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Why unprocessed, vegetarian food was actually bad for our ancestors

Before we could cook meat, we had to learn to slice it. (Bigstock)
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A new study concludes that the invention of processed food may have been a great turning point in human evolution. No, we're not saying that corn syrup and pork rinds were a boon to our ancestors: The research suggests that the consumption of meat and the invention of stone cutting tools may have given humans the nutrients — and free time — they needed to rise above the rest of the animal kingdom.

And it all comes down to chewing.

Previous research has suggested that the invention of cooking gave humankind a much-needed brain boost, allowing our ancestors to get more bang for their buck, nutritionally speaking. With the extra nutrients absorbed, the theory goes, they had more brain power (and more time to use it).

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But the new study, published Wednesday in Nature, suggests that we may have started making important food advances way before we first dropped meat in the fire 500,000 years ago. Around 2 or 3 million years back, the researchers say, humans had the means to start cutting and otherwise processing the veggies they ate — and they added meat to the menu as well. This shift in diet could have saved individuals a staggering 2.5 million chews per year, according to their experiments.

And those experiments? They were pretty gnarly: Lead author Katie Zink of Harvard University processed food using the simple tools available to humans 2 million years ago, then had human subjects chow down on the grub and spit it back out.

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Volunteers were given raw, sliced, pounded and cooked goat (which is stringy enough to approximate undomesticated game that early humans might have hunted) along with several similarly prepared vegetables. They chewed until the point of swallowing, then spit their masticated morsels out for Zink's appraisal.

With a modern human jaw, a sliced piece of goat meat could go down the hatch after an average of 30 chews or so. But unprocessed, that same meat remained basically intact indefinitely.

“It’s almost like chewing gum,” Zink told Science Magazine.

"Chewing is one of the key characteristics of being a mammal," her co-author Daniel Lieberman explained in a statement. "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."

Even our closest relatives, the chimpanzees, spend about half their day chewing. Our use of tools has clearly cut down on that dramatically. And later inventions, such as cooking and more elaborate food processing, have made chewing even less of an issue for our species — though it could be argued that we'd now benefit from our food being a little harder to eat.

Zink and Lieberman think the food processing craze might even have triggered changes in face shape that gave humanity its je ne sais quoi. 

"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 meat into smaller pieces, and pounding vegetables before you chew them."

"We are partly who we are because we chew less," he said.

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