Which came first, the chicken or the egg?
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It's time for another episode of Unexplainable or Not, the game show where we finally get some answers. This week, our guest is Pablo Torre. He's the host of Pablo Torre Finds Out, a sports and culture and kind of everything podcast where Pablo asks the questions I've always wanted answered.

You might also know him from his time at ESPN. Welcome, Pablo. Thank you so much. That is more or less what my show is. I appreciate you being even vaguely aware of it, let alone kind of liking it. I mean, it's one of my favorite shows. It's a great listen. Pablo, how are you feeling about answering some science mysteries outside of sports? I'm both excited and terrified. Wyatt Cenac was your previous guest in this chair, and it's big shoes to fill. So I'm excited, but trepidatious.

All right. I think that's a reasonable zone to be in. That's right. So unexplainable or not, it's a game show where you have to guess what we know and what we don't.

You're going to hear three stories about scientific mysteries. You're going to hear them from me, from Bird Pinkerton. Hello. And from Meredith Hodnot. Hey there. Two of these mysteries are still unexplainable, but one of them has recently been figured out. After you hear all of these three mysteries, you're going to get a chance to guess which one you think scientists have actually explained. And this week, we're doing a whole bunch of mysteries about eggs. ♪

Oh, boy. Pablo, do you have a relationship with eggs? Do you have any egg thoughts? I have many egg thoughts. I'm Filipino, and so one of the horrifying delicacies of the Philippines is something called balut,

which is a sort of partially embryonic duck egg that I encourage all of you after this episode is done to Google. It is scary. I stand by it. But this is a real loaded topic for your boy. Culinarily? Culinarily, psychologically. I just now feel an immense pressure to actually get this right. Okay.

Okay, so we've established your eggs-pertise. No. Well, Noam, I am here to crack this case. So let's get to the game. We've got three egg mysteries, or I guess three potential unexplainable egg mysteries. And our senior producer, Bird Pinkerton, is going to go first. I'm still recovering from the egg puns. I got so many more. All right. My egg mystery is about a discovery at the bottom of the sea.

So NOAA, the National Oceanic and Atmospheric Administration, they have this program where they go and just explore the ocean, basically. So I spoke to this expedition coordinator, his name's Sam Candio, and he basically told me that, like, instead of having a hypothesis and going to check it out, they basically go out to generate hypotheses, to just, like, figure out what we don't know. Okay. So in this case, they're in this ship. They're traveling through the waters off of Alaska, right?

And their job was to like map the bottom of the ocean with sonar and then send out a robot that explores and can kind of like pick up things and vacuum up samples.

And when they have this robot out, they sort of live stream it so scientists and the public can watch. And so, yeah, it's very compelling. I can only imagine the comment section on that live stream. But it's like genuine nerds watching and having like a delightful time. Oh, I love this. They found like sponges that they think are new to science. The sea star that might be a new, not just a new species, but like a whole new genus. And then this is sort of where we get to the egg bit.

One day this summer, they have this robot down there. It's like two miles deep, streaming video. And Sam and two of his colleagues are just talking to each other, watching the stream. Camera's traveling over these like gray rocks, looking at sponges. And then they see this thing. Here, I'll send you a picture in one sec. Oh my God. So if I may describe this. Yes, please. It doesn't look immediately like an egg. It's

it's yellowish gold-ish. It's hard to tell the consistency of the surface, but it's certainly like almost pyramid-shaped with some sort of like wrinkles and pockmarks. Yeah. So some people have been describing it also as like an orb. It's just like big golden blob. Yes, that's a better description, admittedly. It doesn't look

man-made it's kind of like flaking off as you can see at the edges can I say why this is already very scary to imagine because I imagine if you're an oceanic explorer at NOAA the idea that like this thing is weird everything I've seen ever when like just google imaging deep sea creatures they're all aliens so the alien that scares the alien uh

Researchers is Jarek. Yep. But so they're curious about what it is. They start to approach it and they're talking to each other while they do. So I'll play you that audio. It's like the beginning of a horror movie. Pretty sure this is how the first episode of The Exile started. And as they move in, they sort of keep changing their minds about what it is. Like first they think it's a sponge. Then they're like, no, definitely not a sponge. Moved on to potentially coral. Coral.

Now we're thinking egg case. There are a lot of like weird egg cases in the ocean. So that's sort of like why they're gravitating towards this. And they make a mistake that perhaps you and I would not make, which is they decide that they're going to not just witness this thing, but bring it on board. Oh, no. Let's give it a little tickle.

I think maybe a scrape with the slurp nozzle. It's very soft. This has turned into a very different kind of live stream. This is only fans for oceanic explorers now. The slurp nozzle? A technical term for like a vacuum attachment for their robot, which doesn't sound any better now that I'm thinking about it. No. But they've captured this mysterious thing.

that seems biological, but it's, you know, as we've mentioned, not immediately sortable into our book of known things.

And because it's like weird and gold and seems like an alien, right, it kind of blows up on the Internet. It's spread across Twitter, like some pieces were written. Lots of people developed very advanced theories about it, like Sam's five-year-old nephew, who is pretty convinced that it's a dragon egg. Reasonable. But now the egg slash orb slash golden object is at the Smithsonian.

where it will have its DNA cataloged and researchers can figure out sort of what it is. Is it a golden goose egg? Is it a weird anemone? Like, what's happening? Unless I am pulling your egg and they have already DNA barcoded it and they already know. I got to say, this entire story is shell-shocking.

I will say that this feels already like another genre of scientific cinematic inquiry, I believe, when it's sort of like, hey, we're going to find out what's in this sarcophagus. And everyone's just like, no, you don't need to know what's in the sarcophagus. Nothing good is in a sarcophagus. But I am, of course, morbidly curious.

So no need to make a firm guess now, but what are you leaning here? Do you think unexplainable, solved? I am currently leaning towards solved just because I don't think my impulse control, would I be an oceanic explorer, would be so prodigious as to just like, we haven't done it yet, but we're going to get to it. Right. I probably attend to it immediately. Give it a little tickle. Just a little tickle.

But the chest bursting would be a concern. Maybe they're just being cautious in that way. Something to think about. Yeah, maybe for the first time in sci-fi movies, someone is deciding to not open the egg. What a cliffhanger. What a cliffhanger. So that's our first egg mystery. Next up, I've got an egg mystery for you. And it goes back to one of the most important moments in the history of life.

So life on Earth started in the ocean. And then at some point, a few hundred million years ago, the first land vertebrates, so our ancestors, the ancestors of all mammals, reptiles, birds, all

They somehow made it onto land. And the question is, how were they able to do it? How were they able to get there and stay there? Oh, did it involve comically tiny arms? Arms are one thing. That's obviously a requirement. Another one would be lungs. That's a good point by you. These are the things that we would assume are necessary to go onto land. Like the breathing. Yeah. The breathing, the walking, right? It's useful. It's useful.

But the first vertebrates that were able to make it onto land, amphibians, they were still totally tied to water. They had lungs, they had legs, but they still had to lay these super squishy, permeable eggs in the water. And for decades, scientists have thought that the key to this transition to getting on land more than lungs, more than legs, they've thought that the key was the hard-shelled egg. It's this incredible innovation. It's astounding.

It's essentially a portable ocean. You don't have to lay your eggs in an ocean. It packs the ocean inside it. Scientists call it a private pond. This is we need to. OK, the people selling eggs are totally messing up how to brand their product. Yeah. Buy your own private pond. Precisely. A dozen at a time. Oh, my gosh. There's money on the table. So the idea is that the shell prevents the embryo from drying out on land. It surrounds it with all the nutrients it needs.

And then animals, they could get as far from water as they needed. They could lay eggs further away from predators. So essentially, this has been the accepted wisdom for decades. The hard-shelled egg, huge revolution, the key that allowed vertebrates to make it onto land and stay there.

But there's kind of a pretty big problem with this neat little story, which is that there's no fossil evidence of these first hard eggs. There's a really long time when the first vertebrates were on land, like over 100 million years, that we have no fossil evidence of any hard eggs.

And if the first land vertebrates were laying hard eggs, if that was the key, we'd assume that we would find some hard eggs. But at the same time...

This is sort of a classic trap with paleontology because fossils are really hard to find. You know, for all we think we know about dinosaurs, we've only found something like one dinosaur for every like 10,000 years. Wow. So, yeah, we're left with this big question. We still don't really know how land vertebrates were able to make this huge transition from ocean to land, basically changing the history of life on Earth. Right.

We don't know how or whether the eggshell was involved. Or maybe we do. Maybe I've been tricking you. Maybe scientists have found that super ancient hard-shelled egg.

And actually, maybe that golden egg orb that Bird just showed you, like, maybe that is actually the first hard-shelled egg. Yes. I love this show because I genuinely, again, keeping to my show's title, I find out stuff I did not know. One dinosaur every 10,000 years alone. Just like, mm, mm. Yeah, right? Noted. But I am inclined to think if there was an egg in our past, we would have found some evidence of it. Okay. So we've got...

Mysterious golden orb. We've got the first hard-shelled egg. And we got one last egg mystery from our supervising producer, Meredith Hodnut. All right. So my mystery is something completely different because my mystery is about eggs.

And sperm. It's about eggs and sperm. Finally. So we've all heard the story of the race, right? Millions of little sperms swimming as fast as their little tails can take them, hurtling towards the finish line, the egg. The winner reaches the egg first, and together they begin a new generation of life. This is called random fertilization because there's no, like, genetic rhyme or reason behind which sperm makes it to the egg. It's just whichever happens to be the fastest one.

And this randomness is like a bedrock foundation for our modern understanding of genetics and biology. Going back to Mendel playing with pea shoots in the 1800s. Yes. And now scientists are starting to question everything. So in 2005, a geneticist named Joe Nadeau was carefully breeding lab mice for a series of experiments...

And he found something that should have been impossible based on everything that we know about biology. Classic rom-com premise, by the way. Exactly. A meet cute. Absolutely. So as he bred these mice, there were way more babies with healthy gene combinations than he was expecting from a random race to the finish line. It was almost as if something was like tipping the scales towards a good genetic match between egg and sperm.

Other scientists had seen these discrepancies before, but dismissed them as unimportant and

But Joe is obsessed with controls, and he started checking and double-checking results. And the only explanation that made any sense to him was that this fertilization wasn't random at all. What was it, Joe? So instead of a first-to-the-finish-line random sperm race, could it be that the egg and sperm are choosing each other? That's right.

That's a classic rom-com premise. A meet cute by any other name. There we go. So as far as we understand, like once egg and sperm touch, that's it. There's no going back. The embryo either lives or dies from there.

So how could an egg and sperm choose a good genetic match without touching? Are they exchanging signals somehow? Are they attracted to each other chemically? Is there, like, some way that they're testing each other's genes from a distance? How did they hatch this plant? It's happening. How are they in cahoots without talking to each other, right? So...

Any way you look at it are assumptions of how egg meets sperm are being shaken up. Like instead of the egg as a receptacle, as like a finish line for whichever sperm happens to be the fastest, there is growing evidence that there's something much more unexpected and interesting going on here. I love that the egg in this mystery has agency.

We have long ignored the egg's ability to choose. And now we're finally getting to that in the discourse. You tell them, Pablo. I mean, yeah. Like, so maybe it's less of a race and maybe more of a dance. But like with profound implications for our fundamental understanding of biology. And we just don't know how it's happening. Right. Or...

Do we? It's enticing and egg-citing. I'm sorry. I feel like you're up to four or five. I don't know. I had that in the chamber, as it were.

So, Pablo, you've got three mysteries here. We've got the mystery of the golden egg slash orb. We've got whether animals used eggshells to take over the land. And then we've got the rom-com of how eggs choose sperm. They're all unexplainable, or at least they all were unexplainable at one point. One of these mysteries has recently been figured out, and you'll get a chance to guess after the break.

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This podcast brought to you by Ring. With Ring cameras, you can check on your pets to catch them in the act. Izzy, drop that. Or just keep them company. Make sure they're okay while you're away. With Ring. Learn more at ring.com slash pets. Hey, unexplainable listeners. Sue Bird here. And I'm Megan Rapinoe. Women's sports are reaching new heights these days, and there's so much to talk about and so much to explain. You mean, like, why do female athletes make less money on average than male athletes? Yes.

Great question. So, Sue and I are launching a podcast where we're going to deep dive into all things sports, and then some. We're calling it A Touch More. Because women's sports is everything. Pop culture, economics, politics, you name it. And there's no better folks than us to talk about what happens on the court or on the field.

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And now that I'm grown, I eat five dozen eggs, so I'm roughly the size of a barge. Okay, we're back. It's unexplainable or not. Pablo, welcome back. This has all been very overwhelming. Racking your brain during the ad break to figure this out? Yes. So we've got three mysteries to choose from, and only one of them has been fully explained.

Mystery one, what is this mysterious golden egg orb thing at the bottom of the ocean? Mystery two, were hard eggs the biggest reason animals took over the land? And mystery three, how do eggs choose sperm?

So without making your final guess, just sort of tell me how these are all adding up for you. Like, what are you thinking? Where are you leaning? Yeah, I noticed that in each of these mysteries, there is a search for something resembling like documentary proof. And in that way, I'm sort of now also trying to sort of feel out who is the most voracious of all of these researchers that might not rest until they found the solution. And so I, man, this has been a heavy yoke conversation.

to bear. Oh, man, it's still happening. You're egging him on, Noam. It's never gonna stop, guys. I'm really coming out of my shell on this show. So, for me, I am left pondering the image. And maybe it's now I am just a victim of the visual aid that Bird provided. But I'm...

I'm leaning that way? God, all of these are... All of these change the way I think about myself, to be clear. You sound a little scrambled. All right. I believe that the golden sarcophagus of marine life has been studied and understood in a way that has solved this mystery. I'm sticking with my first instinct, final answer, weirdo, golden, yellow thing, blob. Okay. Okay.

Here is the answer, Pablo. Which came first is clearly the land animal, and the hard egg is later. And... The question was, how did vertebrates make it onto land permanently? And it turns out the hard-shelled egg was not the magic key. Egg on your face, Pablo. Damn! So, I talked to Mike Benton. He's the professor you just heard from. He's a professor at the University of Bristol in England.

And he told me that this gap in the fossil record, he thinks that that gap is explained by just the fact that there weren't hard eggs back then. You expect to find them because they fossilize very easily. They're hard, for goodness sake. They're crystalline. You find them. And he's pretty sure there were no super ancient hard eggs because he used a different way to get information from

on ancient animals besides fossils. Basically, you make this super complicated family tree. It's called a phylogenetic tree. And you arrange it looking for one specific trait. You put in as many species as you can and their trait value, which in this case is hardshell egg. You assemble all the branches of the tree. You follow their path to the trunk and then down to the root and

And you can get a pretty good sense of what was at that root without finding the fossil of that root. Hmm.

So in 2023, Mike got together with a bunch of paleontologists at the University of Bristol and the University of Nanjing in China, and they tried to build one of these huge family trees. Our question was, how did it happen? What was it that enabled these first reptiles to truly break their reliance on the water? They started by adding all the species with ancient hard-shelled eggs that had been found. So we add a load of dinosaurs with hard-shelled eggs. Hard, hard, hard.

That's one branch. Then they added some older dinosaurs that were discovered just a couple years ago. That's another branch. But these dinosaurs had eggs that were pretty different. These earliest dinosaurs had soft-shelled eggs. And then they added a couple of recently discovered fossils that pointed even earlier to ancestors of dinosaurs and crocodiles. So before dinosaurs and crocodiles split. And they showed that these animals likely could give birth to live young.

So when they put all this together, they followed all these branches back to what they think was the first land vertebrate. And then they project down to the root and you say, well, actually, there's very little evidence for the hard egg at all. Damn. Essentially, this family tree that they've made shows that these oldest animals probably gave birth to live young. And that might have been the main advantage these earliest animals had. Not that they could lay hard-shelled eggs, but that they could hold on to their embryos inside of them and

And if you hold on to the embryos, the whole private pond that nourishes the embryo, the private pond is actually inside the body of the mother. Like we were the private pond the whole time. Damn. I knew this whole episode was about my mom. This whole thing. Exactly. We got to get down to the root. It always ends up being about my mom. Damn it.

And this is basically turning a pretty major story we've told about evolution fully on its head. Mike actually used to teach this in his paleontology classes. We kind of think, yeah, yeah, of course, the typical bird egg is primitive. But when we looked more closely at the question, we discovered that's not the case at all.

we're not like evolutionarily better than ancient reptiles. Like we think that humans are, our live birth is like the thing that, you know, oh, it must've come later because we're humans and we're better and we're such hot stuff. But like, we're not, it's a lot more complicated than just like, here is the key to having this big transition onto land. I got to call my mom, I think. Just say thanks.

For being my private pond. But there's one more piece to the story here, and it might be my favorite part, because after Mike and his team did all this research, he kept getting asked the same question. Yeah. So people will ask that question, which came first, the chicken or the egg? Yes. It's not like he was trying to answer this, but he likes to say that if you go deeper than the chicken, like way back in that family tree of all vertebrates,

to the most ancient, ancient chicken ancestor. And you ask what came first, the first land vertebrate or the egg, right?

A few years ago, scientists probably would have said... Well, obviously the egg. And now we've got a totally different answer. You could now say, yeah, the ancestral ancient chicken, whatever, blah-de-blah, came before the hard egg. It's wild. So after all of this, Pablo, what do you think of eggs or, like, existence? I... Genuinely, you have changed how I will forever consider the egg. And also, like...

how I see myself and humanity. And I'm not even kidding. Like, this is... My brain's a bit scrambled, if you haven't caught on. It's an extreme change. That's right. Oh, egregious. I mean, look, this has been a dark episode in many ways, but you've taught me to always look at life on the sunny side up. Oh. Well, on that note, Pablo, one last thing before you go.

Even though you didn't get the answer right, we do have a consolation prize for you. Oh, right. I forgot. I wrote a song about eggs, vertebrates, and some super ancient chicken ancestors.

What came first, the chicken or the egg? Everybody asked if the chicken or the egg came first or second. The egg or the chicken? Nobody knows what was there at the beginning. Nobody knows what was there at the beginning. Nobody knows what was there at the beginning. But that beginning isn't really the beginning. So scientists are trying to find out. Did the first bird of bread on land? Did the earliest reptilian ancestor of the chicken make eggs?

Scientists thought it was obviously yes All of them must have laid a bunch of eggs That's the only way that they could leave the waves And make it out onto the land The egg isn't the key The egg isn't the key There are tons of branches on the evolutionary tree But the egg isn't the key The egg isn't the key The egg isn't the key There are tons of branches on the evolutionary tree But the egg isn't the key

Isn't the key

I mean, what a delight that was. Thank you. Top to bottom. Yeah, I was with my family over Thanksgiving and I have seven nieces and nephews. And I got all of them. There are seven nieces and nephews singing on this song. And they were singing it nonstop.

for days because it was stuck in their head. Did you tell them, oh, did you think that the egg came before the chicken? Well, you're wrong. I got in kind of an argument with my nephew. He was like, the egg definitely came first. I was like, you gotta listen to this episode.

That's it for Unexplainable or Not. Thank you so much to Pablo Torre. Yes, thank you for helping me resolve some unresolved traumas in my life. Thank you to our presenters, Bird Pinkerton. Hello. And Meredith Hodnot. Thank you so much. And thank you to our audience for joining us. If you have a mystery or a solved mystery you want us to tell on an upcoming game show, let us know. You can write us at unexplainable at vox.com. And that's it this week for Unexplainable or Not.

This episode was reported by Bird Pinkerton, Meredith Hodnot, and me, Noam Hassenfeld. Brian Resnick handled the editing with help from Jorge Just and Meredith, who also manages our team. I did the producing and the music. Erica Huang was on mixing and sound design. Tian Nguyen hit the facts. Mandi Nguyen is probably off diving into some deep, unexplored cave or something. And Christian Ayala is getting married. Huge congrats to you, Christian.

Thanks so much to Pablo Torre for playing our game this week. Go check out his excellent show, Pablo Torre Finds Out. You can learn all about things like the history of why everyone who plays sports seems to say, let's go! Or why so many athletes have tattoos of the Joker. It's great stuff.

Special thanks this week to Bao Yu Zhang and to my nibblings, Noah Hassenfeld, Amal Hassenfeld, Julian Hassenfeld, Hila Hassenfeld, Sienna Hassenfeld, Moshe Hassenfeld, and Asher Hassenfeld. Their ages 10, 9, 8, 7, 5, 4, and 2. And they all sang on the song, so thank you so much to all of you.

Also, if you want to read more about myth-busting around the sperm and egg narrative, Emily Martin's essay, The Sperm and the Egg, is a great place to start. There's also an excellent Vox video that explores it from a different angle, and we'll link to both in our transcript. If you have thoughts about this episode or ideas for the show, please email us. We're at unexplainable at vox.com. And as always, we'd love it if you wrote us a review or a rating. Unexplainable is part of the Vox Media Podcast Network, and we'll be back next week.

Excellent. One more time.

Life is full of complicated questions. I want to know how to tell if my dentist is scamming me. What age is it appropriate or legal to leave your kid at home? From the silly to the serious and even the controversial. Can I say something that will probably just get me canceled? I'm John Cullen Hill.

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