Raw Deal

At Estela restaurant in New York City, chef Ignacio Mattos makes what may be the city’s best steak tartare. His version features fish sauce, lemon zest, and sunchokes, but like all steak tartare, the basis is raw beef sliced into tiny pieces.

That slicing or chopping is the secret to not only the dish’s appealing texture but also to our ability to eat it at all. Human teeth are nearly incapable of breaking down raw meat. Instead of the scissor-sharp points found on canine teeth, most of our teeth have a flat, grinding surface. A new study looks at how we may have overcome our dental limitations—and finds that chopping raw meat with stone tools may have reduced the need for heavy jaws and teeth and freed up our heads for evolutionary change.

“If I were to give you a piece of raw goat or game, you would not be able to chew it. It would be like bubblegum—you would just chew and chew and chew,” says Daniel Lieberman, an evolutionary biologist at Harvard University in Cambridge, Massachusetts. Humans are the only primates who eat meat in quantity. Our cultural ability to cook makes meat easier to break down and has famously been put forth as the cause of a suite of physical changes in the Homo genus, from smaller teeth, to smaller guts, to reduced jaw muscles.

But as steak tartare proves, humans can eat raw meat as long as it’s cut into bite-size pieces. Lieberman and evolutionary biologist Katherine Zink, also at Harvard, were curious about the role this “mechanical processing” might have played in our evolution, especially since there is evidence that hominins were making tools and eating meat as far back as 3.3 million years ago—and that they increased their meat consumption around 2.6 million years ago—yet evidence for cooking doesn’t turn up until about 500,000 years ago.

To get at this question, Zink and Lieberman recruited some test chewers. Since many biologists believe that roots and tubers would have been key food sources for early hominins, the researchers gave their chewers beets, carrots, and yams: some whole, some cut up or pounded, and some roasted. To simulate wild game, they used goat meat with the same three treatments: raw and whole, raw but chopped or pounded, and roasted. They measured the number of times subjects chewed each mouthful and the force of their chews, using electrodes on the face.

Their results, published today in Nature, were clear-cut. Whole raw meat was impossible to chew into pieces and emerged as a tattered bolus. Sliced meat required 31.8 percent less muscle force to chew, and it was broken down into small pieces that would be easier to digest. Over the course of a year, switching from a diet of pure raw plants to one that was composed of two-thirds raw plants and one-third raw sliced meat would require 17 percent fewer chews and 20 percent less force.

“If I were to give you a piece of raw goat or game, you would not be able to chew it.”

Cooking made the food even easier to chew, especially the plants. But Zink and Lieberman believe that the major changes to the head and teeth seen in early species of Homo, namely the decrease in teeth and jaw-muscle size that emerged in Homo erectus (which dates from 1.89 million to 143,000 years ago), could have occurred before cooking, purely due to the invention of tartare.

Richard Wrangham, an evolutionary anthropologist in the same Harvard department as the researchers, is unconvinced. He has no doubt that mechanical processing was important, he says, but he is skeptical that it was enough to cause the head and jaw remodel seen in the Homo lineage. For Wrangham, just because there’s no clear evidence of cooking until about 500,000 years ago doesn’t mean hominins were not doing it much earlier. Control of fire dates back to at least a million years ago, and he imagines it would take those early fire users “about an hour and a half” to figure out that they could use it to cook.

Henry Bunn, a paleoanthropologist at the University of Wisconsin, Madison, says he’s waiting for more evidence to be persuaded by Wrangham’s early-cooking hypothesis. “If control of fire was significant enough that it impacted what happened next in human evolution, then there should be evidence everywhere,” he says.

Either way, Zink and Lieberman’s study suggests that slicing and dicing were enough to at least begin transforming heads and jaws that were ideal for continuous vegetarian munching into those suited to our current lifestyle, which allows us to use tools and technologies to pack in a large number of calories at once. This change freed up time for cultural innovations like language, agriculture, and haute cuisine, so we may have our ancestors’ gazelle tartare to thank for the delicious beef tartare with sunchokes available on Houston Street today.