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Enter Meat Eaters

In a way, the history of life on Earth is a history of eating meat. It’s a story of cheating, of growing larger and larger, of trying to hide. It’s a story of an arms race between predators and their prey. This story begins about 1.5 billion years ago, in the temperate waters of Earth’s only ocean. There were no animals back then, no creatures with complicated body plans—no legs to walk on, no hearts to pump blood, no teeth to shear off meat. And there was no meat, either, not in the common sense of the word—the edible flesh of animals was still a long way off.

All life on Earth was simple and single celled 1.5 billion years ago. Only two types of organisms probably existed: bacteria and archaea. The latter are bacteria-like creatures that are nowadays known for their ability to live in extreme environments, such as in deep-sea thermal vents where temperatures reach over 212 degrees Fahrenheit, in the supersaline waters of the Dead Sea, and even in petroleum deposits. For these ancient bacteria and archaea, the world might have resembled a garden of Eden, with no predators and no killing. They fed themselves on energy from the sun or from inorganic sources such as elemental sulphur or hydrogen. But the peace was soon about to end.

According to Gáspár Jékely, a youngish researcher at the Max Planck Institute for Developmental Biology in Germany, the story of predators and carnivores on Earth began with cheating. Ancient bacteria were unable to eat one another, Jékely says. Bacteria don’t have mouths. To consume something, a bacterium has to engulf its prey with its entire single-cell body in an act known as phagocytosis. But the problem is that the cell of a bacterium has a rigid wall, a bit like bark on the trunk of a tree, which prevents it from opening up and swallowing the flesh of others. Bacteria can’t easily get rid of the wall, either. If they did, they would expose themselves to the forces of the outside world, which could mean death. And yet, at some point around 1.5 billion years ago, some of the ancient bacteria did begin to shed their cell walls and did start eating others. They could do it because they were cheaters.

As Jékely told me, bacteria are social creatures. In the Garden of Eden, they lived communally, just as they often do nowadays, in foam-like, slimy biofilms that floated on water or covered the rocks on the bottom of the ocean. In such biofilms each bacterium has to secrete something for the common good. “It’s like a community building a house, where everybody is supposed to bring a brick,” Jékely said. But some cheat. “They just pretend to bring the brick, and yet still live in the house. They exploit the community.” In the safety of the biofilm, such cheating bacteria were able to get rid of their cell walls and become predators. Instead of synthesizing energy from the sun or from inorganic compounds, they would crawl up, amoeba-style, to other bacteria and swallow them whole. It made perfect sense. Eating others was an efficient way of getting nutrients.

Of course, phagocytosis done by ancient bacteria was hardly like modern meat eating. These, though, were the first predators, organisms eating other organisms by killing them, and even some scientists call these earliest predators “carnivores,” as if what they were doing was indeed devouring meat.

These first acts of predation, many researchers agree, held great consequences for life on Earth. They were essential to the emergence of eukaryotes, organisms with complex cells containing organelles. After the predators started hunting down other bacteria, the engulfed prey would sometimes develop defense mechanisms to avoid being digested and would survive inside the predator. With time and generations, these fortified prey would evolve into organelles such as mitochondria—and eukaryotes emerged. All animals and all plants are eukaryotes.

Once the ancient bacteria got hooked on the “meat” of others, it started a chain of events that led not only to the emergence of eukaryotes with their complex cells but also to many other vital transitions in evolution: going from unicellular to multicellular (it’s harder to get eaten if you have multiple cells instead of just one), from small to large, from soft bodied to hard shelled, from slow to fast. Without that first bacterium eating up another, there would have been no eukaryotes on Earth, no multicellular organisms, no animals, no meat eaters, and no meat.

The game of life was changing. Soon enough, specialized predators would be hunting the muscled flesh of others, and meat eating as we know it today would be born.

 

In the warm oceans of late Precambrian Earth, some time around 550 million years ago, one of the first true carnivores began eating meat. We know of this carnivore’s existence because it left traces in the fossilized carcasses of animals called Cloudina. But this ancient predation couldn’t be further from the primal scene we might imagine of a shark-like predator in hot pursuit of a dolphin-like victim.

Although we still don’t know the identity of this Precambrian carnivore, it almost certainly wouldn’t have done much damage to a modern human. It was probably rather small (about 0.02 inch long—like a short grain of rice), and instead of ripping its prey apart with a mouthful of sharp teeth, it bored holes into it. The prey wasn’t exactly fleeing in terror, either. Cloudina was an anemone—a coral-like animal—and formed shells that resembled towers made of shot glasses. It lived out its life attached to the bottom of the sea, which is where it met its fate, eaten by a creature that drilled holes as thin as an average human hair into its shells.

This may not sound much like carnivorous behavior. Still, if we define a carnivore (after Encyclopedia Britannica) as an “animal whose diet consists of other animals,” then the predator of Cloudina most likely fits the bill. But was there even any actual meat to be eaten on a Cloudina? After all, an anemone doesn’t look much like a sirloin steak. Although the word meat is usually understood to mean the edible parts of an animal, the most important component of meat is skeletal muscle—muscles that we can contract voluntarily, as opposed to heart muscle and the smooth muscles that make up blood vessels, the bladder, or the uterus. Did Cloudina have skeletal muscles, a real meat to be eaten? Quite likely, yes. Scientists believe that skeletal muscle has been around for at least six hundred million years. Jellyfish-like animals, of which Cloudina was most likely one, were the first to evolve skeletal muscles—and so they were the first meat animals on Earth. Of course, how that meat would have tasted remains a mystery, but it would have probably been a bit similar to modern anemones, which are eaten in Chinese and Spanish cuisines and which, according to one present-day food blogger, taste like “a hybrid of pork and veggies with a fishy aftertaste.”

Odds are that the mysterious, hole-drilling predator of Cloudina wasn’t even the first meat eater on Earth. But it was the first meat eater whose traces we have found so far, even though we still have no idea what it might have looked like.

The first carnivores that we can actually identify appear later. One of those earliest meat eaters still exists today and is known as the penis worm. Disturbing as the name may seem, if you search the web for images of these animals, it becomes obvious they were named for their looks: they were long, sausage-like, pale pink, and considerably thicker on one end. Yet penis worms weren’t fierce, Jurassic-like predators, either (an image that would have been even more disturbing). They resembled tubes through which food passed, and they fed on almost anything in their path, including shrimp-like arthropods, cone-shaped hyolithids, and trilobites—basically, meat, in all of its early forms.

With the appearance of another strange new carnivore, the story of meat eating becomes a bit more gripping than drilling holes in shells or sifting through ocean sediments. The squid-like Nectocaris, although as bizarre in its looks as the penis worm, was probably a far more skilled carnivore. It had two tentacles, effective for manipulating prey, a conveyor-belt-like tongue with teeth on the surface, eyes on long stalks, and a weird-looking funnel, used to squirt itself around. No longer than six inches, Nectocaris may be a rather small predator by today’s standards, but it was quite big for the early Cambrian. What did it hunt? Nectocaris squirted itself after little shrimp-like animals, mollusks, worms, and maybe a jellyfish here and there. Fierce? Dangerous? If you are a small Cambrian mollusk, then certainly yes.

As time passed, meat-eating predators got bigger. By the mid-Cambrian, about five hundred million years ago, Anomalocaris entered the scene. It was truly large and fierce: three feet long, its body was streamlined for fast movement, complete with stalked eyes for clear vision and a round mouth full of sharp, teeth-like plates. It was the largest meat eater of the Cambrian and the first known apex predator, a carnivore that sits at the top of its food chain. In its time, Anomalocaris was the king of meat eaters.

An evolutionary arms race had begun. Once predators like Anomalocaris and Nectocaris (and yes, the penis worms, too) got hooked on meat, the battle between predator and prey became one of the driving forces for evolution, leading to the Cambrian period’s explosion of biodiversity.

It worked like this: a big, hard-bodied animal is better off than a small, soft-bodied animal, which is more easily snapped up by a passing meat eater. It’s a good idea for prey to grow larger so that a predator won’t be able to swallow it. On top of that, a nice hard shell offers protection, too. Once prey animals hid themselves in shells, the predators had to find ways to get to them anyway. They drilled holes; they grew teeth-like plates and sharp, conveyor-belt tongues. As their prey increased in size, so did the predators. First a few inch-long penis worms appeared, then six-inch Nectocaris, then over three-foot-long Anomalocaris, and, down the evolutionary road, the enormous meat-eating dinosaurs, some of which were as long as eight male lions put in a row. The whole animal kingdom started to bulk up, to invent new ways of eating and of avoiding being eaten.

There are other factors behind the world’s growing appetite for meat and the proliferation of species that followed. Some scientists believe that the boom of carnivory that started in the Cambrian couldn’t have happened if the oxygen levels on Earth, and especially in Earth’s oceans, remained low. In the period preceding the Cambrian, the oxygen levels in the atmosphere were only about 15 percent of what we have now, which means that if you time-traveled back to 650 million years ago, you would have suffocated within minutes. To truly blossom, carnivores need oxygen. Chasing prey is energetically costly, as is digesting big chunks of meat. Even today, there are relatively few meat eaters in the oxygen-poor waters of the oceans. According to one hypothesis, once the climate got warmer and the glaciers that had enveloped Earth before 650 million years ago started to melt, large amounts of nutrients were released into the oceans, which increased the population of tiny algae, which in turn produced more oxygen. This would have given the meat eaters the necessary boost to proliferate, speeding up the arms race. If Earth hadn’t become well endowed with oxygen, it seems, it wouldn’t have become the planet of meat eaters it is now.

 

The next chapter of the story of carnivory on Earth—and the tale of how humans became such avid meat eaters—begins sixty-five million years ago. The dinosaurs have just gone extinct, together with over half of Earth’s species. In rain forests that carpet vast areas of the planet, among soaring trees ribboned with vines, the next line of our ancestors has just evolved. It’s the first primate ever known—Purgatorius. It doesn’t look much like you or me, or even like a chimp. It resembles a cross between a mouse and a squirrel. And if it were still alive today, it would likely pass for a cute pet.

Purgatorius was an accomplished tree climber—and a vegan. It gave up the insect-based diet of its ancestors in favor of newly abundant fruits and flowers, carving for itself a comfortable niche high in the branches. For tens of millions of years, the descendants of Purgatorius, some of which would later evolve into us, were committed to their plant-based diets. From small monkeys to gorilla-size apes, they survived mostly on tropical fruits—spicing their meals with occasional worms, often by accident. About fifteen million years ago, they diversified a bit, adding hard seeds and nuts to their diets, but stayed true to their vegan roots.

Then, around six million years ago, Sahelanthropus tchadensis entered the African primate scene. With the advent of Sahelanthropus, our lineage likely split from that of our closest cousins, the chimps and bonobos. In the language of paleoanthropology, the word hominin stands for modern humans and all the extinct species closely related to us—and Sahelanthropus was the first. A short, flat-faced, small-brained creature, it most likely walked upright on two legs. It had smaller canine teeth than its ancestors and thicker tooth enamel, which suggests that its diet required more chewing and grinding than Purgatorius-like meals of fruits and flowers.

Nevertheless, meat eating still hadn’t caught on among our ancestors. Sahelanthropus probably ate tough, fibrous plants supplemented with seeds and nuts. The several species of Australopithecus that lived between four and three million years ago in woodlands, riverine forests, and on seasonal floodplains of Africa weren’t hooked on meat, either. Their dental microwear—the pattern of microscopic pits and scratches left on the surface of their teeth by the foods they ate—suggests a diet similar to that of modern chimps: some leaves and shoots, lots of fruits, flowers, a few insects here and there, and even tree bark. Did australopiths ever eat meat? It’s possible. Just as modern chimps occasionally hunt colobus monkeys, our ancestors may have occasionally dined on the raw meat of small monkeys, too. Yet the guts of early hominins wouldn’t have allowed them to have a meat-heavy diet, like the one Americans eat today. Their guts were characteristic of fruit-and-leaf eaters, with a big caecum—a bacteria-brimming pouch at the beginning of the large intestine. If an australopith gorged himself on meat—say, ate a few zebra steaks tartare in one sitting—he likely would have suffered twisting of the colon, with piercing stomach pains, nausea, and bloating, possibly resulting in death. And yet in spite of these dangers, by 2.5 million years ago, our ancestors had become meat eaters.

It seems that our bodies had to adjust gradually—first getting hooked on seeds and nuts. Seeds and nuts are rich in fats but poor in fiber. If our ancestors ate a lot of them, such a diet would have encouraged the growth of the small intestine (where the digestion of lipids takes place) and the shrinking of the caecum (where fibers are digested). This would have made our guts better for processing meat. What’s more, a diet of seeds and nuts could have prepared our ancestors for a carnivorous lifestyle in another way, too: it could have given them the tools for carving carcasses. Some researchers suggest that the simple stone tools used for pounding seeds and nuts could have easily been reassigned to cracking animal bones and cutting off chunks of flesh. And so, by 2.5 million years ago, our ancestors were ready for meat: they had the tools to get it and the bodies to digest it. But being capable is one thing; having the will and skill to go out and get meat is quite another.

So why would our ancestors have made such a shift? What inspired them to look at antelopes and hippos as potential dinners? The answer, or at least a part of it, may lie in a change of climate approximately 2.5 million years ago. As the rains became less abundant, so did the fruits, leaves, and flowers that our ancestors relied on. Much of the rain forest turned into sparsely wooded grasslands with few high-quality plants to eat but with more and more grazing animals. During the long, dry spell from January through April, our ancestors would have had problems getting enough food, and to find their usual fare, they would have had to expend more time and calories. Early hominins were at an evolutionary crossroads. Some, like the so-called robust australopiths, chose to eat large quantities of lower-quality plants; others, like early Homo, went for meat. The robust australopiths ended up extinct, but early Homo survived to evolve into modern humans.

Interestingly, while the ancestors of humans chose to profit from the new wealth of savanna herbivores and their flesh, the ancestors of chimps and gorillas never did. One of the reasons might have been their inability to walk on two legs. Searching for meat is costly, requiring more long-distance walking—and, in turn, more energy—than eating grass or fruit. Moving on two legs is more energy efficient than chimp- or gorilla-style knuckle walking, and longer legs better dissipate temperature, which prevents overheating and boosts endurance. It seems that if Sahelanthropus or its ancestors didn’t stand up straight (or at least straight-ish) six million years ago, a few million years down the road early Homo wouldn’t have been so well equipped to search for meat and might not have developed a taste for animal flesh—and there might not now be steaks or burgers on the dinner tables of today.

Still unanswered, however, is the question of what actually happened: Why was it that one day our ancestors were passing the animals grazing the savanna without a second thought, and the next day they saw them as food? Maybe a few of our ancestors were walking among acacia trees and saw a saber-toothed cat feed on a gazelle. Maybe they stumbled upon a dead zebra, with its guts spilling out and meat exposed, and thought, hey, why not give it a try? Even dedicated herbivores such as deer or cows will sometimes try meat if they chance upon it. There are records of cows devouring live chicks and munching dead rabbits, of deer eating birds, and of the duiker, a tiny African antelope, hunting frogs. (If you want to see a few of these carnivorous herbivores caught on camera, check out YouTube.) So it comes hardly as a surprise that our ancestors, who might have already been supplementing their diets with the meat of an occasional small monkey, saw the new abundance of savanna grazers as a way to get a few additional calories. The hominins were already omnivorous and opportunistic. If something was edible and it was there, they ate it. By 2.6 million years ago, there was a lot of meat around. Just as Purgatorius took advantage of the climate change and a new wealth of fruits, their descendants, early Homo, successfully adapted their diets to the changes in their environment. But this time it meant going after meat.

 

There are bones all around me: elephant bones, jaws of saber-toothed cats, a few skulls of extinct hyenas, even hominin skulls. I’m standing in the lab of Briana Pobiner at the Smithsonian National Museum of Natural History in Washington, DC. Pobiner studies bones, which she either digs out of archaeological sites in Africa or steals from lions, to understand how and when our ancestors started to eat meat.

As we talk, Pobiner opens a drawer and pulls out a rib of an elephant, a million years old and scarred with cut marks by one of our stone-tool-wielding ancestors. Tracing her finger along a groove, she explains that human-made cut marks differ from the marks left by the teeth of a lion or by water dragging the bones across rocks. “Cut marks are V shaped, more linear in comparison to carnivore tooth marks and deeper than sedimentary abrasions,” she says, and then shrugs. “This one is pretty obvious, but sometimes it’s rather hard to tell.”

For modern scientists, cut marks are important because they are the earliest hard evidence of our meat eating. Yet for our ancestors, cut marks were just mistakes. Instead of smoothly slicing meat, some prehistoric butcher cut the bone with his stone tool, leaving a mark. Today, by studying these cut marks, researchers like Pobiner can tell what our ancestors ate, whether they hunted or scavenged, which parts of an animal they usually consumed, and whether the butchers were skilled professionals or amateurs. It’s a whole story written in a Braille-like language.

The oldest undisputed record of cut marks tells us that humans started to butcher savanna animals 2.6 to 2.5 million years ago. Someone back then in what is now Ethiopia filleted a Hipparion, an extinct three-toed species of horse, and cut out the tongue of a medium-sized antelope. We have no idea, though, if this was just an occasional foray into carnivory, a once-in-a-lifetime event, or if the butchers were eating meat on a regular basis. But by two million years ago, meat appears to have entered the diets of our ancestors for good. Pobiner and her colleagues have recently found evidence of what she calls “persistent carnivory” in Kenya. “These early humans came back to the same place, over and over, to butcher and eat animals,” she tells me.

Our ancestors weren’t particularly picky eaters. They ate their way through the kingdom of savanna grazers: they butchered warthogs, small gazelles, rhinos, giraffes, waterbucks, elephants, and a few extinct species, too. One such prey, Hippopotamus gorgops, was a larger cousin of living hippos, with rather bizarre-looking eyes perched on long stalks. Another, Deinotherium (Greek, meaning “terrible beast”), resembled a cross between a giant elephant and an anteater. Some of the butchered animals were truly impressive in size, weighing up to 5,500 pounds. Some were much, much smaller (think hedgehogs). In the minds of our ancestors, almost any animal was meat—even fellow hominins: a few hominin bones scarred with cut marks have been identified as proof of cannibalism.

The big question scientists continue to argue about is how much of the meat that our ancestors ate about 1.8 to 1.5 million years ago was scavenged and how much of it was actually hunted. To find some answers, scientists study not only the pattern of the cut marks but also the behavior of modern carnivores. In Pobiner’s case, this means driving around the East African savanna in a Toyota Land Cruiser with an armed guard, seeking out recent kills made by lions and leopards. Once a predator is done eating, Pobiner hauls the leftover, bloody carcass of a zebra or an antelope into the trunk of her car (she has to take out the backseats to make room for the dead animals). Later, back at the camp, her assistant boils the carcass to clean the bones so that Pobiner can study the tooth marks and the damage that the carnivores have inflicted. Pobiner also weighs the meat to calculate how much is left over. “The lions leave lots of meat,” she tells me, stretching the o’s in lots. That’s an important finding because it means a feast of animal flesh didn’t necessarily require our ancestors to go hunting—stealing the kills of big carnivores would have worked just fine.

And at the start of our ancestors’ serious meat eating, that’s probably what they did. They could have found a carcass of a giraffe abandoned by a lion but not yet discovered by hyenas or vultures or, more likely, a carcass of an antelope pulled up a tree by a leopard (leopards hide their untouched kills in trees for a later meal). Since our ancestors could still climb pretty well at this point, they had an obvious advantage over other scavengers. On the ground, they would have to compete for meat with a multitude of other hungry creatures: jackals, hunting dogs, lions, hyenas. But even if they weren’t lucky enough to arrive before other scavengers did, there was still a good chance for leftover brains and bone marrow. Although brains and bone marrow may not sound particularly appetizing to modern humans, Westerners in particular, our ancestors would have considered them a lucky find because they are fatty and loaded with calories. Marrow from a tiny, thirty-pound gazelle would have provided about five hundred calories—as much as a large serving of french fries at McDonald’s. A scavenged wildebeest would have meant six times that.

Although we might have started as regular scavengers (what scientists call “passive” scavengers), who grabbed whatever flesh they stumbled upon, most likely quite early on hominins became “power” or “confrontational” scavengers and stole the kills right from underneath the noses of hungry lions, leopards, and saber-toothed cats. The pattern of cut marks on some of the ancient butchered bones suggests that once in a while early Homo ate those parts of prey that carnivores prefer as their first bites. The cats had little chance to munch on whatever they had just hunted, because coordinated groups of our ancestors chased them off and won the dinner. The hominins would then drag the meat to their day camp for butchering and sharing. They would start with the parts they liked best: fleshy limbs and fatty tongues. But to do the butchering, they needed tools: sharp flakes to scrape the meat off the bones, bigger stones to hammer them open to extract the marrow. Without stone tools, our ancestors couldn’t have become full-time meat eaters. They just didn’t have the bodies of carnivores.

One claim in particular gets repeated over and over on forums and blogs: we have pointy canine teeth, which means we are “designed” to eat animal flesh. Yet that is simply not true. Yes, we do have canine teeth, but that’s not proof that we are made for meat-based diets. Canine teeth are just one of the basic kinds of teeth of mammals. Most mammals have them, including such plant chewers as deer and horses. The water deer, native to China and Korea, have large, sharp canines, over two inches long, and so formidable that they look like they might belong to a saber-toothed cat.

Besides, human canines are not exactly sharp and pointy, as some bloggers and forum writers claim. In fact, they are relatively small and stubby. Even though canine teeth in apes (including humans) are indeed used for slicing and shearing food, their size and shape don’t have much to do with diet: they have much more to do with sex and fighting. Take gorillas. They eat primarily leaves and fruits but have dagger-like canines—especially the males. They don’t need these canines to tear apart flesh; they need them as weapons against other gorillas, particularly when battling over who gets the females. Fighting with members of their own species is also why the water deer have such weirdly big canines. Most likely the canine teeth of our ancestors shrank in size (which allowed space for bigger molars—better for chewing tough plants) because they didn’t fight as much among themselves as other apes did and because they were much more monogamous. Also, development of weapons enabled our ancestors to forgo big canines. They no longer needed to bite each other; they could pierce each other with spears instead. This gradual scaling down of hominin canines has been happening for at least six million years. Our early ancestor Sahelanthropus already had reduced canine teeth. These smaller canines are actually considered to be one of the main features distinguishing our ancestors from other apes. Rather than proof of some inherent carnivorous nature, our canine teeth are a sign that, for better or for worse, we should stick with the same mate.

The true meat-eating teeth are not the canines but the carnassials. If those sound unfamiliar, it’s because we humans don’t have them. Cats, dogs, and even skunks have carnassials. If you manage to open the muzzle of a friendly Fido, you will see them at the back of the jaw: they are blade-like and sharp and perfect for slicing meat. Carnassials are the key characteristic of members of the order Carnivora, which includes primarily predatory mammals, such as lions, tigers, seals, raccoons, and domestic cats.

What we humans also don’t have are the jaws of carnivores. Watch any savanna-based nature documentary, and you’ll likely see a lion roar. These cats can really open their jaws wide. Hominin yawns, both those of modern humans and our ancestors, don’t even come close. We also lack the impressive temporalis muscles of lions (that’s the muscle that will hurt if you chew gum too long). All this means that we not only can’t kill prey with our mouths, carnivore-style, but we also have trouble eating raw, unprocessed meat.

If you are a hominin, whether an early Homo or a modern human, and you find a dead, untouched zebra on a savanna, unless you have some sharp tools with you, you have a problem. All that zebra meat is hidden inside a thick wrapping—skin—that your teeth are completely unable to break. Just imagine taking a bite of a living cow. Although our ancestors had bigger teeth than we do, their teeth weren’t much better when it came to chewing through fur and skin. You can rip apart a small monkey with your hands, chimp-style, but to get to the meat of a dead giraffe, you would need the help of true carnivores. You would need to wait, as vultures do, until other, better-equipped animals tore through the skin of your dead zebra, exposing the meat. Or you could simply wait a bit longer. With time, the carcass would rot, and the skin would become easier to break. But even if you did manage to get a chunk of zebra in your mouth, your blunt teeth would likely be unable to reduce the meat into pieces small enough to swallow. Before the invention of stone tools circa 2.6 million years ago, early humans were simply unable to hunt big game. Their bodies were just not equipped for that.

But thanks to tools, our ancestors likely became quite skilled at hunting small gazelles as recently as 1.8 million years ago. Although scientists have yet to find the weapons used to hunt them, the mere presence of the bones of such animals (bearing cut marks suggesting they had tons of meat on them) likely means that they were hunted, not scavenged. Since lions and hyenas can devour a tiny gazelle in minutes, hominins would not have had enough time to steal the kill.

How did we hunt? If the prey was truly small, we could have done it with our bare hands. The famed British-Kenyan paleoanthropologist Louis Leakey, who in the early twentieth century excavated Tanzania’s Olduvai Gorge, was proud of his ability to catch small hares and antelopes by hand and reasoned that if he could do it, our ancestors probably could, too. Another possible scenario involves acacia trees. Acacias are widespread on the African savanna and have branches spikier than barbed wire. Their thorns are the reason why locals surround their livestock with acacia branches for nightly protection against predators. They are also the reason why one-eyed giraffes are not uncommon: they feed on acacia leaves, and accidents happen. At first, our ancestors could have used acacia branches as a power-scavenging tool to scare away lions or cheetahs from their kills. From there, it’s not a long way from waving a thorny branch in front of a carnivore’s nose to stabbing an antelope with a branch that has been sharpened at one end. Once early Homo had stone tools, they could have used them to make the tips of their acacia branches more pointy and deadly. You don’t need a particularly big brain to come up with such an idea. Chimps did, after all. In the jungles of Senegal, groups of chimpanzees use their teeth to sharpen sticks into spears, which they then use to stab bush babies—tiny primates as cute as their name suggests.

Once hominins controlled fire, they could have used it to further harden the tips of their spears. Shoving a stick into a campfire makes it much more resistant—and much more lethal. But it probably took our ancestors quite a long time before they invented the stone tips that would make their spears even more efficient. The earliest evidence of such weapons comes from a site in South Africa, five hundred thousand years old. Thus it seems that we hunted for over a million years with little more than sharp sticks. This seems almost impossible, considering we are not particularly big animals (and our ancestors were even smaller), we don’t have claws, and we’re not very fast. So how were we able to kill prey in the years before stone-tipped spears? The first reason, and the most obvious, was that we were social creatures who hunted cooperatively. The second was our ability to climb trees.

Imagine a warm, sunny day on an East African savanna a million and a half years ago. But don’t think of the Serengeti—imagine a landscape much more wooded. Numerous trees and shrubs dot the landscape, providing shade, food, and places to hide. Among the trees, a gazelle is slowly munching on the grass, unaware that high among the branches a group of hominins is waiting, preparing to strike. The gazelle moves closer and closer. Suddenly, the apes cast their spears. A few of the pointy sticks pierce the prey’s body. The animal falls, and gazelle is on the menu.

With time, hunting became part of life for early humans. We “invented” sticks, then discovered how to sharpen them and harden them in fire and how to add stone tips. A spear found between the ribs of an elephant in Germany dating to about 400,000 or 300,000 years ago (yes, there were elephants in Germany back then) proves that by that time our ancestors were skilled crafters of javelins—light spears designed for efficient throwing. Over 7.8 feet long and made of the hardest part of yew wood, from near the base of the tree, they were shaped so that the maximum thickness and weight were about a third of the way from the tip, which allowed for the easiest throwing. Our ancestors had learned the art of killing large animals at a distance.

Yet, as many researchers point out, we should not overromanticize hunting. Modern cultural mores cause us to look at hunting as something noble and evolved, while shrugging off scavenging as dirty, easy, and almost indecent. So it is that we tend to think of lions as the kings of the jungle—they are the hunters after all—and of scavenging hyenas as lowly and cowardly. But there is no reason to assume that scavenging is somehow a lesser way to obtain meat. Lions scavenge frequently—in the Serengeti more than 40 percent of their diet is stolen from other hunters. And hyenas hunt more often than they scavenge. Scavenging is both difficult and dangerous. To be a good scavenger, you need to watch out for signs of a kill, you need to arrive at the site before your competitors do, and you may even need to fight off the hunter or other scavengers. Thinking of hunting as a superior, more virtuous way of obtaining meat is just our present-day bias.

Even if early on we were “only” scavengers, 2.5 million years ago we were definitely already meat eaters. We got hooked on meat because of climate change and because our usual fare became harder to find. Simply put, we went for meat because it was there. Just as it had been for the cheating bacteria in the Garden of Eden, swallowing others was a more efficient way to get nutrients, and scavenging dead antelopes helped our Paleolithic ancestors fend off hunger in times of scarcity.

Meat had entered the hominin diet for good—and this sea change would have immense consequences. Once early Homo started to hunt, a chain of events was set in motion that led to profound changes in our bodies, in our societies, and in our lifestyles. From the earliest days, meat was not just about nutrition. It was about politics and sex, too.