字幕列表 影片播放 列印英文字幕 Thanks to CuriosityStream for supporting PBS Digital Studios About 2 and a half million years ago, in the Middle Awash Valley of Ethiopia, one of our ancient human ancestors -- or maybe a group of them -- crouched over a carcass of an antelope on the shore of a lake. One of these hominins took a sharp stone flake and sliced into the flesh on the inside of the jaw, grazing the bone and leaving three cut-marks. These ancestors were after the meaty tongue of the animal, and in trying to remove it, they left traces of this remarkable moment: the use of a tool by a human ancestor. They also left behind the technology itself, in the form of a few scattered stone tools. This site, now known as Bouri, is one of the earliest confirmed locations where a human ancestor or relative permanently modified some part of the environment around them to suit their needs - chipping raw stone into a tool. In the broadest sense, this is what technology is: making tools and using them to interact with the world around you. These simple stone flakes and the cores of rock they were struck from are what anthropologists call Oldowan tools - named for Olduvai Gorge in Tanzania, where they were found. And while these tools don’t seem like much when you compare them to the screen you’re watching right now, their creation represents a pivotal moment in the origin of technology and in the evolution of our lineage. This is when our ancestors first started to make the world around them fit their needs. But what they didn’t know at the time was that this use of technology would change them, too. Because the fact is, the use of tools has not only enabled our lineage to take over the world, it has also shaped our very biology, from our brains to our skeletons. Of course, hominins didn’t invent the use of tools. The first of our ancestors to make and use technologies like the Oldowan tools were just expanding on the behavior of our primate ancestors and cousins. Chimpanzees, our closest living relatives, and capuchin monkeys, a much more distant branch on our family tree, make and use tools to get at choice foods, like termites and nuts. But hominins - the branch of our family tree that’s more closely related to us than to chimps and bonobos - took things a step further. They created permanent tools out of carefully chosen materials that were then sometimes carried around and re-used. And the Oldowan instruments weren’t the first tools that hominins ever made. In 2011, anthropologists working in West Turkana, Kenya, found evidence of a different type of stone tool that pre-dates the Oldowan by around 700,000 years. These tools are even simpler than Oldowan choppers and flakes, they’re called Lomekwian tools, after the site of Lomekwi where they were found. And they’re dated to 3.3 million years ago. They also seem to have been made in a different way. Oldowan tools were made by hominins holding rocks in both hands and striking them together. But Lomekwian tools seem to have been made by holding only one rock and striking it against another that was sitting on a flat base, or against the flat base itself, to break it and create a sharp edge. And it seems likely that the tool-makers at Lomekwi were doing this for the same reasons that the hominins at Bouri were: to try to get hidden foods, like bone marrow or the insides of hard-shelled nuts. But we don’t know for sure, because, unlike at Bouri, the Lomekwi hominins didn’t leave behind butchered bones . Still, in both cases, these tools allowed our early ancestors to get at more nutritious foods more often. And this might’ve kickstarted a feedback loop that affected our bodies forever -- starting with our brains. We don’t know for sure who the tool-makers at Lomekwi and Bouri were, but they were most likely australopithecines, members of that early and diverse group of hominins found mostly in eastern and southern Africa. And members of this genus typically had smaller brains and smaller bodies than hominins that followed them: the early members of our genus Homo, who appeared on the scene in eastern Africa around 2.4 million years ago. These early members of our genus probably used Oldowan tools, too, like the hominins at Bouri. And the ancestors that used these tools seemed to do pretty well for themselves. For example, the earliest known site with clear evidence of long-term and consistent meat-eating is an Oldowan site called Kanjera South in Kenya, dated to about 2 million years ago. Over a period of hundreds to thousands of years the hominins there acquired and butchered many small ungulates, like gazelles, and occasionally larger antelope,. And all that meat and marrow is really high in calories, compared to things like fruits and tubers. So regular access to all those calories might’ve paved the way for our large brains and, in turn, further technological innovation. Now the next phase in the history of our tool use is where things get even more interesting, and more complicated. Because, this is where we start to find tools outside of Africa … but we’re not sure who made them. The traditional story from this point in the anthropological record is that, a little less than 2 million years ago, we see both a new hominin and a new, more complicated type of tool emerge. This is when Homo erectus makes its first appearance in Africa, about 1.9 million years ago. And this species had a larger brain, larger body, and smaller teeth compared to earlier hominins - all hallmarks of a higher quality diet. Brains are especially expensive, when it comes to how many calories they require to develop and to maintain. And so are larger, more muscular bodies. So it was thought that this might explain why a new, more sophisticated toolkit started to appear regularly around 1.7 million years ago. These were large cutting tools, including things like hand-axes, which are made by flaking hand-sized rocks to a point on both sides, with a rounded end for gripping. These newer more complex instruments became known as the Acheulean toolkit. And until very recently, those tools were thought to have first been made by African members of Homo erectus, and this development was seen as the next pivotal step in our ancestors’ use of tools. But new finds from China might make this story much more complicated. In 2018, researchers published their discovery of Acheulean tools from the site of Shangchen, which were dated to 2.1 million years old. That date pushes back the appearance of Acheulean technology some 400,000 years. And it’s also 300,000 years before the time when the earliest hominins were thought to have made it out of Africa. The earliest known fossils of human ancestors that we’ve found outside of Africa belong to a population of Homo erectus, found at a site called Dmanisi in the Republic of Georgia, dated to 1.8 million years ago. But who made the tools found in China is still unknown. The general consensus is that it was probably Homo erectus. Because, fossils of Homo erectus have been found at another site in China that are 1.7 million years old, so we know they made it there at some point. But other researchers have suggested that maybe it was an earlier member of genus Homo that made the tools, like maybe Homo habilis. It’ll take more research to figure out what exactly is going on here, but that’s part of what makes paleoanthropology so interesting: New discoveries are made all the time. And all of these technological innovations - from the very simplest to the more complex stone tools - were major breakthroughs for our lineage. For our australopithecine ancestors, the use of tools meant they could incorporate more animal resources, like meat and bone marrow, into their diets, consuming more calories than they’d been able to get before. And more calories meant more available energy, allowing those early hominins to develop and maintain larger brains and bodies over time, leading to taxa like Homo erectus. And the very circuitry of our brains might also have started to change when we began making and using tools. In 2008, researchers at a medical school in Indiana used PET scans to study the brains of modern expert stone toolmakers while they made Oldowan and Acheulean tools. And the scans showed that toolmaking activated parts of the brain associated with visual-motor coordination and planning. Demands in those parts of the brain also grew as the toolmaking became more complex. So the researchers concluded that these neural signatures of tool-making may suggest that our brains and our technological capabilities may have co-evolved. And of course, the act of toolmaking may also have had an effect on what we use to make them: our hands. In 2018, a team of anthropologists conducted an experiment to learn more about how the biomechanical stresses of tool making might have shaped our anatomy. Their study subjects wore special gloves with sensors in them and then did things like nut-cracking, breaking bones for marrow, and making stone tools, to see how much stress these things placed on each of their fingers. And the research showed that the two activities that created the most stress were breaking bones for marrow and making stone flakes using hammerstones. So, these two activities might have been especially important in driving the evolution of our hands. Because, using tools in these ways would have exerted powerful selective pressure on things like increased stability and better gripping ability, and maybe even having bigger, stronger thumbs. From the size of our bodies to the wiring of our brains and the capabilities of our hands, we owe some incredibly important aspects of our modern anatomy to stone tools. But of course, they were only the beginning of our capacity for technology. Their legacy continues to this day, and the reason you can watch me talk to you right now is because our always-evolving ability to create new things to help us interact with the world around us. Thank you to CuriosityStream for supporting PBS Digital Studios. CuriosityStream is a subscription streaming service that offers documentaries and non¬fiction titles from a variety of filmmakers, including CuriosityStream originals. For example, you can watch Deep Time History, the story of how our evolution has been shaped by forces you might not have thought of -- not just our biology, but also the physics, geology, and chemistry of the natural world. You can learn more at curiositystream.com/Eons Thanks for joining me today in the newly named Konstantin Haase studio! And extra big thanks to our current Eontologists, Jake Hart, Jon Ivy, John Davison Ng and STEVE! If you’d like to join them and our other patrons in supporting what we do here, then go to patreon.com/eons and make your pledge! Now, what do you want to learn about? Leave us a comment, and don’t forget to go to youtube.com/eons and subscribe.