Intro. [Recording date: March 4, 2025.]
Russ Roberts: Today is March 4th, 2025, and Iâm pleased to welcome back author, naturalist, and scientist Matt Ridley to EconTalk. This marks Matt’s fifth appearance, previously gracing our airwaves in August 2020 to discuss innovationâa conversation that was voted as one of the top episodes of that year by our listeners.
Today, weâll explore Mattâs latest book, Birds, Sex, and Beauty.
A quick heads-up for those with young listeners: we may touch on some adult themes during our discussion.
Matt, welcome back to EconTalk.
Matt Ridley: Thank you! My goal this time is to climb to the second-best talk of the year.
Russ Roberts: Aiming high, I see.
Russ Roberts: This book is remarkable. You deftly weave together your own extensive observations of birds and their mating rituals with a comprehensive history of how these behaviors have been understood since Darwin’s time. Your objectives span from deciphering the “extravagant sexual displays of birds,” to reviving Darwin’s emphasis on sexual selection, while simultaneously instilling a sense of wonder about the natural world, particularly the fascinating behaviors exhibited by the black grouse.
Let’s kick off with a fundamental distinction that runs through your book: the difference between natural selection and sexual selection.
Matt Ridley: Natural selection, often summed up as âsurvival of the fittest,â focuses on the ability to endure adverse conditionsâwhether thatâs harsh weather or diseases. If you can withstand these challenges, youâre more likely to survive and pass on your genes to the next generation.
Sexual selection, on the other hand, can be boiled down to the art of seduction. Essentially, your success in reproducing hinges on your ability to attract a mate. In many species, this competition can lead individuals to make decisions that detract from their survival. Think fancy tails, eye-catching plumage, and elaborate courtship displaysâactivities that, while detrimental to survival odds, significantly enhance oneâs appeal to potential mates.
This distinction between the twoâoften dismissed as minorâis, in fact, profound and leads to vastly different evolutionary outcomes. I refer to sexual selection as the âfun versionâ of evolution because it gives rise to bright colors, melodious songs, and extravagant displays, which may not directly correlate with survival but certainly enhance mating success. Once you start contemplating this idea, it opens up a captivating rabbit hole.
Russ Roberts: Indeed, your book is that rabbit hole, and I look forward to discussing your personal encounters with these fascinating displays as dawn breaks over the bird world.
Russ Roberts: Letâs place this discussion within the broader historical context, particularly regarding Darwin and his contemporary, Alfred Russel Wallace. Both are credited with the discovery of evolution and natural selection, though Darwin tends to receive a touch more acclaim. After Darwinâs passing, Wallace consistently criticized Darwinâs views on sexual selection. Your overview of the implications of beauty in evolution raised eyebrowsâafter all, as a scientist, isnât the crux of the matter how many genes make it to the next generation? The notion that beauty or sheer enjoyment could play a role in evolution is unsettling for some. We crave an explanation, a cause. Letâs delve into Wallace and Darwin and the question of beauty.
Matt Ridley: Absolutely. It raises an essential question about the rationale behind the striking colors and songs of birds.
Darwin, even before penning The Origin of Species, expressed his desire to understand beauty. He posited that the beauty we observe in the natural world wasnât merely to please human observers but was instead a mechanism for attracting the opposite sexâa form of evolution itself.
In his 1871 work, The Descent of Man, he famously stated,
The most refined beauty may serve as a sexual charm and for no other purpose.
Here, he draws a parallel between his observations and those of a friend who bred bantams, suggesting that if humans can influence the beauty of domesticated birds, then female birds could similarly select for beautiful males over generations, leading to notable evolutionary changes.
Russ Roberts: Itâs crucial to note that, in the avian realm, itâs typically the males who flaunt their vibrant colors and flamboyant displays, while the females remain more subdued. So, when discussing the “sexiest male,” thatâs the context weâre considering.
Matt Ridley: Precisely. Iâm not being sexist; Iâm merely stating a biological fact that, in the realm of birds, males generally exhibit the most vivid traits. There are exceptions, of course, but they are few. The iconic peacock tail serves as a classic example, as does the Argus Pheasant, which sparked debates between Darwin and Wallace regarding the purpose of its intricate displays. Wallace and others argued that such traits couldnât possibly enhance female attraction, likening it to the appreciation of art by an elite few.
Darwin and Wallace had a remarkable relationship, discovering the principles of evolution by natural selection independently. Despite Wallace publishing his findings first, Darwin had been wrestling with these ideas for decades. When they jointly presented their work at the Linnean Society, Darwin emerged as the one who garnered most of the creditâalbeit Wallace graciously accepted his role as the runner-up.
Yet, when it came to the subject of sexual selection, their paths diverged. Darwin was eager to explore why beauty mattered, while Wallace remained skeptical, insisting that the vibrant displays were merely indicators of strength, thus reverting to natural selection principles. They held a famous summit to debate their differences, but ultimately, they left with their views unchanged.
Wallace suggested that males flaunt bright colors merely to help females identify their species, while Darwin maintained that females were drawn to beauty for its own sake. Sadly for Darwin, by the time he passed away, the prevailing belief had shifted, and few accepted that a peacockâs extravagant tail existed solely to attract mates.
Wallace, on the other hand, proposed that males exhibited such traits because they had more energy to spare, an assertion that lacks merit. As the 20th century advanced, Wallaceâs perspective gained traction, emphasizing that females chose colorful males to ensure their offspring possessed advantageous genes. Though attempts to revive Darwin’s perspective occurred, they failed to gain traction until recent voices, like Richard Prumâs, began advocating for a broader recognition of Darwin’s original ideas about beauty in avian evolution.
Russ Roberts: Before we delve deeper into this foundational differenceâwhich intriguingly parallels discussions in economicsâlet’s first discuss Ronald Fisher, the statistician.
For those new to the concepts, the terms ânatural selectionâ and âsexual selectionâ can be confusing, especially since both include âselection.â Initially, Darwin’s argument may seem far-fetched. After all, attributing aesthetic sensibility to birds raises eyebrows. Birds possess brains so small that “bird brain” has become a synonym for lacking intelligence. They lack a culture that would suggest a shared aesthetic or appreciation of beauty, making the notion of them prioritizing beauty almost laughable.
Then there’s Wallaceâs adaptation, which implies that favoring flashy males is acceptable because it could lead to gaudy offspring that future females will prefer. While this perspective carries merit, it simplifies the complex interplay of traits.
Fisher’s contribution comes into play here, proposing that if females all prefer the same traits, then individual females must conform to that preference to ensure they produce attractive offspring. This leads to a co-evolution of the preference and the trait itself, spiraling into a âvicious circle.â Fisher encapsulated this with the idea that while âtasteful hensâ donât necessarily raise more chicks, their sons will be more appealing, thereby increasing their chances of mating.
This “Sexy Son Hypothesis” provides Darwin with a rationale for his observations. The more selective females are, the more vibrant and exaggerated male traits become. However, this argument tends to overlook a crucial point: the flashy tail may not signal strength or fitness but rather aptitude in seduction, creating a circular logic.
Russ Roberts: As an economist, I find it amusing how Fisher’s theory mirrors concepts in economics. For example, Keynes likened the stock market to a beauty contest, where investors donât always choose the best stock but rather the one they believe others will also consider the best. This concept of beauty contests echoes Fisher’s theory.
However, the stock market isnât devoid of fundamentals. Eventually, a stockâs intrinsic value prevails, contrasting with Fisherâs theory where gaudy traits could dominate selection without tangible value. This analogy raises concerns; why would an equilibrium emerge favoring detrimental traits rather than advantageous ones?
Additionally, consider the notion of a bad equilibrium in economicsâwhere fixed costs limit innovation. Itâs conceivable that some species, like certain birds, may evolve traits detrimental to survival because those traits are preferred by females, leading to an inefficient evolutionary equilibrium.
Matt Ridley: Thatâs a fascinating analogy. I recall a stockbroker friend urging me to invest in British Biotech because they had a supposed cure for cancer. My skepticism was warranted; the stock skyrocketed, then plummeted. What could be the equivalent failure in the bird world?
Russ Roberts: Perhaps some species become so extravagant that they jeopardize their survival in the wild.
Matt Ridley: Exactly! Take the giant elk, for example; its massive antlers hindered its mobility in the wild, making it vulnerable. While this theory is debated, itâs plausible that the extravagant traits of some birds could increase their extinction risk compared to their more subdued relatives.
Russ Roberts: This “Sexy Son Theory” by Fisher seems to ignore the fundamentals, similar to the stock market’s beauty contest. Itâs perplexing why a destructive trait would be favored over a beneficial one, and Fisher’s theory doesnât delve into that.
Russ Roberts: Letâs pivot to the black grouse. I want you to summarize their peculiar behavior regarding whatâs known as a lek. Can you explain what a lek is and how the black grouse participate in this fascinating ritual?
Matt Ridley: Certainly! The term ‘lek’ originates from Swedish, meaning ‘play.’ It describes a system in which a group of one sex gathers in a particular location to display competitively to members of the opposite sex. This behavior is especially evident in certain bird species, including grouse and birds of paradise.
In my observations of the black grouse, I noted that they inhabit Northern Europe and parts of Asia, including Northern Britain. The females are brown and mottled, whereas the males boast striking black plumage accented with bright blue necks, vivid red combs on their heads, and lyre-shaped tails that fan out impressively. Each morning from October to June, adult male black grouse convene predictably at their chosen spotâan event I plan to witness tomorrow. If you arrive an hour before dawn, youâll likely see a dozen to twenty males gathering.
Russ Roberts: To clarify, this doesnât involve the entire population of black grouse; there are multiple leks across their range, correct?
Matt Ridley: Exactly. Each lek hosts a subset of malesâtypically between 10 to 30âreturning time and again to the same location. The lek itself resembles the size of a tennis court, squeezing these males into close quarters, where territory size varies significantly.
Russ Roberts: So the males develop these territories, and the closer one is to the center, the more likely they are to mate?
Matt Ridley: Correct. Those on the periphery enjoy larger territories, while those centrally located have minimal space yet have a higher likelihood of success. Whatâs intriguing is that these males, despite being competitors, often leave the lek together, exhibiting camaraderie outside of their competitive displays.
When returning to the lek, however, they assume a state of alertness, rushing to their designated spots as if to claim ownership. When itâs time for mating, females visit the lek, demonstrating agency in their selection process, which contrasts starkly with many mammalian mating rituals.
Once females arrive, they casually explore and assess the males without being pounced upon. When theyâre ready to mate, they signal their choice, leading to a brief yet competitive mating encounter with the chosen male.
Interestingly, I observed a particular male known as Black Spot, who dominated matings that season. This illustrates the phenomenon of female choice in action, where despite the malesâ similarities, subtle distinctions in vigor or display lead to their mating success.
Russ Roberts: I want to clarify some extraordinary points. You mentioned that the lek activity starts in October, even before the females arrive. The males gather daily, engaging in their displays without any females present?
Matt Ridley: Correct. They commit to this routine for months, even when the likelihood of encountering females is slim. Itâs a fascinating, albeit costly, expenditure of energy.
Russ Roberts: So theyâre essentially performing for an empty audience while foraging for food elsewhere?
Matt Ridley: Precisely. While activity levels may wane during the winter months, their commitment to gathering at dawn remains unwavering. As the season progresses toward April, their displays crescendo in anticipation of the femalesâ arrival, creating an exhilarating atmosphere.
