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"Evolving to Eat Mush": How Meat Changed Our Bodies

 

Hillary Mayell

for National Geographic News

 

February 18, 2005

Meat-eating has impacted the evolution of the human body, scientists reported

today at the American Association for the Advancement of Science's annual

meeting in Washington, D.C.

 

Our fondness for a juicy steak triggered a number of adaptations over countless

generations. For instance, our jaws have gotten smaller, and we have an improved

ability to process cholesterol and fat.

 

 

Our taste for meat has also led us into some trouble-our teeth are too big for

our downsized jaws and most of us need dental work.

 

"It's really amazing what we know now that we didn't know 15 or 20 years ago,"

said Mark Teaford, a professor at Baltimore's Johns Hopkins University. Teaford

helped organize a panel discussion on human diet from a number of perspectives:

 

.. How did the ability to eat meat shape the evolution of humans?

.. What can we learn about early humans from tooth shape?

 

Carnivorous humans go back a long way. Stone tools for butchering meat, and

animal bones with corresponding cut marks on them, first appear in the fossil

record about 2.5 million years ago.

 

How Did Meat-Eating Start?

 

Some early humans may have started eating meat as a way to survive within their

own ecological niche.

 

Competition from other species may be a key element of natural selection that

has molded anatomy and behavior, according to Craig B. Stanford, an ecologist at

the University of Southern California (USC).

 

Stanford has spent years visiting the Bwindi Impenetrable Forest National Park

in Uganda, Africa, studying the relationship between mountain gorillas and

chimpanzees.

 

"It's the only forest where mountain gorillas and chimps both live," he said.

"We're trying to understand the ecological relationship-do they compete for

food, for nesting sites?"

 

The key difference between chimps and gorillas ecologically is that chimps eat

meat and gorillas don't. A total herbivore is able to coexist with an omnivore

because they have significantly different diets.

 

"From there we can extrapolate back to what two species of early humans may have

done vis-à-vis each other two or three million years ago," Stanford said.

 

Better Fat Processors

 

When humans switched to meat-eating, they triggered a genetic change that

enabled better processing of fats, said Stanford, who has worked extensively

with gerontologist Caleb Finch of USC.

 

"We have an obsession today with fat and cholesterol because we can go to the

market and stuff ourselves with it," Stanford said. "But as a species we are

relatively immune to the harmful effects of fat and cholesterol. Compared to the

great apes, we can handle a diet that's high in fat and cholesterol, and the

great apes cannot.

 

"Even though we have all these problems in terms of heart disease as we get

older, if you give a gorilla a diet that a meat-loving man might eat in Western

society, that gorilla will die when it's in its twenties; a normal life span

might be 50. They just can't handle that kind of diet."

 

Diet and Teeth

 

Tool-use no doubt helped early humans in butchering their dinners. But there is

evidence that the advance to cooking and using knives and forks is leading to

crooked teeth and facial dwarfing in humans.

 

Today it's relatively rare for someone to have perfectly straight teeth (without

having been to the orthodontist). Our wisdom teeth don't have room to fit in the

jaw and sometimes don't form at all, and the propensity to develop gum disease

is on the increase.

 

"Virtually any mammalian jaw in the wild that you look at will be a perfect

occlusion-a very nice Hollywood-style dentition," said Peter Lucas, the author

of Dental Functional Morphology and a visiting professor at George Washington

University in Washington, D.C. "But when it comes to humans, the ideal occlusion

[the way teeth fit together] is virtually never seen. It's really the only body

part that regularly needs attention and surgery."

 

Lucas argues that the mechanical process of chewing, combined with the physical

properties of foods in the diet, will drive tooth, jaw, and body size,

particularly in human evolution.

 

Essentially, by cooking our food, thereby making it softer, we no longer need

teeth big enough to chow down on really tough particles. By using knives and

forks to cut food into smaller pieces, we no longer need a large enough jaw to

cram in big hunks of food.

 

"We're evolving to eat mush," said Bernard Wood, a paleoanthropologist at George

Washington University.