字幕列表 影片播放 列印英文字幕 In 1924, a worker at a limestone quarry in the town of Taung, South Africa made an incredible discovery. It was the fossilized skull of a juvenile hominin, a member of the human lineage that includes us and all of our ancestors that came after our split with chimpanzees and bonobos. That little skull became the type specimen for Australopithecus africanus, and it would become one of the most important fossils in the study of human evolution. Today, the specimen is known as the Taung Child. Its discovery revolutionized our thinking about our past for a number of reasons. For one thing, at about 2.8 million years old, it was the first fossil evidence that our early human ancestors originated in Africa. But there was something else. The skull had been found among lots of bones from other, mostly small animals, and many of them had been badly damaged, as if the animals had been butchered. So for decades, these fossils were read by experts as evidence that hominins like Australopithecus weren’t fruit-eating apes -- they were carnivorous hunters, so-called “predatory ape-men.” It would be more than 80 years before scientists would realize that, in fact, the Taung site was not proof that australopithecines were hunters. Instead, it was actually evidence that the hominins themselves were being hunted. No one noticed it at the time, but the skull of the Taung Child bore the telltale marks of violent trauma: puncture holes in the base of the eye sockets, a depressed fracture in the top of the skull, and scratches on the sides. These would eventually prove to be the hallmarks of a predator that no one suspected. But this child’s skull is just one example of the evidence that, not too long ago, our early human ancestors were under constant threat of attack from predators. And it turns out that this difficult chapter in our history may be responsible for the adaptations that allowed us to become so successful. We may be who we are today, because of the time when we were prey. The notion that our ancestors were once hunted by other animals would have come as a surprise to the anthropologist who first studied the Taung Child. His name was Raymond Dart, and he proposed that one of the driving forces of human evolution was what he called “the thirst for blood.” To Dart and many anthropologists of his time, the impulse to kill prey was seen as a deeply ingrained part of our heritage. Dart observed baboons that appeared to “spontaneously” hunt down prey, and he noted that living hunter-gatherers seemed to be hunters first and gatherers second. So, Dart built the case that australopithecines were ravenous carnivores, as more and more fossils emerged that seemed to support his model. One such fossil was unearthed in a South African cave in 1949: the bony skullcap of a juvenile hominin with two very suspicious puncture marks. This partial cranium belonged to a young member of Paranthropus robustus dating to between 1.8 and 1.5 million years ago. It was found alongside other fossil mammals, like antelope and baboons, many of which were also damaged or had only their skulls preserved. The child’s skull was labelled SK 54, and it had suffered two punctures at the back of the head. And the bone on the inside of the cap, where those punctures were, flaked upward - indicating that the victim was probably alive, or only very recently dead, when it was attacked. At the time, a science writer named Robert Ardrey took this fossil as evidence of interpersonal violence: SK 54, he said, was the victim of two blows to the back of the head with a pointed object, by another hominin. Soon, the idea began to take hold that our evolution was deeply shaped by violence, including between humans. Ardrey gave this idea the rather sensational name of “The Killer Ape Theory.” Dart described it as “the predatory transition from ape to man.” And this view seemed to get another big boost from a discovery made at a South African cave site called Makapansgat. The cave was found to be filled with the bones of Australopithecus africanus and many other mammals - most of which, like at the Taung site, were broken. Raymond Dart studied more than 7000 remains from this site and was struck by the fact that the fossils consisted almost entirely of skulls and neck vertebrae. So he concluded that the fractures on these bones were evidence of blows by hunters and that the high proportion of skulls meant that the hominins were taking the heads of their prey as trophies -- including the heads of their own species. But within the field of anthropology, changes were in the works. Just as the Killer Ape Theory was reaching its peak of popularity, more scientists began to suspect that we had actually spent most of our evolutionary history being prey of other, better hunters. Enter the American anthropologist Sherwood Washburn. While doing research on a game reserve in Africa, he noticed how modern predators ate carcasses selectively - eating the soft, meaty parts and leaving skulls, jaws, and upper vertebrae behind. It struck him that this was the same pattern of bones that Dart saw at the sites of supposed hominin “headhunters”. Washburn also observed hyenas carrying off parts of carcasses and stashing the bones around their dens - again, creating a pattern like the one Dart was seeing in the South African caves. Washburn published his observations in 1957, and argued that australopithecines weren’t headhunters - instead, they were the prey of carnivores like hyenas. This was a major turning point in our understanding of our evolutionary history. For decades, Dart and his contemporaries had been studying human nature in the violent social context of World Wars I and II, so it made sense that they understood our history as being shaped by aggression. But while they stuck to that model, younger anthropologists began to explore Washburn’s ideas. And his work made enough of an impact that when another damaged hominin fossil was found -- this time at Olduvai Gorge, Tanzania, in 1960 -- other hominins were not considered the top suspects. In this case, the fossil was OH8, a slightly mangled partial left foot of Homo habilis, discovered by anthropologist Louis Leakey. The ankle bone had tooth marks on it, and Leakey’s wife and partner, Mary Leakey, concluded the marks came from a carnivore that was probably not a hyena, but nor was it another hominin. So by the mid-1960s, anthropologists were at least starting to think that hominins could’ve been prey. Then, in 1970, paleontologist C.K. Brain revisited the cave site where SK54, that skullcap with the puncture wounds, had been found. He wanted to try to figure out why all of those fossils had accumulated where they had. And he realized that the fossils weren’t signs of hominins hunting, much less fighting each other. Instead, he argued, those fossils had been the victims of a hungry ancient leopard. For one thing, he pointed out, modern leopards often stash their kills in the trees that grow around these types of caves. And the bones often end up dropping down into the caves. But the more convincing evidence was that the puncture wounds in SK54 perfectly matched the lower canine teeth of a leopard. Which means some big cat must have attacked Sk 54, and dragged it by its head up into a tree, its bones later falling into the cave. So, just like with Washburn, Brain’s observations of the behavior of living carnivores were fundamental to rethinking whether our hominin ancestors were the hunters or the hunted. Big cats and hyenas turned out to be very good at making just the kinds of bone assemblages that Dart had seen in those South African caves. And once anthropologists started thinking about how bones become deposited and preserved in different settings, it seemed less likely that small hominins like the australopithecines were mighty, bloodthirsty killers. And this new thinking eventually worked its way back to that crucial, early hominin fossil: the Taung Child. In 1995, researchers took another look at the fossils from that site, and noticed a whole new set of clues. For example, they noticed that the nature of the damage to the Taung skull was similar to that found on the skulls of baboons found there. And they were struck by the fact that the other bones were generally of small animals. And, there were also the remains of large eggshells in the area. So the team proposed that the Taung Child, along with the other animals found with it, were in fact the victims of a large bird. They found even more convincing evidence in 2006, when they compared the Taung Child’s skull to those of modern monkeys that had been preyed upon by eagles. The gouges and punctures in the base of its eye orbits matched the damage done to those monkey skulls. So the Taung Child was likely killed by an ancient, giant bird of prey. Likewise, remember OH8, the Homo habilis foot found by the Leakeys? Well in 2012, researchers took a second look at that fossil, too, and noticed something new. The puncture wounds in the bone had two extra grooves in them that matched the ridges found on the teeth of crocodiles. Crocs are ambush predators, and those kinds of attacks leave characteristic marks and patterns of damage on the bones of their prey, which, again, matched the damage done to that Homo habilis. We’ve come a long way from Raymond Dart’s ideas about bloodthirsty hominins. Today it seems that our evolution was shaped less by our need to kill than by our need not to be killed. After all, Africa in the Pliocene and Pleistocene was a dangerous place for our fossil ancestors and relatives. And with selective pressure comes adaptation and evolution. So the evolutionary legacy of that time when we were prey is enshrined in our bodies today. Having become larger than our ancestors, for example, has helped protect us from birds and smaller mammal predators. And some experts argue that becoming bipedal allowed us to better scan the horizon for threats, to move quickly while carrying food or infants, and just generally look bigger. Plus, with our hands freed up, we could also throw things at potential predators, which chimps still do today, though not as well as we can. Some experts also point out that speech has given us the ability to plan, rather than to just react. Living primates have alarm calls that are specific to certain predators, but speech allows us to figure out in advance what to do when we hear one of those calls. But, it’s worth pointing out: the Taung Child, SK54, and OH8 were all bipedal hominins - and they still got eaten. So other researchers have suggested that maybe our evolutionary legacy from that dangerous time is simply our ability to cooperate. Hominins would have needed to live in groups, and also to work together to ward off threats. And studies have shown that our brains are still activated in specific ways when we do things like play cooperative games, triggering our reward centers when we work together. By contrast, studies of chimps have shown that they don’t help others, even when there is no cost to doing so. But even if all of these adaptations evolved out of a need to defend ourselves from predators, they obviously didn’t work every time. Researchers in Poland recently discovered the finger bones of a Neanderthal child who lived just 115,000 years ago. And those bones were covered with dozens of small, distinctive holes that could only have come from passing through the digestive tract of a large bird. So, as recently as the Late Pleistocene, our ancestors were still being preyed upon, or maybe scavenged, by birds, just like the Taung Child was. But being able to recognize the signs of predation in our past has marked a major shift in how we think about ourselves -- one that allowed us to better understand the selective pressures that helped make us who we are today. Thanks as always, fam, and extra big thanks to our current Eontologists, Jake Hart, Jon Ivy, John Davison Ng and everyone’s favorite hominin, STEVE! Do you want to join them and have me maybe mispronounce your name and make fun of you? Then go to patreon.com/eons and make your pledge! Now, what do you want to learn about? Leave the dude a comment, and don’t forget to go to youtube.com/eons and subscribe.