Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Seriously? A public-school musical play about evolution got canceled in England? And because religious parents complained? That’s not supposed to happen!
Here are the stories from the BBC and The Independent (click on screenshots to read):
Note that the musical was written by a Christian.
From the BBC:
A school has axed a musical on evolution over its suggestive lyrics and portrayal of Christian views.
Darwin Rocks, about the scientist Charles Darwin, was due to be performed by about 90 pupils at Hartford Manor Primary School, Cheshire, next month.
The move follows six “expressions of concern” from parents, the school said.
The musical’s publishers Musicline said it was written by a Christian, adding “we can’t ever recall having courted controversy before”.
The play has been performed for two years without a complaint, but the lyrics and the treatment of a bishop—Bishop Samuel Wilberforce, according to The Independent—riled up some parents. The BBC continues
According to its website, the production is a “light-hearted look” at the work of Darwin, whose theory of evolution, published in 1859, shocked Victorian society by suggesting animals and humans shared a common ancestry.
Head teacher Simon Kidwell told the BBC that the school, in Hartford near Northwich, received six “expressions of concern” over lyrics that refer to “bump and grind” – a sexually suggestive dance move.
He said three of those parents also believed a bishop was “mocked” in a separate scene.
“There were concerns about caricature,” he said, adding the complainants, who include a science teacher from another school, felt its representation of Christian views on science “wasn’t accurate”.
One parent said they did not want their daughter to think her ambition to be an engineer contradicted Christian beliefs, Mr Kidwell said.
He added the school board was not involved in the decision to drop the production and denied newspaper suggestions a local vicar who is on the board had influenced the move.
If you want, you can go to the “Darwin Rocks” website and listen to some of the songs yourself. As for me, I’m off to O’Hare so I don’t have time.
What bothers me is that there’s censorship of evolution because of Christian offense, and I’m not at all sure that censorship is justified. And, of course, Bishop Wilberforce is reported to have embarrassed himself in the famous 1860 Oxford debate on evolution. Lots of people, including Huxley, are supposed to have made fun of Wilberforce, including Benjamin Disraeli, whose comments about Wilberforce’s unctuous nature led to his nickname “Soapy Sam.”
What bother me almost as much—or perhaps even more, is that the BBC saw fit—at the end of this report, to stick in some accommodationist editorializing by the religion editor. Good lord!—have a look at this “analysis”.
What the bloody hell does this have to do with a news article? It’s just the same tired old trope that because there are religious scientists, there isn’t conflict between science and religion. But the very article above this pathetic bit of apologetics shows that, in the case of this play, there is a conflict between faith and science. If there were no religion, there would be no opposition to evolution.
And why did the BBC let the religious camel stick its nose in the tent? Can’t somebody complain about this?
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.
With the publication of his book The Evolution of Beauty (subtitle: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World—and Us), Yale ornithologist Richard Prum gained an extraordinary amount of publicity in the popular press. His theme was that “beauty”—that is, the evolution of extreme and stunning displays and ornamentation in male birds—results from a form of “runaway sexual selection” in which females’ random preference for extreme male traits produces amazing sexual dimorphism that has nothing to do with natural selection. (The peacock is perhaps the most famous example.) Prum’s book got two separate reviews in the New York Times, at least one other notice, and two big reportorial pieces, including recent the one below. The book was also nominated for a Pulitzer Prize for nonfiction, though it didn’t win.
Prum’s book is worth reading for two reasons. First, it presents a strong defense of the “runaway” model of sexual selection Prum calls it the “beauty happens” model, in which random female preferences lead to the exaggeration of male traits up to the point at which those traits actually hurt the male’s reproductive success (a peacock with a bigger tail would presumably not only be unable to fly, but would be a target for predators and find it hard to get around). Second some of Prum’s writing is very good, and his examples of exaggerated male behaviors and plumage engrossing and yet unknown to many laypeople.
But the book, as I’ve written before (see posts here), is tendentious. It ignores other models of sexual selection (except to denigrate them), it ignores the weaknesses of his own favored runaway model, and it misrepresents the views of evolutionary biologists (many of whom agree that the runaway may be important, but won’t buy into Prum’s view that it’s ubiquitous). Prum claims that the runaway model is universally rejected by biologists in favor of “good genes” models (male traits indicate their genetic endowment). But that claim isn’t true: we just don’t have much data to distinguish all the competing models we have for how sexual selection works.
Further, Prum ties his model to progressive politics, saying that female choice in animals should hearten us because it shows that female “sexual autonomy” is natural. But such autonomy isn’t always present: many animals, for instance, have forced copulation. Bedbugs, for example, exhibit “traumatic insemination”, in which males bypass copulation by simply injecting sperm through the female body wall, with that sperm finding its way to the female eggs. Females don’t get to choose their mates, and copulation can actually kill them.
And there are many cases of forced and unwanted copulation by males, as well as male-male competition (viz., elephant seals) in which females are simply constrained to mate with whichever male wins a contest. Prum’s evocation of politics therefore demonstrates the “naturalistic fallacy”: that what happens in nature is what we should emulate. However, a lot of what happens in nature is stuff we shouldn’t emulate.
Prum also ties other models of sexual selection, including those in which a male’s traits indicate his vigor, health, or presence of “good genes”, to eugenics, and Nazi genocide, tarring the theories he doesn’t like with the social-justice cry of “Nazi”. This is unconscionable. I can’t help but think, though, that Prum’s tying sexual selection to feminism was partly responsible for the book’s popularity and its Pulitzer nomination.
As I’ve written before, however, while Prum’s book received public approbation and good reviews—mostly from reviewers with no science background)—the reaction of the scientific community itself has been tepid and mostly critical for reasons I gave above. The three reviews I’ve read in scientific journals, including one by Gerald Borgia and Gregory Ball and another by Doug Futuyma, both highlight serious problem’s with Prum’s presentation, including the ignoring of alternative theories, the misrepresentation of the “beauty happens theory”, and the unwarranted connection between women’s rights and mate choice in birds. A more recent and much longer review, by Patricelli, Hebets, and Mendelson, published in Evolution (click on screenshot below for free access), was severely critical, and rightly so, though the authors did their best to be evenhanded and polite:
I’ve discussed this review before (full disclosure: I gave the authors some suggestions on a draft of their piece), and so won’t go over its contentions here. But if you want to read a review of Prum’s book—and one that is objective but critical—Patricelli et al. is the one to read. It is a good palliative for the publicity Prum gets repeatedly about his book.
That aside, several readers sent me the link to Ferris Jabr’s NYT piece above, suggesting that I write about it. I intended to, but was in Hawaii where I was having too much fun to work. Now that I’m back, I’ll summarize it as briefly as I can. (The piece is very long, and appeared in the NYT Sunday Magazine, an indication of how important the editors deemed the topic.)
Upshot: Jabr’s piece is a mixed bag. (He’s a contributing writer to the New York Times and and often writes about science.)
The good bit is that Jabr at least indicates, as many writers haven’t, that the scientific community is lukewarm about The Evolution of Beauty and that Prum is somewhat dogmatic and dismissive of his critics. For example:
Despite his recent Pulitzer nomination, Prum still stings from the perceived scorn of his academic peers. But after speaking with numerous researchers in the field of sexual selection, I learned that all of Prum’s peers are well aware of his work and that many already accept some of the core tenets of his argument: namely that natural and sexual selection are distinct processes and that, in at least some cases, beauty reveals nothing about an individual’s health or vigor. At the same time, nearly every researcher I spoke to said that Prum inflates the importance of arbitrary preferences and Fisherian selection to the point of eclipsing all other possibilities. In conversation, Prum’s brilliance is obvious, but he has a tendency to be dogmatic, sometimes interrupting to dismiss an argument that does not agree with his own. Although he admits that certain forms of beauty may be linked to survival advantages, he does not seem particularly interested in engaging with the considerable research on this topic. When I asked him which studies he thought offered the strongest support of “good genes” and other benefits, he paused for a while before finally responding that it was not his job to review the literature.
Of course it was Prum’s job to review the literature, and especially to weigh his favored theory against alternatives, including “good genes” models and “sensory bias” models, in which female preference are not random but the byproduct of natural selection based on the species’ environment. How could it not be an author’s duty, when defending a theory, to review the literature for and against that theory?
Jabr also says this:
Like Darwin, Prum is so enchanted by the outcomes of aesthetic preferences that he mostly ignores their origins. Toward the end of our bird walk at Hammonasset Beach State Park, we got to talking about club-winged manakins. I asked him about their evolutionary history. Prum thinks that long ago, an earlier version of the bird’s courtship dance incidentally produced a feathery susurration. Over time, this sound became highly attractive to females, which pressured males to evolve adaptations that made their rustling feathers louder and more noticeable, culminating in a quick-winged strumming. But why, I asked Prum, would females be attracted to those particular sounds in the first place?
To Prum, it was a question without an answer — and thus a question not worth contemplating. “Not everything,” he said, “has this explicit causal explanation.”
Here Prum simply dismisses something that scientific reviewers mentioned repeatedly—where do female preferences come from? Prum assumes they are random, but there is a thriving field of sexual selection studying female preferences, showing how they might result from natural selection instead of just being “random” (i.e., aspects of neuronal wiring that have nothing to do with natural selection for the preference). Jabr also says, properly, that not all biologists have dismissed the runaway model, as Prum contends they have, but see it as one of a competing panoply of models that are hard to resolve. (Getting this kind of data from nature or even the lab is very difficult, and we weren’t there to see how sexual selection operated in the past.)
But in the rest of the article, Jabr seems to buy a lot of Prum’s contentions without properly evaluating the criticisms of other scientists. For example:
1.) The runaway model is not “Prum’s theory.” This model was first suggested by Ronald Fisher and elaborated and developed by scientists like Russ Lande and Mark Kirkpatrick. Yet Jabr repeatedly refers to the “beauty happens” model as “Prum’s theory”, as when he says that “Prum’s indifference to the ultimate source of aesthetic taste leaves a conspicuous gap in his grand theory.” (That statement is correct except that it’s not Prum’s grand theory.) This misleading attribution of the theory happens repeatedly. Let us be clear: Prum’s book is about presenting, defending, and applying a theory developed by other scientists.
2.)Jabr buys into Prum’s contention that sexual selection is fundamentally different from natural selection. Most biologists, I think, would disagree, seeing sexual selection as a subset of natural selection. That is, sexual selection is a form of selection based on female mate choice rather than other factors. But both sexual and natural selection involve enhancing those traits that affect reproductive success. (Jabr seems to mistake natural selection as a form of selection that enhances survival rather than reproductive success, but in fact the currency of all selection is the number of offspring that survive to spread your genes.). This may seem a semantic question, but both Jabr and Prum use this distinction to suggest that the runaway theory is a big and revolutionary improvement over previous notions of natural selection. This further inflates the runaway theory into something that it’s not.
In fact, natural and sexual selection blend into each other, and in some cases you can’t distinguish them. If a male produces sperm that swim faster than the sperm of other males in his species, and thus he gets more offspring, is this natural or sexual selection? It’s not based on mate choice, but does involve reproductive success. This is a form of male/male competition, analogous to those bull elk who butt horns during mating season, with the winner getting a harem of females. No female choice is involved in either case, but both could be seen as sexual selection. But they also represent natural selection—selection based on some individuals having traits (horns, fighting ability) that enables them to leave more genes. My own judgment is that sexual selection is simply a subset of natural selection that involves mate choice, and not something fundamentally different.
3.) Jabr leaves out some aspects of Prum’s views that scientific critics have homed in on. Jabr doesn’t mention, for example, that Prum views the runaway model as the “null model” of sexual selection. That is, Prum deems it the model that we should accept unless we have good evidence for other models. But the runaway model isn’t null in that way: it does carry its own assumptions that themselves have to be justified and tested, such as female preference being “random” and not itself initially the result of natural selection or subject to stabilizing selection. The runaway assumes that male traits and female preferences are genetically correlated, and so on. No single model of sexual selection can be regarded as a “null model” to be regarded as a default option in the absence of any evidence.
4.)Jabr doesn’t fairly summarize the extent of scientific criticism of Prum’s book. While he does cite Borgia and Ball’s criticism, he neglects those of Futuyma and especially the thorough paper of Patricelli et al., and thus leaves out some important problems with Prum’s views (see below). Further, Jabr seems to have consulted critics at only the University of Texas at Austin, including my colleagues and friends Gil Rosenthal, Molly Cummings, and Mike Ryan. These people generally work on the sensory bias model of sexual selection, and thus emphasize theories different from Prum’s, but it would have been good to consult others who work on Prum’s model itself. These would include both Mark Kirkpatrick (also UT Austin!) and Russ Lande. I have talked to several “runaway” modelers, and their take is different from Prum’s: while they think the theory can operate, they are wary of its ubiquity in the absence of empirical evidence. This view, by the very proponents of Prum’s favorite model, shows a scientific caution far more admirable than Prum’s dogmatism.
5.) Jabr doesn’t mention at all an important aspect of Prum’s book: Prum’s view that because in some species females have “sexual autonomy” in choosing males, that hearten feminists who, rightfully, are against sexual coercion by human males. This omission by Jabr is a mistake, for this part of Prum’s message is one of its selling points, and surely explains some of the book’s popularity. But we shouldn’t buttress our morals by looking for parallels in nature, for, as I’ve said repeatedly, doing that makes our morality subject to revision via new information about nature. While some moral judgement can depend on empirical information (abortion may be one example), arguments about human rights and autonomy should be independent of how other species behave.
Jabr further ignores Prum’s invidious use of eugenics and comparisons to Nazis and genocide to tar models of sexual selection based on “good genes”. Ball and Borgia explicitly mention this, as do Patricelli et al. in the section of their review called “Birds and bedbugs make bad politics” (all three authors of that review are women).
My view then, is that Jabr’s summary of Prum’s work and the “beauty happens” theory is better than that of any of the summaries in popular venues, but still suffers from a general laziness manifested in contacting only scientists at UT Austin and in failing to summarize much of the criticism leveled by scientists at The Evolution of Beauty. Jabr didn’t do his scientific homework. The definitive popular critique of Prums’s views, as opposed to those that have already appeared in scientific journals, has yet to be written.
The results of sexual selection: male and female Manadrin Ducks (Aix galericulata). Photo from Wikipedia.
I’m scheduled to go to Antarctica in the fall of next year, lecturing on evolution on two separate cruises to Patagonia, Antarctica, and the Falklands, so I was excited when reader Daniel Shoskes sent me some photos of a trip he took recently to Antarctica and Chile. I present his photos (bonus Darwiniana!), with Daniel’s words indented.
Darwin visited Santiago Chile as documented in Voyage of the Beagle. Here is a plaque dedicated to his visit on St. Lucia hill that he wrote about (page 279)
Punta Arenas Chile at the “end of the road”, just beyond where the Transamerica Highway ends. I found this local owl having a rest. HMS Beagle sailed through this strait and Darwin may have seen some of the trees here as they are hundreds of years old. Perhaps the owl is a descendant of those Darwin saw (page 252):
Model of the Beagle at Straits of Magellan museum:
Landing on an active volcano. The sand was so hot that krill [order Euphausiacea] were cooked on the beach. You can see the stomach filled with green phytoplankton, organisms responsible for 20% of all oxygen on the planet:
I’m going to add here that another reader, Peter Nothnagle, wrote me telling me this about Daniel:
Danny is an accomplished performer on renaissance and baroque lute, and I have engineered three CDs for him. But that’s only his avocation – in his day job he is a highly respected kidney transplant surgeon in Cleveland.
And he sent a link to Daniel playing the lute, which is here:
When I got my new driver’s license last week, I was asked if I still wanted to be an organ donor (that stipulation is put on the license). I said, “Of course.” There’s no reason not to be a donor: it doesn’t cost you anything since you’re dead and don’t need the organs (unless you’re the kind of Christian who thinks he needs a heart and corneas to meet Jesus), and it gives you some satisfaction that even after death you can help someone else.
People call that an “altruistic” gesture, but it isn’t, really—it isn’t “cultural”altruism” and it isn’t “biological altruism”. “Cultural altruism” is simply sacrificing something you want to help someone else, without getting anything of equal value in return for your sacrifice. Examples are people like volunteer firemen—women are included here, I just don’t know if “firepersons” is a word)—who risk their lives for no pay, and soldiers who fall on grenades to save their fellows. In such cases it’s hard to make an argument that what you get back is equal to losing your life. Another example is Lennie Skutnik, who risked his life in 1982 diving into the Potomac to save the life of a passenger in the water after the Air Florida Flight 90 crash.
But things get a bit dicier with lesser acts of “heroism”. If you tutor illiterate adults to help them learn, as I once did, was that altruistic? After all, I got a great deal of satisfaction from watching people learn to read as adults, so was what I reaped less than what I sowed? How do you know? After all, I get bragging rights (I just bragged), and even if others didn’t know about it, there’s still an internal sense of satisfaction. Those who donate big sums of money to colleges to build buildings with the donor’s name on them are in the same position: they have lots of dosh and don’t lose much—but they get to see their name on a building, and have everybody refer to that building as “Cowles Hall”. Gestures of generosity are often publicized, so they’re less “unselfish” than you think.
It’s hard to judge most acts as “altruistic” since the currency of action versus personal satisfaction aren’t comparable. One could claim, for instance, that “everyone does what they want, which is more or less a claim that you always reap at least as much as you sow. Nevertheless, you have to admire those who risk their lives, like Skutnik, to help others, for he could have died doing that, and would reap no reward. It is for these reasons that I don’t like to use the word “altruism” as shorthand for “doing something costly”.
Biological altruism is very different, and has to do with genes rather than emotional satisfaction. (People are always mixing up biological and cultural evolution, and mixing up both with kin selection, as I note below.) Biological altruism is a genetically coded behaviors for actions that lower your lifetime reproductive success while enhancing the reproductive success of some other member of your species (or even of another species). If fighting fires had a genetic component, volunteer firemen would be an example of biological altruism, for they lower (on average) their net reproductive success while enhancing that of the people whose lives they save. I doubt, though, whether there’s a genetic component to fighting fires, though there may be for risk-taking.
A better example would be a baboon risking its own life to save the life of a baboon from another troop. Or an individual warning other unrelated individuals that a predator is near, and risking its life by so doing (perhaps giving an “alarm call” focuses the predator’s attention on you). There are alarm calls, but they may incur no reproductive cost (after all, you’ve already seen the predator), or they may help save your relatives more than others, in which case their evolution could be understood by kin selection (see below).
Biologically altruistic behaviors are not expected to evolve under Darwinian natural selection, because the genes promoting them would be eliminated by selection from populations. The only way they can evolve is by group selection—groups with higher proportion of genetic altruists may do better than groups having a lower proportion. And although within each group altruists are selected against, that might be outweighed by the higher proliferation and longer persistence of groups that contain more altruists. If the “group-persistence-and-reproduction” effect is strong enough, it could outweigh selection within groups and increase the proportion of altruists in a species.
But that kind of group selection would have to be strong, and even if it did work, after the altruists come to dominate a species the genes for altruism will continue to be selected out of the species. Altruism is genetically unstable under group selection.
Because of this, we don’t expect to see much true biological altruism in animals. And we don’t: I’m not aware of any examples in which an individual reduces its lifetime reproductive success (“fitness”) to help another individual without gaining a genetic benefit. Even in cases that look like altruism (creches in which mothers suckle young of other individuals), there’s always a potential individual-selection explanation (reciprocity is one: someone may suckle your cubs if you suckle theirs). The altruism that we see in humans is almost certainly the result of social and moral conditioning rather than of genes encoding “altruistic behaviors.”
What about helping your kids at the expense of what you want to do? Well, that’s not altruism at all, but the result of a form of Darwinian selection: kin selection. Genes for behaviors that help your kids (nursing, parental care, etc.), so long as they’re not too detrimental to your own future reproduction, will spread in populations through the offspring that are helped. That’s why many animals show parental care, which isn’t a sacrifice in reproduction (though it is in energy!), but an adaptively favored trait.
The take-home lesson: “altruism” in humans isn’t the same thing as biological altruism.
Richard Prum’s 2017 book on sexual selection, The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World—and Us, has gotten a lot of popular press, and a fair number of positive reviews, but it hasn’t fared very well in the scientific community. Prum’s thesis, which is that the “runaway” model of sexual selection, in which random and nonadaptive female preference drive male-specific traits like elaborate plumage, behavior, and calls, may well be correct, but we simply lack the evidence in favor of that theory as opposed to other theories for sexually dimorphic traits. (Prum considers the runaway to be the “null model” that, if not falsified, should be taken as correct). I’ve highlighted the problems with Prum’s book in several posts (especially here) and called attention to two reviews in the scientific literature, one by Gerald Borgia and Gregory Ball, the other by Doug Futuyma, that highlight serious problem’s with Prum’s presentation.
Further, Prum failed to lay out the problems with his own favored theory (e.g., any selection on female preferences themselves makes the “runaway” harder to occur)—a rather tendentious and misleading way to present a theory to the public. Finally, as I wrote in my own mini-review, Prum falls victim to the naturalistic fallacy in his book, arguing that the supposed ubiquity of nonadaptive female choice buttresses “female sexual autonomy” in humans. Here’s what I said:
The tie to feminism is a particularly invidious way to sell his theory, as female choice in birds is a direct product of evolution, while human feminism is a rational conclusion our species draws to improve society by treating people equally. Feminism should not be buttressed by biology, as that makes it susceptible to further knowledge from biology. If you study other species, for example, you could draw other conclusions and support other forms of sexual behavior in humans. Many species, for instance, have “traumatic insemination,” in which the male simply bypasses female choice by either forced copulation or, in the case of bedbugs and some invertebrates, injects the sperm directly into the body cavity, bypassing her genitalia and often injuring or killing her. Here are two bedbugs going at it, with the smaller male sticking his genitals directly into the female body cavity; you can see the puncture wound he’s making. (The sperm somehow still find their way to the eggs.)
If you studied deer or elephant seals, you might find support for the existence of harems in humans, in which powerful males, by virtue of their status, are able to dominate and mate with many women, while the “losers” go childless. This underscores the big mistake of using your favorite brand of biology to support ideological or moral conclusions. (I note that biology can, however, inform some aspects of morality: learning about fetal pain may, for instance, affect one’s views about abortion.)
Prum further demonizes “good genes” models of sexual selection (i.e., females looking for traits indicating that males have good genes or are in good condition to provide for their offspring) by tying them to Nazi eugenics, urging us to embrace his “beauty happens” model as a palliative against racism and genocide!
All reviewers have, however, noted that Prum’s book has good parts, most notably his lively writing and the often mesmerizing descriptions of some of the bizarre male traits produced by sexual selection. But distorting a theory in a popular science book, which happens to be a way to bypass peer review, is not so kosher, and disturbed that such a flawed book was not only one of the New York Times‘s ten best books of 2017, but was even one of three finalists for the 2017 Pulitzer Prize in Nonfiction (it didn’t win). Sadly, none of the reviewers in the popular press picked out the scientific problems with Prum’s book, as they were journalists or writers and not scientists, leading me to suggest that the media should find scientists to review “trade books” on science. (There are plenty of scientists who can write an incisive but lively review.)
That’s a long introduction to what I want to point out: the appearance of another review of Prum’s book, and a long one, by three scientists who work on sexual selection. It’s in press in Evolution, the premier journal of evolutionary biology, but is already on the journal’s website. If you have the free and legal Unpaywall app, you can find it by clicking on the screenshot below (pdf is here):
The three authors are, respectively, from the University of California at Davis, the University of Nebraska, and the University of Maryland Baltimore County. Full disclosure: I looked at a draft of the piece for the authors and made a few suggestions, which didn’t affect the tone or substantial conclusions of the review.
Patricelli et al.’s review is quite critical. To be sure, the authors take care to point out the useful parts of Prum’s work. Their overall take is in the first paragraph:
We were eager to read Richard Prum’s recent book, The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World—and Us (2017). As behavioral ecologists and evolutionary biologists studying animal mating behavior and communication, we appreciated the book’s focus on the aesthetics of mate choice, its engaging descriptions of the natural world, and its representation of a diverse group of scientists and their research. The book is beautifully written and accessible to nonscientists, and we recognize its value in engaging the public in the study of evolution. We disagree, however, with the book’s advocacy of a single evolutionary explanation for beauty in nature, and we were disappointed by its portrayal of modern sexual selection research, which was strikingly out of step with our own research programs and those of our colleagues.
As with other scientists who have reviewed the book, Patricelli et al. find the angels in the prose but the devil in the scientific details. You can read this long review for yourself if you want to see the scientific problems and tendentious nature of the book, as I regard this as the definitive scientifically informed response to The Evolution of Beauty.
I note that the three authors are all women, and so one can’t accuse them of sexism when they fault Prum for his naturalistic fallacy about sexual autonomy in animals —> humans:
Finally, we offer a critical reminder that the behavior of nonhuman animals, sexual or otherwise, cannot and should not be used as a moral compass for our own lives. The book explicitly uses “sexual autonomy” in birds to support feminism in humans (see pp. 177–178). As previously pointed out by Borgia and Ball (2018), not only does this argument commit the naturalistic fallacy, but it opens the door to the justification and rationalization of other common, arguably undesirable, behavior. Lions and coots, for example, are notorious child killers; cuckoldry is relatively common in birds; male bed bugs traumatically inseminate females by injecting sperm into their abdomens; and numerous insects and arachnids engage in coercive mating or sexual cannibalism. Indeed, male self‐sacrifice and subsequent sexual cannibalism has evolved in multiple spider species, but we suspect no man would use this as a justification to encourage such behavior in humans.
The examples of bird sexual autonomy highlighted throughout the book are evolved phenomena resulting from millions of years of selection on individuals. By comparison, the choice to treat men and women equally is a rational, moral decision for the good of individuals and society. Resting our politics and morality on what we see other animals do is the real “dangerous idea” here. Despite the book’s narrow taxonomic worldview (restricted to birds), animals and their sexual behavior are tremendously diverse, each with their own unique evolutionary history. Indeed, it is this diversity that personally drew each of us to the study of sexual selection. Within this diversity, humans could find justification for almost any behavior. Using nonhuman animals as our moral compass would be not only devastating to our society but would also bias our scientific approach to the study of nature.
But in the end these women are scientists, and their scientific judgment is summed up in the review’s conclusions:
If the book’s main goal is to explain the evolutionary origin of “beauty,” as it seems to be, it falls short in numerous ways. The book’s central argument is that indicator models [JAC: i.e., those models in which male traits indicate good genes, good health, or other signs that they could foster better offspring or produce more grandchildren] have been accepted without evidence and that Fisherian selection has been defined out of existence. Ironically, it proposes that we instead accept Fisherian selection without evidence and redefine sexual selection to explicitly exclude adaptive mate choice. This does not advance our understanding of mate choice or aesthetics. Nor does creating a false dichotomy between adaptation and aesthetics, assuming that beauty only arises from coevolving female preferences, and dismissing or ignoring decades of research on receiver psychology. The book also unfairly caricatures most sexual selection researchers as not only failing to acknowledge the subjective experiences of nonhuman animals, but also of supporting human eugenics and antifeminist politics. Moreover, by arguing that beauty is “irrational,” “unpredictable,” and simply “happens,” the book seems to simultaneously argue for the scientific study of beauty while setting it outside the bounds of scientific understanding.
Nine years ago, Radio 4 in England invited several of us to write a letter to Charles Darwin, telling the old guy what we think he’d like to know 200 years after his birth in 1809 and 150 years after he published On the Origin of Species. We read these “Dear Darwin” letters on the air (you can hear them here; the other participants were Craig Venter, Sir Jonathan Miller, Peter Bentley, and Baruch Blumberg). Later, Oxford University Press, the British publisher of Why Evolution is True, published my letter on its website. In honor of the publication of The Origin on this day in 1859, I’ll put that letter below.
My Dear Mr. Darwin,
Happy 200th birthday! I hope you are as well as can expected for someone who has been dead for nearly 130 years. I suppose that your final book, the one about earthworms, has a special significance for you these days. Are the worms of Westminster Abbey superior to the ones you studied so carefully in the grounds of your home at Downe in Kent? They’ve certainly mulched some distinguished people over the years!
But enough of the personal questions: let me introduce myself. I am one of thousands – maybe tens of thousands – of professional biologists who work full time on your scientific legacy. You’ll be happy to know that Britain remains a powerhouse in what we nowadays call evolutionary biology, and your ideas now have wide currency across the entire planet. I work in Chicago, in the United States of America. But even the French have finally reluctantly relinquished their embrace of Jean-Baptiste Lamarck, whose misguided evolutionary ideas you did so much to discredit.
Your Origin of Species turns 150 this year. I just re-read it in your honour and must say that, though you did not always have the snappiest turn of phrase, it really is a wonderfully comprehensive and insightful work. It is remarkable, considering what you did not know when you wrote it, how robust the book has proved over the years. The findings of modern biology, many of them inconceivable to you as you beavered away in your Down House study, have provided ever more evidence in support of your ideas, and none that contradicts them. We have learned a huge amount in the past 150 years, but nearly all of it still fits comfortably into the framework you outlined in The Origin. Take DNA, for example. This is what we call the hereditary material that is passed down from generation to generation. You knew nothing about it – remember how you wished you understood more about how heredity works? Now we have full DNA sequences from dozens of species, each one a string of billions of the four DNA letters—A, T, G and C—each a different chemical compound. What do we find when we compare these sequences, say between a mouse and a human? We see the DNA equivalent of the anatomical similarities – as mammals – that you noted mice and humans share because they are descended from a common ancestor, an early mammal. Strings of As, Gs, Cs, and Ts tell precisely the same evolutionary story as traits like lactation and warm-bloodedness. It is absolutely marvelous that your 150 year old insight on common ancestry should be so relevant to the very latest discoveries of the new field we call molecular biology.
In The Origin, you gave very little evidence for evolution from the fossil record, wringing your hands instead about the incompleteness of the geological record. But since then, the labors of fossil-hunters throughout the world have turned up plenty of evidence of evolutionary change, and many amazing “transitional” forms that connect major groups of animals, proving your idea of common ancestry. You predicted that these forms would exist; we have found them. These include fossils that show transitions between mammals and reptiles, fish and amphibians, and even dinosaurs with feathers—the ancestors of birds! Just in the past few years, paleontologists have unearthed an astonishing fossil, called Tiktaalik, that is intermediate between fish and amphibians. It has the flat head and neck of an amphibian, but a fishy tail and body, while its fins are sturdy, easily able, with slight modification, to give them a leg up when they left the water. The fossil record has given us a direct glimpse of an event of great moment in the history of the planet: the colonization of land by vertebrates. And we have evidence just as convincing for the recolonization of the sea by mammals: the group that gave rise to whales. In The Origin, you were correct in suggesting that whales arose from land animals, but you got it wrong on one point. You thought they may have come from carnivores like bears, but we now know this is not true. Instead, the ancestral whale came from a small hooved animal rather like a deer. And in the last thirty years we have discovered a whole series of intermediate fossils spanning the gap from those ancient deer to modern whales, showing them losing their hind legs, evolving flippers, and moving their breathing hole to the top of their head. Both Tiktaalik and these ancestral whales put paid to the objection, which you yourself encountered, that no transitional form between land and water could possibly have existed.
Perhaps the most remarkable set of intermediate fossils, however, come from an evolutionary transition rather closer to home. In 1871, you more predicted that, since humans seem most related to African great apes, gorillas and chimpanzees, we would find human fossils on that continent. And now we have them—in profusion! It turns out that our lineage separated from that of chimpanzees, our closest living relatives, nearly 7 million years ago, and we have a superb series of fossils documenting our transition from early apelike creatures to more modern human forms. Our own species has become an exemplar of evolution. And we know even more: evidence from our hereditary DNA material has told us that all modern humans came from a relatively recent migration event—about 100,000 years ago—when our ancestors left Africa and spread throughout the world.
The idea you were proudest of was natural selection. That too has had a good 150 years, holding up well as the main cause of evolution and the only known cause of adaptation. Perhaps the most dramatic modern example involves bacteria that are now known to cause disease, including the scarlet fever that was such a plague upon your family. Chemists have developed drugs to cure diseases like this, but now, as you might well predict, the microbes are becoming resistant to those drugs—precisely in accord with the principles of natural selection—for the most drug-resistant microbes are the ones that survive to breed. There are hundreds of other cases. One that will especially please you is the observation of natural selection in the Galápagos finches you collected in the Beagle voyage—now called “Darwin’s finches” in your honor. A few decades ago, zoologists observed a great drought on the islands that reduced the number of small seeds available for the birds to eat. And, just as predicted, natural selection caused the evolution of larger-beaked birds within only a few years. These examples would surely be a centerpiece of The Origin were you to rewrite it today.
All told, the resilience of your ideas is remarkable. But that is not to say that you got everything right. On The Origin of Species was, admit it, a misnomer. You described correctly how a single species changes through time, but you came a cropper trying to explain how one species splits into two. Speciation is a significant problem, because it underpins the branching process that has yielded the tree of life – that extraordinary vision you bequeathed us of the natural world as one vast genealogy. Speciation is the key to understanding how, starting with the very first species on earth, evolution has resulted in the 50 million species that are thought to inhabit our planet today.
You once called speciation the “mystery of mysteries,” but it’s a lot less mysterious these days. We recognize now that species are separated one from another by barriers to reproduction. That is, we recognize different species, like humans and chimpanzees, because they cannot successfully interbreed. To modern evolutionary biologists, studying “the origin of species” means studying how these barriers to reproduction arise. And now that we have a concrete phenomenon to investigate, we are making remarkable progress in understanding the genetic details of how one species splits into two. This is in fact the problem to which I’ve devoted my entire career
I wish I could end this letter by telling you that your theory of evolution has achieved universal acceptance. As you well knew, evolution has proved a bitter pill for religious people to swallow. For example, a large proportion of the American public, despite access to education, clings to a belief in the literal truth of Genesis. You will find this hard to believe, but more Americans believe in the existence of heavenly angels than accept the fact of evolution. Unfortunately, I must often put aside my research to fight the attempts of these “creationists” to have their Biblical views taught in the public schools. Humans have evolved extraordinary intellectual abilities, but sadly these are not always given a free rein by their owners. But this probably won’t surprise you – remember the Bishop of Oxford and his attempt to put your friend Thomas H. Huxley in his place?
You wrote in your introduction to The Origin of Species that
“No one can feel more sensible than I do of the necessity of hereafter publishing in detail all the facts, with references, on which my conclusions have been grounded; and I hope in a future work to do this.”
It seems that, distracted by other projects, you never got around to it, but my own effort along these lines is represented in a book (which I enclose) called Why Evolution is True. It goes further to describe the evidence supporting you than a letter this size ever could, but it’s just one book at just one moment in the history of biology. When I myself am as long gone as you are, somebody else will certainly need to write an update, for the facts supporting your theories continue to roll in, and I wager they will continue to do so.
So, rest in peace, Mr. Darwin, and here’s hoping that the next hundred years will see a steady evolution of rationality in a troubled world.
