Radiolab - The Beauty Puzzle

Episode Date: February 8, 2019

When a female animal is checking out her prospects, natural selection would dictate that she pay attention to how healthy, or strong, or fit he is. But when it comes to finding a mate, some animals seem to be engaged in a very different game. What if a female were looking for something else - something that has nothing to do with fitness? Something...beautiful? Today we explore a different way of looking at evolution and what it may mean for the course of science. This episode was reported by Robert Krulwich and Bethel Habte and was produced by Bethel Habte. Support Radiolab today at Radiolab.org/donate. 

Wait, you're listening. Okay. All right. You're listening to Radio Lab. Radio Lab. From W. N. Y. C. See?

Yeah. Whose pad is this? Oh, I think that's mine. Oh, my gosh, Bethel. Your handwriting is awful. Your handwriting is not awful. It's actually very elegant. Legible, not so much, but elegant.

Jet here. This is Radio Lab. So not too long ago. Robert and our producer Bethel Hoppe. It has a nice lean to it. Pulled me into the studio to walk me through this story that they'd been working on together for quite some time. Everybody? Here's everybody?

Yes. Here we are. All right. So shall we start this? Yes. So what are we doing? You guys are just going to tell me this story? I could rather tell you a riddle.

Okay. Once upon a time, birds evolved. They evolved from dinosaurs. So there was originally scaly things and the scales turned into feathers and the feathery things began. to fly, and we call those things birds. But they have a, I guess I'm going to just ask this to you out of the blue, because it's a basic appendage. How many birds have penises?

Oh, okay. And by the way, before you answer, there are like 10 to 20,000 different kinds of birds by modern times. So again, how many of those species have penises? What percentage of currently existing birds? Of all the modern bird species have, the males, of course, yeah. With penises as we would identify? Like, little things and hang out.

Yeah, we don't have to talk about. Yeah, yeah, yeah, yeah, those things. Yeah, I don't know. This is making you uncomfortable. You know, making this draft, I was saying the word penis like so many times. At one point she wrote on the page, do you know how many times we said penises are there? 27 in four minutes. Okay, yes.

So how many birds have penises? Well, I have absolutely no frame of reference to answer this question. I don't know. I mean, I'm going to throw out a number, 40%. No. No, 70%. Let's say 70. No.

30. Lower. 10? Lower. Wow. Five? Lower. One?

Three. Three? Three percent. Yeah, 97 percent of birds don't have penises. Wow. Yeah. So we learned this little fact from a scientist named Patty Brennan. The thing that's so weird about birds is precisely the fact that they lost the penis.

Well, you know, you. You just used an interesting verb, so you say the birds lost the penises. So does that mean that earlier additions of birds did have them? That's right, yeah. So penises are widespread trait of all vertebrates, right, except for, you know, some amphibians and fish. And according to Patty, if you go back 200 million years or so, birds were like all those other creatures. Yeah, like basically 100% of them had penises. Exactly right.

But over time, in the vast, vast, vast mass. majority of birds? The penis was then lost. Now, the... Wow, why would that be? Well, that's the question. How do you lose a penis? Like, it seems like a pretty handy thing to have when you want to put your sperm close to female eggs.

So the 97% of birds that don't have a penis now, what do they have? Well, they have a kind of hole? Both birds, the male and the females, have these holes, and they sort of open up and then they line them up. Yeah, it's called a cloaca. Oh, they have a cloaca. They have this cloaca, and they just briefly touch their cloaca when they're mating, and that's it. That's it. And it works just fine.

But if you're thinking about the engineering, what appendage is going to work best for you to make babies, penis is the one. Because it gets your sperm closer to female eggs. So for all of these penises to just vanish, like she says that evolutionarily, that just doesn't make any sense. Like, why would you lose a thing that's so useful? So for there to be selection for the penis to go away,

there's going to be a very important reason. What's the reason? Well, there's a few possibilities. Number one. People have speculated, for example, that it might have been sexually transmitted diseases. You're putting this penis way deep into the female, and then you're pulling your penis back into your cloaca.

Like, they could be potentially a very easy exchange of sexually transmitted diseases. Because you're, like, digging the germs deeper, I guess. Exactly. Yeah, yeah, yeah. So even though the penis has its advantages, obviously, maybe it slowly went away because the birds that had the penises just kept getting these infections. That could be. But so far, nobody's found a link between penises and STDs.

So then the other possibility that's really intriguing, actually, is the maybe it's because penises are heavy. And birds started flying, and getting rid of the penis would have been an easy thing for lowering your body weight. Maybe they lost them so they could fly further. But I don't believe that. I mean, I think that's unlikely to have been a strong enough selection, because ducks, for example, are among the most long-distance migrants,

and they still have penises. They're in the 3%. And sometimes they have penises that are bigger than their own bodies. They do? Oh, my God. They do, yes. You mean you watch a penis go by with wings, kind of? Pretty much.

Oh, my God. Yeah, so I think the record is a male that had a 43-centimeter long penis, and this is a male that was only about 40 centimeters long himself. So apparently you can have a pretty large penis and fly just fine. But oddly enough, the ducks are also sort of a key to a third theory for the disappearance of the penis. Oh, yeah. So I was going to say my favorite is this idea that actually it had to do with female choice against males that controlled reproduction. To explain, Patty actually thinks that the original bird penises...

Back when they had penises. Yeah. Might have been a lot like the modern-day duck peopies. penis, which is essentially a weapon. And so one of the things that we learned when we were studying the ducks is that the males have evolved this erection mechanism that is crazy. They have an explosive erection mechanism. What that means is that the male actually averts his penis and ejaculates in a third of a second. Basically a pistol penis?

Exactly. Yeah. Yeah, it just goes poaching. Yes. Wow. What that does, though, is that it allows these males to forcefully inseminate females, even when females don't want to be inseminated, right? So if this male is anywhere near a female, he's just going to go, you know, push right through.

And so as you can imagine, that's not, you know, that's not something necessarily desirable for females. Oftentimes with females will be struggling, right? They're trying to get away from these males that are trying to forcibly copulate. So Patty thinks that what might have happened here is that Female birds trying to get away from males with large penises and these really violent ways of approaching reproduction began systematically choosing gentler and smaller males with smaller penises. Right. So if females start selecting males that are less violent, less sexually violent, that that might lead to the disappearance of the penis. What I think you just said is over time, because the ladies were discomforted, the gentlemen,

changed and lost their penises. Yeah, you got it. She's saying that females essentially castrated the males? Well, this is a slower process than that. I mean, over time. Over time, castration over time. Yeah?

Yes, I suppose. Now, what makes you... What evidence is there for such a thing? So, none, I mean, none in a way, because we're talking about penises, which are soft tissue and they don't fossilize. So even if we went back into the fossil record, it would be really hard to find evidence of what was happening.

So that's the part that is difficult. You know, it's kind of like a wonderful story that I think makes a lot of sense, given what we know about the way these penises work now. But we can only speculate. I like this idea. Good. But is this just a one-off?

I mean, what about gorillas and... moose who fight and clashed their horns. I mean, there are so many species where it just seems like the females have zero choice. So I know that there are a lot of cases like that. Bedbugs are especially horrifying. Just Google it. I don't even talk about bedbugs.

But there are actually a lot of cases where when the females do get to choose, they choose in ways that completely change what we see in nature. And we found a group of scientists who now argue that if you look around nature, you will see females driving evolution in ways that I certainly didn't expect. And when they get into the details of how this actually works, I think it's going to flip your ideas about evolution

in a way that you are totally unprepared for. Do they have evidence for this idea? Because I've got to say that you haven't yet convinced me of the first thing they said, that females have evolved the penises away. Like I still have it. Because that was a guess. She said it was a guessing. Yeah.

Fair enough. I will introduce you to a bird called a Bowerbird that I think will, it speaks for itself in these regards. And it's also, it's penisless. They are really cool birds. They have beautiful plumage. The satin-bowerbird is a beautiful iridescent blue with a violet blue eyes. This is Gail.

Gail Patricelli, and I'm a professor of evolution and ecology at UC Davis. Do I want to say that again without stuttering on and? No, no, it's fine. Anyway, so the Bowerbird, what makes them most amazing is that they build bowers. So a bower, these things, a bird spilled, is basically a structure made out of sticks, which can be up to three feet tall. Three feet tall? Yeah. This tiny little bird making this huge... You can put a five-year-old in it in some of these things. Wow. Yeah. And it looks like a nest. But it's really a kind of seduction theater with one seat. And that's for her.

This is Richard Prum of Yale University. He's a biologist there. And he says that on and around this bower, mail will array a whole bunch of found objects. Precious objects. Beautiful things. Parrot feathers and berries and flowers and leaves. Stuff that the bird gathers from the forest. So these structures can be very ornamented and elaborate. And every Bowerbird species has its own style.

In some species, it will all be blue everything, blue feathers, blue flowers, and then, of course, blue trash, like drinking straws and bottle caps. And the male Bowerbird basically dedicates his whole life learning how to build these structures. Like take the satin Bowerbird. They take seven years before they reach sexual maturity. And during that period of time, they look just like females. And they'll often fly around the valley and get courted by adult males. So they play the role of the female and learn how courtship works from other males in the valley.

And then when they get a little older, as teenagers, they'll start building practice bowers and they'll court each other. And eventually, once a Bowerbird, figures out how to make a really good structure, a female has arrived. Females show up. And so they'll fly down to the bower and they'll often check out the bower itself. Is it symmetrical? Is it well built?

She seems interested. And if she likes what she sees, she'll enter the bower. Now, this is where things get interesting because the bower has a very particular and purposeful architecture. So one of the classic bower designs is called an avenue So it's two parallel walls of sticks that are close to one another, and the female sits between them.

There are different variations on this basic design, but in all cases, the female is in a protected position. There's always some kind of barrier or wall between her and the male. So the male wants to try to force himself on her for whatever reason. He has to run around the back, and she can just fly away out the front. Even as he's trying to win her attention completely, he's built a building that keeps her at a distance? Absolutely. The Bower is like insurance against date rape for the female.

It allows the female to observe him at an intimate close distance for as long as she likes while still maintaining her freedom of choice. So the female, if she likes the bower, she'll settle into this protected space where she can back out whenever she likes. And then? Time to begin the show. So he'll start out with his own displays. Many of them make very loud,

electronic sounds. Busing and whirring sounds. And they do imitations of cuckabra, you know. Sometimes they imitate cockatoos. Then, along with singing, they dance. huff up and they run vigorously back and forth right in front of the female. And she's standing between the walls of the bower. So the female watches all this from her safe spot for as long as she likes,

and she can decide if she would like to mate with this guy or... No, not good enough. Up and fly away, all of a sudden. For the female, the moment has gone. Now what's particularly interesting here is that Gail has done studies that show when the males play very close attention to the female. Like when the male really watches her body position, the way that she's, like, postured,

that can actually signal whether she's interested or not. The males that respond, the most of those signals are the most successful in mating. In other words, if the male makes his move too early and too aggressively, she's gone. And that male doesn't have any babies. But it also seems like the females are kind of toying with the males, like seeing what they're willing to do for them.

Like if you watch a video of this, you can see in one Bowerbird, she comes in, he like lifts up his wing like a cape and then just like sort of rotates his wing like this. Like it's so funny. Oh, like a matador kind of? Like a matador, totally like a matador.

And then right after that, she like picks up a blueberry from the ground and then she drops the blueberry, and then he does the Matador thing with the blueberry in his mouth. Like he has a rose in his mouth. That's hilarious. She's like, you know, it's all right.

This is good, but... It would be so much better with this. It seems to be all about her. I see what you mean in this case. Yeah, the females are definitely driving the bus here. And when you start to really think about the implications of this, supposed to being all about her. That can lead you to a fairly deep rethink of the very basic rules of how evolution works.

Really? Meaning what? Well, normally, the classical argument, and you've heard it, like, the reason this male bird is so colorful, so red or whatever, the reason the peacock has these gigantic and beautiful feathers on its tail is sort of a signal that the male is sending to the female of fitness. Look at me. I am healthy to have a tail like this. I don't have parasites.

I'm strong. I'd be a great mate. Like survival of the fittest. Right. But let me ask you, you just heard the Bowerbird story. You have these females with these crazy tastes. Like this one likes blue, only blue.

And this one likes iridescent shells. So it's shells, shell, shell, shell, shells. And this one likes green leaves, but they have to be right side up and never right, you know, upside down. Are these fitness signals or is a certain? Is this more like art? Maybe she just likes blue, or she just likes shells. Wait, you're saying that these birds have evolved based on whims and tastes?

Well, Rick, and there's other scientists like him say... Absolutely. Yes, it's about beauty. I'm really focusing in on aesthetic choices, choices that are based on what it is the animal likes. I thought the whole Darwinian thought was, well, yeah, okay, there might be beauty there, but on some level the logic behind those beautiful things is survival, survival of the fittest. This does not sound very Darwinian. Well, since you drop the name, I propose that my view is the legitimately, authentically Darwinian view.

Darwin, he had an idea about beauty? Oh, yes. He actually... You want to read the quote? Did I bring it to her? Yeah, you brought it. Okay. Page 397, Descent of Man.

Stripes and marks and ornamental appendages have all been indirectly gained through the influence of love, jealousy, through the appreciation of the beautiful, and through the exertion of a choice. Oh, interesting. So he's saying that it's love, jealousy, and beauty, and choice. Yeah, and choice. Yeah, that is definitely not what I learned when I learned about Darwin. So it's over 130 years later, and I'm still pissed. He thinks there was some kind of plot to reduce Darwin's idea into something smaller and eventually eliminated entirely.

I would like to go historical. Let's go about what Darwin said. Let's go what Wallace said, and then let's go to the 20th century and where we got so screwed up. Okay. So Darwin spent 20 years working on his theory of natural selection. he was not particularly noisy about it because he knew it would very much disturb his wife who was quite religious and other people in his church.

So during the 20 years while Darwin was working away at his book, this other guy comes on the scene, his name is Alfred Russell Wallace. Kind of skinny and scrappy and self-taught, 14 years younger than Charles Darwin, but Wallace also... Went around the world, collecting specimens. And he also came up with a theory of natural selection.

independently. What was their relationship to each other? I mean, were they friends? Were they collaborators? Were they... Well, you know, they were close collaborators. At first, they kind of both got credit for the idea. But a little later...

Darwin rocketed out his book into press. When he published his On the Origin of Species. A very popular book. Darwin got the lion's share of the credit, as I think rightly so, because he'd been working on the idea for literally for decades. Then 20 years later, Darwin dies. Meanwhile, Wallace lived until the dawn of World War I. And during that time, this is Rick's argument.

After Darwin died, Wallace kept saying over and over and over again that when it came to female choice, animals didn't have the sensory and cognitive capacity to make aesthetic judgments in nature. So these elaborate decorations and artistic behaviors could only evolve if a community, indicates information about vigor, quality, and general fitness to survive. And Rick would say that because Darwin wasn't around to argue back?

Wallace may have lost the battle over credit for the discovery of adaptation by natural selection, but he won the war over what evolutionary biology would become in the 20th century. We have inherited both the science and the culture, a flattened, dumbed down, and ideological purified version of Darwin's actual richness. Whoa, those are fighting words. Well, you see, Rick is pretty fired up about this, and he's written a book, a Evolution of Beauty,

where he argues that ever since Alfred Russell Wallace, scientists have been trying to squeeze everything they see in these male patterns, male dances, male songs, male plumages, into a single explanation, a dogmatic category called fitness, and that female choice they claim is always, always about fitness, fitness, fitness.

But Rick argues, no, you know, that is, that's a stretch. There's no way to boil down all this variety into fitness. I'm not saying that the emperor wears no clothes. I'm saying that the emperor is wearing a loincloth. And what I mean by that is that humble garment covers about the same percentage of the human body as the idea of adaptive mate choice covers all the ornaments of sexual ornaments to the world. Oh, my God.

What you just said is that most or most of what you see... Vast majority. Most of what you see in the world you think is desire of... The desire between creatures expressed in beautiful forms. Absolutely. And that... Not a fitness. Not that, oh, that she's just looking at him thinking he's strong.

He's genetically trustworthy. None of those. Just, I love him. Yeah. Yeah. So what he's saying most of the time? when you see the ornaments, that's not fitness at all. That's beautiful.

Yeah, most. That's what he says. Most. Yeah. He's big time on most. Well, how would you even know that? I mean, as a human, how would you ever even know the inner workings of another creature's mind to know enough to say what it is that it's driving them or not? I asked this very question to anathologist Kim Boswick.

Right. Isn't it impossible for you as a human being to have any idea what a lady animal wants to see? in a guy if that lady animal is a peahen, which you aren't, or a trout, which you aren't? I'm ready to answer this. I mean, here it is. I don't know what she wants now, but I know historically she's wanted exactly what you see in those males. The peahen has wanted that big old tail. She's wanted the show.

She's wanted the blue chest. She has, at some time or another, in the last, I don't know how many thousands of years, she has wanted everything you see on him, from the fancy feathers to the white skin around his eye, to the ear doesn't blue, the shaking. That's what she has wanted in the past. How do you know that? Because it's there. Seriously. Isn't there some lawyer in the room we can say, wait a second, wait a second.

What do you mean because it's there? How else did it get there? Well, how else did it get there? Well, it could have gotten there by accident? Yes. Yeah. So you just happen to have this like fine nanostructured. iridescent colors in your feather because like 42 interacting genes across five different chromosomes came together to give you iridescent blue?

No. The way you get to iridescent blue, says Kim, is you start small. You give your female a bunch of choices, which are the males and her block. So imagine a female bird surrounded by a bunch of males who are all just boring or gray or black or whatever. Then totally randomly, a male shows up who just happens to have a little bit of blue on him. and she notices. When the sun glanced off of his black plumage,

there's just a little hint of blue in that black. It's kind of a glossy, shiny blue black. And she's like, I like that. I like that. That is a little different than everybody else, and I like it. And who knows why? It could be totally random, too. But for whatever reason, she decides to mate with the blue guy.

I like that. And because she's passing on his jeans, her sons are likely going to be a little bit blue too. Her offspring are going to have those beautiful jeans. And we already know that the females chose him because he was attractive, and so she's going to have attractive sons, and her daughters are going to also find those traits attractive. And so what you get are generations and generations of females who say,

I like that. I like that. And then off it goes, you're creating, you're evolving the males to please the females. And it all starts with, I like that. But I like that. It doesn't feel to me opposite. of fitness. Like, I like that could be a desire

that is driven by instinct. I mean, couldn't, like, a Wallace person walk in and be like, yeah, she likes that because she was designed to like that. She's not thinking about the why there. She's just having a desire. But behind that desire is maybe a drive to get her

to the male that is the fittest. Like, and I, frankly, it could be the same with us, too, with people. Like, what we find sexy might have a deep logic to it. Yeah, I see that. Maybe in the end is about fitness. Okay, that's a perfectly reasonable objection.

Thank you. But what if I told you about an animal who has a fierce desire for beauty and this particular desire for beauty is so strong that fitness is out of the picture? It's another bird. It's another bird. Fixed fries, I know.

Don't hate them because they're beautiful, Chad. We'll just take a break. We'll take a break, and afterward we'll come back with a third bird. Hi, this is Sarah calling from Scarceau, New York. Radio Lab was supported in part by the Alfred P. Sloan Foundation, enhancing public understanding of science and technology in the modern world. More information about Sloan at www.org. Chad, Robert. Bethel.

Radio Lab. We're back mid-battle between beauty and fitness. Bird battle. Bird battle. And we're about to introduce our third bird. Yeah, you want me to go? Yeah, go ahead. All right, okay.

So there's a bird out there called the club-winged mannequin. And this mannequin lives in the jungles of, I forgot where she was, somewhere in the jungles. In South America. In South America, that's true. I think Columbia. Well, okay, so the club wing mannequin has a very small range in Columbia in Ecuador. Is it a big bird? No, very little.

It's a tiny bird. The males are mostly red. He's got a bright red head. Kind of an Auburn body and black and white wings with little flex of yellow underneath them. So these are small birds, lots of color. And the female can raise the babies all in her own. So she doesn't need guys except for the sexual act. Right.

He doesn't have to provide for her. He just has to attract her. So to that end, this is what our little red Romeo will do. He'll sit on a branch in the Andean jungle, and he'll wait a while until a female shows up. And then when she does... He has a courtship display, and he bounces back and forth on the purge. And while he's bouncing around...

Every so often he stops, lowers his head, sticks his butt up in the air. It's his wings all positioned, and he throws them up. Behind his back. And then he vibrates, or just shivers. He shivers his wings together. So that the only things that touch are those feathers across the back. Their tips of those funny feathers are going knock, knock, knock, knock, knock, knock, knock. They knock 39 times in a row.

And it takes about a third of a second for those 39 knocks. Their wings vibrate so fast that they make this sound. Can you make the sound that he makes? Dik, ding! Whoa! It's impossible for a human to make with their voice. Is that seriously? the sound it makes? Yeah.

Yeah. It's like a truck backing up. Exactly. Yeah. So he's not using his voice for that. It's just his wings? He's got this instrument. Yeah, it's like, it's called stridulation. So this is a cricket-winged mannequin would be a perfectly good name for this bird. In any case, something about that sound, that specific sound, excites the female.

We don't know why or when it started, but somewhere in the bird's past, a female decided she liked that. sound and so the males just started to make it. But here's a thing. In order to make that sound? Yeah, they really have paid. They have paid. Because to vibrate your wings that fast, 107 times per second, you need a rigid wing bone that you can really control. And so the club wing mannequin has done something unheard of. Their wing bones, they're wing bones went solid. It's just like a rock inside there. This is a big deal because all flying birds have hollow wing bones.

Right, so they can fly. Yeah, well, actually, even Velociraptor and T-Rex have hollow four limb bones, right? So this is a feature that predates the origin of birds and the origin of flight. But this guy has given this up in order to make these extraordinary wing songs. Well, doesn't that hurt your ability to fly? Yes. But yes, they aren't slow, heavy, unable to leap buildings in a single bound. It's the cost of doing business for a displaying male, right?

Think about that. You're in a crowded forest, lots of competitors, lots of predators trying to eat you, and you have made yourself slower, more vulnerable. And it gets worse, because the mannequins have to start this process of building these hard bones really early. like when they're very, very tiny in the embryo. Before the embryo has become either male or female. So you've got an embryo that can go either way, and they're already making the big bones,

and some of them are going to be male, but some of them are going to be female. So by choosing males with weird wing bones, because they make great songs, the female also has daughters with distorted and inferior wing bones that they will never use. Both the females and the males,

get these thick bones. So she is choosing to hear that sound and has designed him to produce that sound, but in the bargain, he comes out with heavier bones and can fly less well. And weirdly enough, she comes out with heavier bones

and can fly less well. So both of them are hurting their chances to survive for the chance to hear the beautiful tone that she wants to hear and that he wants to give her. Wait, what? Wait, so she has heavy bones too? Yeah. But she doesn't use them?

Nope. Oh. Rick saw it immediately. I was like, oh, this is weird. The females got the bumps on her bones too, and he's like, oh, decadence. I was like, what? What are you talking about decadence? He's like, the females have it, but they don't use it.

She's bearing the cost of her own choices, decadence. And this was like 20 years ago. You science people have such strange moments of ecstasy. So when he said decadence, what did he mean? So everybody in the population becomes worse off because females are so choosy and choose beauty. So from Rick's point of view, you've got a contest going on here,

two primal drives. And on one hand, there's the desire to survive. It's a rebel the fittest, right? And according to that logic, the mannequin should go for the things that make him swift and powerful and agile. But on the other hand, there's a second drive to see, or in this case, to hear something they like, something beautiful.

And in this case, that second drive is so strong that it's winning. It's pushing the birds, like, away from fitness. So we've gone through the math, and others have as well. And there is nothing, in theory, nothing to prevent this kind of process from leading to extinction. Oh, my God. Right? You've just turned, wait, you've just turned what I normally think of as Darwinian evolution

on its head. Like, we've always been taught that what these animals are doing is they're adapting as best as they can to new and changing conditions, and they're getting better. But here you say that they are so hung up on desire and beauty that they even are willing to get worse. Right. Well, you know, that's why this example is checkmate. But there are biologists.

Eminent biologist. Hello? You don't want to be sucking a lollipop or whatever you're doing there, Jerry. Like Jerry Coyne of the University of Chicago. I'll be through with it when I go in the air. Who disagree with Rick? Is it a lollipop? No, it's a cough drop.

Oh, it's a cough. So Jerry read Rick's book and is not convinced by his argument. Well, I think it's a good book. But it's not a great book. It's good because it has really great stories about mating behavior, which are accurate stories, as far as I know, and they're quite absorbing. Prima is a good writer.

The reason it's not a great book is that it's tendentious, that is it's written to promote a cause. Which is, of course, that males with beautiful ornaments are shaped by female sense of beauty, not fitness. I think that the word fitness is a huge problem, and I don't use it anymore. You can't just say that and have it accepted by scientists unless you can test it. Okay.

And that is the problem. For Jerry, when it comes to the stories that we've just heard, like the Bowerbird or the mannequin, he thinks that... More is going on here than what Richard says in his book, you know. Take the female Bowerbird's preference for Bauer as a keeper apart from males. I mean, Richard's explanation that it allows the female more time to choose that doesn't freak her out because she feels protection. That might be the right explanation, but we don't know. I mean, it could be that females have an innate preference for being sheltered because it gives them a sense of security. She, like cats.

Cats like to be in boxes, right, because they feel sheltered and they feel safe. And it could be that female bear birds are the same way. And that will lead to exactly the same situation, but with a completely different explanation. And it's not just a random aesthetic phenomenon. Or he says maybe some female bowerbirds like blue so much because blueberries are. are really good for them, and they're innately drawn to blue because of that. Or that go to the mannequin tail with that, you know, 1,500-hurt's tone. Rick says that simply delights the females, but...

Suppose that the females prefer males that have a certain frequency of wing-beating, because they were attuned to that frequency, perhaps because it indicates something in their environment that's useful to them, like the presence of a predator. Could be anything, really. Sound of some, you know, mannequin-friendly animal, or a protective animal, or maybe they call their own babies, the baby chicks.

And so they just have their nervous system innately tuned to that frequency. That's called sensory bias, and that's another theory of sexual selection. So they... Gary doesn't dispute the fact that female birds like bowers. They do. Or that they like a beautiful tone, they do.

He just thinks that there might be a reason behind their liking, and that reason could include fitness. Correct, yeah. But are you hoping, I guess, is that the right word, hoping that there might be a parasite signal involved here? Like, you don't know. You just want to keep... No, I don't know.

I mean, that's my whole point. And that's why I don't think... I don't propose my own theory of sexual selection. I'm not sure which one does account for these mannequins with the heavy bones. We just don't know. Oh, my God. This conversation we're having keeps ending up in the same place, which is we just don't know. Well, but the difference between me and Dr. Prim is I admit I don't know.

The suggestion here is that Rick is clinging to a faith in one explanation for Wallace it was fitness, for Rick its beauty, but it's still that dogmatic insistence. I just think that adaptation by natural selection is pretty boring. You know, we've been, you know, 150 years in, we've whipped that pony quite a bit. And we made a whole bunch of progress. But you know what? There's this huge world of opportunity in aesthetic evolution that has been missed. In fact, Rick would say the whole point of a sense of beauty is it can be many, many different things. It is fundamental, beauty is fundamentally subjective.

So the aesthetic model requires that we put the subjective experience, desire itself at the center of our scientific explanation. But can you even have a science that's based on science? subjective experience? I think that a science of subjective experience is not only a good idea, it's necessary to understand the natural world. Yeah. There is idiosyncrasy. Again, ornithologist Kim Bostwick. You can't take the individuals out of it. So you don't, is that science or is that just saying, okay, it really comes down to she the carp likes what that male carp has, she the worm, likes what the worm has, she the bird, likes what the bird has. And then you have a lot. And then you have a

a trillion explanations. Each one different, and depending upon the lady, a different one, so you don't, doesn't it worry you that to call beauty and desire a category of an explanation

is to not tell you very much? That doesn't worry me at all. I, I doesn't worry me at all. I, you, all of us, we are individuals. We have unique histories. And life on this planet has a unique history.

Science has a hard time dealing with unique instances. But biology is just in your face with it. There are individual females making choices. If that individual female had not made that choice, history might have been different and the species might look different. And that is true. That's just true.

In physics and in chemistry, there's this sort of conceit that what a scientist is supposed to do is take all this variety that you see in front of you and say, look, I can boil this down to a rule, which is always, always true. Yeah, which transcends. And usually it's one rule. And transce everything. So what the job of science usually is is to find some kind of oneness inside the

manyness. But now we've got nature and living things, and they have this crazy, spectacular variety. And now you've got a group of people who say, you know, maybe we shouldn't even try to explain all this with one rule or one paradigm. But, you know, I wonder if that's still science, or is it more like history? What if every species or every animal comes with its own story? That's interesting.

So it's once upon a time, and then once upon a time, and once upon a time, and once upon a time, and once upon a time, and once upon a time, and once upon a time, and once upon a time, once upon a time. Once upon a time. Once upon a time. This was reported by you, Robert Krollwich, and Bethel Hoptic. And Bethel produced the story. Thank you, Bethel. That's your thing.

And special thanks also to Jessica Yorinsky for her work on Peacocks and Michaela Gunther, for her work on hyenas. We didn't mention the peacocks and the hyenas as much of you thought, but we are very grateful to both of you. All right, well, we should say goodbye. Goodbye. Well, to our audience. To our audience. I'm not done with you. No, okay.

I'm Chad I'm Bromrod. I'm Robert Grohlidge. Thanks for listening. To play the message, press to start of message. Hi, this is Kim Boswick calling from Trumanburg, New York. Radio Lab was created by Chad Abumrod and is produced by Zorin Wheeler. Dylan Keith is our director of sound design. Susie Lechtenberg is our executive producer.

Our staff includes Simon Adler, Becca Bressler, Rachel Cusick, David Gebel, Bethel Hapta, Tracy Hunt, Matt Guilty, Robert Krollwich, Julia Longoria, Annie McEwen, Latif Nassar, Melissa O'Donnell, Kelly Prime, Sarah Kari, Ariana Wack, Pat Walters, and Molly Webster, with help from Shima Oliyae and Neil Danisha. Our fact checker is Michelle Harris, and I can verify that Michelle Harris is also cool. Bye. End of message.