字幕表 動画を再生する 英語字幕をプリント Hi everybody, It's Hank. We've got new merch. I'm wearing it right now. It's this new tee shirt! It's got an Eons pocket on it. It's comfy, it's nice thick fabric, it's got a good design, it has a functional pocket! And now I have one of my very own. If you want one too, you can get one at DFTBA.com. There's a link in the description! And we would appreciate it so you can show everybody all over the place how much you love this show Now, it's time to talk about fire. In the early 1980s, archaeologists working at a site in Kenya called Koobi Fora noticed some peculiar markings in the land they were excavating: distinctive patches of reddish-orange sediment. This wouldn't have been all that exciting, except that those patches looked a lot like the patches of baked earth left behind by the campfires made by modern people in the area. Interestingly enough, this site had also turned up the jawbone of a fossil hominin and evidence of stone tools having been made there, about 1.6 million years ago. So this got the researchers thinking: Was it possible that these red patches were the signs of an ancient fire that was used by some of our distant ancestors, more than a million and a half years ago? Well, maybe. There are still some big questions to answer. Like, could the hominins at this site have actually made fire? Or did they happen to find some fire occurring naturally, like from a lightning strike, and just used it for as long as they could? It's likely that our ancestors started out this way, taking advantage of fire as a fleeting natural phenomenon. But eventually they took it one step further-- scavenging a burning twig left behind by a wildfire, and using it to start their own fires. The use of fire wouldn't become truly visible in the archaeological record until it became widespread - when fire started to be used consistently, across many different sites. This could've been the moment in our history that sparked evolutionary change, triggering an expansion into new environments. And when we learned how to actually make fire when we wanted, it would forever change our relationship with the world around us. Now, the fact is, we don't know exactly when hominins harnessed the power of fire. And we're not totally sure what species among our ancestors was the first to master it -- although there's one candidate that seems most likely. And it wasn't us. Nevertheless, we do know that the ability to make and use it has fundamentally changed the arc of our evolution. The bodies we have today were, in many ways, shaped by that time when we first tamed fire. The use of fire in human history is notoriously difficult to study, because fire is ephemeral. It's more difficult to see in the archaeological record than, say, stone tools, because it's a transient phenomenon that leaves little evidence behind. Ashes can easily blow away in the wind or be washed away by water. But we know that the use of fire has had enormous impacts on our bodies and our behavior. So some experts have looked at the gradual changes in how hominins looked, and how they lived, to hypothesize which of our ancestors may have mastered it. The first impact that fire has had on our evolution is that it allowed us to cook food. And it's hard to overstate how important that was. The main advantage of cooking is that it breaks down food, making it easier to chew and digest. You can actually think of cooking as a way of starting the process of digestion, before you even put the food in your body. Which sounds gross when I put it like that. It's actually delicious But heat causes the large, complex molecules in food to break up into smaller, simpler nutrients. So if you heat food with an external source of energy, like fire, then you're saving the energy that your body would have to put into chewing and digesting the food if you had eaten it raw. Cooking also breaks down toxins in plants and kills pathogens. And again, this saves your body from having to invest energy in defending itself from poisons and disease. Together, these things make cooked foods much more energetically efficient than uncooked foods, so you end up getting more calories out of what you eat. And when you're trying to survive, every calorie counts. But of course, the other advantage of fire is that it like … keeps you warm. And so the use of fire likely helped our ancestors expand their geographical range, migrating to places with different climates and opening up a whole new world of ecological possibilities for our species. Now, there's one hominin, besides us, that fits both of these descriptions -- a species that needed a lot of calories and that had to live in lots of different environments -- and that's the earliest definitive member of our genus, Homo erectus. Some anthropologists propose that Homo erectus might have been able to cook food, based on its physical adaptations. Specifically, it had smaller teeth than its predecessors, suggesting that it didn't need to do the heavy-duty chewing that a diet of raw food would require. But maybe more importantly, it also had many of the traits that we know require a lot of calories -- like a larger body size, more muscle mass, and most importantly, a larger brain. And as for its ability to live in different environments, Homo erectus is the first hominin known to have migrated out of Africa, eventually spreading from what's now the Republic of Georgia all the way to Southeast Asia. But here's the problem: Homo erectus dates back about 1.89 million years. But the earliest possible evidence of repeated, regular cooking doesn't show up until hundreds of thousands of years after its appearance. Likewise, Homo erectus began its excursions out of Africa hundreds of thousands of years before the first definitive evidence of widespread fire use. So how could fire have helped this species develop a bigger body and brain, and help it migrate to other places? Well, as in many aspects of studying the distant past, there are a lot of dots to connect. And in this case … we're just missing a lot of dots. So let's look at what the evidence does tell us -- about the use of fire in general, and then cooking specifically. In the past few years, anthropologists have gone back to that red-stained site in Koobi Fora, Kenya. And recent excavations have turned up more definitive evidence of fire use than those red patches of earth found in the 1980s. Archaeologists have discovered shards of rock with tell-tale signs of having been heated to high temperatures, as well as bits of burned animal bone. And these bits of rock and bone seem to be clustered in distinct patches. Which is important, because it suggests that the fires were small and made intentionally, and not a natural wildfire, which would have burned across the whole site. As for who made these fires, the burned rocks and bones were all found in an area associated with artifacts that were likely made by Homo erectus. But there aren't any remains of those hominins to be found there. Instead, the only hominin fossils from the site are of Paranthropus boisei, a smaller brained species. The next earliest site with /widely-accepted/ evidence for fire is a site in South Africa that dates back 1 million years, in a place called Wonderwerk Cave. There, archaeologists have found burned bones and plants, as well as the larger and more complex stone tools, like hand axes, that are known as Acheulean tools. These tools have often been associated with Homo erectus. And some experts have speculated that, based on the date as well, Homo erectus may be the hominin that built those fires. Other more recent evidence of fire has been found at a site in Israel called Gesher Benot Ya'aqov. And there, at a site that's about 790,000 years old, burned seeds, wood, and flint have been found clustered together into what researchers call phantom hearths - areas where fire might have been, but without a neat campfire ring of stones. These clusters, and the fact that they occur throughout time at the site, suggest that the hominins who visited there were very familiar with fire and could create it any time they wanted. Again, no hominin fossils have been found there, but Homo heidelbergensis, a large-brained species that might've been the last common ancestor of humans and Neanderthals, is one candidate. So that's what we know about when hominins used, and maybe made, fires. But things get even more interesting when we try to figure out which of our ancestors was the first to actually cook with it. Those bits of burned bone found at Koobi Fora aren't necessarily proof that hominins were regularly cooking meat 1.6 million years ago. Instead, as with fire use in general, anthropologists are much more interested in when cooking became widespread enough to actually influence our evolution. And evidence for regular cooking behavior doesn't appear until very recently, at least in geologic terms -- about 350,000 to 400,000 years ago, in the region of the Eastern Mediterranean known as the Levant. Here, another cave site, called Qesem, preserves a large, central hearth that was used repeatedly, and which one group of researchers thinks was commonly used for roasting meat. Hominin teeth found in the cave resemble those of both Homo sapiens and Neanderthals. But whoever was cooking at Qesem, they left behind lots of butchered and burned bones. Finally, there's still the question of when and where fire was used outside of Africa. If fire was so helpful in fueling human migration, then can we track its use around the world, to retrace our steps? Well, the first species that we have fossil evidence of outside of Africa is -- you guessed it! -- Homo erectus, at a site called Dmanisi in the Republic of Georgia, which dates back 1.8 million years. But there's no evidence for fire at the site, even though winter temperatures likely got just slightly above freezing. And again, as with cooking, we only see really solid evidence for fire use in colder climates much, much later -- at around 400,000 years ago in Europe, at two different sites. At Beeches Pit in England, areas of burned sediment with heated stone tools and burned bone have been interpreted as the remains of hearths. And at Schöningen in Germany, the evidence is heated flints and charred wood. These two sites have been suggested to be the work of Homo heidelbergensis, the same potential fire-maker from Gesher Benot Ya'aqov. But there are a lot of other hominin sites, both open-air and in caves, scattered across Europe that /don't/ show evidence of fire, even though winter temperatures there couldn't have been comfortable without it. Those hominins must have found other ways to cope - maybe through other cultural adaptations like clothes and shelter, or just cuddling a lot or by migrating - being the Pleistocene equivalent of today's snow birds. So the origins and spread of fire in our evolutionary history remain full of paradoxes. Like, how did Homo erectus evolve to have such a large brain and body without the bump in energy and calories gained by cooking? We see these changes in the anatomy of our ancestors before we see evidence of fire in the archaeological record - though some researchers have suggested that we didn't need fire, just good cutting tools, to start the process of breaking down meat before consuming it, allowing us to efficiently extract more calories. And how did this same species migrate out of Africa and into colder climates without the warmth of a campfire? Dmanisi in the Republic of Georgia has a wealth of fossils, but no signs of fire. It seems pretty likely that the first fire made intentionally, by the hands of a hominin, sparked to life somewhere in Africa, probably in an open-air site like Koobi Fora. And maybe those hands belonged to a member of Homo erectus. As with many other early chapters of our history, we have a lot more research to do. But each of us lives with the legacy of that moment, captured in our own bodies. Our size, our musculature, and our big, clever brains, are all influences from that time -- somewhere, by someone -- when we first tamed fire. Thanks for watching this episode of Eons, which is produced in partnership with PBS Digital Studios and Complexly. Complexly produces over a dozen channels, including Nature League, where host Brit Garner explores life on Earth and questions what we think we know about the natural world. For a taste of what you can expect, we've linked to their “Best of” playlist in the description below. Thanks for joining me today in the 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!