Radiolab on sexual selection in birds

Here’s the latest Radiolab podcast, this time about sexual selection in birds and about Richard Prum’s revival of the idea of “runaway sexual selection,” which he calls the “beauty happens” theory. (It’s in his book, The Evolution of Beauty: How Darwin’s Forgotten Theory Shapes the Animal World—and Us.) I’ve written about Prum’s book before, and about my criticisms of his ideas—or rather, how he presents other people’s ideas—so I won’t go into that here.

I was interviewed by the Radiolab hosts last summer about sexual selection, but the show has just appeared today (click on screenshot below and then on the “listen” button to hear the 45-minute podcast). Note that the show claims to “present another way of looking at evolution.” One could construe “another way of looking at evolution”  as simply the widely accepted view that sexual selection (rather than “survival of the fittest”) explains sexual dimorphism, or, alternatively, as Prum’s view that runaway sexual selection based on “random” female aesthetic preference is the best explanation for sexual dimorphism of color and behavior instead of “good genes” models positing that such traits indicate a male’s genetic quality.

When I talked to the hosts last summer, I got the idea that they had bought into Prum’s idea of runaway sexual selection as the best explanation of sexual selection, although, of course, there are other models, as described in the review of Prum’s book in Evolution by Gail Patricelli, Eileen Hebets, and Tamra Mendelson (if you’ve read Prum’s book, you must read that review).

It turns out that this show is not entirely—or even largely—about runaway sexual selection, though that process figures heavily in the last half. Much of the show is simply about the wonders of sexual selection and the traits it creates, and features interviews with scientists working on duck penises (the show begins with a discussion of that issue, which is of course a way to attract ears) and on bowerbirds (Patricelli), and it’s not bad.

The discussion of sexual selection and Prum’s “beauty happens” model begins about halfway in, with Prum calling evolutionists’ acceptance of “good genes” models, in which male traits indicate their genetic fitness, a “flattened, dumb down and ideologically purified version of Darwin’s actual richness.” Well, that’s grossly unfair, as all of us recognize that there are a variety of models for how sexual selection works, with Prum’s “runaway” model being just one of them. (Behavioral ecologists tend to concentrate more on good genes, though.)

But, as I said, there are more than just the runaway model and “good genes” models. There are, for instance, “sensory bias” models, in which female preference is not a random phenomenon that gives the female “aesthetic” preferences, but that such preferences themselves are a product of evolution. Female may prefer certain traits or behaviors of males because (as I say in the show), those preferences are either a byproduct of evolution on their sensory system, or a direct result of selection. (Females may be attuned to some sounds more than others, for instance, because those sounds give them useful information about their environment.)  And if that’s the case, then there may be natural selection operating on female preference by itself.

And if female preferences are subject to this kind of selection, Prum’s “beauty happens” model runs into trouble, for it assumes there are no selective constraint on female preference. (This is taken up in the Patricelli et al. review). If such selection occurs, the runaway often doesn’t work.

Further complicating attempts to distinguish the models is the fact that they can work together. The paper below, for instance, shows that in many cases—at least according to theory—runaway sexual selection can create a situation in which females are also choosing males with good genes, so experiments to distinguish the runaway vs. the good-genes model for the origin of sexual selection would be hard or impossible. (Click on screenshot to go to the paper.)

When I talked to Krulwich et al. in our 90-minute conversation (they managed to insert in the podcast the noises of me sucking on a coughdrop before the interview began!), I had two aims:

1.) To point out that Prum’s “beauty happens” model was not NOT a “null model” of sexual selection that should be assumed to be true in the absence of other information. Further, I wanted to point out that there were problems with this model itself, as it makes assumptions that may not be true (i.e., that there’s no direct selection on female preference itself). While I think the runaway model is certainly plausible, and must have played some role in the evolution of male traits and female preferences, there are other plausible models as well.

2.) To point out that hard data on which model explains a given case of sexual selection are sorely lacking. It’s hard to distinguish the various models, especially because selection happened in the past and because the models can operate together. To assert, as Prum does, that we know one model explains nearly all sexual dimorphism for ornaments and calls, is to make an unwarranted claim. It’s not that we know Prum is wrong; it’s that we don’t know much about how any of these systems evolved.

How did I do? Well, my bit begins at about 35:30; you tell me. I was surprised that the show let some of my more critical remarks about the book appear. But I think it’s good that the public knows how scientists can disagree on matters where there is no dispositive data.

In the end, Krulwich goes into a soliloquy in which he seems disappointed that we don’t know the answer, and almost depressed because future research may show that different models may explain different cases of sexual dimorphism. This would mean that we don’t have a “rule” for how sexual selection works, but a series of anecdotes that give us statements about the relative frequencies of different processes.

So be it: this is evolution, not physics, and evolution works in multifarious ways. I had a few pithy statements about this issue in my phone interview, but, sadly, these didn’t make it onto the show.

As a whole, I’m not sure how well the show hangs together. I can’t listen to it as if I were a nonscientist hearing about this for the first time, so give your take below. I think the Radiolab folks will be reading this, so be civil but also be honest.




  1. John Harshman
    Posted February 8, 2019 at 9:15 am | Permalink

    One thing I don’t like about Prum’s position (not forgetting that he’s a great guy and a great biologist) is that he puts a line between sexual selection and natural selection and says they’re completely different things. But of course sexual selection is just a subset of natural selection.

    The “good genes” model is also a subset of the “good contribution” model. Parents can have more to offer than genes. For example, a parent in good condition, regardless of the reasons, can provide better parental care, so a signal of general health in a male can be advantageous for a female to recognize in species where males provide care.

    It’s interesting to me that in a large subset of bird species, males and females are equally colorful, suggesting that sexual selection is operating on both sexes in a similar way.

    • Posted February 8, 2019 at 11:31 am | Permalink

      I’ve noticed that when both sexes are equally colorful, the birds tend to be species that mate for life. Not sure why this is.

      • Liz
        Posted February 8, 2019 at 11:35 am | Permalink

        This is also interesting.

  2. Liz
    Posted February 8, 2019 at 9:41 am | Permalink

    “…those preferences are either a byproduct of evolution on their sensory system, or a direct result of selection.”

    This is interesting.

    Is there a list of all of the different models?

  3. pablo
    Posted February 8, 2019 at 10:07 am | Permalink

    I used to be a huge fan of Radiolab. I few years ago they did a story on the alleged Soviet use of chemical weapons in Laos. They found no evidence for it but a natural phenomena that explained the eyewitness accounts. The daughter of one of the alleged victims of the chemical attack accused Radiolab of racism, and of erasing the lived experiences of victims. It was maybe the first time I had seen that regressive tactic in operation. The two hosts of Radiolab stood by their story. Even though the show has the same hosts, I very much doubt that if this were to happen today, that they would stand by their story. Given the show’s PC bent it has displayed over the last two years I fear they would retract their story and make multiple obsequious apologies.

    • TD2000
      Posted February 8, 2019 at 12:42 pm | Permalink

      I too stopped listening to Radiolab a few years ago. Aside from its annoying SJW bias and cutesy pop science approach, it has a tendency toward juvenile contrarianism — like the Slate of radio.

      The worst example was an entire show defending big-game hunting in Africa. It was so deplorably one-sided that I haven’t listened to it since.

  4. aljones909
    Posted February 8, 2019 at 1:32 pm | Permalink

    Another “Beauty Puzzle”. Why do humans find the members of most other species more beautiful than humans? Is it a bias because we are hyper critical of the appearance of other humans? Or are we just ugly, lumbering naked apes (not all).

    • Michael Fisher
      Posted February 8, 2019 at 2:45 pm | Permalink

      “…Why do humans find the members of most other species more beautiful than humans?”

      Do we? How do you know this? And are you referring to just fauna or flora too & just the fluffy mammals & avians?

      Most other species are hidden to us by virtue of locale &/or small size & they’re pretty unlovable to look at! 🙂

      • aljones909
        Posted February 8, 2019 at 5:01 pm | Permalink

        How do I know? I’ve never seen an ugly squirrel, wolf, deer or rat. But go out on the street and look around….

        You mentioned fluffiness. That’s my point. Fur and feathers are more aesthetically pleasing.

        • Michael Fisher
          Posted February 8, 2019 at 5:22 pm | Permalink

          Well then it seems you find affinity most with organisms only a few twigs away from you in the tree of life & not actually “most other species”. The fur & feather brigade represent only 0.17% by number of species over number of all species. 🙂

          15k fluffy/8,700k all species.

  5. Christopher
    Posted February 8, 2019 at 2:15 pm | Permalink

    I’m listening to this now. I’m having trouble understanding their claim that somehow seeing sexual selection from the female POV, that females choose mates based on sometimes seemingly bizarre reasons, is somehow a novel, revolutionary way to see evolution in general and sexual selection specifically. What am I missing? Why is female choice, whatever it might be, not an sign of fitness? Why is having a male go through weird behavioral patterns, or develop unwieldy ornamintations not a “proof” of fitness? Where’s the revolution here?

    • Posted February 8, 2019 at 3:15 pm | Permalink

      Of course it is a sign of fitness. Why do they claim that females liking males with anti-fitness genes will make the anti-fitness genes take over the gene pool? In my opinion, these females will just see their own genes go down the drain, tied to the bad male genes like in a suicide pact.

      • Christopher
        Posted February 8, 2019 at 4:32 pm | Permalink

        Exactly. I was thinking maybe I was misunderstanding this argument. I always have to assume I’ve made a mistake in understanding the nuances of evolutionary biology, being a history major who probably isn’t intelligent enough to be a biologist.

  6. Posted February 8, 2019 at 3:03 pm | Permalink

    Highly decorative males are on the whole, cads, love ’em and leave ’em. No male parental investment beyond supplying a quantity of genes. I would say a very strong argument towards female selection for good genes. Energy and time spent on raising weak, sickly and unlikely future prospects for grandchildren is not something NS would stand for. The runnaway sexual selection hypothisis also stands, simply, once it was established by female preference that it was effective and true there was no stopping the behaviour. An intra species ‘arms race’ for a better conditioned and prepared male was prefered, sexual selection was entrenched.

    • Posted February 9, 2019 at 4:17 pm | Permalink

      I think you’re saying that runaway sexual selection IS an example of “good genes”. I agree.

      What if a female peacock said to herself, “All these other females are crazy to prefer males with such long tails. I don’t want my boys to have long tails, it might get them killed!” So she chooses an ugly (by peacock standards) male.

      Then her male chicks are also ugly, they don’t reproduce, and her genes vanish from the gene pool. Voila! Runaway sexual selection for the win.

      • Posted February 11, 2019 at 3:39 pm | Permalink

        What i am saying is, NS must have ‘set’ up the initial behaviour before SS commandeered the proccess. The preference of females forasthetically, good genes, robustness etc. meld and the resistance from males, as in, the energy/ time, costs spent growing and maintaining appenages as the runaway (sexual) selection. Males are pushed to the bounderies of what is possible by SS and still survive and propagate. These males are non parental investment ‘cads’ and SS keeps a female/ male equilibrium when the costs are on the table.

  7. danfromm
    Posted February 8, 2019 at 3:30 pm | Permalink

    Interesting. I’ve always wondered how mate selection works in organisms that broadcast gametes. Parallel to that, why some of them, e.g., some, not all, redd spawning fishes are quite sexually dimorphic, at least in breeding season.

  8. peepuk
    Posted February 9, 2019 at 8:29 am | Permalink

    Interesting and excellent review by Gail Patricelli, Eileen Hebets, and Tamra Mendelson.

    Ironically this book was nominated and even made the final for a Pulitzer Prize in nonfiction. Wrong category.

    Bad non fiction books are often easy to recognize because good science is always value free.

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