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 Scientists said on Wednesday the advent of meat-eating combined
with the use of simple tone tools to make food easier to consume
meant that members of the human lineage about 2.5 million years ago
all of a sudden had less need for chewing.
Without needing to spend much of the day chewing food as chimpanzees
do, our ancestors underwent significant evolutionary changes,
acquiring smaller teeth, jaws and chewing muscles while losing the
snout possessed by their predecessors.
"Shortening the snout might have been beneficial for producing
articulate speech, for having a more balanced head, especially
useful when running, or perhaps for other reasons," Harvard
University evolutionary anthropologist Daniel Lieberman said.
The changes also may have enabled the development of larger brains
in early human species like Homo erectus compared to earlier members
of the human lineage like Australopithecus, who combined ape-like
and human-like traits.
 Meat compared to plants added a calorically dense food to the diet
of these early humans as their brains and bodies got bigger.
The researchers conducted experiments measuring how much chewing
effort was expended in eating the type of diet our ancestors are
thought to have had. Cooking was not commonplace until roughly
500,000 years ago.
Study volunteers chewed on tough raw goat meat, selected to mimic
wild game, and three root vegetables: beets, carrots and yams.
Electrodes were placed on their faces to measure chewing activity.
Harvard evolutionary anthropologist Katherine Zink, the study's lead
author, said the amount of chewing declined markedly when the food
was processed with the type of basic stone tools used at the time:
slicing the meat into smaller pieces and pounding the vegetables six
times.
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The number of chews dropped by 17 percent and the chewing force by
20 percent while the volunteers were able to swallow meat bits that
were about 41 percent smaller and thus more digestible.
Lieberman served as a test subject before the volunteers stepped in.
"I can tell you that eating raw goat is not pleasant. It's a little
on the gross side," Lieberman said. "It's really amazingly like
chewing gum."
Lieberman said unlike carnivores, whose teeth are tailor-made for
slicing meat, human teeth are "really designed like mortars and
pestles, for crushing."
The research was published in the journal Nature.
(Reporting by Will Dunham; Editing by Sandra Maler)
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