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This is the Science Podcast for December 18th, 2025, I'm Sarah Presby. It's the last episode of the year, we're off next week, but before we take our long winter nap, we have highlights from 2025. Starting off with the top online stories, with online news editor David Graham, fun roundup, and after that, it's the breakthrough of the year, with producer Megan Cantwell, and news editor Greg Miller, and they also touch on some of the runners up. It's the end of the year, and our last episode of the year, and to celebrate 2025 in science style, we're looking back at the top stories with online news editor David Graham. Hi Dave, welcome back, happy 2025, Sarah, happy, happy end of 2025 to you. The end of the year, so let's just briefly recap how you put these end of the year list together. What counts for a top online story? Yeah, so every year we go through all the stories, hundreds and hundreds of stories. Hundreds and hundreds. We posted online, and what we're always interested in is a few things. One is personal favorites, what stories do we get really excited about? Reader favorites, what stories at the most eyeballs, but also exclusives, a lot of those stories are end up being our favorites, because we're excited about it, because we're the ones that sort of got to tell the world first about a lot of these things. And they usually they meet both criteria, personal favorite, and really popular with our audience. Yeah, and in fact, you know, we're putting together our top ten, it's like most of these stories sort of fulfill all three, they were really popular for the readers, we love them, and they were exclusives. So we're not going to share the top most of the top ten. We'll leave that as a surprise for online visitors, but we're going to talk about a few fun ones here. Let's start with the story. It's really surprising if you've ever made sugar syrup for your hummingbirds, and you put it in this feeder that makes it look like flowers, and it's like, why does this work so well? But it turns out that this has had a bigger effect on hummingbirds than just making them popular animals with people who love birds. This is one of my favorite types of stories, which is an evolution in action story, where we often think of evolution as taking thousands, millions of years, and this is a story where we're seeing evolution happen in just a few generations. And it's evolution, as you alluded to, Sarah, that was sort of instigated by human activity. Yeah. And I love this part of the story. There's an illustration of the early patents for these bird feeders, they're like shaped like a bubble full of sugar water, and then they have little flower openings for the birds to sip from. How long ago were they first produced? Well, this is one of the questions, but story because one of the questions was in this regard to a type of bird called the Anna's Hummingbird, which is a species that's popular in the Western US. And the question was, did hummingbird feeders have any impact on these birds? And the question you have to ask yourself as well, when did hummingbird feeders even try to come and do existence, which apparently is very hard to answer. Isn't that funny? It's true. Do you think there would be an answer for this? And then so the team was sort of back to the newspaper archive and patent archives. And they found these old patents. They know these feeders were popular after World War II, which means that they probably came into inception maybe even a few decades before that. But we know that starting in the 1940s, these backyard hummingbird feeders really started to take off. Why do they think they had an effect on the birds? What they're seeing is in places where there's going to be a lot of these hummingbird feeders in use. First of all, you had this really massive explosion of the population of Anna's Hummingbirds, which makes sense because if you've got more food out there, you're going to have more birds. You've got these museum specimens and these old samples of hummingbirds. The other seemingly obvious was that the actual shape of these birds, in particular their beak shape, really seemed to change over time. Their beak's got a lot longer and larger, which makes sense because they have to really get these beaks into the feeder and birds with longer beaks are going to be more successful on getting this food. They can really fill up their mouths. There's just never going to be this much sugar water in the plant, right? The beak's actually got a lot sharper too and one of the suggestions for that is males fighting off other males that are trying to get at the feeders and so if you've got a sharp or beak, you've got a sharp or a weapon. It's really interesting. Just a few generations are seeing all these really interesting changes in the hummingbirds. Is this pretty fast? The research is saying that a lot of these changes that they saw happen in just 10 generations, which is really short. Again, we think of evolution happening over maybe thousands or millions of years and just to see these changes happening so fast is pretty remarkable. I got a shout out the backyard birders, the people who do bird counts or keep track of birds on apps. That is where all this data came from. Yeah, a lot of the data came from that. This might be happening with other animals that we have this weird relationship with. It's going to be a lot harder to see it than it is in birds because there are so many bird watchers. Yeah, there's been speculation that foxes and a lot of other animals are sort of domesticating in our presence and what's cool about the studies, they actually really studied this in detail. Okay. The next story we're going to talk about, we did cover a little bit on the podcast. It's actually one of my favorites, so I'm glad that we're getting to revisit it. This is about trees that you really, really don't want growing next to your house. These are called almentro trees and the study took place in Panama, so I don't have to worry about it right now. Right. These are really tall trees. They're about 55 meters tall. This is also, you know, it's another class story I really like, which is just counterintuitive story because you would think a tree getting hit by lightning would be a really bad thing. And for this tree, it seems like actually a really good thing. Like these trees seem to want to get hit by lightning. This is really interesting because you need a certain kind of observation in order to understand this. And we know kind of where lightning hits, but we're not going and visiting every place a lightning strike happens in a forest, but that's what the researchers had to do here. Right. They're looking at a particular island in Panama called Barrack, Colorado Island. And they had a bunch of trees there, outfitted with cameras and electromagnetic sensors. And the researchers studied them for about five years, 2014, 2019, and over this time they observed where the sensors actually picked up 94 lightning strikes. And the really interesting name the researcher saw is not only did the lightning not seem to hurt the tree, almentro trees, it actually hurt the trees around that tree. And it also seemed to kill these parasitic vines that were growing around the almentro trees. So this is like a statistical analysis. You have all these trees in a forest with different chances of getting hit. These are hit maybe more and their surrounding trees suffer more when the almentro is hit by lightning. Do they know how this happened? What is the tree doing to like not only survive lightning, but hurt the competitors around it? They're trying to be conducting this lightning in a way that they're trying to do these trees around them. In fact, the trees that grew around the almentro trees were 40% more likely to be killed by a lightning strike. And the trees that weren't near these trees. So it's like, it's not dangerous to be an almentro tree, but it's dangerous to be a neighbor of an almentro tree. On top of all of this, these trees are so tall, like 55 meters, you said, they're taller than their neighbors. They might actually be drawing down this lightning to clear themselves of parasites and then kill off their competitors and live to grow another day. Yeah. I mean, this is another interesting evolution story because the ideas these trees have essentially evolved to be lightning rods. They're so tall. They have this internal structure whereby water flows through the wood in a particular way that, again, these trees are able to sort of absorb these strikes without being not being killed, but actually being able to kill things that are around them or even on them. I'll be really interested to see if this happened anywhere else. Yeah. The next one that we're going to talk about comes with a video. Definitely check this out. I would love to see this in person. If you watch this video, you can see sharks playing with toys. And obviously, I've entertained, perhaps they're entertained, but there's a lot more to the story. Because again, another really funny animal story, again, one of our favorite types of stories. In fact, we have a few animal stories in the top 10 of us this time around. And again, I also know another counterintuitive story because sharks are given credit for a lot of things, but not necessarily giving credit for being very smart. And that kind of goes with fish in general. So when you have aquariums, you have your mammals, your dolphins, and your sea lions and things like that that are not only being fed, but also get all this enrichment things to play with. And then you've got your sharks and your fish, which are basically just sort of swimming around these very not interesting tanks all day. Looking dead eyed. Looking bored. Looking dead eyed. And so it's like, you don't think there's a lot going on behind those dead eyes. And so these animals have virtually not be given a lot of what's called enrichment and these things. So play with and investigate because the idea is they're not going to care about it anyway. And this was an experiment that took place at an aquarium where someone was just like, you know, maybe they just need some pool toys in there. The research is actually ordered a bunch of pool toys online, rings and balls and other types of things. And they essentially just threw them into a tank that had 12 sharks of three different species. There was a leopard sharks. There's skates. There's orange shark. So in the video, you can see them playing. How often did that happen? Did they all do it? Was there a difference between the animal? At first, nothing really happened. It took a few weeks for the sharks to get them skates to get used to these new objects. But once they did, there was a plastic squid toy that a shark was sort of playing a game of chicken with and sort of rushing towards it and then getting out of the way. The horn shark had this yellow hoop that it was swimming through. And then there was a skate that was actually grabbing and orange ring with her mouth rolling it around with her tongue. So there's actually really kind of interaction going on with these. They're not just hunting them. They're not just getting away from them. They're doing all these different interactions. And this looks like play to me in you, but maybe a researcher would disagree. And this definitely came up when we had this story a couple years ago on bumblebees playing with wooden balls. And there's like, this means bees can feel your emotions. This is play. And then there's a lot of pushback when you say that about any kind of animal, really. Right. Because play is actually, it's a scientifically defined term when we talk about play. We're talking about things that are for fun, for joy, for entertainment. Like one of the pushbacks on this is, is it really play or is it something scientists called exploration, where animals are basically just trying to learn more about their environment. And they're not necessarily like having a good time, you know. I think they're having a good time. For the last one we're going to talk about today, we're going to switch over into physics. And this is a bit of a brain twister, actually. This is about micro robots. And there's a ton of research in this field and what they want to be able to do is make very small robots that can go in the body and carry out tasks that you don't want to do with surgery or with medicine. When you make a micro robot, you want to offload as much as possible. It could be you don't want it to have power or you're going to kick away sensor or something. You still got to make it as small as possible. You have to reduce the amount of stuff on your robot. In this case, they're going to remove onboard navigation. We're talking about robots that are sometimes as small as a grain of sand. Or robots in this particular study, they're less than a millimeter long. So as you said, Sarah, you can put a lot of equipment in something that's that small. And so if we're talking about things like navigation, that's got to be done externally. But how do you do that? How do you get these things to move around and do what you want them to be doing? And I've seen magnets. The robot has certain kinds of magnets on it and then you steer it from outside the body, but that's not always going to work. In this case, they decided to use light. They outfitted these release super tiny robots and you can actually see a video on the site. These H-shaped robots and they contain these ring of microscopic solar cells. Researchers put the robots into the solution, which is all ions, and this electric yield around the robots exert a force that propels the bots sort of around the fluid. But how do you steer them? That's where things get really interesting. The research is very the amount of light that's delivered to them, quote unquote, "motors" on these robots. And that can steer them in particular ways, but to really get fine to steering, they have to create this custom light intensity pattern that uses a digital projector that focuses light on these little areas of this feature dish that these robots are living in, which helps the robots swim around in particular directions. This is where space time, artificial space time comes into things. So it's not complicated enough that you have light in a pattern at a very small scale moving a robot around in three dimensions, but you also need space time for this wide-day. Right. So the researchers are actually utilizing Einstein's theory of general relativity. And the robots are sort of kind of navigating around this maze, and the maze and its boundaries are converted into this virtual space where the robots can fall straight lines to the target. Just like spacecrafts or beams of light, and even though they appear to be following these curved paths around gravitational objects, they actually move them straight lines. These four dimensions of space time, and once the light is patterned to repel the robots along these lines, and that's what the researchers are doing here, with a darker region placed at the maze's target, so that gives them a way to help the robots hone in on something. It's kind of like a mini-black hole, and a map gets converted into this physical space. It's all very complicated, but the bottom line is that doing all these sort of relativistic shenanigans, the researchers can actually make these robots move the way they want them to and to where they want them to. And again, you can see a video of this, which is kind of on the site. I'm going to assume that this is an efficient way for them to find paths, and that hopefully it doesn't use too much computing power to map it out. I mean, I think that's another advantage here, because we're not just talking about robots that would move inside the body, but we're talking about swarms of robots that can potentially clean up toxic waste spills in the ocean, and again, you're going to want a way to control all these guys, and every one of them has the little control panel inside of them. Things are going to get really complicated really fast, and this offers a way to control potentially an entire swarm of robots. Okay, Dave. Do you want to give us a hint as to what else is on the list this year? Yeah. As I mentioned, a couple of other really cool animal stories, some other cool stuff, including some of our most popular stories in the year, and even one that could potentially save your life. So be sure to check out all of these stories. They're not all just fun. That's some serious hype there, saving your life with your top of the year. Okay, that's great. This will be fun to read, but also really important as well. All right. Thanks, Dave. Thanks, sir. David Grimm is the online news editor for science. You can find a link to the top 10 stories of the year at science.org/podcast. Next up, drum roll, please. Science is breakthrough of the year with producer Megan Cantwell and the editor of the section, Greg Miller. Do solar power and the greenhouse effect have in common? The science behind these discoveries was pioneered by women. At Lost Women of Science, we've made it our mission to give forgotten female scientists the credit they deserve. Take Eunice Newton-Foot. I mean, she demonstrated the greenhouse effect before John Tindall. Or Cecilia Paine Caposhkin. At just 24 years old, what she figured out would change the understanding of the very nature of what the stars are made of. Lost Women of Science, wherever you get your podcasts. As we're nearing the end of the year, it's time for a long-held tradition at science announcing our breakthrough of the year. Sciences editors and reporters come together and pick what they think is the most significant advance or trend of the year, along with nine runners up in a variety of different disciplines. I'm here with Greg Miller who edited this section and we're going to talk through just a few of the highlights. Thank you so much for joining me, Greg. I could be here. So I thought we could kick things off with something that maybe people saw in the headlines this year, which was the transplant of two pig kidneys into humans that lasted about nine months in different people. This approach of transplanting an organ from a different species into another one, which is called Xenotransplantation, it isn't something that's brand new, right? It's been around for a while, could you talk a little bit about how that field has evolved over the years? Yeah, the idea has been around for a long time. There's been a ton of hype and hope that this could be a way to address the chronic shortage of donor organs. Historically, one of the big challenges to Xenotransplants has been that the human immune system will attack the transplanted organ as a foreign invader. And until recently, immunosuppressive drugs were the main strategy for dampening those immune responses. But what's happened in the last few years is the advent of genetic engineering and particularly genetically engineering pig organs to make them last prone to rejection by the human immune system. This is still something that's pretty early on despite us kind of putting decades of research into it. What's going on right now in clinical trials? Is it mainly focusing on kidneys, are they looking at other organs from pigs as well? It's mostly kidneys, and the other big news this year is that two companies won approval from the US Food and Drug Administration to stage clinical trials. So these will be the first bonafide clinical trials for Xenotransplantation. And that's a really critical step towards establishing a regulatory pathway for their approval. Well, we're going to switch gears now to a discovery made on a species that is actually more closely related to us, but we're not getting organs from them. They have been long gone for a while. What is the story behind how these early humans called denisovins were discovered? The denisovins are ancient humans who were discovered about 15 years ago, identified from DNA found in bone fragments in a cave in Siberia, denisovachev. So that's where the name comes from. They existed from a couple hundred thousand years ago to, I think, maybe 40, 50,000 years ago. And they lived in parts of Asia and Eastern Europe that Neanderthals also lived around the same time and modern humans lived around the same time. They were the first ancient humans to be identified from DNA evidence, not from physical remains. So one of the big mysteries and intrigues about the denisovins as we don't even really know what they look like. They actually were able to find what they think is a skull that belongs to denisovins. It's not that they just recently discovered the skull though. They've had it in collections for a while. The skull was discovered, I think, maybe 90 years ago. 90? Yeah. Oh, wow. Actually, there's a really interesting story about it. It was discovered in China and the Japanese had constricted some Chinese workers on some road building project and one of the workers found this skull and just wrapped it up and kept it kind of secret, didn't want to show the Japanese bosses what he had found. And it was kind of hidden away for a long time and was only described in a scientific paper in the last four or five years. So when they first described it four or five years ago, how did they think it fit into sort of the history of humans and early humans? It was thought that this was likely the skull that belonged to the denisovins, but for a long time, they weren't able to confirm that just because the skull is about 146,000 years old. So the DNA was pretty degraded. The breakthrough this year was taking an unconventional approach to the DNA testing and using some of the dental plaque that they were able to scrape from the one remaining molar, one tooth that remained in the skull. How are they able to sort of disentangle what's in the plaque from the DNA coming from the actual human? The DNA that they get from the plaque mostly comes from bacteria, but the plaque also contains little bits of anything you might find in your mouth. So including blood and saliva fluids that would contain your own DNA. In this case, because the plaque preserves DNA in a kind of mineral matrix, the DNA is well preserved, even though there's not as much of it. And so that's what enabled them this year to get enough of the DNA of the actual, you call them persons, but people, right? The owner of the skull get enough DNA from the owner of the skull to confirm that it was, in fact, a denisovin by comparing with other known samples. Now that they know that this skull belongs to a denisovin, how is that going to accelerate research on this ancient human? Now that we have the skull, that's literally putting a face on the denisovins. And also it gives anthropologists something to look for in museum collections around the world. They can now go look at bones and skulls and other fragments and just based on appearance begin to hopefully identify more samples that they can use to study these ancient humans that we don't really know much about. The next runner up seems like it's going to be something super helpful for agriculture. I didn't realize that hot nights were way more of a problem for rice than hot days. Can you get into why that is? I didn't either, but hot nights throw off the biological clock of rice and cause them to ramp up respiration at night, which means they burn through their energy stores. And so that turns out to affect both the quality of the grain that they produce and the quantity, the yields and many parts of the world where rice is grown, which is large parts of the world. The nights are in fact getting hotter and it's becoming a problem. Finding a way to make rice that can withstand this heat has been in the works for almost a decade. What breakthrough did they make this year on it? They first started by growing over 500 different varieties of rice in areas that are prone to out nights and looking for the varieties that did better and then crossbreeding those varieties and looking for genes that might be involved in heat tolerance. As a result of that, they found this gene that they call 2T12 because it resides on chromosome 12 of rice and they found that there's a particular version or a leal of this gene that seems to protect rice against the nighttime heat. And so when they compared it to commercially grown varieties, now that aren't doing so well with these hot nights, how much better did it do? What happens with some of the conventional rice is that it gets chalky and pasty when cooked, when it's grown in hot conditions at night. And the rice that had the good allele didn't have that effect, the rice was still good. In one commercial variety of rice, the yield was almost 80% higher when the rice was exposed to nighttime heat after it had been bred to have this protective allele. Do they think this discovery could also help make other varieties of rice grown throughout the world more resilient as well? It could be especially helpful for Japanica rice, which are strains of rice, short grain rice, like sushi rice would be a classic example. This traditionally grown in cooler parts of the world, like in Japan and Korea, as opposed to, say, jasmine rice, long grain rice grown in Thailand, Southeast Asia. So Japanica rice does not have this allele, but conceivably, if you could breed it into those varieties, they might fare better under heat as of now they don't do well in nighttime heat. We'll move on to another story that also involves gene editing for a very different purpose. There is a baby boy named KJ, who became the first ever to receive a personalized gene editing treatment. Why was baby KJ's condition a good fit for the first time to try this approach? He has an incredibly rare metabolic condition that's seen in fewer than one in a million births. And it's caused by a gene mutation that results in the liver being unable to break down ammonia, which is a byproduct of metabolism that can build up in the blood and damage the brain and other organs. So like threatening condition and people who have it eventually need a liver transplant. So there are a few reasons why KJ was particularly well suited to try this method. One is that in his case, the genetic glitch is just a single base substitution. So like a one letter spelling mistake in the gene, it's a gene that encodes an enzyme that's found in the liver that's crucial for the breakdown of ammonia. The other reason, sort of from an ethical point of view, the potential benefits in his case outweighed the risks of trying this new therapy because without a treatment, you would need a liver transplant pretty early in life to prevent the damage that can accrue as ammonia builds up. How exactly does this gene editing work as a treatment? This is a version of the CRISPR gene editing tools that have really begun prominent in the last decade or so. In this case, it's something they call a base editor where the CRISPR enzymes are altered so that they just cut one of the DNA double strands and another enzyme comes in and swaps out the DNA base, so essentially correcting that single letter misspelling. In this case, they delivered it through an infusion of lipid nanoparticles that has the genetic constructions to make the components of the base editor. Is this sort of thing a one time treatment? Does it have to be administered progressively or how does that work? In his case, I believe they got approval to do three infusions of the base editor. He could, in theory, get more doses as he grows, which might prevent him from needing a liver transplant later. How long has it been since KJ received this treatment and how is he doing today? It's been about 10 months, and it seems to be working well. He's able to eat more protein, he's gained weight, and he's sitting his developmental milestones. It's important to say he hasn't been cured. He's still taking medication to keep his ammonia levels down. He's able to take less now than he was before. So this is a one-off case, and like you said, it's a single sort of mutation. Even though it's personalized for baby KJ, they do have a good foundation to sort of work off for other treatments, maybe for similar conditions. Is that in the works right now? That's the hope. So the strategy should work for other people with different mutations, and there are a lot of people out there with very rare disorders or even unique disorders that could potentially benefit from this kind of bespoke gene editing therapy that's customized to fix their particular genetic glitch. We've saved the big selection for last. Greg, what is this year's breakthrough of the year? This year's breakthrough is the rise of renewable energy. There are some pretty significant thresholds that renewables have crossed this year that warrant the sort of celebration of the rise of renewables. It's a trend that's been gaining momentum for some time, but this year most notably for the first time since the Industrial Revolution, more electricity was produced from renewable sources than from coal. And the amount of renewable energy, it's really accelerating. The amount of solar capacity that goes online every single day now is double what we were able to put online in a year, 20 years ago. Such countries have sort of been leading the charge to herald in this sort of shift in energy. China is leading the charge on green energy. So China now makes 80% of the world's solar cells, 70% of the world's wind turbines. Their solar and wind capacity would be sufficient to power the entire United States. And it's not just those things. It's other related technologies as well, like lithium batteries to store the solar power that's generated during the day so that it can be used at night, electric vehicles, China's making something like 70% of the world's EVs, bulb million cars a year, and they're exporting them to many parts of the world, not to the US because of our trade policies, but it's becoming a really important part of the Chinese economy. And they've been able to really get the cost of solar wind, all these renewable technologies down a significant amount. How has that sort of benefited the world that is trading with them? Solar and wind power are now cheaper in most places to generate electricity than it is to generate electricity through fossil fuels. Well, you see in a lot of parts of the world is kind of like what we saw with cell phones where people in a lot of countries jump straight to cell phones and building mobile towers without ever going through the landline stage. And in this case, something similar is happening with solar in parts of Africa and South Asia where people can just throw these small solar systems on their rooftop and use the power to charge their cell phones and light their homes at night in places that have never had a more conventional power grid or a reliable power grid. So you're seeing the affordable Chinese technology being taken up quickly in other parts of the world. Like when we first started talking about the need to shift to renewables to reduce carbon emissions, a lot of the growth was driven by sort of subsidies or incentives to produce it. And it seems like we've kind of reached the moment where it's now sufficient on its own. Is this growth and switchover expected to continue at this rate? A lot of experts are optimistic. I think that's probably what you touch on there is the real breakthrough here. It's the switch from governments promoting green energy with subsidies because it's the right thing to do to go back climate change to people adopting green energy because it's in their own selfish economic best interest to do it. So that switch in motivation is getting a lot of experts reason to believe that this is a trend that's going to continue. Thank you so much for talking to me, Greg. Yeah. Thank you. Greg Miller is a contributing editor at science. You can find links to all the content we discussed from the Breakthrough of the Year package, which also includes a really cool photo essay at science.org/podcasts. And that concludes this last edition for 2025 of the science podcast. If you have any comments or suggestions, write to us at
[email protected] to find us on podcasting apps, search for science magazine, or you can always listen on our website, Science.org/podcast. This show was edited by me, Sarah Cresby, Kevin McLean, and Megan Cantwell. Special thanks to all of our listeners. We so appreciate any feedback you send and all the times you've tuned in this year. We had production help from Podgey. Our music is by Jeffrey Cook and Wenquay Wen on behalf of Science and it's publisher, Triple A.S. Thanks for joining us.
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