Meat-Based Diet Made Us Smarter

NPR online has published online an article discussing the role of meat-eating in human brain evolution.  The author, Christopher Joyce, interviews both Leslie Aiello, co-author of the Expensive Tissue Hypothesis, and Richard Wrangham, the vegetarian primatologist who believes that cooking meat played a very important role in brain evolution.

This article has some real choice passages, like this one from Aiello:

"You can't have a large brain and big guts at the same time," explains Leslie Aiello, an anthropologist and director of the Wenner-Gren Foundation in New York City, which funds research on evolution. Digestion, she says, was the energy-hog of our primate ancestor's body. The brain was the poor stepsister who got the leftovers.

Until, that is, we discovered meat.

"What we think is that this dietary change around 2.3 million years ago was one of the major significant factors in the evolution of our own species," Aiello says.

In fact, new data suggests that this change took place at least 3.4 million years ago.

Previously unknown to me, Aiello says we have some extraordinary data that indicates that our ancestors scavenged meat from carcasses shared with wild dogs and hyenas:

"The closest relative of human tapeworms are tapeworms that affect African hyenas and wild dogs," she says.

So sometime in our evolutionary history, she explains, "we actually shared saliva with wild dogs and hyenas." That would have happened if, say, we were scavenging on the same carcass that hyenas were.

But dining with dogs was worth it. Meat is packed with lots of calories and fat. Our brain — which uses about 20 times as much energy as the equivalent amount of muscle — piped up and said, "Please, sir, I want some more."

 This "dining with dogs" may have had other consequences for human evolution.  MSN online reports that dogs, not chimps are most like humans in social behavior.  I feel inclined to turn this around to say that humans behave more like dogs than like chimps--more like pack hunters and less like solitary mostly vegetarian chimps.  The lead author of this comparative study of dog and human behavior, Jozsef Topal explained to Discovery News "that shared environment has led to the emergence of functionally shared behavioral features in dogs and humans and, in some cases, functionally analogous underlying cognitive skills."  In other words, humans who dined with dogs and behaved more like dogs and less like chimps had greater success in the hunt so that today we behave more like dogs than like chimps.

Back to the NPR article:

"As we got more [meat], our guts shrank because we didn't need a giant vegetable processor any more. Our bodies could spend more energy on other things like building a bigger brain. Sorry, vegetarians, but eating meat apparently made our ancestors smarter — smart enough to make better tools, which in turn led to other changes, says Aiello." 

Those other changes included reduction of the size of teeth and mouth as we adapted to use of "external teeth" i.e. knives.  I often remark that this adaptation made the smile possible.  After all, when an animal with hefty canines bears its teeth, it doesn't exactly warm the heart with joy.

The Raw Deal


Currently raw food diets seem popular.  The raw fooders seem fond of pointing out the no other animal cooks food, and they think this shows that cooking is "unnatural."  They also like to point out that cooking can destroy components of food.

Well, no other animal uses computers, composes symphonies, or writes sonnets.  Wrangham points out that we have good reason to believe that we wouldn't have the brain we need to do these things if we hadn't started cooking.  From the NPR article: 

Wrangham explains that even after we started eating meat, raw food just didn't pack the energy to build the big-brained, small-toothed modern human. He cites research that showed that people on a raw food diet, including meat and oil, lost a lot of weight. Many said they felt better, but also experienced chronic energy deficiency. And half the women in the experiment stopped menstruating.

It's not as if raw food isn't nutritious; it's just harder for the body to get at the nutrition.

Wrangham urges me to try some raw turnip. Not too bad, but hardly enough to get the juices flowing. "They've got a tremendous amount of caloric energy in them," he says. "The problem is that it's in the form of starch, which unless you cook it, does not give you very much."

Then there's all the chewing that raw food requires. Chimps, for example, sometimes chew for six hours a day. That actually consumes a lot of energy.

"Plato said if we were regular animals, you know, we wouldn't have time to write poetry," Wrangham jokes. "You know, he was right."

Wrangham eats a vegetarian diet, but notes that the art of cooking meat gave our ancestors important advantages: 

Besides better taste, cooked food had other benefits — cooking killed some pathogens on food.

But cooking also altered the meat itself. It breaks up the long protein chains, and that makes them easier for stomach enzymes to digest. "The second thing is very clear," Wrangham adds, "and that is the muscle, which is made of protein, is wrapped up like a sausage in a skin, and the skin is collagen, connective tissue. And that collagen is very hard to digest. But if you heat it, it turns to jelly."

As for starchy foods like turnips, cooking gelatinizes the tough starch granules and makes them easier to digest too. Even just softening food — which cooking does — makes it more digestible. In the end, you get more energy out of the food.

That increased energy goes to our head!  Our brains use about 25% of our resting energy expenditure, compared to 8-9% for a chimpanzee. So if you want to think like a chimp, go for the raw food diet; but if you want to be human, use fire:

Yes, cooking can damage some good things in raw food, like vitamins. But Wrangham argues that what's gained by cooking far outweighs the losses.

As I cut into my steak (Wrangham is a vegetarian; he settles for the mango and potatoes), Wrangham explains that cooking also led to some of the finer elements of human behavior: it encourages people to share labor; it brings families and communities together at the end of the day and encourages conversation and story-telling — all very human activities.

"Ultimately, of course, what makes us intellectually human is our brain," he says. "And I think that comes from having the highest quality of food in the animal kingdom, and that's because we cook."