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How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World – and Us

You know everything there’s to know about evolution, right?

The fittest survive and so on and so forth.

Well, Richard O. Prum would like a chance to change your mind with a new theory, one aptly titled:

The Evolution of Beauty.

Who Should Read “The Evolution of Beauty”? And Why?

The obvious answer is biologists, social biologists, and ornithologists.

However, we think that this is a book that should interest everyone who likes to reread Darwin with fresher eyes.

Or Dawkins.

About Richard O. Prum

Richard O. Prum is an American “evolutionary ornithologist with broad interests in diverse topics,” the William Robertson Coe Professor of Ornithology at Yale University.

After receiving a BA at Harvard in 1983, Prum went on to obtain a Ph.D. from the University of Michigan six years later.

His field of specialty is the evolution of feathers, and his main interests include phylogenetics and sexual selection.

The Evolution of Beauty is his only book so far.

“The Evolution of Beauty PDF Summary”

Darwin’s Biggest Problem

Darwin’s theory of evolution is, quite possibly, the most influential theory ever conceived by anyone.

In fact, when back in 2012, Edge.org, the world’s smartest website, asked the world of science “what is your favorite deep, elegant, or beautiful explanation?” most of the intellectuals surveyed answered something along the lines: “of course it’s Darwin’s theory of evolution, but I suppose everyone will say that, so I’m going with…”

Consequently, Darwin’s theory of evolution is a theory which needs no introduction, and which, by Darwin’s own admission from The Origin of Species, can be summed up in a single phrase of Herbert Spencer: “the survival of the fittest.”

Most of the biologists living today would certainly agree with it; after all, why shouldn’t they: it’s a nice, neat theory which seems to explain the complexity of the world in such an economical manner that it’s difficult to find any flaws with it.

And yet, Darwin himself found a big, almost gaping hole in it: if the biological point of life is to be fit enough so that you can leave some offspring, then why should so many animals be so brightly colored and feature traits which instead of helping them survive, make them more vulnerable?

“The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!” – grappling with this problem, Darwin wrote in a letter sent to Asa Gray on April 3, 1860.

Why should such a beautiful thing as a peacock’s tail make anyone sick?

“Because,” writes Richard Prum, “the extravagance of its design seemed of no survival value whatsoever; unlike other heritable features that are the result of natural selection, the peacock’s tail seemed to challenge everything that [Darwin] had said in Origin.”

Darwin’s Beautiful Solution

So, twelve years later, in his second-most famous book, The Descent of Man, and Selection in Relationship to Sex, Darwin tried to solve this problem, the problem of impracticable beauty.

“In this book,” writes Richard Prum, Darwin “proposed a second, independent mechanism of evolution – sexual selection – to account for armaments and ornaments, battle and beauty. If the results of natural selection were determined by the differential survival of heritable variations, then the results of sexual selection were determined by their differential sexual success – that is, by those heritable features that contribute to success at obtaining mates.”

Put plainly, sometimes it’s not the fittest, but it’s the most beautiful that survive.

This would explain not only the peacock’s lavish tail, but also the elaborate feathers, exquisite songs, and mating dances of numerous other birds; it should also explain the white backside and legs of the Malaysian Banteng bull; it explains the red buttocks of many monkeys and apes as well.

Darwin proposed that within this second dynamic force of evolution – sexual selection – two distinct and sometimes opposing mechanisms are at work:

• The law of the battle, or “the struggle between individuals of one sex – often male – for sexual control over the individuals of the other sex;” according to Darwin, the battle for sexual control was the main reason why some weapons of aggression (such as horns, antlers, and spurs) and large bodies appeared and evolved.

• The taste for the beautiful, or “the process by which the members of one sex – often female – choose their mates on the basis of their own innate preferences;” it’s Nature giving its species a second chance: you better be beautiful if you have no brains or brawn.

The law of the battle explains the evolution of armament; the taste for the beautiful – the evolution of ornament.

The Rejection of Darwin’s Theory

Unless you’re an expert in Darwin, the section above should probably come as a surprise to you (we sure found it quite surprising).

Its full implications: natural selection is not the only driving force behind evolution; as impractical as it has become in the eyes of many precisely because of Darwin’s theory, beauty may be an even more important factor in speciation and survival.

How did it happen that we forget this?

Well, blame it on two Victorians and a bunch of Neo-Darwinists, writes Prum.

The first one among these is St. George Mivart, an English biologist and an ardent believer in natural selection for the fifteen or so years following the publication of the Origin.

Mivart had problems specifically with the taste-for-the-beautiful mechanism mostly because, unlike natural selection, this one presupposed “choice, exercised freely.”

Also, because he lived at a day and age when it was fashionable to be misogynist: “such is the instability of vicious feminine caprice,” Mivart wrote in a review of Descent, “that no constancy of coloration could be produced by its selective actions.”

The other one to challenge Darwin’s belief in the second evolutionary force – “sexual selection” and “mate choice” – was none other than Alfred Russel Wallace, a man largely forgotten by history though he devised the theory of evolution concurrently with Darwin.

“The only way in which we can account for the observed facts,” wrote Wallace in his 1878 book, Tropical Nature, and Other Essays, “is by supposing that color and ornament are strictly correlated with health, vigor, and general fitness to survive.”

And this view prevailed.

Most of the Neo-Darwinists today believe that the flashiness of a peacock’s tail speaks volumes of its fitness: “despite this disadvantage,” it supposedly says, “I made it this far!”

There’s more to it, says Prum.

Richard O. Prum to the Rescue

An “obsessive birder,” Richard O. Prum has studied the world of birds for over four decades, and so far has personally seen (and, in many cases, thoroughly examined) about a third of the world’s ten thousand known bird species.

His view?

As far as birds are concerned, “aesthetic evolution has great explanatory power” – in fact, much greater than the power of the “fitness first” model; rereading Darwin once again, he suggests, and accepting his more complicated evolutionary theory “rescues us from the tedious and limiting adaptationist insistence on the ubiquitous power of natural selection.”

Prum writes:

Aesthetic evolution by mate choice is an idea so dangerous that it had to be laundered out of Darwinism itself in order to preserve the omnipotence of the explanatory power of natural selection. Only when Darwin’s aesthetic view of evolution is restored to the biological and cultural mainstream will we have a science capable of explaining the diversity of beauty in nature.

In other words, humans don’t find symmetrical faces beautiful because they suggest great fitness; they find them beautiful because beauty is an important factor in evolution as well.

Now, how did that happen?

Because (since we don’t know the point of it all) it is inevitable that, at one point, natural selection should make way for sexual selection.

Wallace and Mivart thought that most of the species – in fact, all, excepting humans – are simply not that smart to make aesthetic choices.

The point is: they needn’t be; either way, aesthetic evolution will happen.

Let’s explain this a little bit more.

Remembering the Genius of Ronald Fisher

First of all, as Prum himself indicates, this is far from a new idea.

In fact, the mathematical biologist Ronald Fisher, “the greatest of Darwin’s successors,” proposed quite a few theories that explain the lavishness of the peacock’s tale, as well as sexual attractiveness as an evolutionary factor a century ago.

The most interesting among these are certainly the sexy son hypothesis and the Fisherian runaway.

The Sexy Son Hypothesis

According to the sexy son hypothesis (a theory which wins our vote for the best-named scientific theory in history), a female’s ideal choice for a male partner is one whose genes should produce a male offspring with the best chances for reproductive success.

The result – as Richard Dawkins explains in The Selfish Gene – “is that one of the most desirable qualities a male can have in the eyes of a female is, quite simply, sexual attractiveness itself.”

Sounds a bit tautological, but it makes sense:

Brad Pitt is not healthier than most males; he’s just more beautiful than them and a guarantor that his children will also be beautiful enough to have children themselves.

And this makes even more sense if you add the second of Fisher’s many theories: the Fisherian runaway, basically the foundational block of Prum’s book.

The Fisherian Runaway

According to Fisher, both Wallace and Darwin were right, but in relation to different phases of evolution.

Namely, originally females preferred male traits which were “honest and accurate indices of health, vigor, and survival ability.”

In other words, the first generation of peacock’s with more ornamental tails was necessarily healthier and more fit for survival than those whose tails were ordinary; consequently, these were the ones who survived.

But this is where it gets interesting: with them, the genes contributing to ornamentation survived as well.

Ready for another tautology?

Now precisely because of the fact that these birds were the chosen ones, their genes evolved to make their tails even more ornamental so that their male offspring be the chosen ones as well!

In other words, “the very existence of mate choice would unhinge the display trait from its original honest, quality information by creating a new, unpredictable, aesthetically driven evolutionary force: sexual attraction to the trait itself”:

When the honest indicator trait becomes disconnected from its correlation with quality, that doesn’t make the trait any less attractive to a potential mate; it will continue to evolve and to be elaborated merely because it is preferred.
In the end, according to the Fisher phase-two model, the force that drives the subsequent evolution of mate choice is mate choice itself. In an exact reversal of the Wallacean view of natural selection as neutralizing sexual selection, arbitrary aesthetic choices (per Darwin) trump choices made for adaptive advantage (per Wallace), because the trait that was originally preferred for some adaptive reason has become a source of attraction in its own right.

“Once the trait is attractive,” writes Prum, “its attractiveness and popularity become ends in themselves… Desire for beauty will endure and undermine the desire for truth.”

Manakin Dances and Bowerbird Nests

Now, Prum spends most of his book demonstrating the effects of this theory in practice; and he does this so beautifully that we think summarizing or even paraphrasing his descriptions of bird-mating rituals is both a sin and beyond our capabilities.

Nevertheless, we do like to at least point out to you two interesting examples.

After going over the sex life of the Great Argus (“eminently interesting” for Darwin) as well, Prum spends the third chapter of his book describing the carefully choreographed dances of the manakins.

In lieu of words, here’s a Nat Geo video that will force you to reinterpret the alphaness of movie dance-offs:

What about bowerbird males?

They mastered bower building millennia before humans.

Why?

Because of sex, that’s why.

We guess some of these birds realized that if you’re not fit enough to be a boxer to beat the hell out of your competitors, you can become a poet or an architect and pray that you’ll charm the socks off of ladies through skill only.

Speaking of –

The Two Routes of Evolution and the Queering of Homo Sapiens

Unlike most of the hardcore Neo-Darwinists, Prum thinks that evolution is not merely about the survival of the fittest.

In fact, that mechanism, in his opinion, is just one of the two routes of evolution, the one in which predominantly males make the choice for females; but, there’s another more beautiful route, the one in which ladies are the ones who choose.

Different species have taken different routes.

For example, in the world of gorillas and many duck species, males use threats and force to command exclusivity in their mating access to females; often they even murder the offspring of their predecessors; this is the route of force, survival of the fittest at its brawniest.

The aesthetic route works in a much different manner; in this case, one of the sexes respects the other sex’s priorities and tries to appeal to them through certain behaviors and rituals.

The second route is the route of the modern humans; and it explains why some ostensibly counter-evolutionary behaviors and traits (homosexuality, monogamy, female orgasm, paternal care, the shrinkage of all body parts except the brains and the genitalia, permanent breasts, etc.) appeared.

In a way, most of this happened because we select each other mostly via sexual attractiveness, respecting the choice of the other sex.

And because, consequently, for humans, sex has become a ritual, not unlike the manakin dances or the bowerbird nests.

Key Lessons from “The Evolution of Beauty”

1.      You Don’t Really Know Your Darwin
2.      The Fisherian Runaway: How Natural Selection Becomes Sexual Selection
3.      Beauty Happens – and Is All Around You

You Don’t Really Know Your Darwin

According to Prum, though his thesis may sound a bit controversial to modern Darwinists, Darwin would have undoubtedly approved of it.

Because, in addition to the natural selection theory (from the Origin), he also devised a corollary sexual selection mechanism (in the Descent) which aimed to explain the ornamental qualities which appear in many species – such as, for example, the highly impractical tail of the peacock:

Because the extravagance of its design seemed of no survival value whatsoever, unlike other heritable features that are the result of natural selection, the peacock’s tail seemed to challenge everything that he had said in Origin. The insight he eventually arrived at, that there was another evolutionary force at work, was considered an unforgivable apostasy by Darwin’s orthodox adaptationist followers. As a consequence, the Darwinian theory of mate choice has largely been suppressed, misinterpreted, redefined, and forgotten ever since.

Darwin’s Sexual Selection and the Fisherian Runaway

Darwin’s theory of mate choice includes two mechanisms – the law of the battle and the taste for the beautiful – which should explain the origins and the evolution of both armament and ornament in all species.

However, the latter one was all but scoffed at by everyone – because the female choice was too subjective to be a driving evolutionary force – until Ronald Fisher tried to explain it in an interesting manner.

Namely, according to Fisher, the ornaments originally were practical signals for fitness; however, precisely because of this, in time, they evolved to become signals on their own, and future generations developed them because the individuals with these traits were the individuals with offspring.

Here’s an interesting analogy:

Gout was historically known as the “rich man’s disease” because it appears more often in those who regularly eat meat and drink beer. So, when a poor man happened to develop gout back in the 18^th century, he wore it proudly – it gave him a chance to have sex with a money-grabber.

Beauty Happens – and Is All Around You

Prum demonstrates – through many examples from the avian world – that evolution is not only about the fittest, but also about the most beautiful or about the ones who can produce most beauty.

That’s why some birds dance and others build beautiful bowers; and that’s why humans write poems or sculpt statues of their Muses.

It’s their best shot at getting some.

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“The Evolution of Beauty Quotes”

Our Critical Review

Groundbreaking and alluring, The Evolution of Beauty was a Pulitzer Prize finalist and one of the ten best books of 2017 according to The New York Times.

We believe that it’s one of those books which will be debated for many years to come.

So, read it now – so that you can talk about it with your grandchildren.

Emir Zecovic

Emir is the Head of Marketing at 12min. In his spare time, he loves to meditate and play soccer.