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Well, I guess a good place to start with this is
Jonathan Martin, professor at Northland College in Wisconsin. A number of years ago. 2017. We did some really interesting research with a certain type of tree frog. During his research, Jonathan hears that there's a certain type of frog that's fluorescent, meaning it glows under ultraviolet or black light.
So he starts wondering about the tree frogs that he's studying. You get on the internet, you get a small, cheap, handheld black light. And I think literally within days, I'm in my backyard because we have tree frogs all over the place. He's thinking, I'm going to make history by finding out that, you know, this tree frog is fluorescent.
He wanders around his backyard and pretty quickly, I'm like, oh, there's one. Shine the light on it and nothing. No fluorescence. I'm like, all right, well, that's disappointing, but I've got this light. What else do you do when you live in a remote northern place and you have a black light? You start wandering around. Jonathan starts taking these regular nighttime walks
And under a blacklight, leaves that are normally green... — You know, they're kind of a blood-red color. — ...mushrooms look blue, lichens glow orange... — There's a species of shrub that's very common here. And the sap glows like a glow stick. — He keeps finding plants that fluoresce, and he wonders if he's discovering something for the first time.
I found a number of plant species. I was like, that's crazy. And then you look it up, and in 1950, so-and-so documented that honeysuckle has fluorescent sap. He does the same thing with animals, but so many fluorescent animals have already been documented. Insects, fish, you know, scorpions. There was a sea turtle and a shark and things like that. But then, one night, John hears this weird sound coming from his bird feeder. This...
And I was like, "Oh, flying squirrels are here." And so I just instinctually turned the light on this and poof, this blaze of pink jumps back into the trees. I was like, "That is crazy. I can't believe that." - Fluorescent fish, insects, amphibians,
None of that was new, but Jonathan had never heard that a mammal could fluoresce. Like that didn't just happen, did it? And so I sit quietly and they come back and I very slowly kind of move the flashlight up and yeah, that thing is glowing, absolutely hot pink under the beam of the UV light. And I'm floored.
I'm Noam Hassenfeld, and this week on Unexplainable, how Jonathan's accidental discovery of one flying fluorescent squirrel led scientists to wonder, how many mammals glow?
Before we go any further, we need to talk about what fluorescence actually means and how it works. Okay, yeah, that seems like a good idea. This is Cara Gimo. She's been reporting on pink flying squirrels for the New York Times. Hello. So there's lots of different kinds of glowing. There's things like glow-in-the-dark stickers, which absorb light and then release faint light back into the darkness. There's bioluminescence, where animals generate and emit their own light.
And then there's fluorescence, which is actually shifting one wavelength of light into another. So when you're looking around at the world, you're seeing light from what we call the visible spectrum. That's all the colors we can normally see, from longer, low-energy wavelengths like red to shorter, higher-energy wavelengths like violet. So then if you go even beyond that, you get to ultraviolet, super short-wavelength, high-energy light that we can't see.
Unless something can fluoresce. There are some molecules that can absorb ultraviolet light, downshift that light, and re-emit it. That pushes it into the visible spectrum so that we can see it. So when Jonathan's flying squirrel glows pink under ultraviolet light, it's not that it's somehow generating the pink light. It's that ultraviolet light is being absorbed, stretched out, and emitted as wavelengths we can see. Ultraviolet to flying squirrel to pink. Yeah, exactly.
So, back to Jonathan. He's just seen this hot pink flying squirrel, which is a mammal that scientists had no idea was fluorescent. I quickly, you know, get on the horn and I'm like, Eric and our other colleague Paula, you're never going to believe this. Some of his colleagues were already studying flying squirrels, so they had, you know, traps where they were able to kind of keep the squirrel contained for long enough to shine a light on it and see what happened to them. To have this organism in your hand and then to turn a light on it and to see this flurid
fluorescent pink come from their fur, that's what really did it. Yes, under UV light there are three species of flying squirrels that glow sort of various shades of very bright pink. So when they saw that then of course they're like okay you're not crazy and that's where it just kind of steamrolled and so we we got to the point where we're like okay we really need better pictures we need to really understand how far this goes.
They went to some natural history museums and did more rigorous tests with different kinds of lights and filters. We start turning the lights off and open a drawer and you put that flashlight in there and it's like, "Yep, that one's pink and look at that one and all of these are pink and maybe that one's not so much but that one's really bright." And then we started documenting these things. They decided, "Hey, like if squirrels were doing this and we didn't know, maybe some other animals are too." So like, here's a platypus, check it out.
And I was like, "You guys have to see this. This is crazy." Platypuses also glow under UV light, and they tend to glow sort of like a greenish-blue. And there was another species, the spring hare, and Eric was the one looking at that, and he said, "You're not going to believe this." And so, yeah, we'll run over there, we look at these things, like, "Okay, we have to get pictures of that." It's just absolutely bonkers.
Okay, so Cara, how bonkers is this really? Like Jonathan and his team, they end up publishing this research that spring hares and platypuses and flying squirrels, they all fluoresce.
But did scientists really not know about fluorescing mammals before this? Yeah. People have done a lot of studies with birds, insects, fish, even amphibians and reptiles, kind of trying to figure out whether this happens with them. But mammals haven't really been looked at very much, I think. Back in the 80s, there was another group of researchers that decided to look into this. And they found that pretty much all opossums also fluoresce. But they spent a couple of years investigating it and then just sort of like,
the paper fell into the void and nobody ever followed up. So by 2019, I guess people just assumed they wouldn't be finding it in mammals? Yeah. Most people have either assumed that they wouldn't find this in mammals or just not really thought about it at all. So it was one of those kind of like
I don't want to call it a eureka moment. It's more of like random pink squirrel moment that then unfolded into this whole set of questions and investigations that this team has been pursuing since then. I mean, is it just a random pink squirrel moment? Do we know what it means that all these mammals can do this? We have no idea what it means.
Okay. Good place to start. Yeah. I don't think we even know in terms of how it evolved or whether it did evolve independently or whether it's a trait that's conserved in particular lineages or anything like that. Some people think that there could possibly be a reason for this, like a utility for it. And then other people think that it's totally incidental and there's no way that there's any use for it.
Okay, so what's the case that there is an actual use for fluorescing under UV light? So the theory that people seem to think is most plausible is that the fluorescence could actually make these animals less visible, specifically to predators. Okay. There are a lot of predators like owls, for example, that are known to be somewhat sensitive to UV light. They can detect it.
So if the fur of these animals is absorbing UV light and then emitting light at a different frequency, that could act as a kind of camouflage and it could help them hide from predators. And that's kind of interesting because
Pretty much all the mammals that we've found to display this trait are prey species. They're not predators. So essentially the argument that the UV fluorescence is meaningful is that the predators have UV vision, and so the fur that absorbs UV light and reflects it in the visible spectrum is making it less visible to the predators. Exactly.
What's the counter argument? What's the argument that this is just sort of a thing that happened and it doesn't really help the animals? Yeah, so the counter argument is sort of tricky and counterintuitive because when you look at these pictures online, it's kind of a short hop to think like, oh, OK, I'm seeing this platypus that's glowing greenish blue. That's probably what other platypuses see when they look at a platypus. But that's not actually true in natural light, for example, like full daylight.
the visible light would swamp out any fluorescence that was detectable to us and probably to platypuses. Right. Like if you want to see these squirrels glow pink under a black light, you got to do it at night. Yeah. But another counter argument is sort of just like your fingernails glow under black light. Like what's the utility of that? It's really hard to come up with any reason that that would happen. And so similarly, the idea that
like a spring hair glows orange under UV light. Like maybe it's just like we glow, but it's no big deal. We just happen to do it. So basically it could just be a coincidence, not something that evolved because it helped animals survive. Yeah, exactly. Is there a reason we're still unsure? Are these experiments hard to conduct? Is the research too new? Are people sort of not on board with the whole topic yet? Like, why is this still sort of a mystery?
Yeah, it's only just started getting a lot of attention. But I think the thing is, you kind of have to get to a critical mass of people being interested before you really start drilling down into the extent of a phenomenon.
Because, you know, like it's totally possible that people in the past have kind of incidentally figured this out and just never written it down. Or maybe forgotten about it, like with the opossums. Yeah. And it's only pretty recent that we've had someplace like the Internet where people can share cool pictures of an interesting phenomenon. And it just could like, you know, go all around the world in a second. There are a few research groups kind of exploring with different groups of animals. But it's not COVID, right? It's not like a bunch of different labs are trying to get
grants to study this right now or feeling like we need to figure it out right away. Yeah. And I mean, is there any sense that maybe it's a problem that we're researching something just because it looks cool and pretty on the internet? Yeah. So that's actually something I think a lot about as a science journalist. Like I know that when I'm looking for studies to cover, it's a lot easier to get attention for a story that has a really cool visual element.
or is about something really surprising. And this set of studies about fluorescent mammals really checks both of those boxes. Right. And at the end of the day, scientists could construct an enormous experiment and find out that this is all just like a fluorescent pink herring. Animals just do this and it doesn't really matter, right? Yeah, totally. I mean, but that's how it works, right? That's one of the cool things about science is you just trace all the threads and some of them lead to dead ends and some of them lead somewhere else.
It's always worth it to kind of ask the next question or like point the next UV light at the next animal because maybe we're going to figure out like this fluorescence totally has a utility. It's led us to the discovery of these forest raves that we didn't know about before. Forest raves. Or, you know, we're going to say, you know, we haven't found any biologic utility, but we've learned a lot about fluorescence and we can apply that to XYZ things. Or like in the very worst case, that's not actually that bad. We've just discovered something really cool that we can't explain.
Before you go, Kara, can you take me to a forest rave? Oh gosh, okay. Well, you know, maybe there are some hot nights in August. Maybe there are some hot nights in August. Maybe there are some hot nights in August. Maybe there are some hot nights in August. Suddenly turns into a huge goopy light. Leaves that were previously green turn bright red.
Butterflies and moths, flowing, flitting from flower to flower Red sand and orange rose, turquoise blue The squirrels come out, emitting pink fluorescence A spring hare too, ready to party Maybe a platypus Maybe a platypus saunters through
And the opossums are just like trundling through. There's blue, there's salmon, there's rose. Bright red, there's blue, there's salmon, there's rose. Bright green, there's green, there's salmon, there's rose. Bright blue. Maybe there's some hot nights in August.
Maybe there are some hot, hot, hot nights in August. Hot nights, hot, hot nights, hot nights, hot, hot nights. Maybe there are some hot, hot, hot nights in August. And the opossums are just like doing little opossum dances. Maybe playing dead is actually an opossum rave dance. There's really limitless possibilities. So many possibilities. Hot nights in August. Hot nights in August. So many.
Pot knife, pot, pot knife, pot knife, pot, pot, pot knife in August. Support for Unexplainable comes from Greenlight. People with kids tell me time moves a lot faster. Before you know it, your kid is all grown up, they've got their own credit card, and they have no idea how to use it. But you can help. If you want your kids to get some financial literacy early on,
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Unexplainable, we're back. Before the break, we heard about the accidental discovery of a bunch of fluorescent mammals and how science doesn't really know what to make of them all yet. But our reporter Bird Pinkerton makes the case that pursuing these weird accidental discoveries is completely worthwhile.
It's 2008 and we are at the Swedish Academy of Sciences. The room is packed, there are all these scientists in ties sitting at a long table with microphones in front of them. And then one Swedish scientist takes the mic. The Nobel Prize in Chemistry 2008.
celebrates three scientists that have given us tools to light up and see individual proteins inside living cells. So he explains that this Nobel Prize is going to be awarded for the discovery of something called green fluorescent protein, or GFP. And this protein, it's become the basis for a bunch of really important scientific tools. Tools that have revolutionized the molecular life sciences over the past decade.
GFP turns bright green when you shed certain lights on it. And today these tiny molecular flashlights are used to study any and all processes in cells and living organisms. Basically, you can add the genetic code from making GFP to cells or proteins or viruses, and then they'll have what is essentially a little green flag attached to them.
This is Nobel-worthy because it means you can track these cells or proteins or viruses as they grow or see how they move through a body in real time. Thank you. A powerful protein, a powerful technique. One of the three men who got the Nobel Prize for this powerful protein is Martin Chalfie, also known as Marty. There have been tens of thousands of papers. People have used GFP in many, many inventive ways.
where they have discovered basic facts about biology that no one even imagined existed. You can ask how HIV spreads, or how cancer metastasizes, or even how Alzheimer's works, all by attaching this little green flag of GFP to cells or viruses and then tracking them as they move. And then there are these absolutely wonderful discoveries and directions of
that I at least would never have imagined. So today, GFP is an almost miraculously useful tool. But 60 years ago, it looked a lot more like a random flying pink squirrel. More like a cool little footnote than a crucial medical discovery. Yeah. So the story of GFP starts with a series of mistakes or accidents, right?
The series of accidents that led to GFP began back in the 1960s with one of the other people who won that Nobel Prize with Marty. Osamu Shimomura. Osamu was a Japanese scientist, and he was studying a jellyfish that glowed a bright, beautiful green color. And he wanted to understand what were the components
that allowed this organism to produce this beautiful light. Osamu's grinding up lots of jellyfish and trying to figure this out. And no matter what he does, it fails. He doesn't get a glimmer, so to speak, out of the preparation. Until accident number one. One day, he's worked into the night. Again, no success. And he takes all the samples and he throws them away in the sink.
He turns off the light and is just about to leave, and he sees that the sink is glowing brightly. It's the first time that he's gotten this glow. So he's trying to figure out what's different. The sink had probably some jellyfish parts in it and some seawater. That seawater was the key, specifically the calcium in the seawater. Osamu tried his experiments again, this time with some calcium added, and he got a glow.
Because of a sink accident, Osamu was finally able to isolate the protein that is making these jellyfish glow. Slight problem.
In the wild, these jellyfish are green. But the flashes that Osamu is seeing, they're not green. They're blue. He solved the problem. What produces light? But he now has a new problem. And the new problem is, what produces green? This is the second accident. And he thinks about that for a while. And he realizes, maybe there's a different protein. But this protein doesn't make light green.
It converts light. In other words, it fluoresces. It turns one type of light into another, just like the pigments in the fur of the flying pink squirrel. You put blue light in and it converts it to green light. Osamu publishes his research, the jellyfish, the calcium, and he puts his accidental discovery, this protein that changed the color of light, in a footnote.
But it didn't actually get the chance to revolutionize molecular science for decades. Until 1989. That's when Marty came into the picture. He was a researcher working with worms. And the question that he was trying to answer was the one that would eventually lead to him winning the Nobel. Which genes control what inside of a worm's body? Marty had a technique to figure this out, but it involved killing the worms. So he couldn't watch things unfold in real time. Until...
Accident number three. One day, I decided I would go to hear a talk. It was on something I had no information on, but it seemed like a nice seminar. By complete chance, the introduction of the seminar was about Osamu and his work. And I hear the seminar speaker in 1989 describe Shimomura's work, that there is a protein that you can see in the
All you have to do is shine blue light on it and you'll get green light back. I got so excited after hearing this introduction to the seminar that I just fantasized the entire time about what I wanted to do. And so I don't actually know what the seminar speaker talked about, but the introduction was spectacular.
Marty was so excited because he thought, okay, what if I could take a worm gene and then swap out a little piece of that gene so that every time that gene was turned on, it made some of this green fluorescent protein, this GFP. All we have to do to look at it is shine blue light on it. And wherever it's being made, we'll see green. And what this means is we can follow that.
the animals and say, "Okay, when during development is this made? Oh, I don't see it in the larval stages. I see it in this later stage." We now know when it's starting to be made. In other words, he thought he could use GFP like a little green tracker to watch his genes produce cells over time. Over the next few years, Marty turned his seminar daydream into a reality, into a new tool. And then other scientists took that tool in entirely new directions.
There was a book my daughter loved as a child, which was "If You Give a Mouse a Cookie." You give the mouse a cookie, and he asks for a glass of milk to go with it. And once you give the mouse a glass of milk, it asks for a straw. And then it wants a napkin. And on and on and on and on. And I think that mouse is a pretty good metaphor for scientists, because you give them a perfectly wonderful green fluorescent protein, and almost immediately they ask the question,
What other colors are there? Where can we get other things? What other improvements are you going to give us? Everyone wants more. GFP is used to track diseases in the body, like I talked about at the top.
But scientists are wringing all kinds of weird, wonderful cookies and glasses of milk out of it. Like, there are Japanese researchers who are using GFP to make silk moths that spin fluorescent silk. And other researchers are putting GFP in bacteria that detect TNT so that they might be able to detect lamb minds. And this blossoming of discoveries and applications is
It's why Marty and Osamu and another man, Roger Chen, won the Nobel Prize in 2008. But again, it took a long time and at least three weird accidents for these applications to become apparent. Which is why diving into unknowns that seem inconsequential, like why a flying squirrel fluoresces pink, it's wise for a while. Maybe it's a dead end. But also, interesting discovery can come from truly unexpected places.
It comes, I feel in many cases, from completely left field where someone will be discovering something and say, you know, it's interesting. This actually relates to this other problem. I hadn't thought about it before, but I can draw this connection. So the takeaway from this interview to me is throw stuff in the sink.
Go to seminars and study beautiful things. That's not bad. I'm not so sure about the throwing in the sink, but I think the lesson is to keep one's eyes open, to always ask questions, and to always be wondering and be open to suggestions that come from many, many different directions.
Martin Chalfie is still in pursuit of new discoveries, researching worms and their many secrets at Columbia University. This episode was produced and reported by Bird Pinkerton and Noam Hassenfeld. And there were also edits from Meredith Hodnot, Jillian Weinberger, and Brian Resnick. Noam wrote the music and Christian Ayala did the sound design. Manning Nguyen, that's me. Check the facts. Lauren Katz writes our newsletter and Liz Kelly Nelson is the VP of Vox Audio. And we also owe a special thank you to Audrey Martavich.
And if you want to read more about glowing mammals, Cara Gima has several great articles on them in the New York Times. So for links to those and for a link to Hot Nights in August, our Forest Rave song, you can subscribe to our newsletter at Vox.com slash Unexplainable. And if you have thoughts about this particular episode, please email us at Unexplainable at Vox.com. Unexplainable is part of the Vox Media Podcast Network, and we'll be back in your feed next Wednesday. Don't glow away.
The squirrels come out emitting pink fluorescence. A spring hare, too, ready to party. Maybe a platypus saunters through. And the opossums are just, like, trundling through. There's blue, there's salmon, there's rose. Bright red, there's blue, there's salmon, there's rose. Bright green, there's blue, there's salmon, there's rose. Bright blue, oh yeah.
Possibilities.