In a 1964 book, The Raw and the Cooked, anthropologist Claude Levi-Strauss charts a winding course through the myths of the Bororo people of South America. Beginning with a story of the rape of a mother and subsequent attempts at revenge by the father culminating in the eventual murder of the father’s wives by the youth, Levi-Strauss weaves myth upon myth with the larger objective of showing how empirical opposites – such as raw and cooked, moistened and burned, fresh and decayed – constitute the conceptual foundation of culture. Levi-Strauss claims that concealed in the myth of rape and revenge is the story of the origin of cooked food and what distinguishes us from animals. We cook our food. We transform nature just as cooking transforms food. That is what sets us apart from the animal and makes us human.
While Levi-Strauss’s exercise was about myth, a new book, Catching Fire: How Cooking Made Us Human, by Richard Wrangham argues the Bororo myths may be scientifically true. It is all about energy.
Wrangham begins with trying to understand what transformed us from our australopithecine ancestors. The australopithecines ate primarily plant matter. They had large jaws for grinding a coarse diet and the large digestive tract necessary for assimilating it. They were small, between 3 and 4 feet in height, and had brains barely larger than modern apes. In many ways they were like other modern apes, such as chimpanzees, except they normally walked upright and probably lived in a woodland environment. Lucy, one of the more famous fossils, is an example of the genus.
In a 2006 experiment nine volunteers with spent twelve days eating like apes. They ate fruits, vegetables, and nuts – what was called the Evo Diet, essentially a raw food diet. They consumed adequate calories, but, by the end of the diet, they had lost significant amounts of weight, almost ten pounds on average, slightly less than a pound per day. Cholesterol levels, blood pressure, and other health indicators had also improved.
This would seem to be a strong argument in favor of a raw food diet. Is this diet sustainable? Can humans eat this diet day after day, week after week, year after year? Apparently few, if any, people actually do. Studies of people on raw food diets find constant hunger, significant preparation of food even if it does not involve application of heat, and quite of bit of cheating. A study of raw foodists found over 80% included cooked food in their diet. Certainly no raw foodists are consuming anything like the diet of chimpanzees and apes. The jungles and savannas where the earliest humans evolved are not gardens of Eden with low hanging, sweet fruit on every tree. Foods consisted of relatively unsweet or even bitter fruit, leaves, insects, and an occasional kill. The food of the modern raw foodists consists of food engineered by hundreds of years of horticulture to be sweeter, more nutritious, and easier to digest or it is highly prepared food ground or pulverized by blenders and food processors.
The point is not to criticize the hypocrisy of raw foodists. If anything, today we suffer by consuming over-processed food. The typical diet today in the United States and the industrialized world is a slurry of easily assimilated calories consisting to great extent of cooked and highly processed carbohydrates. The result has been an epidemic of obesity and diabetes. If anything, we should eat more raw foods and much less processed foods. The question is how humans got to this place in their evolutionary history.
Chimpanzees, our closest genetic relative among apes, have brains about the size of our australopithecines ancestors which is about a third the size of modern humans. Their digestive systems in contrast are 40% larger in length than modern humans. All anatomical indications are that our australopithecine ancestors had a digestive tract of similar size. They require this long digestive tract in order to be able to assimilate enough calories from their raw and predominately plant food diet. Could the length of the digestive system be inversely related to brain size in apes?
In humans the brain consumes more calories than any other organ in our bodies. In chimpanzees and other apes the digestive system itself is a huge consumer of calories. The reason is that the digestive system of the ape must burn and waste a lot of calories to consume the calories in the raw food diet. Chimpanzees hunt and enjoy eating meat; however, a chimpanzee cannot afford to spend too much time hunting. If a chimpanzee spends all day hunting and doesn’t catch anything, then the chimpanzee goes hungry because there is not enough time remaining to absorb sufficient calories from the raw food diet. Chimpanzees and apes have to eat almost all day to get sufficient calories from their diet. The transition from australopithecines to the genus Homo and eventually to modern humans was accompanied by a shortening of the digestive tract which made possible an increase in brain size. Humans could not evolve a larger brain without a shortening of the digestive tract. They could not have evolved the shortened digestive tract without becoming able to absorb calories more easily from their diet. The only thing that could have accomplished this was the control of fire and invention of cooking.
Wrangham’s arguments are on multiple levels but key to his argument is the suggestion that the control of fire and cooking occurred earlier in human history than most have suggested. Concrete evidence for this is rather sparse. Evidence has been found at sites dating to around 1.5 million years ago of charcoal and clay heated to 200-400 degrees. Better evidence for control can be dated to the last 500-800 thousand years ago and definitive evidence certainly is found within the last 200-300 thousand years. Wrangham argues for an even earlier age and believes the control of fire and the development of cooking were the key factors that made possible the development of our large brain. Humans were able to evolve this large brain by developing the technology to convert tubers and other hard to digest foods into easy to digest, high energy foods through cooking. Not only does cooking directly provide more calories it also indirectly allows more energy to be available to the brain allowing for the reduction of the size of the digestive track.
Wrangham points to three major transitions in human evolution with fast and significant changes in anatomy, brain size, and technologies. These are the development of Homo erectus about 1.8-1.9 million years ago, the evolution of Homo heidelbergensis about 800,000 years ago, and finally the development of anatomically modern humans about 200,000 years ago. Homo erectus evolved from more primitive habiline species and spread widely over African, the Middle East, and Asia over the next million and more years. During this time Homo erectus developed an increasingly larger brain until it maxed out at about 75% modern human capacity. Wrangham argues that the control of fire and development of cooking must have occurred with the predecessors of Homo erectus, the habiline species, because this is when we begin to find the increasing size of brain that eventually culminates in modern human brain.