Ancient DNA debunks Rapa Nui ‘ecological suicide’ theory

Nick Petrić Howe

Welcome back to the Nature Podcast, this week: what ancient DNA has revealed about Rapa Nui’s past…

Benjamin Thompson

...and a tiny parasitoid wasp that’s been found in an unexpected place… I’m Benjamin Thompson.

Nick Petrić Howe

And I’m Nick Petrić Howe.

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First up on the show this week, ancient DNA is helping to answer some contested questions about a tiny island in the Pacific known as Rapa Nui.

If you’ve heard of this island, you may be more familiar with it under the name Easter Island and you likely have heard of it due to either its great Moai statues that dot the landscape or because of a popular idea that its population was decimated by its own mismanagement of its natural resources. Now that idea has been challenged by scientists for a long time, as there is a lot of evidence that conflicts with it. And this week in Nature a study on ancient DNA from Rapa Nui people may finally put it to rest. That DNA may also help researchers understand a less controversial, but still hotly debated, question about Rapa Nui: when the people there had contact with the Americas. Modern DNA evidence has shown that the local people have Native American DNA, but it's unclear whether mixing between peoples occurred before or after Europeans arrived. To investigate these questions, Geoff Marsh is here with the story.

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Geoff Marsh

Around eight or nine hundred years ago, a group of Polynesian sailors continued their eastward expansion across the Pacific into the far reaches of what we now know as the Polynesian triangle. A vast area of the Pacific with over 1,000 islands, including New Zealand and Hawaii. They haven't set foot on land since the last island they inhabited nearly 2,000 kilometres back to the west. So it must have been cause for celebration when looming out of the Pacific waves, a tree covered paradise, untouched by humans, broke the horizon.

<island sounds>

Kathrin Nägele

So Rapa Nui was one of the last islands to be settled in remote Oceania, together with New Zealand and around 900/800 years ago. My name is Katrina, and I work on the reconstruction of the past through archeogenomic methods. And my personal focus is very much on tropical regions, both in the Americas and in the Pacific and I have a special interest in islands.

<island sounds>

It's very clear from the genetic evidence, and also from ancient DNA evidence, that people who settled the remote islands in the Pacific came from the west. It very likely started with something called the Austronesian expansion. So somewhere in Island Southeast Asia, people started traveling along the islands into remote Oceania, and then eventually also the extreme corners of the Polynesian triangle.

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Víctor Moreno

Rapa Nui is this super small island. It's just some tens of kilometres around. You can actually use your bike to go around in a single day, and you still have the rest of the day to do other things.

Geoff Marsh

This is Víctor Moreno from the Globe Institute at the University of Copenhagen.

Víctor Moreno

I am an evolutionary geneticist. I am originally from Mexico, but I have been working here in Copenhagen for a while now.

Geoff Marsh

Víctor is first author on a Nature paper published this week about the legacy of this tiny speck of land that had such an outsized influence on the study of human history.

Víctor Moreno

In Rapa Nui, it's actually one of the most isolated places in the world that is inhabited by humans. So it's this very isolated island where you have Polynesian peoples living for the last 800,000 years. And the thing is that once they get there, they get this very rich culture that fascinates us all. They have these huge stone statues called Moai that they put on also these stone platforms they are called ahu so they make it there, and then they develop this amazing culture.

<island sounds>

Then it's in 1722 that Europeans arrived in the island the Dutch and then that starts the usual colonial history that we know in many other places, right?

<island sounds>

But between the 1200s and 1722 we have these classical Polynesian people thriving there. Yeah.

Geoff Marsh

You're more likely to have heard about Rapa Nui by a different name, Easter Island, given to it by its first European visitor, Dutch explorer Jacob Roggeveen, who happened to arrive on an Easter Sunday in 1722. And you might have heard about Easter Island in the context of a widely held theory put forward about the self-inflicted collapse of the islanders. As Kathrin Nägele, who wasn't directly involved in this paper, but who wrote an accompanying News and Views article, explains.

Kathrin Nägele

Yeah the most popularized narrative about Easter Island is one where the Easter Islanders over-consumed their resources, and this led to wars between people, and even to cannibalism, according to some people. And this is basically used as a cautionary tale to tell us what happens when we do not manage very well the resources that we have.

Víctor Moreno

And actually, in a way, it works, right? This story has been used for saying, hey, humans, look at what happens in these different places with these cultures that were so magnificent, and they ended up destroying their environment and finishing their resources and–and they end up eating each other.

Kathrin Nägele

Jared Diamond is the one who popularized the story in his book Collapse, and he said that 15,000 people once inhabited this island, but because they did not manage their resources well, and because they cut down trees, all of the trees, the land eroded and they couldn't produce enough food, and so when the European colonisers arrived, only a few thousand were left. And supposedly the Europeans also encountered not only very few, but also very miserable Rapa Nui Islanders.

Geoff Marsh

But Jared Diamond wasn't the first person to propose these theories about the societal collapse of the Rapanui people. Others had previously made similar claims, although without much backing from the scientific community.

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Another contested question about the history of the Rapa Nui islanders was when they had contact with people from the Americas because analysis of modern Rapanui genomes does show evidence of mixing between their Polynesian ancestors and Native Americans. But it's hard to say for certain when that happened, given that more than 1,000 Rapanui people were taken to the Americas during the Peruvian slave raids of the 1860s before eventually being repatriated. In a peculiar twist of fate, another result of the Rapa Nui colonisation may now answer some of these questions. 15 ancient individuals, labelled as Rapanui, found their way into the Natural History Museum of Paris during the late 19th and early 20th century. After careful talks with the contemporary Rapanui community to get properly informed consent. Victor and his team set to work.

Víctor Moreno

Even though this collection was labelled as individuals from Rapa Nui, we wanted to actually confirm if this was the case, because if they are actually individuals from Rapa Nui, that is indisputable evidence that the Rapanui community can use to repatriate these remains back into the island. Second, we wanted to look for evidence of this alleged collapse, right. If there was a collapse, we would expect to see very little genetic diversity at the time of the collapse, which is the 1600s. And the third thing we were looking for is we wanted to use their DNA to ask whether the ancestors of the Rapanui, whether the Polynesian ancestors of the Rapanui were actually in contact with Native Americans, and if so, we wanted to date when that happened. Was it something that happened before European contact? Was it something that happened before or after the peopling of the island?

<wave sounds>

So, we got access to these individuals, and what we did is to extract DNA from bone powder. What we're doing is we're sequencing the whole genomes of these individuals. So this gives us access to a very wide variety of possible analysis that we can do with the data. So the first thing that we wanted to ask is, are they Rapanui, or are they not? So we took their genomes and we compared to different populations around the world, which one is the most closely related to them? And the answer is, they are most closely related to present day Rapanui. So as we said, that's indisputable evidence that they're Rapanui, and then they can, well, hopefully that starts the process of bringing them back to the island.

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In addition to getting their genomes, we're also radiocarbon dating them, and the radiocarbon dates show us that they are from after the 1600s which is when the collapse is supposed to be happening. Today, we have population genetic methods that if you have genomes from a population, you can ask, how did the genetic diversity look like 10 generations ago? 20 generations ago? 50 generations ago? And because these individuals were postdating the collapse, we thought, well, if we use these methods, then if we detect a sudden drop of the genetic diversity of this population around the 1600s then that's the evidence of the collapse. Well, it turns out that we don't see that. It turns out that what we see is that around the 1600s we get that the population diversity is increasing steadily.

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And the third thing that we wanted to look at is where we could find any genetic evidence of contact between the Polynesian ancestors of these individuals and Native Americans. So what we find is that across the genome of these individuals, the large majority of it is Polynesian in origin, but 10% it's Native American in origin. Then we want to ask, when are these Native American bits coming into the Rapanui genomes? And in order to do that, the idea is that depending on when the Polynesians were in contact with Native Americans, the chunks of Native American DNA, their lengths would change. So every time we have offspring, these genetic chunks get broken apart, and then they are inherited shorter and shorter through time. So we have statistical methods where you feed in the length distribution of these chunks and ask, when is this admixture event happening? What we get is that this admixture event is happening more or less in the 1300s.

Geoff Marsh

And dating this Polynesian Native American mixing event to the 1300s is important for a few reasons.

Víctor Moreno

First, it post-dates the peopling of the island, right. It's something that happens after the island is peopled, but it predates two important dates, right. The first one is it predates European contact with the Rapanui. Europeans made it to the island in 1722, but it also predates the arrival of Europeans in the Americas, right, which is in the 1500s in the 14, 1500s, right. So we have very strong evidence that this admixture event is happening without being mediated by Europeans.

Geoff Marsh

But what the results can't tell us is who made the journey for the mixing to take place. Was it a continuation of the Polynesians eastward expansion before coming back again, or did Native Americans travel west to find Rapa Nui themselves?

Víctor Moreno

We know a lot about Polynesians, and we know they managed to get to every single Polynesian island in a matter of very few 1,000 years. So they were exploring the Pacific, they knew what they were doing, they were very good sailors, right. Probably the best we have had. So if you make it to Rapa Nui, the Americas would be a very hard target to miss, right. It's very unlikely that they stop at Rapa Nui and they never go to the Americas. And if they can go to Americas, of course they can go back. If we consider all the evidence we favoured this idea of Polynesians going to Americas and back. However, that's still an open question, yeah.

Geoff Marsh

There was a well-documented collapse of the people of Rapa Nui in the 19th century when Peruvian slave raiders decimated the population to around 100 people. So how is it that it was the Rapanuis careless ecological suicide narrative that took hold so firmly and for so long?

Víctor Moreno

Many of these narratives, in many cases, like the narrative of the collapse or the narrative that Polynesians couldn't have made that amazing status because it had to be made by Native Americans and so on, they are usually put together as some kind of colonial narrative, right. With different purposes in mind, from getting access to the land to other even more obscure and darker things. And here we have an example of how science can help debunk those narratives and put them to rest and hopefully re-vindicate other cultures. So, yeah.

Kathrin Nägele

Everyone also happily accepted this narrative and perpetuated it, right. And so I think it also tells us something about, you know, maybe sometimes we have to– to check, especially when there's so much evidence speaking against it. And this paper, while I hope that it's the last nail in the coffin it was not the first one, right. There are so many other lines of evidence that for the last decades have shown that this narrative is wrong, but still, this update has not made it through to the general public and also into common knowledge. And I hope that with the attention that ancient DNA research is getting, that this can finally happen.

Geoff Marsh

This narrative around the ecological collapse in Rapa Nui, while false according to many lines of evidence, has been a powerful cautionary tale at a time when we're destroying our own environments at a rapid rate. So what lessons, if any, can we still learn from this remote island and its past?

Kathrin Nägele

Well, I think that rather than being a cautionary tale about the ecocide, it can still be a cautionary tale but with a much more positive outcome, right. I mean, we're facing climate crisis right now, and sometimes one feels like losing hope, because it seems we cannot do anything about it. And I'm sure that maybe at some point, Rapa Nui islanders felt like this, but they were very resilient, and invented new strategies and new agricultural methods to overcome these problems and persisted through them. And I hope that this type of cultural change is also something that we can do on a global scale, right. That is not just possible on a small island, but that globally, we can work to change our culture from a culture of overconsumption to a culture of sustainability.

<island sounds>

Nick Petrić Howe

That podcast piece was produced by Geoff Marsh. In it, you heard from Kathrin Nägele from the Max Planck Institute for Evolutionary Anthropology, in Germany, and Víctor Moreno, from the University of Copenhagen. For more on that story, check out the show notes for some links.

Benjamin Thompson

Coming up, the chance discovery that revealed a new species of wasp with a gruesome lifecycle. Now though, it’s time for the Research Highlights, with Dan Fox.

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Dan Fox

Around 48 million years ago, in a lake in what is now Germany, a few bat-eating fish bit off more than they could chew. Fossilized remains of two species of extinct lake fish — gar and bowfins — were discovered with the remains of a small extinct bat in their jaws. The bats’ wings probably got stuck in the jaws of the fish, and the researchers behind this paper conclude that these mammoth morsels might have impeded the movement of the predators, leaving them to die of starvation and exhaustion. The large number of other bat fossils found in the area suggests that gar and bowfins had lots of opportunities to scavenge on or attack drowning bats. And these tiny mammals may have represented a substantial food source for the fish. If you want to chew over that research a little more, you can find the paper in Biology Letters.

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Lake Amanã in the Brazilian Amazon is known as ‘the home of the manatee’, but new research suggests a better name could be ‘the manatee’s garden’, based on how the gentle aquatic mammals’ dung shapes the local ecosystem. Researchers took advantage of an extreme drought last October, which dropped water levels to reveal grassy, muddy balls of dung from Amazonian manatees around the lake's edge. The team collected 96 dung balls and picked out over 2,000 seeds from nine plant species. The vast majority of the viable seeds were from an aquatic grass previously observed sprouting from manatee dung balls. The grass is even able to use moisture and nutrients from the poo to grow on a scorching hot sandy beach. Seeds take five to nine days to pass through a manatee, which means that this threatened animal can act as a gardener, moving seeds of its favourite foods long distances in the Amazon region. Read that research in full in the Journal of Nature Conservation.

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Benjamin Thompson

Drosophila fruit flies are very well studied insects. For over a century, these tiny animals have been at the centre of many of the biggest molecular and genetic breakthroughs in science. But despite being under the microscope all this time, it looks like researchers have missed something. And that something is a miniscule wasp that preys on some species of Drosophila. Now, this isn’t the sort of wasp — you might call it a yellow jacket — that interrupts your picnic, oh no, this is a parasitoid wasp, belonging to a group of animals with a very unusual and often quite macabre lifecycle. Females of these wasps lay their eggs on, or in some cases in other living insects. In the latter case, these eggs develop into larvae which grow and feast inside the host before bursting out to continue their lifecycle.

A paper describing this wasp is being published in Nature this week. It’s tiny, just a couple of millimetres long, and the team that discovered it did so quite by chance. Unlike many other parasitoid wasps, it lays its eggs in adult insects, rather than the juvenile stages — the larvae or pupae. To get all the gory details, I phoned Matt Ballinger from Mississippi State University in the US, one of the authors of the paper. He told me the story of where the team first found this wasp, which began very close to home.

Matt Ballinger

It did begin in our backyard. We study in my lab microbial symbionts, you know, bacteria that live inside insects and protect them against parasitoid wasps and other types of internal parasites. And so we regularly will go out and we'll collect wild parasites. I had requested that my student and I collect some mushroom-feeding flies because we're interested in nematodes, and we just happened to have collected with those mushroom baits also a fly called Drosophila affinis. And when I was dissecting the mushroom-feeding flies looking for nematodes, I just noticed that this particular fly looked a little strange, its abdomen, the testes, these spiral structures on its abdomen, are bright red in this particular species. They seem to be sort of protruding from its abdomen, like there was something inside. So I took that fly and dissected it, and inside was a parasitoid wasp larva but this should not have been there in an adult fly. There are no cases, whether we're talking about fruit flies or any other flies that are parasitized by wasps during their adult stage.

Benjamin Thompson

So you were looking for nematodes, but instead, you found the larvae of a wasp inside a fruit fly. Did you think it was a mistake, or anything like that?

Matt Ballinger

I did. Initially, I felt like this could be a confused wasp who had oviposited in the wrong host or since we know that many pupal parasitoids exist, that somehow a wasp larva had persisted in the body of a Drosophila affinous fly. But of course, we wanted to test that, so we kept collecting, until we saw very clearly, after hundreds and thousands of collections, that this was a consistent infection of adult flies, and eventually we’re able to expose adult flies to adult wasps that we raised from those in the lab to observe those ovipositioned behaviours into adult flies.

Benjamin Thompson

But it wasn't just physical evidence you collected. You looked in the genomes of wild-caught fruit flies, and it appears that one very famous fly that many of our listeners will be familiar with evidence suggested that it had been infected.

Matt Ballinger

Yeah, there's this fantastic data set, and it consists of genomic data collected from hundreds and hundreds of pools of wild Drosophila so that that data can then be used by researchers to study population scale evolution of the fruit fly Drosophila melanogaster. And so, we used that data set reasoning that if this particular parasite is infecting Drosophila melanogaster in nature, we might see some of this parasitic wasp DNA among those sequence reads from that global data set. And that's exactly what we found. I frankly didn't think that we would, because I thought this is Drosophila melanogaster, right. Like people understand what parasites it has at this point. But my graduate student, Logan, first author on the paper, contacted me and said ‘you're not going to believe this, but I've got the preliminary results from that, and we've got multiple states in the US where the parasite is present in this sequencing data’.

Benjamin Thompson

I mean, let's just back up for a second. Drosophila melanogaster is one of the most studied organisms on the planet, right. It's been studied for what, 100 odd years. It's a model organism. We know a lot about its molecular pathways and what makes it tick, and what have you.

Matt Ballinger

Yeah.

Benjamin Thompson

As you say, there are multiple wasps that attack it in its larval stage, but you're saying that no wasp had been found that attacks the adult stage in all this time.

Matt Ballinger

Yeah, that's right. Drosophila melanogaster, it can be attacked by wasps during the larval and the pupal stages, but no examples of wasps that attack it during the adult stage have ever been described.

Benjamin Thompson

I mean, that must have been quite something when you saw that. As I say, because this is one of the most famous organisms on the planet.

Matt Ballinger

Yeah, that's right. That's why we were so shocked to have found it, and thrilled, quite honestly.

Benjamin Thompson

And so let's talk about this wasp then, Matt. What's its name? What does it look like? How big is it?

Matt Ballinger

Yeah, it's very tiny wasp. This is a wasp that belongs to a subfamily called Euphorinaeand in the genus Syntretus. And this is a group of wasps that is known to specialize on attacking hymenopteran hosts. So that's bees and wasps in general, and quite a surprise then to see it in a fly. But as you could imagine, with such a small host, this particular wasp is a little bit smaller than some of the other wasps in the genus. This particular wasp we named Syntretus perlmani. I named it after a colleague and a former mentor of mine, Steve Perlman, and he's done a lot of work on Drosophila parasite interactions.

Benjamin Thompson

And let's talk about its life cycle, because there's some videos associated with your paper that I have been watching, and they are, they are quite something, I have to say. When a female wasp comes across a fruit fly, what happens?

Matt Ballinger

Yeah, she sort of adopts a new stance. You can see her posture change. She becomes very focused, and you can almost see when she locks in first and says, ‘ah this is a potential host’. And then as she decides she's going to try to lay an egg inside this host, of course, her ovipositor is behind her body, and the host is in front of her. So she will bend her abdomen underneath her body and extend her ovipositor outward in front of her face, and sort of charge in to the host while stretching that ovipositor out.

Benjamin Thompson

And so this kind of egg-depositing lance then, what, pierces the abdomen of the fly?

Matt Ballinger

Yeah she goes for the abdomen. In the case of the fly, after oviposition, the egg takes several days, three to four days, it will develop into a much larger embryo before a larva hatches out, and that larva will be free floating in its body cavity. At the same time, really interesting cells emerge from the membranes of the embryos as well. These are called teratocytes. They disperse into the blood of the fly, and they grow as the larva grows. They accumulate lipids, proteins, everything a growing wasp needs. And so there's some evidence that teratocytes in this group of wasps are sometimes used as nutritional sources, but also that they play important roles in modulating the host's defences, protecting that larva.

Benjamin Thompson

And I've seen in one of your supplementary videos, then this larva kind of writhing inside the fruit fly, and it obviously brings to mind the movie Alien–

Matt Ballinger

–yeah–

Benjamin Thompson

–what sort of size is the larva when compared to the actual size of the fruit fly?

Matt Ballinger

It's shocking to see its size. In fact, those last few moments before the larva is actually emerging, it looks like it must be maybe the size of the flies abdomen or so. Of course, it's squished in there. As you see it emerge, you realize this larva is almost the full body length of its host. So it is really by the end, it is squishing, it's pressing to get out of there. It's ready to move on to the next stage.

Benjamin Thompson

And so it bursts out and I guess then ultimately the wasp develops, and off we go again. Are the fruit flies okay after bursting Matt? Tell me, tell me they're okay.

Matt Ballinger

Shockingly, we have seen them get up and survive up to 24 hours after that. But they are a husk, you know, their abdomen is emptied out. Usually we find them dead within a couple of hours, but you would not expect it, seeing the ordeal that they go through. But they'll pop up and they'll stay active for at least a few hours.

Benjamin Thompson

I was not expecting you to say that–

Matt Ballinger

–I know–

Benjamin Thompson

–but the flies aren't completely defenceless, though, right. In one instance, you can see a fly kind of facing down a wasp. It's kind of pawing away, if that's the right word, with its legs.

Matt Ballinger

That’s one of the very exciting parts of this. Now we have an opportunity to look at interactions between a parasite and an adult host, right. As opposed to a parasite and a larval host. There's a whole different arsenal of potential behavioural defences we've seen in some cases that the flies seem to recognise there's some sort of threat here, whether it's specific to the parasitoid wasp or this is an aggressive behaviour from a fly that we just haven't seen before. In the case of the video you're describing, that flies seem to recognise the wasp and approach it while kicking its legs out. And that interaction goes on for a good 30 seconds to a minute. They're both quite persistent about it, until eventually the fly sort of scampers off.

Benjamin Thompson

I think we've talked a bit about how well studied Drosophila is. I mean, will this lend itself to working out what happens once the egg has been injected? Because I think, as you sort of alluded to, there is almost an arms race of the fly's internal defences versus the larval offenses, that kind of thing.

Matt Ballinger

There is lots of fantastic work on what happens after certain parasitoids lay their eggs inside Drosophila hosts, all in a larval system, some in a pupal system. There's from species to species of parasitoids, different strategies for how they avoid that defence. In some cases, the wasp eggs are coated in sort of a sticky protein, and that protein allows them to stick to host tissues inside the body and protects them from some of the host defences. One of those host defences is production of immune cells, sort of like blood cells. What many of them do is they will wrap around the egg and like a death burrito, and they kill the egg inside those cells. So now we have an opportunity to look at how those interactions proceed in the adult immune system. The occurrence of this wasp in Drosophila melanogaster opens a lot of doors for research into some of the more precise mechanisms of how this type of parasitism works.

Benjamin Thompson

Do you think that you're going to get a lot of correspondence from other fruit fly researchers? Going, ‘oh, that's what that is’ because I guess these wasps are very, very small and difficult to see, but it seems like they're all up and down the certainly the eastern seaboard of the United States, and somebody must have come across this without realising in the past.

Matt Ballinger

Yeah, in some ways, maybe. The folks that I have talked to that I would expect they might encounter this organism had not had the opportunity to see before. Part of that as you said, it's quite tiny, so really, unless you happen to catch it just at the moment where it's encountering a fly in the wild and preparing to oviposit, it doesn't stand out. It's a dark coloured, two millimetre long, one-and-a-half-millimetre long insect. Maybe that's one of the most exciting things about this as well, is it just shines a light on what sort of cool biology is still out there, right. Things that we definitely should have found by now if we had just been looking in a slightly different way.

Benjamin Thompson

That was Matt Ballinger from Mississippi State University. Head over to the show notes for a link to the paper where you’ll find the videos we talked about.

Nick Petrić Howe

Finally on the show, it’s time for the Briefing Chat, where we discuss a couple of articles that have been highlighted in the Nature Briefing. Ben what have you been reading this week?

Benjamin Thompson

Well, I've got a story this week that I read about in Nature, and it's based on a Science paper. And it's all about a new way to observe the organs inside live mice, and it's kind of unexpected because it involves a dye that helps give Doritos their orange hue.

Nick Petrić Howe

I mean, that does sound rather unconventional as a way to do this, but maybe let's back up a little bit. Why would you want to see inside the mice? Why would you want to see its organs in the first place?

Benjamin Thompson

Yeah, I mean a lot of biomedical research necessitates seeing what's going on inside a living animal, and this can be quite difficult to do. And, you know, involves implanting endoscopes or cameras or things like that, obviously, which are quite invasive. And this method it might be a way to avoid that and be a less invasive way to monitor live animals, and it's kind of fascinating. One of the videos in this story shows where this dye has been applied to the skin of a mouse's scalp, and you can see the blood vessels in its brain appear really quite quickly.

Nick Petrić Howe

Oh, wow, that sounds very cool, but I guess I'm wondering how exactly this works. You said this has come from Dorito dye.

Benjamin Thompson

Well, it's come from a dye that's used in a lot of food, which is called tartrazine. Now this dye changes how body tissues that are normally opaque interact with light, okay, and what happens here is, you know, the fluids and fats and muscles that make up tissues, they all bend light to different degrees, right. And so that causes the light to be scattered right, making something opaque. And this got the team behind this work thinking they want to know if they could use a dye to make this bending of light more similar between tissues. Okay, and they've done a bunch of research here, and this is where the tartrazine comes in. And when it's dissolved in water, it makes water bend light more like fats do. So a tissue containing fats and lipids becomes transparent when the dye is added, so they bend light in a more similar way.

Nick Petrić Howe

That's super neat, and I'm guessing as well, because this is something that is used in food is pretty safe to use on the mice.

Benjamin Thompson

That's definitely a pro to this approach. And what happens is, it's massaged in. Okay, so the researchers demonstrated the ability to make things transparent by testing it first on thin slivers of chicken breast, and then they've used mice, as I say, and they've massaged it into various areas of live mouse skin. Now I mentioned the brain there, but they also they can see the intestines contracting during digestion. They can see muscle fibres in the leg — it's quite something to see.

Nick Petrić Howe

I’m certainly going to look at it myself, but I'm wondering what the reaction is from scientists, because, as you said, this could be quite useful for various kinds of research? Has there been any reactions to this in the article?

Benjamin Thompson

Yeah, one of the scientists quoted says that it's a major breakthrough. But of course, it's not ready for prime time just yet. They can only make the skin transparent to a relatively shallow depth, which could make it of limited practical use for thicker tissues or, you know, larger animals like you or I. But as you say there, one of the big pluses is it's something that is a known quantity, and also that it can be used in live animals. But also it's reversible. If you wash the dye off, the skin goes opaque again. So it could be a much more non-invasive way, as I say, to look at what's going on inside. And potentially has a myriad of uses. There's a couple that I mentioned in the article. It could be used to understand a bit more about the nervous system and how it functions in mice, and potentially even more about neurodegenerative diseases.

Nick Petrić Howe

Well, I'm certainly going to be giving my skin a closer inspection next time I eat some Doritos. But thanks for that story, Ben, that's fascinating. For my story this week it's a about climate change, and this is a story I was reading about in Nature, and it's a question that probably you and I and many of our listeners have asked ourselves, how do we change people's mind about climate change?

Benjamin Thompson

Right because, of course, there are sections of society who are sceptical of climate science and climate change to differing amounts.

Nick Petrić Howe

And this story is part of a growing understanding of how best to engage people who are maybe a bit sceptical about climate change, because as scientists have talked more and more about climate change over the years, they've got better understanding what works and what doesn't. And I think it's well understood now that just showing people like melting ice with sad polar bears doesn't really work. Instead, you need to really engage with them. And so this study was testing a specific way of engaging with people, which is to tell them certain facts about climate change — particularly that 97% of climate scientists agree that it's real. Now this has been done before, but mostly it's been done in the US to understand how people's views change when you present them with these facts. This study looked at 27 different countries and saw how people's opinions changed before and after you present them with those facts. And it seems that telling people these facts does actually make them likely to change their perspective. And interestingly, it was people who were maybe more sceptical or less familiar with these facts, who are more likely to change their perspective.

Benjamin Thompson

Right, and does the research explain why this might be the case?

Nick Petrić Howe

Yeah. So as I say, this is the latest in a range of studies that have looked at this. And what they have found is that informing people about the scientific consensus really can change people's attitude, and it speaks a bit to the authority that science has. I think often people who are in science can sometimes despair thinking that some people may not really be taking certain things like climate change seriously. But actually giving these facts like 97% of climate scientists agree that human caused climate change is real, can actually shift their perspective. Now, what we don't know with this is how long this effect lasts, whether these changes in perspectives are enduring, because other studies have shown that maybe this can change people's mind for a little bit, but it may not last that long. And to get that real lasting change, what many researchers are now saying is that you need to engage people with personal conversations. So try and find the things that matter to them, that you can engage with those people on. So maybe they care about jobs or energy or things like that, and try and find the climate perspective there, and that many researchers believe can lead to more long-lasting change.

Benjamin Thompson

So engagement and dialog — as is so often the way — is key. I mean, this seems like it could be very useful in, say, policy spheres. Is there anything on that?

Nick Petrić Howe

Yeah. So there's actually a part of the article that talks about a campaign that persuaded people in a rural town in Canada to support a renewable energy policy, and the people who were involved in that campaign said the top strategy they had was to get out of talking-point-fact-land and instead exchanging personal stories. So rather than saying like, ‘oh, X amount of forest will set on fire by 2030’ or something like that, instead they said things like, ‘you know, there's now six weeks of the year where I can't let my kids outside because there are fires around and there's smoke and things like that’. And so that sort of way of engaging with people may be better. And there was also a study that was done recently not about climate change, but about reducing prejudice towards transgender people. And so what happened here is people went door to door and asked people to share their views on this topic. Then once they'd shared their views, they asked the people to talk about a time that they'd faced judgment for being different from others, and they found that this actually increased support for a non-discrimination law, and the social acceptance that they saw persisted for at least three months when they were re-surveyed later.

Benjamin Thompson

And so it seems then that this approach has shown efficacy and could when talking about climate as well.

Nick Petrić Howe

Obviously, it’ll have to be tested, and that is something that's being done. It's being systematically tested, this approach for climate change. But the thing is, as the world warms, as the world changes because of that warming, there is a climate-change angle to everything. So there are, for better or worse, increasing ways to engage people with conversations about climate change, because it's something that is really affecting them now. And you know, they can really see it and feel the effects. So there are ways to engage with people and try and meet them with the concerns that they have about their lives, and hopefully, with that, more people will be engaged with this issue and move forwards to try and prevent as much as we can the worst effects of climate change.

Benjamin Thompson

Well, it's a topic that's not going to go away anytime soon, and it does seem that conversation is key. But let's leave it there for this week's Briefing Chat. And listeners for more on those stories, and where you can sign up to the Nature Briefing to get more like them delivered directly to your inbox, check out the show notes for some links.

Nick Petrić Howe

That’s all for this week, as always you can keep in touch with us on X, we’re @NaturePodcast, or you can send an email to podcast@nature.com. I’m Nick Petrić Howe.

Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening.