A critical review of Prum’s “The Evolution of Beauty” in Evolution

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.

It’s a good review of a readable but flawed book.