Washburn’s statement captures a core feature of conventional wisdom, which is that the way to explain the evolution of the sexual division of labor is to imagine that, together, meat eating and plant eating allowed a household. An un-stated assumption was that the food was raw. But if food was raw, the sexual division of labor is unworkable. Nowadays a man who has spent most of the day hunting can satisfy his hunger easily when he returns to camp, because his evening meal is cooked. But if the food waiting for him in camp had all been raw, he would have had a major problem.
The difficulty lies in the large amount of time it takes to eat raw food. Great apes allow us to estimate it. Simply because they are big—30 kilograms (66 pounds) and more—they need a lot of food and a lot of time to chew. Chimpanzees in Gombe National Park, Tanzania, spend more than six hours a day chewing. Six hours may seem high considering that most of their food is ripe fruit. Bananas or grapefruit would slip down their throats easily, and for this reason, chimpanzees readily raid the plantations of people living near their territories. But wild fruits are not nearly as rewarding as those domesticated fruits. The edible pulp of a forest fruit is often physically hard, and it may be protected by a skin, coat, or hairs that have to be removed. Most fruits have to be chewed for a long time before the pulp can be fully detached from the pieces of skin or seeds, and before the solid pieces are mashed enough to give up their valuable nutrients. Leaves, the next most important food for chimpanzees, are also tough and likewise take a long time to chew into pieces small enough for efficient digestion. The other great apes (bonobos, gorillas, and orangutans) commit similarly long hours to chewing their food. Because the amount of time spent chewing is related to body size among primates, we can estimate how long humans would be obliged to spend chewing if we lived on the same kind of raw food that great apes do. Conservatively, it would be 42 percent of the day, or just over five hours of chewing in a twelve-hour day.
People spend much less than five hours per day chewing their foods. Brillat-Savarin claimed to have seen the vicar of Bregnier eat the following within forty-five minutes: a bowl of soup, two dishes of boiled beef, a leg of mutton, a handsome capon, a generous salad, a ninety-degree wedge from a good-sized white cheese, a bottle of wine, and a carafe of water. If Brillat-Savarin was not exaggerating, the amount of food eaten by the vicar in less than an hour would have provided enough calories for a day or more. It is hard to imagine a wild chimpanzee achieving such a feat.
A few careful studies using direct observation confirm how relatively quickly humans eat their food. In the United States, children from nine to twelve years of age spend a mere 10 percent of their time eating, or just over an hour per twelve-hour day. This is close to the daily chewing time for children recorded by anthropologists in twelve subsistence societies around the world, from the Ye’kwana of Venezuela to the Kipsigi of Kenya and the Samoans of the South Pacific. Girls ages six to fifteen chewed for an average of 8 percent of the day, with a range of 4 percent to 13 percent. Results for boys were almost identical: they chewed for an average of 7 percent of the day, again ranging from 4 percent to 13 percent.
The children’s data show little difference between the industrialized United States and subsistence societies. In the twelve measured cultures, adults chewed for even less time than the children. Women and men each spent an average of 5 percent of their time chewing. One might object that the people in the subsistence societies were observed only from dawn to dusk. Since people often have a big meal after dark, the total time eating per day might be more than indicated by the 5 percent figure, which translates to only thirty-six minutes in a twelve-hour day. But even if people chewed their evening meals for an hour after dark, which is an improbably long time, the total time spent eating would still be less than 12 percent of a fourteen-hour day, allowing two hours for the evening meal. However we look at the data, humans devote between a fifth and a tenth as much time to chewing as do the great apes.
This reduction in chewing time clearly results from cooked food being softer. Processed plant foods experience similar physical changes to those of meat. As the food canning industry knows all too well, it is hard to retain a crisp, fresh texture in heated vegetables or fruits. Plant cells are normally glued together by pectic polysaccharides. These chemicals degrade when heated, causing the cells to separate and permitting teeth to divide the tissue more easily. Hot cells also lose rigidity, a result of both their walls swelling and their membranes being disrupted by denaturation of proteins. The consequences are predictable. By measuring the amount of force needed to initiate a crack in food, researchers have shown that softness (or hardness) closely predicts the number of times someone chews before swallowing. The effect works for animals too. Wild monkeys spend almost twice as long chewing per day if their food is low-quality. Observers have recorded the amount of time spent chewing by wild primates that obtain human foods (such as garbage stolen from hotels). As the proportion of human foods rises in the diet, the primates spend less time chewing, down to less than 10 percent when all of the food comes from humans.
Six hours of chewing per day for a chimpanzee mother who consumes 1,800 calories per day means that she ingests food at a rate of around 300 calories per hour of chewing. Humans comparatively bolt their food. If adults eat 2,000 to 2,500 calories a day, as many people do, the fact that they chew for only about one hour per day means that the average intake rate will average 2,000 to 2,500 calories an hour or higher, or more than six times the rate for a chimpanzee. The rate is doubtless much more when people eat high-calorie foods, such as hamburgers, candy bars, and holiday feasts. Humans have clearly had a long history of much more intense calorie consumption than primates are used to. Thanks to cooking, we save ourselves around four hours of chewing time per day.
Before our ancestors cooked, then, they had much less free time. Their options for subsistence activities would therefore have been severely constrained. Males could not afford to spend all day hunting, because if they failed to get any prey, they would have had to fill their bellies on plant foods instead, which would take a long time just to chew. Consider chimpanzees, who hunt little and whose raw-food diet can be safely assumed to be similar to the diet of australopithecines. At Ngogo, Uganda, chimpanzees hunt intensely compared to other chimpanzee populations, yet males still average less than three minutes per day hunting. Human hunters have lots of time and walk for hours in the search for prey. A recent review of eight hunter-gatherer societies found that men hunted for between 1.8 and 8.2 hours daily. Hadza men were close to the average, spending more than 4 hours a day hunting—about eighty times as long as an Ngogo chimpanzee.
Almost all hunts by chimpanzees follow a chance encounter during such routine activities as patrolling their territorial boundaries, suggesting that chimpanzees are unwilling to risk spending time on a hopeful search. When chimpanzees hunt their favorite prey—red colobus monkeys—the colobus rarely move out of the tree where they are attacked. The monkeys appear to feel safer staying in one place, rather than jumping to adjacent trees where chimpanzees might ambush them. The monkeys’ immobility allows chimpanzees to alternate between sitting under the prey and making repeated rushes at them. In theory, the chimpanzees could spend hours pursuing this prey. But at Ngogo the longest hunt observed was just over one hour, and the average length of hunts is only eighteen minutes. At Gombe I found that the average interval between plant-feeding bouts was twenty minutes, almost the same as the length of a hunt. The similarity between the average hunt duration and the average interval between plant-feeding bouts suggests that chimpanzees can afford a break of twenty minutes from eating fruits or leaves to hunt, but if they take much longer they risk losing valuable plant-feeding time.
The time budget for an ape eating raw food is also constrained by the rhythm of digestion, because apes have to pause between meals. Judging from data on humans, the bigger the meal, the longer it takes for the stomach to empty. It probably takes one to two hours for a chimpanzee’s full stomach to empty enough to warrant feeding again. Therefore, a five-hour chewing requirement becomes an eight- or nine-hour commitment to feeding. Eat, rest, eat, rest, eat. An ancestor species that did not cook would presumably have experienced a similar rhythm.
These time constraints are inescapable for a large ape or habiline eating raw unprocessed food. Males who did not cook would not have been able to rely on hunting to feed themselves. Like chimpanzees, they could hunt in opportunistic spurts. But if they devoted many hours to hunting, the risk of failure to obtain prey could not be compensated rapidly enough. Eating their daily required calories in the form of their staple plant foods would have taken too long.
Washburn and other anthropologists have proposed that the human division of labor by sex was based on hunting. They suggest that on days when a male failed to find meat, honey, or other prizes, a female could provide food to him. As we now see, this would not have been sufficient, because a returning male who had not eaten during the day would not have had enough time left in the evening to chew his plant-food calories. The same time constraints apply whether our precooking ancestor obtained his staple plant diet by his own labor or received it from a female. A division of labor into hunting and gathering would not have afforded consumption of sufficient calories, as long as the food was consumed raw.
Suppose that a hunter living on raw food has a mate who is willing to feed him, that his mate could collect enough raw foods for him (while satisfying her own needs) and would bring them back to a central place, to be met by her grateful mate. Then suppose the male has had an unsuccessful day of hunting. Even modern hunter-gatherers armed with efficient weapons often fail. Among the Hadza there are stretches of a week or more several times per year when hunters bring no big-game meat to camp. The hungry hunter needs to consume, say, two thousand calories, but he cannot eat after dark. To do so would be too dangerous, scrabbling in the predator-filled night to feel for the nuts, leaves, or roots his gatherer friend brought him. If the hunter slept on the ground, he would be exposed to predators and large ungulates as he fumbled for his food. If he were in a tree, he would find it hard to have his raw foods with him because they do not come in tidy packages.
So to eat his fill he would have to do most of his eating before dusk, which falls between about 6 and 7 P.M. in equatorial regions. If he had eaten nothing while on the hunt, he would need to be back in camp before midday, and there he would find his mate’s gathered foods (assuming she had been able to complete her food gathering so early in the day). He would then have to spend the rest of the day eating, resting, eating, resting, and eating. In short, the long hours of chewing necessitated by a raw diet would have sharply reduced hunting time. It is questionable whether the sexual division of labor would have been possible at all.
The use of fire solved the problem. It freed hunters from previous time constraints by reducing the time spent chewing. It also allowed eating after dark. The first of our ancestral line to cook their food would have gained several hours of daytime. Instead of being an opportunistic activity, hunting could have become a more dedicated pursuit with a higher potential for success. Nowadays men can hunt until nightfall and still eat a large meal in camp. After cooking began, therefore, hunting could contribute to the full development of the family household, reliant as it is on a predictable economic exchange between women and men.
CHAPTER 7
The Married Cook
“The labor of women in the house, certainly, enables men to produce more wealth than they otherwise could; and in this way women are economic factors in society. But so are horses . . . the horse is not economically independent, nor is the woman.”
—CHARLOTTE PERKINS GILMAN,
Women and Economics: A Study of the
Economic Relation Between Men and Women
as a Factor in Social Evolution
A
n evening meal cooked by a woman serves her and her children’s needs. It also helps her husband by giving him a predictable source of food, allowing him to spend his day doing whatever activity he chooses. But while the arrangement is comfortable for both sexes, it is particularly convenient for the male. Why should a female cook for him? A focus on the peculiar properties of cooked food provokes a new understanding of the nature of married life and the human community. It suggests that the reasons why the sexes pair off go beyond the traditional ideas of mating competition, or the interests that women and men have in the product of each other’s labor. It leads to the uncomfortable idea that as a cultural norm, women cook for men because of patriarchy. Men use their communal power to consign women to domestic roles, even when women would prefer otherwise.
That women tend to cook for their husbands is clear. In 1973 anthropologists George Murdock and Catarina Provost compiled the pattern of sex differences in fifty productive activities in 185 cultures. Although men often like to cook meat, overall cooking was the most female-biased activity of any, a little more so than preparing plant food and fetching water. Women were predominantly or almost exclusively responsible for cooking in 97.8 percent of societies. There were four societies in which cooking was reportedly performed about equally by both sexes or predominantly by males. One of them, the Todas of South India, was an error: a 1906 report had been misleading. Murdock and Provost failed to catch a correction showing that Toda women did most of the cooking.