I Cook, Therefore I Am

How dropping food in fire made us human.

Read more from Slate’s Food issue.

It all comes down to those wild hunting men and foraging females, tearing at flesh and gnawing on tubers: By now we’re used to evolutionary biologists, psychologists, and anthropologists invoking our prehistoric hunter-gatherer ancestry to explain our behavior today. But what if the roots of who and what we are lie not in this restless and raw state of nature but in our discovery of the secret to a more sedentary life: the home-cooked meal? That is the bewildering, but brilliant, idea proposed by Richard Wrangham, a Harvard-based biological anthropologist. In Catching Fire: How Cooking Made Us Human, he proposes that the big breakthrough of almost 2 million years ago that generated another 1,000 ideas and changed who we are forever was this: Drop food in fire, eat it. We are because we cook.

Historians of the deep human past generally consider cooking to be a recent activity. A significant number of hearths have been unearthed around the 76,000 year mark, and there is diminishing archeological evidence of controlled fire the further back you go. The assumption is that once we became modern, we worked out how to cook. Wrangham, by contrast, thinks we were cooking 1.8 million years ago—and that the activity was not an outcome of being human but that being human was an outcome of cooking. Cooking physically transformed a creature that was more ape into the earliest version of us, Homo erectus (perhaps more Conan the Barbarian than Jamie Oliver but still fundamentally human).

This is a fantastically weird way of looking at evolutionary change. Basic evolutionary theory teaches us that our physical selves are shaped by a genetic lottery in a cruel world. Random mutations in DNA change our biology, affecting anything from what we look like to how our immune systems work. The environment then selects who will go on to live and reproduce. But if cooking pushed us across a species threshold, it means that our biology is also shaped in completely unintended ways by cultural innovations. The impact of culture on biology was first proposed in the late 19th century by philosopher and psychologist James Baldwin, but it’s only in very recent times that exciting experimental work has tried to gauge the evolutionary effects of behaviors, like language and domestication. In the case of cooking, Wrangham’s proposal counters a universal human understanding of how the world works. Claude Levi-Strauss observed that most human cultures draw a line between nature and culture, thinking of one as raw and the other as cooked. Humans—whether they are hunter-gatherers, friends of the earth, or company officers of Archer Daniels Midland—reliably see themselves as the chefs controlling the transformation. But if Wrangham is right, this simple way of seeing things becomes oddly blurred: If cooking transforms nature, and cooking changed us, then human nature is … cooked?

Apparently, the idea that cooking was the crucial difference between their diet and ours came to Wrangham as he stared into the fire at home. Though there’s no archeological evidence of controlled fire before 800,000 years ago, he realized that a cluster of changes in the human face, brain, and gut 1.8 million years ago could be explained by only one thing—regular cooked meals. His argument begins with the odd spend-money-to-make-money aspect of digestion: You must burn calories in order to release calories from food (a fact deeply cherished by celery-chewing teenage girls). Because raw food is harder to digest, it takes more calories to get the calories out of it, and you get fewer calories from it anyway.

Wrangham illustrates this with an array of observations and experimental evidence. He cites a BBC TV show about an “Evo Diet Experiment” that followed nine volunteers who gave up processed food for 12 days and ate only the kinds of food that humans are supposedly wired to eat, mostly raw nuts, fruits, and vegetables. At the end of the experiment, the volunteers had improved cholesterol and blood pressure, and they also lost a lot of weight, despite the fact that the food was chosen to give them the required amount of calories per day. Wrangham even meets with some modern-day raw foodists, who are all very slim. He finds ample evidence that people who eat mostly raw food “thrive only in rich modern environments,” and they usually feel very, very hungry. An actual “evo” diet, Wrangham notes, would deliver even fewer calories; require some actual hunting and gathering; and, being more like the diet of chimps, need to be chewed for hours and hours every day.

Cooked food, by contrast, is easier to digest, gives you more energy, and takes no time to eat. Cooking also kills bacteria and renders many natural poisons inactive. So the simple expedient of heating food gave us access to many more safe calories every day, which was a survival jackpot. Once we started to eat soft, cooked food, our jaws and teeth were no longer required to munch ceaselessly, and they became smaller and more delicate. That is why we don’t look like apes anymore. Similarly, the more cooked food we ate, the less industrial-strength digestion we had to do, and the smaller our guts became. In the same way that our bodies evolved to better walk on two legs, our bellies changed to better handle well-done over rare. This had two enormous payoffs. First, as our guts got smaller, this freed up energy for our brains to operate on a larger and larger scale. (Leslie Aiello and Peter Wheeler first discovered the relationship between gut size and brain size, dubbing it the Expensive Tissue Hypothesis.) Second, as we spent less time eating, we had more time to do other things with those rapidly expanding brains.

As we noshed our way to modernity, Wrangham explains, our psychology changed as well. We had to develop qualities like restraint and trust. While it’s not novel to suggest that elements of human society arose around the primeval hearth, people tend to think of this in an abstract way—safe, companionable feelings developing around the campfire. Wrangham puts meat on these bones by comparing how other apes act around food. Chimpanzees—whom he knows intimately from decades of observation, many of those years at the Kibale Chimpanzee Project in Uganda—don’t readily share food at all. At best, they tolerate some petty theft. In contrast, humans of all cultures ritually share their cooked food with a network of spouses, children, and more distant relatives. For cooking to get off the ground, we had to divide labor such that some individuals did the cooking and others protected the cook from less-patient individuals.

Ideas like ownership and sharing would have become so fundamental that it’s probably more illuminating to think of these emergent beings as hunter-gatherer-cooks. Here, too, Wrangham apologetically explains, is probably where the global subjugation of women began. Women, he observes, do most of the cooking in most societies (he describes it as a historic phenomenon, not a biological necessity), and the division of labor around food could have been the beginning of the marriage contract and the prototypical human household. If this is the case, Wrangham argues, marriage is not a primitive contract to ensure paternity, as most anthropologists would argue, but primarily an economic contract. In a book of great ideas and otherwise wide-ranging research, this final point will be a nonrevelation to any but the above-mentioned anthropologists. Ask any single mother.

The ambition of Wrangham’s theory gives it great appeal: Cooking is a powerful biological force and the universal activity around which the rest of human history—the households and tribes, the migrations and wars, the religion and science—arranged itself. But the added treat of the I-cook-therefore-I-am idea is the counterintuitive light it sheds on one of our most intense cultural preoccupations—living the right life by eating naturally. For the last few decades, we in the first world have been challenged by a surplus of attractive food with none of the chastening effects of actual hunting and gathering or the rigors of food shortages. We have become rightly concerned about what all the chemicals involved in the growing, packaging, and delivery of food are doing to our health and that of the environment. A trusty rule of thumb has been that food should be as natural—that is, as unprocessed—as possible. But this is no longer as simple as it seems, and it’s not just a matter of calories. Many vital nutrients are better digested once food has been cooked. A recent Scientific American article reviewed a number of experiments that showed that, yes, while some compounds and nutrients, like vitamin C, are damaged in the cooking process, many others, like lycopene and different antioxidants, can be enhanced.

In any case, letting ourselves get carried away with the healthful benefits of organically grown or well-cooked food may not be the evolutionarily correct way to go if Wrangham is right. Remember, the reason cooking had the colossal impact that it did was not that it made our skin clearer and our hair glossier but that it bought us many hours in the day to do and think about other things. The real fruit of cooking was time. There is nothing wrong with free-range eggs, farmers market preserves, or the slow-food movement; complicated cooking and leisurely eating are wonderful pastimes. But come 8 p.m., the natural thing to do is drop food in microwave, eat it, and then go read a book.