Sliced raw meat may have played key role in human evolution

A study in which peoplechewed on pieces of raw goat meat and vegetables smacked with arock is shedding light on how changes long ago in the way ourancestors dined paved the way for physiological advances thathelped make us who were are today.

Scientists said on Wednesday the advent of meat-eatingcombined with the use of simple stone tools to make food easierto consume meant that members of the human lineage about 2.5million years ago all of a sudden had less need for chewing.

I can tell you that eating raw goat is not pleasant. It's alittle on the gross side.- David Lieberman

Without needing to spend much of the day chewing food aschimpanzees do, our ancestors underwent significant evolutionarychanges, acquiring smaller teeth, jaws and chewing muscles whilelosing the snout possessed by their predecessors.

"Shortening the snout might have been beneficial forproducing articulate speech, for having a more balanced head,
especially useful when running, or perhaps for other reasons,"Harvard University evolutionary anthropologist Daniel Liebermansaid.

The changes also may have enabled the development of largerbrains in early human species like Homo erectus compared toearlier members of the human lineage like Australopithecus, whocombined ape-like and human-like traits.

Meat compared to plants added a calorically dense food tothe diet of these early humans as their brains and bodies gotbigger.

Before cooking existed

The researchers conducted experiments measuring how muchchewing effort was expended in eating the type of diet ourancestors are thought to have had. Cooking was not commonplaceuntil roughly 500,000 years ago.

Study volunteers chewed on tough raw goat meat, selected tomimic wild game, and three root vegetables: beets, carrots andyams. Electrodes were placed on their faces to measure chewingactivity.

Harvard evolutionary anthropologist Katherine Zink, thestudy's lead author, said the amount of chewing declined
markedly when the food was processed with the type of basicstone tools used at the time: slicing the meat into smallerpieces and pounding the vegetables six times.

The number of chews dropped by 17 per cent and the chewingforce by 20 percent while the volunteers were able to swallowmeat bits that were about 41 per cent smaller and thus moredigestible.

Lieberman served as a test subject before the volunteersstepped in.

"I can tell you that eating raw goat is not pleasant. It's alittle on the gross side," Lieberman said. "It's really
amazingly like chewing gum."

Lieberman said unlike carnivores, whose teeth aretailor-made for slicing meat, human teeth are "really designed
like mortars and pestles, for crushing."

The research was published in the journal Nature.