Wildfires Changed Human Evolution - Is It Happening Again?

0:28This episode is brought to you by Google Chrome. years ago. That's during a key period when human ancestors were emerging. A reconstruction suggests that wildfires then may have shaped human evolution. So the suggestion is that the fluctuations in the environment then drove these early humans to evolve greater flexibility to use tools or to develop tools and to control fire even and that helped them cope with this fluctuating ever-changing world and it does immediately make us think of well that's what's happening in today's ever-changing world, how will that impact us now? So that's what we're getting into in this episode of The World, the Universe and Us.

1:05I'm Dr Penny Sarsha. And I'm Dr Owen Hooper. Yeah, we've got two subjects colliding today, a climate subject and a human evolution subject. We're joined by reporter Michael LePage and news editor Sam Wong. And Sam, you've reported before on this period of prehistory, of ancient history in this region, the Turkana Basin, the cradle of humanity. Yeah, it's such an important region for human evolution, for fossil discoveries. Ever since the 1960s, when you had Maeve and Richard Leakey discovering some of the most famous kind of early fossils there, about a third of all hominin fossils from Africa actually come from this region.

1:43And they range from the Australopithecus and the Paranthropus, those kind of early hominins, right the way through to Homo sapiens. And they include Turkana Boy, who's one of the most famous, very complete early skeleton of Homo erectus. And as well as bones, you've also got stone tools there. So you can trace the big steps in tool technology that early humans made. About 1.76 million years ago, you start seeing this type of tools called Acheulean tools, which are the first complex tools. They're much more advanced than the Alderwan tools that came before. You have these refined multipurpose hand axes, which were really good for butchery as well as plant processing.

2:20And they lasted for about a million and a half years. So then ever since the 1960s, we've come to see East Africa as this cradle of humanity. But there has been sort of more of a revision recently where other work has been showing sort of human evolution and early humans all over Africa. So why then have so many of these sort of key events, key ancestors, key steps in technology been discovered in this place in East Africa? Is it because we've looked there better than anywhere else or is it because it was also a special site? Yeah, it's a difficult question to answer. I think to some extent, we have looked there a lot and there's lots of fossils there because of the way that all of the layers of rock are exposed in the Rift Valley.

3:01But there is some evidence also that maybe it was kind of a special place, a kind of species factory, if you like. There was a study I wrote about a few years ago that said that the climate got drier in Africa between two and three million years ago, but that that happened first in the Takana Basin. So the species that evolved there had a head start and they were more successful at expanding to other places. But yeah, there's clearly a big link between climate change and how that influenced human evolution. So there's this idea that human traits like large brains and being bipedal, they evolved in response to changes in the environment, particularly kind of climate cycles associated with Earth's orbit.

3:41And these environmental swings might have meant that there was selection for greater flexibility to cope with this changing world and might have driven the evolution of tool use and being able to control fire and that kind of thing. So then this week we've reported on a study with evidence that supports this idea. So what are the details of the new findings? So this was by Rachel Lupien at Aarhus University in Denmark and her team. They used chemical signatures from plants about 1.75 million years ago to reconstruct the rainfall, the vegetation and the wildfire patterns in the West Takana Basin.

4:15So that's around the time that these Acheulean tools were first appearing. So they sampled all these layers of a sediment core to find these chemical biomarkers that allow them to distinguish different ancient leaf waxes, so these chemicals in the leaves, and the combustion products when plants burn. So all of these markers mean that they can really track the amount of rain, the type of vegetation, and wildfire intensity over time. What detail they can get and then recreate the environment from that. Yeah, it's amazing. So they reconstructed this period of 21 ,000 years. That's roughly one cycle of the Earth's axial wobble.

4:51So the axis of the Earth kind of wobbles back and forth and that influences the strength of the climate and the summer monsoons and that kind of thing. It's also coincided with a period of Earth's orbital cycle where the orbit was particularly elliptical, so more like a squashed circle than a perfect circle. And those periods, you've got more solar radiation reaching Earth and you've got more climate extremes. So their results suggest that the Takana Basin yo-yoed between dry and wet extremes over 1 ,000-year intervals, and that's to do with that elliptical orbit. So across the 21 ,000 years, the ecosystem switched from forests to open grasslands to a mixture of grass and limited trees, and wildfires shifted from low to high.

5:33So while you might expect that wildfires would have been highest in the dry times, they actually surged during the wettest times. Well, that is a bit like what we're seeing now, isn't it? If you get wet weather at the beginning of the year, you get a lot of growth, then that might dry out and you get all this basically tinder lying around ready to spark bigger wildfires. Yeah, that's right. So it's higher precipitation leads to more vegetation growth and that allows fires to burn because there's all this extra biomass. But they also found that the fires have limited vegetation growth overall despite the overall precipitation trend getting wetter.

6:09Okay. And so are they saying that this is a causal link, or are they, between this fluctuating environment and then the development of these sophisticated tools that these people were coming up with? That's the hypothesis that they're putting forward. They obviously can't prove any causal link at this point. But Rick Potts, who originally put forward this variability selection hypothesis about the environment and the flexibility, he said this is the first paper he's seen that illustrates the emergence of Acheulean tools as a response to ecological variability and this variability selection idea.

6:43It's also one of the first studies to make the connection with wildfires. So showing that bushfires were happening at this time of evolution in East Africa. and if the fires are there, surely there's a sort of selection pressure to make use of the fire and the resources that it brings. It makes me think a little bit, Michael LePage is here too, Michael, it reminds me a bit of some of these lab experiments where people try to see the mechanics of evolution. If you're doing a thousand years dry, a thousand years wet, it's a little bit like some of these experiments, classic ones that people have done with yeast or E.

7:16coli in the lab where you're kind of constantly switching back between conditions and seeing things evolve. Yeah, and you get a different response to variable conditions and to stable conditions. And obviously, coping with variable conditions is more difficult. So you're going to select for sort of more complex traits that might help you cope with both. Yeah, like flexibility. Yeah, exactly. So there'd be multiple selection pressures to develop tool use. Yes. All right, not just the fluctuating environment. Yes. But this is one, perhaps one major one. It's very circumstantial, isn't it? But it does also pose the question not just about tools, but the use of fire because controllers fire like historically it's been a sort of defining human trait but there's lots of debate about this and we now know that the neanderthals use fire didn't they yeah so the neanderthals were much later but um yeah there's now evidence that tentative evidence that humans started using fire between uh 1.07 and 1.79 million years ago according to this study this year in south africa and and in turkana you've got this tentative evidence of fire going back 1.1 and a half million years ago.

8:20So we still don't really know when humans started using fire. But if there were wildfires, humans would have had lots of opportunities to discover animals that had been burnt in the fire and that got their first taste of cooked meat. And they might have been able to start trying to use the fire, prolong the fire by picking up burning sticks and carrying it places. Well, there's some really interesting stuff with chimps, isn't there? Like their response to fire. So a lot of other animals just flee the fire. Sometimes you can see chimps looking at it and even like rearing up on two legs and performing.

8:54They seem to understand fire in a different way than other animals. And of course, cooking has always been thought to be a key step in human evolution as well, at least that's been suggested. So that switch to eating cooked meat and cooked plants. Yeah. This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome, that's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense?

9:27There's no place like Chrome. Check responses set up required, compatibility and availability varies 18+. So look, all this talk of wildfires inevitably makes us think of what's happening at the moment. Loads of wildfires, horrendous ones across Europe, including the UK, it makes me think of what is the potential that we might be seeing now with the impact of wildfires and us. Let's start by comparing and contrasting then, because when we're talking about thousands of years changes in the actual wobble of the earth or on the shape of the orbit, these are kind of on grand evolutionary timescales that are much bigger than the kind of rapid rate of change that we're seeing now, Michael.

10:09They are, but evolution can happen extremely fast when you put a lot of pressure on a population. So we're talking about human evolution. Let's say, let's hope this doesn't happen, but let's say we had sort of mass heat deaths, which were severe enough that we had large numbers of young people dying. The result of that would be a population where, you know, some of the people dying would have genetic mutations that made them more vulnerable. So you have natural selection against that. you're left with a population that has now evolved over the course of less than a generation to be more heat resistant.

10:42Now, of course, we don't want that to happen. Let's hope we're smart enough to avoid it by adapting. And that means everything from air conditioners to migrating away to some more favorable climes. Yeah, so using adaptation in the climate sense of adaptation rather than the evolutionary sense of adaptation. Yes, if we end up adapting in the evolutionary sense, that's going to be really bad. Yeah, but it's not that long before there are places in the world that are going to become uninhabitable through heat. We're already seeing climate migration for things like sea level rise, aren't we? There's the first official climate migration treaty is between Tuvalu in the South Pacific and Australia.

11:25Australia is accepting migrants and granting them citizenship. Yeah, to a few of them. I think 250 people only so far they've given citizenship to from Tuvalu. But between now and 2050, looking at up to a billion people will be needing to move as a result of basically forced climate migration because of either sea level rise or it's literally too hot to live where they currently live. Yeah. And of course, we should be planning for this like we should be planning for, as we've talked about in the podcast, food security. We should be making much better plans for that as what's going to happen with the result of global heating.

12:01And one thing I read in Gaia Vince's book, Nomad Century, was how China has already done a really good example of this over the last few decades. It's 400 million people have migrated. So this is internal migration in China. I've gone from the countryside to the cities and China has managed this by a massive planned infrastructure building and to let people do this. So that's what we need, but on an international scale. So was that as a result of climate or was that more to do with industrialisation of the economy? Yeah, it's to do with that. People want to live in the cities. But it offers a blueprint.

12:39But the point is exactly the government could see it was happening and they have this advantage of being able to put into play long term plans that are then not just kicked into touch by the next government that comes in. The problem that we've had in tackling or making any kind of tackling climate change over the last 20, 30 years. I read that Cincinnati in the US is positioning itself as a climate sort of welcoming hub for climate refugees, probably from the rest of the US. But they want to be a place where they're going to build lots of new housing and take in people who are forced to leave other parts of the country.

13:11And then, Michael, you sort of you said that, you know, evolution can happen in a generation or two. Climate change has been heating up for a while now. Are we seeing anything in terms of how plants and animals are adapting? Oh, yeah, there are huge changes already. So some of them are adapting in the sense we're talking about of migrating. And we're seeing that particularly clearly in the oceans where there's sort of shifts of hundreds of kilometers in some cases in the habitat where certain animals are being found. Others are staying in place, but we're seeing some plants are showing signs of adaptation to higher temperatures.

13:43But of course, there's a limit because of the time scale is so compressed. There's a limit to how much evolution can happen in such a short time. and the other problem is that there's so many other pressures on wildlife at the same time so we started off talking about fires and wildfires and the natures of wildfires is changing there was a study out earlier this week where they were saying not only we're getting more of these really big mega fires because of climate change but they're often moving faster and apparently these faster moving wildfires burn hotter so they're destroying more of the vegetation and that means we're not going to have time for trees and things to recover after each fire.

14:22And that's going to completely change landscapes. The study was looking at the US and Canada. So there's going to be these sort of huge changes in landscapes. And so there's so many pressures simultaneously on wildlife to adapt, you know, high temperatures, sort of more floods, wildfires, human pressures. It's just, you know, there are going to be a lot of losers. There'll be a few winners, but a lot of losers. Because when we talk about the things or the virtues of being able to adapt and be really flexible, in the plant world, that's weeds. It's not the oak trees that we love. It's the plants that are not very useful or good for it.

14:57So dandelions can move long distances easily, obviously. And they have so many generations that they can adapt quickly, whereas an oak tree takes how many years? Well, that's why we have to be doing it now, right? I'm really worried about all the trees that's going to be happening, what's happening to them in this drought. But how you use it on a scale. So I did see that one Hungarian oak planted in Kew Gardens as a tree of hope. Because is that more resilient to the... Yeah, because it's from the southern Europe and it's a species that's not like the normal English oak, Quercus roba. But you can't replace all the oaks in Britain with Hungarian oaks over the quick enough time period.

15:39Yeah. Well, it would be a huge operation. That's all for this episode. Thanks to our guests, Michael LePage and Sam Wong. And thanks to you for listening. Do subscribe and follow wherever you get your podcasts. Bye. Bye. Bye.

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