Read Catching Fire: How Cooking Made Us Human Online

Authors: Richard Wrangham

Tags: #Cooking, #History, #Political Science, #Public Policy, #Cultural Policy, #Science, #Life Sciences, #Evolution, #Social Science, #Anthropology, #General, #Cultural, #Popular Culture, #Agriculture & Food, #Technology & Engineering, #Fire Science

Catching Fire: How Cooking Made Us Human (10 page)

BOOK: Catching Fire: How Cooking Made Us Human
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The inability of the archaeological evidence to tell when humans first controlled fire directs us to biology, where we find two vital clues. First, the fossil record presents a reasonably clear picture of the changes in human anatomy over the past two million years. It tells us what were the major changes in our ancestors’ anatomy, and when they happened. Second, in response to a major change in diet, species tend to exhibit rapid and obvious changes in their anatomy. Animals are superbly adapted to their diets, and over evolutionary time the tight fit between food and anatomy is driven by food rather than by the animal’s characteristics. Fleas do not suck blood because they happen to have a proboscis well designed for piercing mammalian skin; they have the proboscis because they are adapted to sucking blood. Horses do not eat grass because they happen to have the right kind of teeth and guts for doing so; they have tall teeth and long guts because they are adapted to eating grass. Humans do not eat cooked food because we have the right kind of teeth and guts; rather, we have small teeth and short guts as a result of adapting to a cooked diet.
Therefore, we can identify when cooking began by searching the fossil record. At some time our ancestors’ anatomy changed to accommodate a cooked diet. The change must mark when cooking became not merely an occasional activity but a predictable daily occurrence, because until then our ancestors would have sometimes had to resort to eating their food raw—and therefore could not adapt to cooking. The time when our ancestors became adapted to cooked food also marks the time when fire was controlled so effectively that it was never lost again.
Anthropologists have sometimes suggested that humans could have controlled fire for reasons such as warmth and light for many millennia before starting to use it for cooking. However, many animals show a spontaneous preference for cooked food over raw. Would prehuman ancestors have preferred cooked food also? Evolutionary anthropologists Victoria Wobber and Brian Hare tested chimpanzees and other apes in the United States, Germany, and Tchimpounga, a Congolese sanctuary. Across the different locations, despite different diets and living conditions, the apes responded similarly. No apes preferred any food raw. They ate sweet potatoes and apples with equal enthusiasm whether raw or cooked, but they preferred their carrots, potatoes, and meat to be cooked. The Tchimpounga chimpanzees were particularly informative because there was no record of them having eaten meat previously, yet they showed a strong preference for cooked meat over raw meat. The first of our ancestors to control fire would likely have reacted the same way. Cooked food would have suited their palate the first time they tried it, just as a taste for cooked food, with its immediate benefits, is shared by a wide range of wild and domestic species. Chimpanzees in Senegal do not eat the raw beans of
Afzelia
trees, but after a forest fire has passed through the savanna, they search under
Afzelia
trees and eat the cooked seeds.
Why are wild animals pre-adapted in this way to appreciate the smells, tastes, and textures of cooked food? The spontaneous preference for cooked food implies an innate mechanism for recognizing high-energy foods. Many foods change their taste when cooked, becoming sweeter, less bitter, or less astringent, so taste could play a role in this preference, as some evidence suggests. Koko is a gorilla who learned to communicate with humans, and she prefers her food cooked. Cognitive psychologist Penny Patterson asked her why: “I asked Koko while the video was rolling if she liked her vegetables better cooked (specifying my left hand) or raw/fresh (indicating my right hand). She touched my left hand (cooked) in reply. Then I asked why she liked vegetables better cooked, one hand standing for ‘tastes better,’ the other ‘easier to eat.’ Koko indicated the ‘tastes better’ option.”
When primates eat, sensory nerves in the tongue perceive not only taste but also particle size and texture. Some of the brain cells (neurons) responsive to texture converge with taste neurons in the amygdala and orbito-frontal cortex of the brain, allowing a summed assessment of food properties. This sensory-neural system enables primates to respond instinctively to a wide range of food properties other than merely taste, including such factors as grittiness, viscosity, oiliness, and temperature.
In 2004 such abilities in the human brain were reported for the first time. A team led by psychologist Edmund Rolls found that when people had foods of a particular viscosity in their mouths, specific brain regions were activated. Those regions partly overlapped with regions of taste cortex that register sweetness. The picture emerging from such studies is that hard-wired responses to properties such as taste, texture, and temperature are integrated in the brain with learned responses to the sight and smell of food. So the mechanisms that allow animals to assess the quality of raw foods directly apply to cooked foods and allow them to choose foods of a good texture for easy digestion.
Rolls’s studies suggest that the proximate reasons chimpanzees and many other species like their meat and potatoes cooked may be the same as in humans. We identify foods that have high caloric value not just by their being sweet, but also by their being soft and tender. Our ancestors were surely prepared by their preexisting sensory and brain mechanisms to like cooked foods in the same way. A long delay between the first control of fire and the first eating of cooked food is therefore deeply improbable.
 
 
 
A long delay between the adoption of a major new diet and resulting changes in anatomy is also unlikely. Studies of Galapagos finches by Peter and Rosemary Grant showed that during a year when finches experienced an intense food shortage caused by an extended drought, the birds that were best able to eat large and hard seeds—those birds with the largest beaks—survived best. The selection pressure against small-beaked birds was so intense that only 15 percent of birds survived and the species as a whole developed measurably larger beaks within a year. Correlations in beak size between parents and offspring showed that the changes were inherited. Beak size fell again after the food supply returned to normal, but it took about fifteen years for the genetic changes the drought had imposed to reverse.
The Grants’ finches show that anatomy can evolve very quickly in response to dietary changes. In the case of the drought year in the Galapagos, the change in diet was temporary and therefore so was the change in anatomy. Other data show that if an ecological change is permanent, the species also changes permanently, and again the transition is fast. Some of the clearest examples come from animals confined on islands that have been newly created by a rise in sea level. In fewer than eight thousand years, mainland boa constrictors that occupied new islands off Belize shifted their diets away from mammals and toward birds, spent more time in trees, became more slender, lost a previous size difference between females and males, and were reduced to a fifth of their original body weight. According to evolutionary biologist Stephen Jay Gould, this rate of change is not unusual. Drawing from the fossil record, he suggested that fifteen thousand to twenty thousand years may be about the average time one species takes to make a complete evolutionary transition to another. While a species that takes many years to mature, such as our ancestors, would take longer to evolve than a rapidly growing species, such rapid rates of evolution are sharply inconsistent with some previous interpretations of the effects of cooking. Loring Brace suggested that the use of fire for softening meat began around 250,000 to 300,000 years ago, followed by a supposed drop in tooth size that began about 100,000 years ago. This would mean that for at least the first 150,000 years after cooking was adopted, human teeth showed no response. Because such a long delay before adapting to a major new influence does not fit the animal pattern, we can conclude that Brace’s idea is wrong. The adaptive changes brought on by the adoption of cooking would surely have been rapid.
In addition to following quickly, the changes would have been substantial. We can infer this from pairs of species in which lesser differences in diet have large effects. Take chimpanzees and gorillas, two ape species that often share the same forest habitat. In many ways their diets are very similar. Both choose ripe fruits when they are available. Both also supplement their diets with fibrous foods, such as piths and leaves. There is only one important difference in their food choice. When fruits are scarce, gorillas rely on foliage alone, whereas chimpanzees continue to search for fruit every day. Unlike gorillas, chimpanzees never survive only on piths and leaves—presumably because they are physiologically unable to do so.
The relative ability of these two apes to rely on foliage might at first glance appear to be a trivial matter—especially compared to the introduction of cooking. But many consequences follow from it. To find their vital fruits, chimpanzees must travel farther than gorillas, so they are more agile and smaller. There are differences in distributional range. Unlike chimpanzees, gorillas successfully occupy high-altitude forests without fruits, such as the Virunga Volcanoes of Rwanda, Uganda, and the Democratic Republic of Congo. Chimpanzees are limited to lower altitudes. Like other primates that are able to rely on a leaf diet, gorillas mature earlier, start having babies at a younger age, and reproduce faster.
Grouping patterns of these species also differ strikingly as a result of the difference in diet. The terrestrial foliage gorillas rely on is easily found and occurs in big patches, allowing their groups to be stable all year. But during food-poor seasons, chimpanzees are driven to travel alone or in small groups as they search for rare fruits. The difference in grouping patterns has further consequences. Gorillas form long-lasting bonds between females and males, whereas chimpanzees do not.
More than the relatively slight dietary difference that distinguishes gorillas from chimpanzees, cooked food had multiple differences from raw food. Effects of cooking include extra energy, softer food, fireside meals, a safer and more diverse set of food species, and a more predictable food supply during periods of scarcity. Cooking would therefore be expected to increase survival, especially of the vulnerable young. It should also have increased the range of edible foods, allowing extension into new biogeographical zones. The anatomical differences between a cooking and a precooking ancestor should be at least as big as those between a chimpanzee and a gorilla. So whenever cooking was adopted, its effects should be easy to find. We can expect the origin of cooking to be signaled by large, rapid changes in human anatomy appropriate to a softer and more energy-rich diet.
 
 
 
The search for such changes proves to be rather simple. Before two million years ago, there is no suggestion for the control of fire. Since then there have been only three periods when our ancestors’ evolution was fast and strong enough to justify changes in the species names. They are the times that produced
Homo erectus
(1.8 million years ago),
Homo heidelbergensis
(800,000 years ago), and
Homo sapiens
(200,000 years ago). These are therefore the only times when it is reasonable to infer that cooking could have been adopted.
Most recent was the evolution of
Homo sapiens
from an ancestor that is now usually called
Homo heidelbergensis.
It was a gentle process that began in Africa as early as three hundred thousand years ago and was largely complete by around two hundred thousand years ago. The transition was too recent to correspond to the origin of cooking, however, because
Homo heidelbergensis
was already using fire at Beeches Pit, Schöningen, and elsewhere four hundred thousand years ago. Nor does the transition to
Homo sapiens
show the kinds of change we are looking for.
Homo heidelbergensis
was merely a more robust form of human than
Homo sapiens
, with a large face, less rounded head, and slightly smaller brain. Most of the differences between these two species are too small and not obviously related to diet. We can be confident that cooking began more than three hundred thousand years ago, before
Homo sapiens
emerged.
Homo heidelbergensis
evolved from
Homo erectus
in Africa from eight to six hundred thousand years ago. The timing of the
erectus-heidelbergensis
transition provides a reasonably comfortable fit with the archaeological data on the control of fire becoming particularly scarce. The main changes in anatomy from
Homo erectus
to
Homo heidelbergensis
were an increase in cranial capacity (brain volume) of around 30 percent, a higher forehead, and a flatter face. These are smaller modifications than the differences between a chimpanzee and a gorilla, and the modifications show little correspondence to changes in the diet. So this Pleistocene transition does not look favorable. It is a possibility for when cooking began, but not a promising one.
The only other option is the original change, from habilines to
Homo erectus
. This shift happened between 1.9 million and 1.8 million years ago and involved much larger changes in anatomy than any subsequent transitions. Recall that in many ways habilines were apelike. Like the australopithecines, they appear to have had two effective styles of locomotion. They walked upright and can be reconstructed as having had sufficiently strong and mobile arms to be good climbers. Their small size must have helped them in trees. They are estimated to have stood about 1 to 1.3 meters tall (3 feet 3 inches to 4 feet 3 inches) and appear to have weighed about the same as a chimpanzee, around thirty-two kilograms (seventy pounds) for a female and thirty-seven kilograms (eighty-one pounds) for a male. Despite their small bodies, they had much bigger chewing teeth than in any subsequent species of the genus
Homo
: the surface areas of three representative chewing teeth decreased by 21 percent from habilines to early
Homo erectus
. Habilines’ larger teeth imply a bulky diet that required a lot of chewing.
BOOK: Catching Fire: How Cooking Made Us Human
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