Viko thinks what actually takes years of study can be explained in a few posts 1) because he can ask his questions in a few posts and 2) his book explains such things in only a few verses in 1 or 2 chapters.

So easy isn't it viko?

Sorry if there are things on the world that neither you or I will ever understand.

But while have confidence that there are people who can and do, you have faith that they dont and never will.

See the difference?


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