by John McQuaid
Their own remains have not been found—they may have disintegrated over a million years, or been buried elsewhere—so it’s not clear what, exactly, these early humans were. They may have been members of Homo erectus, a species whose brain was about three quarters the size of that in modern humans, and who had a facility for toolmaking. Homo erectus had migrated out of Africa by this time, ranging as far as the Caucasus and into East Asia before disappearing about three hundred thousand years ago. Or they could have been another, perhaps still-unknown, predecessor to modern humans. Either way, they were radically different from their immediate ancestors.
“They were pretty impressive. One may say that they were pretty modern,” said Goren-Inbar. “They knew the cycle of life of many animals and their drinking, eating, and social habits. They knew what plants to eat, and they knew where to go and grab raw materials to produce the stone tools: basalt, limestone, and flint. Those materials are very different, and they had to go and pick them up in different places. Even the fracture mechanics are very different, so making tools out of each required different skills. All in all, they were very sophisticated.”
Over a few million years, a blip in the history of life, toolmaking, talking, self-aware beings evolved from groups of apes living in trees. The Gesher Benot Ya’aqov site offers a tantalizing glimpse of this transformation, in which taste, smell, sight, sound, and touch coalesced into our own flavor sense—a new type of perception that helped give birth to the human form and to culture.
Human evolution bears some resemblance to what happened in the Cambrian explosion and many times between: in the never-ending search for the next meal, bodies grew more agile, perceptions clearer, brains larger, behavior more complex—and flavors richer. But each story is different, each species’s sense of flavor the result of a singular set of evolutionary conditions. As our monkey ancestors munched on fruit, natural selection pushed the tastes of other mammals in radically different directions. Whales and dolphins, which evolved on land, lost the ability to taste sweet, bitter, sour, and umami when they moved back into the sea, leaving only a sensitivity to salt—perhaps because most swallow fish whole and have no need to taste them. On their diet of meat, cat species grew insensitive to sweetness. And after they abandoned meat for bamboo, the ancestors of giant pandas could no longer taste savory umami. Humanity’s emergence was a singular event, the result of an unlikely series of twists. If geography, habitat, natural selection, and plain luck hadn’t converged in exactly the right way, we wouldn’t be here.
Exactly how this happened is mysterious, but there are clues in the archaeological record and hints in our own anatomy and behavior. One element was nearly constant chaos. Early humans lived on an ecological precipice that was always giving way beneath their feet. Around the time monkeys developed three-color vision 23 million years ago, the African continent shuddered and split. The ground over the fault collapsed, and rising plateaus on either side blocked the passage of rain clouds. That and other climatic changes dried out the African jungles and fragmented them like a dropped jigsaw puzzle. The forest scavenger’s mix of fruits, nuts, leaves, and insects that had sustained monkeys and apes was scattered farther and farther apart, separated by dangerous open spaces. Natural selection went into overdrive; dozens of ancestral human species branched off in these changing environments.
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Roughly two million years ago, the ground suddenly opened up under the feet of an adolescent male and an older female. (It’s unknown whether they were together, or whether this happened to each separately.) Each fell dozens of feet into a vaulted underground chamber. They landed hard on the bones and rotting carcasses of other animals, and either died instantly or lay gravely injured until their end. Over time, layers of grainy, cement-like mud encased and preserved their remains.
In 2008, nine-year-old Matthew Berger was chasing his dog near an archaeological dig in the dolomite hills outside Johannesburg, South Africa, when he tripped on a log. “Dad, I found a fossil!” he shouted to his father, paleoanthropologist Lee Berger. It was the remains of the adolescent boy, who would have been four feet two inches tall. The elder Berger soon found bones from a female skeleton. They were the first of their species ever found, dating to just under two million years old and dubbed Australopithecus sediba. (Sediba means “fountain” or “wellspring” in the local Sesotho language.) Since then, the remains of an adult male and three infants have also been unearthed at the cave site, known as Malapa.
Australopithecines were descended from the first human ancestors to split off from the ape family tree, a few million years before the time of the Malapa fossils. “Lucy,” from the related species Australopithecus afarensis, is the most famous such fossil; her 3.18-million-year-old bones were discovered in Ethiopia in 1974. She walked upright, but had long arms and powerful hands for grasping branches. The sediba pair lived a million years later than Lucy. They had the larger brains and nimbler bodies typical of later species. But when it came to food, they were curiously backward, standing at the threshold of change, but seemingly unable to cross it. The fossils were unusually complete and revealing, given their age, and among the remains were jaw fragments with nearly perfectly preserved teeth. As any watcher of police procedurals knows, dental records tell a story: what their owners ate, how they ate it, who they were.
To reproduce that two-million-year-old menu, scientists led by Amanda Henry, a paleobiologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, analyzed residues on the teeth. The plaque contained telltale signatures of various foods, microscopic flecks of plant matter called phytoliths. (As the name, Greek for “plant-stone,” implies, phytoliths are composed of silica from the soil that plants absorb and distribute through their cells. When the plant matter rots away, the silica remains, providing an identifiable afterimage of the cells.)
Henry expected that the pair had lived on a savanna diet, heavy on grasses and roots, consistent with the environment in which they lived. But when she analyzed some of the tartar from their teeth, she was surprised. The Australopithecus sediba diet came almost entirely from the shrinking forests, which contained a different carbon isotope than savanna roughage: nuts with hard shells, broad leaves pulled from bushes and reedy trees growing low under the forest canopy, bark stripped off the younger trees and chewed like prehistoric jerky. Sometimes they would have eaten fruit, but such finds would have been rare. Bitter, leafy, herbal flavors were the highlights of eating.
It was a taste mystery. They could strike out across the savanna anytime it suited them. In order to keep eating their forest-based diet, they would have had to travel far, moving across grasslands, ignoring the food they offered. This diet was, on some level, a choice. Perhaps the flavors and textures of savanna foods repelled them. Did other groups behave differently? Did this group later change its behavior, or die when its favored foods ran out? It’s sad to think of this species employing its emerging intelligence on a quest to keep eating a familiar but increasingly spartan diet, seemingly ignoring one key to its survival.
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Shifting habitats forced human evolution onto an improbable path. Food sources grew unreliable and farther apart, so bodies became more upright, lean, and mobile. Brains grew larger to devise more sophisticated strategies for getting food. But these two trends conflict.
Compared to that of our closest relatives, chimpanzees, the human body is an improbably fragile vessel. Chimps have big guts and large, powerful jaws, and can open their mouths twice as wide as we can. Smaller human jaws and faces are traced to a 2.4-million-year-old mutation in a gene that makes myosin, a muscle protein, and produces weaker, finer muscles. The human gut is also small. Yet our brains are large, and demanding. An adult human brain consumes about a quarter of the body’s energy. In other primates, it’s only a tenth. On paper, this anatomy looks like a recipe for disaster. Chimps must spend many hours of each day chewing to sustain themselves. Ho
w did our ancestors ever eat enough to survive?
The Homo sapiens body works for one principal reason: bigger brains helped humans create better, tastier food. Our ancestors made up for their physical weaknesses by becoming skilled hunters and chefs.
In the 1930s, the legendary anthropologists Louis and Mary Leakey excavated a trove of fossils in Kenya’s Olduvai Gorge that illustrated this progression over two million years. The earliest tools, from the time of the australopithecines and before, had been fished from the smooth quartz and basalt of the Omo River cobble and smashed and cracked to produce a flat surface that could be used for pounding. As time went on and more sophisticated species appeared, a craft developed: rocks were chipped away to create a characteristic spade-like shape of concave impressions and edges. Such a tool could be used for chopping and scraping. The most obvious use for such implements was butchering animals, and excavators also found stone tools and animal bones marked by cuts and hammer blows.
Meat became a dietary staple for members of our own genus, Homo. This changed eating forever. Unlike industrially produced meats, which are succulent and fatty, wild game is exceedingly tough. Cutting and tenderizing made it possible to eat more game. Starchy roots, another important staple, could be sliced or mashed. In other words, food was partially digested before the first bite was taken. Now constant chewing was no longer necessary, and meals were briefer and filled with strong tastes from start to finish: the savory, umami flavors of raw meat, the iron bitterness of blood, the richness of fat, the odd complexities of brains and kidneys.
Then came fire. It might have started like this: A lightning strike ignited the savanna scrub, the breeze sending a wall of flame dancing through the grass. Animals panicked and fled in all directions, eyes mad with fear. But a few dozen pairs of more practiced, nearly human eyes assayed the scene from a distance. They had seen this many times. They gauged the wind and the direction the flames were advancing, and moved together to make way, reaching a slight rise in the land for a better view. They would have felt the heat on their faces and chests as the blaze passed by, and a rush of excitement. After waiting for things to cool off, they inspected the charred wake of the fire, scanning the ground and the bushes for food. Heat-scarred fig tree branches and nuts littered the ground, their shells cracked by the heat. Perhaps one of the group swept up a few nuts and tasted one. The flesh had turned tender, and the flavor, the richness of seared fats under the charcoal, was delicious. Nearby, others also ate cooked figs, hot juice running down their cheeks.
The above description is based on primatologist Jill Pruetz’s observations of savanna chimps, who maneuver around wildfires, then move in afterward seeking treats. Australopithecines and their descendants likely employed similar strategies, developing a feel for how to manipulate flame. Chimps, in fact, appear just a conceptual step or two away from controlling fire and cooking. Kanzi, a bonobo (a species of chimp) at the Iowa Primate Learning Sanctuary in Des Moines, became fascinated with fire at a young age. He repeatedly watched the movie Quest for Fire, about early humans struggling to rekindle their hearth, mimicking the actors and building small piles of sticks. When his keepers taught him how to light a match, he began setting fires. He’d manage them, tossing on extra wood when the flame started to die. Soon he was cooking: he’d take a marshmallow and put it on the end of a stick, and later began using a frying pan to cook hamburgers.
Like our ancestors, bonobos know that cooked food tastes better. Roasting makes meat tender, the toughest tubers mushy, and eggs palatable. Intense heat triggers a series of distinctive chemical reactions that allow flavor to bloom. At around 300 degrees Fahrenheit, the tightly coiled proteins in the muscle fibers of meats begin to break up and unwind. Their uniform shape is replaced by thousands of different configurations, which then clump together in a process called denaturing. The meat turns tender. Then amino acids combine with sugars, the start of a chain reaction that spins out thousands of distinct, flavorful chemicals in trace amounts. This process is known as the Maillard reaction, after the French physician and chemist Louis Camille Maillard, who discovered it a century ago. The Maillard reaction also generates pigments, turning baked bread, cooked meat, and roasted coffee beans brown. Today, manipulating the Maillard reaction is a cornerstone of food science.
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The Gesher Benot Ya’aqov cave site’s million-year-old hearths are the earliest widely accepted evidence of cooking, and archaeologists have discovered many more suspected ancient hearths dating back to four hundred thousand years ago, the time of the immediate forerunners of modern Homo sapiens. But there is evidence that cooking transformed human biology, and with it, the human flavor sense, sometime between one and two million years ago, providing the crucial calorie boost larger brains demanded.
Richard Wrangham, a Harvard primatologist, looked at the mechanics of eating and digesting raw food and wondered if it could really provide enough fuel for Homo erectus to survive. After the calories burned in chewing and digesting are taken into account, raw meat almost isn’t worth the time and energy expended to consume it. Karina Fonseca-Azevedo and Suzana Herculano-Houzel of the Federal University of Rio de Janeiro calculated exactly how long such a raw meal would have lasted. Using data on body and brain size of primates, along with information on the time each species spent eating, they projected that a Homo erectus eating raw food would have to chew for eight hours—leaving him little time to get the food, and none to do anything else.
Cooking solves this problem by making food easy to eat and to digest. There’s time to obtain, prepare, and savor a meal. And when food can be consumed in small, concentrated bursts, the unlikely combination of a small gut and a big brain starts to make sense. “Humans are biologically adapted to eat cooked food,” Wrangham said. He did a number of experiments to test this idea: in one, he and Stephen Secor, a University of Alabama biologist, fed pythons diets of raw and cooked meat, and found they expended far less energy digesting the latter. Wrangham concluded that cooking must have been instrumental in Homo erectus’s large burst of brain growth starting around two million years ago.
Given the limited archaeological evidence of cooking fires more than one million years old, this theory is controversial. (Wrangham points out that evidence of fire use tends to disappear over time.) It also doesn’t account for a second burst of brain growth after one million years ago, leading up to Homo sapiens, that has convinced many anthropologists that early humans began to cook later. But if the theory is true, a cooked diet had a large hand in our evolutionary success and anatomy.
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As brains grew, natural selection redesigned the entire human head, including the interior of the mouth and nasal cavity. Smell returned in a new guise. In most mammals, a bone called the lamina transverse divides the nasal cavity. Chewing food liberates aromas in the back of the mouth, but this bone keeps them from reaching the nose, allowing animals to focus on smells around them. As apes evolved, the lamina transverse disappeared. Then, in humans, the passage from the mouth up into the nasal cavity shrank. It was merely a few centimeters’ difference, but it supercharged our ancestors’ capacity to experience flavor. As people chewed, a cascade of aromas reached olfactory receptors via this back passage.
Smells had tightly knotted our ancient ancestors’ expanding awareness to the world around them. This anatomical legacy is still with us. As it was in the earliest mammals, the human olfactory bulb remains just a single synapse removed from the neocortex, where sensations become perceptions. This isn’t true of the other senses; taste signals pass through the brain stem and hypothalamus before they reach the neocortex. Smells are unfiltered, immediate. As they entwined themselves with taste and the other senses during meals, flavor came alive.
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At the Gesher Benot Ya’aqov site, people likely gathered for meals, savoring cooked fish and deer meat dripping with bubbling fat and the crackle of seared skin.
They ate, drank, talked, and rested, satisfied. They’d reached the last link in a long chain of cooperation—planning, gathering, hunting, butchering, preparation—and the reward, a feast and fellowship.
In his second book on evolution, The Descent of Man, Darwin linked the rapid expansion of human intelligence to man’s social nature: our talent for communicating, and for living and working together as a unit. The hardships our human ancestors faced likely pulled them together into tight-knit groups. A group of chimps in southeastern Senegal that Jill Pruetz studies follows this dynamic. Most chimps live in woodlands. But this area is mostly savanna, and food is sometimes sparse—conditions that have forced the Fongoli chimps, nicknamed for a stream in their habitat, to work more cooperatively. They form a larger, more cohesive group than typical woodland chimps, and are more willing to share food; in one encounter Pruetz observed, dominant males declined to challenge a hungry female who wanted to take fruit from a pile they’d made. They also fashion basic tools: sticks to scoop termites out of mounds, and spears to skewer tiny creatures known as bush babies that slumber in the nooks of tree branches. This yields a few ounces of meat.
One might expect to find that animals belonging to larger groups, with more complex dynamics, had larger brains. In the 1990s, the California Institute of Technology’s John Allman set out to investigate this theory among primates. He was surprised to find that primates with bigger brains relative to body size didn’t form larger social groups. But when Robin Dunbar of Oxford University narrowed the question down, he found something surprising. Overall brain size might not vary with group size, but the size of the neocortex did. Humans have the largest neocortex relative to body size of any animal; it’s what gives the cathedral of flavor its magnificent architecture. It braids the basic urges and sensations around food together with thoughts, memories, feelings, and language. And it helps tie groups, and society, together.