[RADIOLAB INTRO]

JAD: Whose pad is this?

BETHEL HABTE: Oh, I think it's mine.

JAD: Oh my gosh, Bethel, your handwriting ...

BETHEL: Awful.

JAD: Your handwriting is not awful. It's actually very elegant.

BETHEL: Is it?

JAD: Legible, not so much, but elegant.

JAD: Jad here, this is Radiolab. So not too long ago, Robert and our producer Bethel Habte ...

JAD: Has a nice lean to it.

JAD: ... pulled me into the studio to walk me through this story that they've been working on together for quite some time.

ROBERT KRULWICH: Everybody, here's everybody?

JAD: Yes.

BETHEL: Yeah.

JAD: Here we are.

ROBERT: All right. So shall we start this?

JAD: Yes. So what are we doing? You guys are just gonna tell me this story or ...

ROBERT: I'd rather tell you a riddle.

JAD: Okay.

ROBERT: Once upon a time, birds evolved. They evolved from dinosaurs, so they were originally scaley things and the scales turned into feathers and the feathery things began to fly, we call those things birds.

JAD: Mm-hmm.

ROBERT: But they have a—I guess I'm gonna just ask this to you out of the blue, because it's a basic appendage, how many birds have penises?

JAD: Oh! Okay.

ROBERT: And by the way, before you answer, there are, like, 10,000 to 20,000 different kinds of birds by modern times. So, again, how many of those species have penises?

JAD: What percentage of currently existing birds ...

ROBERT: Of all modern bird species have ...

BETHEL: The male ones, obviously.

ROBERT: The male ones of course.

JAD: Would penises as we identify?

ROBERT: Yeah, little things that hang out ...

JAD: Ah! We don't have to talk about it! Okay.

ROBERT: Yeah, yeah. Those things.

BETHEL: This is making me so awkward.

JAD: Is this making you uncomfortable?

BETHEL: You know, I'm making this draft, I was saying the word "penis" so many times.

ROBERT: At one point, she wrote on the page, "Do you know how many times we said penises? 27 in four minutes." [laughs]

JAD: Okay, yes, 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 gonna throw out a number, 40 percent.

ROBERT: No.

JAD: No, 70 percent. Let's say 70.

ROBERT: No.

JAD: Uh, 30?

ROBERT: Lower.

JAD: [laughs] 10?

ROBERT: Lower.

JAD: Wow, five?

ROBERT: Lower.

JAD: One?

ROBERT: Three.

JAD: Three?

ROBERT: Three percent.

PATTY BRENNAN: Yeah, 97 percent of birds don't have penises.

JAD: Wow!

BETHEL: Yeah. So we learned this little fact from a scientist named Patty Brennan.

PATTY BRENNAN: The thing that's so weird about birds is precisely the fact that they lost the penis.

ROBERT: Well, you just said—you just used an interesting verb. So you say the birds lost the penises, so does that mean earlier editions of birds did have them?

PATTY BRENNAN: That's right, yeah. So penises are a widespread trait of all vertebrates, right? Except for, you know, some amphibians and fish.

ROBERT: And according to Patty, if you go back 200 million years or so, birds were like all those other creatures.

BETHEL: Yeah, basically 100 percent of them had penises.

PATTY BRENNAN: Exactly right.

ROBERT: But over time, in the vast, vast majority of birds ...

PATTY BRENNAN: The penis was then lost.

ROBERT: Now ...

JAD: But why would that be?

ROBERT: Well, that's the question.

PATTY BRENNAN: 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.

JAD: So the 97 percent of the birds that don't have a penis now, what do they have? They have a ...

ROBERT: Well, they have a kind of hole. Both birds, the males and females, have these holes and they sort of open up and then they line them up.

BETHEL: Yeah, it's called a cloaca.

JAD: Oh, they have a cloaca.

PATTY BRENNAN: They have this cloaca, and they just briefly touch their cloaca when they're mating and that's it. That's it.

ROBERT: And it works just fine. But if you're thinking about the engineering, what appendage is gonna work best for you to make babies? Penis is the one.

BETHEL: Because it gets your sperm closer to female eggs.

JAD: Oh.

BETHEL: So for all of these penises to just vanish, like, she says, "Evolutionarily, that just doesn't make any sense." Why would you lose a thing that's so useful?

PATTY BRENNAN: So for there to be selection for the penis to go away, there's gotta be a very important reason.

JAD: What's the reason?

BETHEL: Well, there's a few possibilities. Number one ...

PATTY BRENNAN: People have speculated, for example, that there 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, there could be potentially a very easy exchange of sexually-transmitted diseases.

BETHEL: Because you're, like, digging the germs deeper, I guess.

PATTY BRENNAN: Exactly. Yeah, yeah, yeah.

BETHEL: 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.

PATTY BRENNAN: That could be.

BETHEL: But so far nobody's found the link between penises and STDs.

PATTY BRENNAN: So then the other possibility that's really intriguing actually, is that maybe it's because penises are heavy, and birds started flying, and getting rid of the penis would be an easy thing for lowering your body weight.

ROBERT: Maybe they lost them so they could fly further.

PATTY BRENNAN: 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.

BETHEL: They're in the three percent.

PATTY BRENNAN: And sometimes they have penises that are bigger than their own bodies, so ...

ROBERT: [laughs] They do?

BETHEL: Oh my God!

PATTY BRENNAN: They do. Yes. [laughs]

ROBERT: You mean you watch a penis go by with wings kind of?

PATTY BRENNAN: [laughs] Pretty much.

ROBERT: Oh my God!

PATTY BRENNAN: Yeah, so I think the record is a male that had a 43-centimeter-long penis and this is a male who was only about 40 centimeters long himself.

ROBERT: So apparently you can have a pretty large penis and fly just fine, but oddly enough, the ducks are also sort of the key in the third theory for the disappearance of the penis.

PATTY BRENNAN: Oh yeah, so I was gonna say my favorite is this idea that actually it had to do with female choice against males that control reproduction.

BETHEL: To explain, Patty actually thinks that the original bird penises ...

ROBERT: Back when they had penises.

BETHEL: Yeah, might have been a lot like the modern day duck penis, which is essentially a weapon.

PATTY BRENNAN: And so one of the things that we learn 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 everts his penis and ejaculates in a third of a second.

ROBERT: Basically a pistol penis? Like, peew!

PATTY BRENNAN: Exactly. Yeah, yeah. It goes bajoing. Yes.

ROBERT: Wow!

PATTY BRENNAN: 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 gonna go poof, you know? Push right through. And so as you can imagine that's not—you know, that's not something that's necessarily desirable for females. Oftentimes females will be struggling, right? They're trying to get away from these males that are trying to forcefully copulate.

BETHEL: 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.

PATTY BRENNAN: Right. So if females are selecting males that are less violent, less sexually violent, that that might lead to the disappearance of the penis.

ROBERT: What I think you just said is over time, because the ladies were—the ladies were discomforted, the gentlemen changed and lost their penises.

BETHEL: Yeah. You got it.

JAD: She's saying that the females essentially castrated the males?

ROBERT: Well, this is a slower process than that. [laughs]

JAD: [laughs] I mean, over time.

ROBERT: Over time. Castration over time.

BETHEL: Yeah.

ROBERT: Yes, I suppose.

BETHEL: [laughs]

ROBERT: Now what made—what makes you—what evidence is there for such a thing?

PATTY BRENNAN: 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—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—that I think makes a lot of sense given what we know about the way these penises work now. But we can only speculate.

JAD: I like this idea.

ROBERT: Good.

JAD: But is this just a one off? I mean, what about gorillas and moose who fight and clash their horns? I mean, there are so many species where it just seems like the females have zero choice.

BETHEL: So I know there are a lot of cases like that, bedbugs are especially horrifying.

ROBERT: Horrible.

BETHEL: Google it.

JAD: Yeah, don't even talk about bedbugs.

BETHEL: 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.

ROBERT: 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.

JAD: Do they have evidence for this idea? Because I gotta say that you haven't yet convinced me of the first thing they said, that females have evolved the penises away. Like, I still haven't ...

ROBERT: Well, because that was a guess. Patty said it was a guess.

JAD: She said she's guessing, yeah.

ROBERT: Fair enough. I will introduce you to a bird called a bowerbird that I think will—well, it speaks for itself in these regards.

BETHEL: And it's also—it's penis-less. [laughs]

GAIL PATRICELLI: They are really cool birds. They have beautiful plumage. The satin bowerbird is a beautiful iridescent blue with violet blue eyes.

BETHEL: This is Gail.

GAIL PATRICELLI: Gail Patricelli, and I'm a professor of evolution at—and ecology at UC-Davis. Do I wanna say that again without stuttering on "and?"

BETHEL: No, no. That's fine.

GAIL PATRICELLI: [laughs]

BETHEL: Anyway, so the bowerbird ...

GAIL PATRICELLI: What makes them most amazing is that they build bowers.

BETHEL: So a bower, these things the birds build, it's basically a structure made out of sticks which can be up to three feet tall.

JAD: Three feet tall?

BETHEL: Yeah. This tiny little bird making this huge ...

ROBERT: You could put a five year old in it, in some of these things.

JAD: Wow.

BETHEL: Yeah. And it looks like a nest.

RICHARD PRUM: But it's really a kind of seduction theater with one seat. And that—and that's for her.

ROBERT: This is Richard Prum of Yale University. He's a biologist there. And he says that on and around this bower ...

RICHARD PRUM: The male will array a whole bunch of found objects.

BETHEL: Precious objects.

RICHARD PRUM: Beautiful things.

GAIL PATRICELLI: Parrot feathers and berries and flowers and leaves.

BETHEL: Stuff that the bird gathers from the forest. So these structures can be very ornamented and elaborate.

ROBERT: And every bowerbird species has its own, like, style.

RICHARD PRUM: 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.

BETHEL: And the male bowerbird basically dedicates his whole life learning how to build these structures. Like, take the satin bowerbird.

GAIL PATRICELLI: 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.

ROBERT: And eventually, once a bowerbird figures out how to make a really good structure ...

[ARCHIVE CLIP, David Attenborough: A female has arrived.]

ROBERT: ... females show up.

GAIL PATRICELLI: 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?

[ARCHIVE CLIP, David Attenborough: She seems interested.]

ROBERT: And if she likes what she sees, she'll enter the bower.

BETHEL: Now this is where things get interesting, because the bower has a very particular and purposeful architecture.

RICHARD PRUM: So one of the classic bower designs is called an avenue bower. So it's two parallel walls of sticks that are close to one another, and the female sits between them.

BETHEL: There are different variations on this basic design, but ...

GAIL PATRICELLI: In all cases, the female is in a protected position.

BETHEL: ... there's always some kind of barrier or wall between her and the male.

GAIL PATRICELLI: So if 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.

ROBERT: Even as he's trying to win her attention completely, he's built a building that keeps her at a distance?

RICHARD PRUM: Absolutely. The bower is like insurance against date rape for the female. It allows the female to observe him at an intimately close distance for as long as she likes while still maintaining her freedom of choice.

BETHEL: 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 ...

[ARCHIVE CLIP, David Attenborough: Time to begin the show.]

GAIL PATRICELLI: So he'll start out with his own—his own displays.

RICHARD PRUM: Many of them make very loud, electronical sounds.

GAIL PATRICELLI: Buzzing and whirring sounds.

RICHARD PRUM: [bird sounds] And they do imitations of kookaburra, you know [bird sounds].

BETHEL: Sometimes they imitate [bird sounds] cockatoos. Then, along with singing, they dance.

GAIL PATRICELLI: They puff up and they run vigorously back and forth right in front of the female, and she's standing between the walls of the bower ...

BETHEL: 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 ...

[ARCHIVE CLIP, David Attenborough: No. Not good enough.]

BETHEL: ... up and fly away all of a sudden.

[ARCHIVE CLIP, David Attenborough: For the female, the moment has gone.]

ROBERT: Now what's particularly interesting here is that Gail has done studies that show when the males pay very close attention to the female ...

BETHEL: 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.

GAIL PATRICELLI: The males that respond the most to those signals are the most successful in mating.

ROBERT: 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.

JAD: Huh!

BETHEL: 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—if you watch 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. [laughs]

JAD: Oh, like a matador, kind of?

BETHEL: 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.

JAD: [laughs]

ROBERT: Like, he has a rose in his mouth.

BETHEL: [laughs]

JAD: That's hilarious. She's like, "You know, it's all right, but ..."

BETHEL: "This is good, but, like ..."

JAD: "It'd be so much better with this."

ROBERT: It just seems to be all about her.

JAD: I see what you mean in this case. Yeah, the females are definitely driving—driving the bus here.

ROBERT: And when you start to really think about the implications of this, about it being all about her, that can lead you to a fairly deep rethink of the very basic rules of how evolution works.

JAD: Really? Meaning what?

ROBERT: 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."

BETHEL: Like survival of the fittest.

JAD: Right.

ROBERT: 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, shells, shells, shells, shells. And this one likes green leaves, but they have to be right side up and never right but, you know, upside down. Are these fitness signals or is this more like art? Maybe she just likes blue, or she just likes shells.

JAD: Wait, you're saying that these birds have evolved based on whims and tastes?

ROBERT: Well, Rick, and there's other scientists like him, say ...

RICHARD PRUM: Absolutely.

ROBERT: Yes. It's about beauty.

RICHARD PRUM: I'm really focusing in on aesthetic choices, choices that are based on what it is the animal likes.

JAD: Wait, 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.

RICHARD PRUM: Well ...

ROBERT: Since you dropped the name ...

RICHARD PRUM: ... I propose that my view is the legitimately, authentically Darwinian view.

JAD: Darwin, he had an idea about beauty?

ROBERT: Oh yes. He—he actually ...

BETHEL: Do you want to read the quote?

ROBERT: Did I bring it here?

BETHEL: Yeah, you brought it. Yeah.

JAD: Okay. Page 397, Descent of Man. "Stripes and marks and ornamental appendages have all been indirectly gained through the influence of love?" Huh. "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.

ROBERT: Yeah. And choice.

JAD: Yeah, that is definitely not what I learned when I learned about Darwin.

RICHARD PRUM: So it's over 130 years later and I'm still pissed.

ROBERT: He thinks there was some kind of plot to reduce Darwin's idea into something smaller and eventually eliminated entirely.

RICHARD PRUM: I would like to go historical. Let's go about what Darwin said.

ROBERT: Okay.

RICHARD PRUM: Let's go with what Wallace said. And then let's go to the 20th century, and where we got so screwed up.

ROBERT: Okay.

ROBERT: 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 Russel Wallace. Kind of skinny and scrappy and self-taught. 14 years younger than Charles Darwin. But Wallace also ...

RICHARD PRUM: Went around the world collecting specimens.

ROBERT: And he also came up with a theory of natural selection. Independently.

BETHEL: What was their relationship to each other? I mean, did they—were they friends, were they collaborators, were they ...

RICHARD PRUM: Well, you know, they were close collaborators.

ROBERT: At first, they kind of both got credit for the idea, but a little later ...

RICHARD PRUM: Darwin rocketed out his book into press.

ROBERT: When he published his On The Origin of Species, a very popular book.

RICHARD PRUM: 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.

ROBERT: Then 20 years later Darwin dies. Meanwhile, Wallace ...

RICHARD PRUM: Lived until the dawn of World War I.

ROBERT: 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 ...

RICHARD PRUM: Animals didn't have the sensory and cognitive capacity to make aesthetic judgments in nature.

ROBERT: So these elaborate decorations and be—artistic behaviors ...

RICHARD PRUM: Could only evolve if it communicates information about vigor, quality and general fitness to survive.

BETHEL: And Rick would say that, because Darwin wasn't around to argue back ...

RICHARD PRUM: Wallace may have lost the—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 of flattened, dumbed down and ideologically purified version of Darwin's actual richness.

JAD: Whoa, those are—those are fighting words!

ROBERT: Well, you see Rick is pretty fired up about this. And he's written a book, Evolution of Beauty, where he argues that ever since Alfred Russel 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. No, that is—that's a stretch. There's no way to boil down all this variety into fitness.

RICHARD PRUM: 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 in the world.

ROBERT: Oh my God! What you just said is that most, or most of what you see ...

RICHARD PRUM: Vast majority.

ROBERT: Most of what you see in the world, you think is—is desire of—the desire between creatures expressed in beautiful forms.

RICHARD PRUM: Absolutely. And ...

ROBERT: Not of fitness. Not that oh, she's just looking at him thinking, "He's strong. He's genetically trustworthy." None of those. Just, "I love him!"

RICHARD PRUM: Yeah.

JAD: Yeah, so he's saying most—most of the time when you see the ornaments, that's not fitness at all, that's beauty?

BETHEL: Yeah, most.

ROBERT: That's what he says.

JAD: Most.

BETHEL: Yeah.

ROBERT: He's big time on most.

JAD: 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's driving them or not?

ROBERT: I asked this very—no, I asked this very question to ornithologist Kim Bostwick.

KIM BOSTWICK: Right.

ROBERT: 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?

KIM BOSTWICK: Oh, yeah. I'm ready to answer this.

ROBERT: Okay.

KIM BOSTWICK: 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 ol' 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 iridescent blue, the shaking, that's what she has wanted in the past.

ROBERT: How do you know that?

KIM BOSTWICK: Because it's there. Seriously.

ROBERT: Isn't there some lawyer in the room that can say, "Wait a second, wait a second!" Is that—what do you mean, because it's there?

KIM BOSTWICK: How else did it get there? Well, how else did it get there?

ROBERT: Well, it could've gotten there by accident.

KIM BOSTWICK: By chance?

ROBERT: Yes.

KIM BOSTWICK: Yeah, so, you just happen to have this, like, fine, nano-structured, iridescent colors in your feather because, like, 42 interacting genes across five different chromosomes came together to give you iridescent blue? No.

BETHEL: The way you get to iridescent blue, says Kim, is you start small.

KIM BOSTWICK: You give your female a bunch of choices, which are the males in her block.

BETHEL: So imagine a female 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.

KIM BOSTWICK: When the sun glints 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, "Mmm. I like that. I like that. That is a little different than everybody else and I like it."

BETHEL: And who knows why, it could be totally random too, but for whatever reason she decides to mate with the blue guy.

KIM BOSTWICK: "Mmm. I like that."

BETHEL: And because she's passing on his genes, her sons are likely gonna be a little bit blue, too.

KIM BOSTWICK: Her offspring are gonna have those beautiful genes, and we already know that the females chose him because he was attractive, and so she's gonna have attractive sons. And her daughters are gonna also find those traits attractive.

BETHEL: And so what you get generations and generations of females who say ...

KIM BOSTWICK: "Mmm, I like that."

[ARCHIVE CLIP: I like that. I like that. I like that. I like that.]

KIM BOSTWICK: And then off it goes. You're—you're creating—you're evolving the males to please the females.

BETHEL: And it all starts with ...

KIM BOSTWICK: "I like that."

JAD: But "I like that" 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—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, the—what we find sexy might have a deep logic to it.

ROBERT: A hidden—a hidden logic.

BETHEL: Yeah, I see that.

JAD: A deep, hidden logic to it that maybe in the end is about fitness.

ROBERT: Okay, that's a perfectly reasonable objection.

JAD: Thank you.

ROBERT: 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?

JAD: It's another bird?

ROBERT: It's another bird.

BETHEL: Big surprise, I know. [laughs]

ROBERT: [laughs]

BETHEL: Don't hate them because they're beautiful, Jad. Geez. We'll just take a break. We'll take a break, and afterward we'll come back with a third bird.

[LISTENER: Hi, this is Sarah calling from Scarsdale, New York. Radiolab is 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.sloan.org.]

JAD: Jad.

ROBERT: Robert.

BETHEL: Bethel.

JAD: Radiolab.

ROBERT: We're back, mid-battle between beauty and fitness.

JAD: Bird battle?

ROBERT: Bird battle. And we're about to introduce our third bird.

BETHEL: Yeah, you want me to go?

ROBERT: Yeah. Go ahead. Go.

BETHEL: All right. Okay, so there's a bird out there called the club-winged manakin. And this manakin lives in the jungles of—I forgot where she was. Somewhere in the jungles. [laughs]

ROBERT: South America.

BETHEL: In South America. I think Colombia.

KIM BOSTWICK: Well, okay. So, the—the club-winged manakin has a very small range in Colombia and Ecuador.

JAD: Is it a big bird, small bird?

ROBERT: No, very little.

BETHEL: It's a tiny bird. The males ...

KIM BOSTWICK: The males are mostly red.

RICHARD PRUM: He's got a bright red head.

BETHEL: Kind of an auburn body, and black and white wings with little flecks of yellow underneath them. So these are small birds, lots of color. And ...

RICHARD PRUM: The female can raise the babies all on her own.

ROBERT: So she doesn't need guys except for the sexual act.

RICHARD PRUM: Right.

BETHEL: 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 awhile until a female shows up.

[birds chirping]

BETHEL: And then when she does ...

KIM BOSTWICK: He has a courtship display. And he bounces back and forth on the perch. And while he's bouncing around ...

BETHEL: Every so often he stops, lowers his head, sticks his butt up in the air.

KIM BOSTWICK: Gets his wings all positioned, and he throws them up.

BETHEL: Behind his back.

KIM BOSTWICK: And then, he's—he vibrates. Or just shivers. He shivers his wings together so that the only things that touch are those feathers across the back. The tips of those funny feathers are going knock-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.

BETHEL: Their wings vibrate so fast that they make this sound.

ROBERT: Can you make a—can you make the sound that ...

BETHEL: Tick, tick, tick ...

[bird flipping]

JAD: Wow!

BETHEL: It's impossible for a human to make with their voice.

[bird flipping]

JAD: Is that seriously the sound it makes?

BETHEL: Yeah!

ROBERT: Yeah.

JAD: It's like a truck backing up.

ROBERT: Exactly. Yeah.

JAD: So he's not using his voice for that? It's just his wings?

KIM BOSTWICK: He's got this instrument.

[bird flipping]

RICHARD PRUM: Yeah. It's called stridulation. So this is a cricket-winged manakin would be a perfectly good name for this bird.

[bird flipping]

BETHEL: 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 the thing: in order to make that sound?

KIM BOSTWICK: Yeah, they really have paid. They have paid.

BETHEL: Because to vibrate your wings that fast—107 times per second—you need a rigid wing bone that you can really control.

[bird flipping]

BETHEL: And so the club-winged manakin has done something unheard of: their wing bones went solid.

[clunk]

KIM BOSTWICK: It's just like a rock inside there.

RICHARD PRUM: This is a big deal because all flying birds have hollow wing bones.

ROBERT: Right. So they can fly, so they're light.

RICHARD PRUM: Yeah. Well actually, even velociraptor and t-rex have hollow forelimb 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.

ROBERT: Well, doesn't that hurt their ability to fly?

KIM BOSTWICK: Yes. Yes. They are slow, heavy, unable to leap buildings in a single bound.

RICHARD PRUM: It's the cost of doing business for a—a displaying male, right?

BETHEL: 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 manakins have to start this process of building these hard bones really early, like when they're very, very tiny in the embryo.

RICHARD PRUM: Before the embryo has become either male or female.

BETHEL: So you've got an embryo that can go either way, and they're already making the big bones. And some of them are gonna be male, but some of them are gonna be female.

RICHARD PRUM: 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.

ROBERT: 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 that he wants to give her.

JAD: Wait, what? Wait, so she has heavy bones too?

ROBERT: Yeah

BETHEL: Yep.

JAD: But she doesn't use them?

BETHEL: Nope.

ROBERT: Nope. Nope.

KIM BOSTWICK: Rick saw it immediately. Like, I was like, "Oh this is weird. The female's got the bumps on her bones too," and he's like, "[gasps] Decadence!" And 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. [laughs]

ROBERT: You science people have such strange moments of ecstasy.

KIM BOSTWICK: Oh, yes.

ROBERT: So when he said "Decadence!" what did he mean?

RICHARD PRUM: So everybody in the population becomes worse off because females are so choosy and choose beauty.

BETHEL: 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. Survival of the fittest, right? And according to that logic, the manakin 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.

RICHARD PRUM: So—so we've gone—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.

ROBERT: Oh my God!

RICHARD PRUM: Right?

ROBERT: You just—wait, you've just turned what I normally think of 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.

RICHARD PRUM: Right. Well, you know, that's why this example is checkmate.

BETHEL: But there are biologists ...

ROBERT: Eminent biologists.

JERRY COYNE: Hello?

ROBERT: You don't want to be sucking a lollipop or whatever you're doing there, Jerry.

BETHEL: ... like Jerry Coyne of the University of Chicago ...

JERRY COYNE: I'm not—I'll be through with it when I go on the air.

BETHEL: ... who disagree with Rick.

BETHEL: What is it? Is it a lollipop or ...

JERRY COYNE: No, it's a cough drop.

ROBERT: Oh, it's a cough drop. Okay.

ROBERT: So Jerry read Rick's book, and was not—not convinced by his argument.

JERRY COYNE: 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. Prum 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.

BETHEL: Which is, of course, that males with beautiful ornaments are shaped by female sense of beauty, not fitness.

RICHARD PRUM: I think that the word "fitness" is a huge problem. And I don't use it anymore.

JERRY COYNE: That—you can't just say that and have it accepted by scientists unless you can test it, okay? And that is the problem ...

ROBERT: For Jerry, when it comes to the stories that we've just heard, like the bowerbird or the manakin, he thinks that ...

JERRY COYNE: More is going on here than what Richard says in his book, you know?

ROBERT: Take the female bowerbird's preference for bowers that keep her apart from males.

JERRY COYNE: I mean, Richard's explanation that it allows the female more time to choose, it doesn't freak her out because she feels protected, 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 bowerbirds 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.

BETHEL: Or, he says, maybe some female bowerbirds like blue so much because blueberries are really good for them, and they're innately drawn to blue because of that.

ROBERT: Or go to the manakin tale with that, you know, 1,500-hertz tone. Rick says that simply delights the females, but ...

JERRY COYNE: 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.

ROBERT: It could be anything, really. The sound of some, you know, manakin-friendly animal or a protective animal, or maybe the call of their own babies, the baby chicks.

JERRY COYNE: 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 ...

ROBERT: Jerry 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.

JERRY COYNE: Correct, yeah. I mean ...

ROBERT: But are you—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 ...

JERRY COYNE: 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 is—does account for these manakins with the heavy bones. We just don't know.

ROBERT: Oh my God! This—this conversation we're having keeps ending up in the same place, which is we just don't know.

JERRY COYNE: Well, the difference between me and Dr. Prum is I admit I don't know. [laughs]

ROBERT: [laughs]

ROBERT: The suggestion here is that Rick is clinging to a faith in one explanation. For Wallace it was fitness, for Rick it's beauty, but it's still that dogmatic insistence.

RICHARD PRUM: I just think that adaptation by natural selection is—is pretty boring.

ROBERT: [laughs]

RICHARD PRUM: You know? You know, 150 years in, we've—we've whipped that pony quite a bit, and we've made a whole bunch of progress. But you know what? There's this huge world of opportunity in aesthetic evolution that—that has been missed.

ROBERT: In fact, Rick would say, the whole point of a sense of beauty is that it can be many, many different things. It is funda—beauty is fundamentally subjective.

RICHARD PRUM: So the aesthetic model requires that we put the subjective experience—desire itself—at the center of our—of our scientific explanation.

JAD: Can you even have a science that's based on subjective experience?

RICHARD PRUM: I think that—that a science of subjective experience is not only a good idea, it's necessary to understand the natural world.

KIM BOSTWICK: Yeah. There is idiosyncrasy.

BETHEL: Again, ornithologist Kim Bostwick.

KIM BOSTWICK: You can't take the individuals out of it.

ROBERT: So, you don't—is that science, or is that just—it's 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 trillion explanations, each one different, and depending upon the lady a different one, so you don't—does it worry you that to call beauty and desire a category, an explanation is to not tell you very much?

KIM BOSTWICK: That doesn't worry me at all. I—that 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's 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.

ROBERT: 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 true."

JAD: Yeah, which transcends ...

ROBERT: And usually it's one rule. And transcends ...

JAD: Yeah. Transcends everything.

ROBERT: 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—if that's still science, or is it more like history?

JAD: Hmm.

ROBERT: What if every species or every animal comes with its own story?

JAD: Oh, that's interesting.

ROBERT: So it's once upon a time, and then a once upon a time, and a once upon a time, and a once upon a time, and a once upon a time and a once upon a time ...

JAD: This was reported by you ...

ROBERT: Yeah.

JAD: Robert Krulwich. And Bethel Habte. And Bethel produced this story. Thank you, Bethel.

BETHEL: Sure thing.

ROBERT: And special thanks also to Jessica Yurinsky for her work on peacocks and Micaela Gunther for her work on hyenas. We didn't mention the peacocks and the hyenas as much as we thought but we are very grateful to both of you.

JAD: All right, well we should say goodbye.

ROBERT: Goodbye.

JAD: Well, to ...

ROBERT: To our audience.

JAD: To our audience.

ROBERT: [laughs]

JAD: I'm—I'm not done with you.

ROBERT: No, okay.

JAD: I'm Jad Abumrad.

ROBERT: I'm Robert Krulwich.

JAD: Thanks for listening.

[ANSWERING MACHINE: To play the message, press 2. Start of message.]

[KIM BOSTWICK: Hi, this is Kim Bostwick calling from Trumansburg, New York. Radiolab was created by Jad Abumrad and is produced by Soren Wheeler. Dylan Keefe is our director of sound design. Suzie Lechtenberg is our executive producer. Our staff includes Simon Adler, Becca Bressler, Rachael Cusick, David Gebel, Bethel Habte, Tracie Hunte, Matt Kielty, Robert Krulwich, Julia Longoria, Annie McEwen, Latif Nasser, Malissa O'Donnell, Kelly Prime, Sarah Qari, Arianna Wack, Pat Walters and Molly Webster. With help from Shima Oliaee and Neel Danesha. Our fact-checker is Michelle Harris. And I can verify that Michelle Harris is also cool. Thank you. Bye.]

[ANSWERING MACHINE: End of message.]

 

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