100 Million Years of Food (8 page)

Our closest ancestors have a marked fondness for fresh flesh. Bonobo apes supplement their fruit diet by snatching unwary small mammals like antelope, while chimpanzees use their intelligence to form hunting packs and trap and ambush their colobus monkey prey.
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Though not as nimble as bonobos and chimps, orangutans and gorillas also take advantage of opportunities to hunt.
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Our ancestors seem to have increasingly enjoyed the taste of meat. Scientists have unearthed cut-marks on bones and tools from 2.6 million years ago.
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Genetic analysis of tapeworms, picked up by eating infected meat, suggests that humans, tapeworms, and meat eating went together as far back as 1.71 million to 780,000 years ago.
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But how exactly did our
Homo
ancestors obtain their meat, and how much of it were they able to get? This topic has been at the center of perhaps the most vociferous debate regarding the history of humankind, because the answer reveals whether you think the “natural” human behavioral pattern is hunter or scavenger. One can see immediately how this research has ramifications for today's quarrels about the merits of meat-heavy diets versus vegetarian diets.

The original hypothesis was that our early ancestors were first and foremost hunters. However, African predators typically rely on stalking and powerful bursts of speed, often hunting at night; by contrast,
Homo
was a daytime creature and could not sprint as rapidly as a lion or cheetah, nor did it have the claws, powerful jaws, or fearsome teeth of carnivores. How could any ape using sticks and stones hope to scratch, much less kill, a springbok antelope that could race down a savannah at 62 mph and catapult twelve feet high on a whim?

A popular counterproposal in past decades was that our ancestors filched bones and braincases of leftover game from under the sleepy gazes of sated lions and hyenas. The transformation of Man the Macho Hunter into Man the Bone-Heap Diver was also more politically correct. Since our ancestors were believed to be bargain-bin hunters rather than cold-blooded executioners, modern humans could be imagined as natural pacifists by extension. As an added bonus, the scavenger scenario was less sexist, because rather than being the family provider, Dad supplemented the main meal, Mom's plant-based stew, with marrow, brain, and scraps of meat. The scavenger proposal, alas, may not have enough meat to it. How was early
Homo
able to fuel a dramatic doubling in brain size in a million years on greens and tubers flavored with marrow and brain bouillon? Moreover, no mammal today lives entirely or even mainly from scavenging carcasses, because such opportunities are inherently unpredictable, meager, or putrid. Even hyenas get most of their protein by hunting, contrary to popular belief.
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The coolest how-did-we-get-meat proposal is the endurance-running hypothesis. Most land mammals reduce heat load by panting, which channels away body heat through secretion of saliva, along with some sweating. When the animal is not in rapid motion, air trapped within its fur insulates it from overheating or from getting too cold. (Large African mammals such as elephants and hippopotamuses are hairless because they have a greater proportion of body mass to surface area and thus are in danger of internally overheating.) Panting and air-trapping fur work brilliantly for brief surges of power interspersed with long stretches of laziness, but champion sprinters like cheetahs have to call it quits after a quick dash because heat buildup could kill them outright.

By contrast, early
Homo
had an upright posture and was likely hairless. Running generates airflow over a naked body, sucking away heat; since mammalian fur traps air, it prevents this air convection effect, especially if the fur is matted down from moisture. In addition, primates are unique in having special eccrine sweat glands, which are scattered over the surface of the skin and dissipate heat through fine perspiration. Running efficiency increases in proportion to leg length, and thus
Homo
evolved longer legs, as well as Achilles tendons to absorb and release spring energy and larger buttock muscles to augment running power. As a result of these adaptations, humans are able to outrun and capture four-legged, fur-insulated animals such as small antelopes, kangaroos, and hares over long distances in high heat conditions. Endurance running could also have enabled early
Homo
to reach fresh carcasses killed by big predators more quickly, before heat and scavengers finished off the dinner for good.
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However, the endurance-running hypothesis also faces some problems. Endurance running is great for pursuing animals over desert terrain, where hunters can follow tracks in sand for miles, but it's unlikely to be a useful strategy in brush or forest. Between 3 million and 2 million years ago, our ancestors may have lived in grasslands, in forests, or by lakes and rivers, so endurance running probably did not work for many or most of them.

While the debate over how our ancestors obtained meat continues among paleoanthropologists, it's reasonable to conclude that our ancestors were, like their orangutan, gorilla, bonobo, and chimp relations, strongly motivated to get their grubby little hands on a piece of meat. Our ancestors, though, were better than their relations at running down prey, better at lobbing stones at scavengers, better at making tools, better at picking up nifty hunting tricks from their peers and elders. As a result, our ancestors had more and more meat to eat as time went on.

Did getting more meat allow our ancestors to evolve bigger brains? It's true that around 2 million years ago our ancestors started acquiring a lot more meat; their brains evolved to increase dramatically in volume, but eating more meat wasn't necessarily the reason behind the brain boom. Predators like sharks and alligators eat a lot of animal protein but aren't reputed for being especially bright. Conversely, gorillas, orangutans, and elephants eat very little animal protein but are well recognized for their intelligence, so animal protein isn't necessary to evolve intelligence, either.

There is another link between meat and brains: Animals that are good at coordinated team combat against one another are also good at hunting other species. Male chimps, working in teams, can kill other chimps that happen to be caught without allies nearby. They also pursue monkeys in coordinated assaults and are able to acquire around 10 percent of their calories from prey like colobus monkeys (chimps are bigger and smarter than monkeys). Male chimpanzee hunting packs can decimate populations of monkeys despite the agility of the latter. Other animals that are good at working together to hunt big animals, like wolves and hyenas, use their fangs and teamwork to eliminate rivals. Wolves have high kill rates, especially during the winter, when groups of them may encounter a straggler. Conversely, animals that do not team up against one another in combat tend to make poor group hunters. Bonobo apes are close relations of chimps but do not engage in lethal coordinated combat against one another; they also do not hunt in teams and instead individually catch small animal prey when chance occasions arise.
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It's possible that our ancestors hunted in coordinated packs, using cunning instead of brawn and fangs. There's every reason to believe that our
Homo
ancestors were more skilled at killing one another and hunting animals than chimps, using weapons like clubs, spears, and rocks, in teamwork with other assailants. Around 2 million years ago,
Homo
skeletons showed signs of adaptation to a terrestrial lifestyle—shorter toes, narrower pelvises, the neck shifting to support the skull in an upright position, the upper thigh bones (femurs) tilting inward to improve gait. Braincase volume more than doubled from about fifteen ounces in Australopithecines to thirty-two ounces in our
Homo erectus
predecessor.
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Thus the increase in brain size was closely related to the shift to walking fully upright. Walking around on the ground all the time—and especially sleeping on the ground—would have been a hazardous habit for our ancestors in territory inhabited by lions and other predators, unless our ancestors themselves had become formidable creatures.

The primatologist Richard Wrangham argues that the mastery of fire and cooking could have enabled our
Homo
ancestors to obtain more calories from raw meat and starches; fires could also have helped fend off predators at night. It's an intriguing proposal, though for the moment the cooking hypothesis remains unproven, awaiting evidence of fire usage 2 million years ago. Solid evidence for the use of fire in Europe currently dates back to 300,000 to 400,000 years ago.
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Alternatively, instead of running down prey, perhaps our
Homo
ancestors were using their hands coupled with ingenuity. To learn more about the history of stone tools, I headed to Africa, the place where our ancestors first mastered the art of tool making.

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Through the management of a bed and breakfast in Nairobi, Kenya, I arrange for a driver to take me out to Olorgesailie. No one that I talk to has ever heard of the place, including the driver, so I show them the location on Google Maps. It's early afternoon by the time we set out to the site, and the sweltering heat has subsided. The road ascends over a ridge, the dilapidated buildings of the city soon giving way to an expanse of acacia and burnished red sands. The driver swings the car wildly back and forth to avoid potholes. He doesn't speak much, except to ask for directions. We pass Maasai, wearing cloaks or school uniforms, loping with a graceful stride. An old man and a little boy hop into the car to guide us and catch a lift. We finally spot the sign directing us to an open-air museum, Olorgesailie Prehistoric Site, operated by the National Museums of Kenya.

A guide leads me to the first exhibit. Scattered in the sand, beneath a wooden catwalk, are dozens of rocks. Something about their shapes immediately catches the eye. The stones are approximately the length of a hand or two. Their silhouettes are pleasing, resembling almonds or perhaps teardrops shed by a grieving volcano.

Nestled within the arc of the Great Rift Valley, Olorgesailie is one of the most enigmatic sites in our evolutionary history, as inscrutable as Stonehenge, but vaster in geographical scope and implications for the development of humankind. Gathered at this site are hundreds of rocks that were meticulously crafted approximately 800,000 years ago and then left inexplicably behind. These rocks were sculpted in this fashion starting as far back as nearly 2 million years ago, with little variation in design for over a million years.
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The same design was found in Africa, Europe, and Asia, so the stones must have been indispensable for doing
something
—but what? Most anthropologists surmise that these rocks were Paleolithic Swiss Army knives, capable of carrying out a range of functions, such as cutting meat and scraping hides. These Acheulean hand-axes can indeed be held, in inverted fashion, with the bulge of the tear pointing upward, but because the rocks were sharpened on both sides, they're uncomfortable to grip tightly. Imagine trying to wield a butcher knife that has a cutting edge on both sides and no handle. Other dedicated stone tools found at the same time as these teardrop rocks seem much better suited for the purposes of cutting and scraping.

Another problem with the Swiss Army knife idea is that in some places, large quantities of the tools were made and then apparently abandoned. It's been proposed that the makers may have simply forgotten where they had laid their finished products. Alternatively, these stones may have been cores from which smaller, more useful blades were hacked off. This raises the question of why these leftover cores were shaped in the striking teardrop fashion, with the center of gravity displaced to one side, rather than being molded with the center of gravity dead in the middle, as you might expect from simple raw material for making blades.

One recent conjecture is that the hand-axes were made by men to court women, with onlookers blushing over the teardrops that emerged as the most symmetrical and skillful. As the anthropologist Steven Mithen proposed, “The thrill of holding a finely made symmetrical hand-axe is an echo of the Stone Age past … when these objects played a key role in sexual display.”
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It has also been pointed out that the proportions of many Acheulean hand-axes conform to the golden ratio (the ratio of the length to the width is the same as the ratio of their sum to the length) that the ancient Greeks and others held in such high esteem in their buildings.
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But could such an object help Great-grandpa get Great-grandma into the bush? Some large hand-axes, on the order of twelve inches long and four and a half pounds or larger, seem poorly suited for practical use, and may have functioned as show-off items, but the idea that hand-axes were made to woo women has attracted scorn from some anthropologists.
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Another suggestion is that the smaller hand-axes were chucked rather than wielded. This gets around the problem of the sharp edges—knives are typically thrown from their blades. Since chimpanzees and gorillas can throw sticks and stones, it's arguable that 2 million years ago our
Homo erectus
relation could have been a formidable thrower. In the human record, there are many other examples of weapons that were thrown. The best known are the boomerangs made by Australian and Tasmanian groups. In the hands of a skillful thrower, nonreturning boomerangs could deliver a formidable wound if thrown overhand or knock down large animals if thrown horizontally at their legs. Similar throwing sticks have been discovered in Peru and Africa.
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When I learned that some researchers believed hand-axes may have been thrown discus-style and that many others pooh-poohed the hand-axe-throwing idea altogether, I asked Professor Gail Kennedy at the University of California, Los Angeles, if I could borrow a hand-axe to try some experimental throws.
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To my surprise, the professor handed me a real Acheulean hand-axe from her personal collection. The hand-axe felt heavy when I tossed it with an overarm throw at some branch targets laid on a grass embankment. Just a few throws wore me out, and my hand was gashed. Nonetheless, there was a fascinating, macabre heft to the stone tool.