Michael J. Ryan: A Taste for the Beautiful

Darwin developed the theory of sexual selection to explain why the animal world abounds in stunning beauty, from the brilliant colors of butterflies and fishes to the songs of birds and frogs. He argued that animals have “a taste for the beautiful” that drives their potential mates to evolve features that make them more sexually attractive and reproductively successful. But if Darwin explained why sexual beauty evolved in animals, he struggled to understand how. In A Taste for the Beautiful, Michael Ryan, one of the world’s leading authorities on animal behavior, tells the remarkable story of how he and other scientists have taken up where Darwin left off and transformed our understanding of sexual selection, shedding new light on human behavior in the process. Vividly written and filled with fascinating stories, A Taste for the Beautiful will change how you think about beauty and attraction. Read on to learn more about the evolution of beauty, why the sight of a peacock’s tail made Darwin sick, and why males tend to be the more “beautiful” in the animal kingdom.

What made you interested in the evolution of beauty?

For my Masters degree I was studying how male bullfrog set up and defend territories. They have a pretty imposing call that has been described as ‘jug-a-rum;’ it is used to repel neighboring males and to attract females. In those days it was thought that animal sexual displays functioned only to identify the species of the signaler. For example, in the pond where I worked you could easily tell the difference between bullfrogs, leopard frogs, green frogs, and spring peepers by listening to their calls. Females do the same so they can end up mating with the correct species. Variation among the calls within a species was thought of to be just noise, random variation that had little meaning to the females.

But sitting in this swamp night after night I was able to tell individual bullfrogs apart from one another and got used to seeing the same males with the loudest deepest calls in the same parts of the pond. I began to wonder that if I could hear these differences could the female bullfrogs, and could females decide who to mate with based on the male’s call? And also, if some calls sounded more beautiful to me, did female frogs share with me the same aesthetic?

I never got to answer these questions with the bullfrogs but I decided to pursue this general question when I started at Cornell University to work on my PhD degree.

Why did Darwin say that the sight of the peacock’s tail, an iconic example of sexual beauty, made him sick?

Darwin suffered all kinds of physical maladies, some probably brought on by his contraction of Chagas disease during his voyage on the Beagle. But this malady induced by the peacock’s tail probably resulted from cognitive dissonance. He had formulated a theory, natural selection, in which he was able to explain how animals evolve adaptations for survival. Alfred Russel Wallace developed a very similar theory. All seemed right with the world, at least for a while.

But then Darwin pointed out that many animal traits seem to hinder rather than promote survival. These included bright plumage and complex song in birds, flashing of fireflies, male fishes with swords, and of course the peacock with its magnificently long tail. All of these traits presented challenges to his theory of natural selection and the general idea of survival of the fittest. These sexy traits are ubiquitous throughout the animal kingdom but seem to harm rather than promote survival.

Sexual selection is Darwin’s theory that predicts the evolution of sexual beauty. How is this different from Darwin’s theory of natural selection?

The big difference between these two theories is that one focuses on survivorship while the other focuses on mating success. Both are important for promoting evolution, the disproportionate passage of genes from one generation to the next. An animal that survives for a long period of time but never reproduces is in a sense genetically dead. Animals that are extremely attractive but do not live long enough to reproduce also are at a genetic dead-end. It is the proper mix of survivorship and attractiveness that is most favored by selection. But the important point to realize is that natural selection and sexual selection are often opposed to one another; natural selection for example, favoring shorter tails in peacocks and sexual selection favoring longer tails. What the bird ends up with is a compromise between these two opposing selection forces.

In most of evolutionary biology the emphasis is still more on survival than mating success. But sometimes I think that surviving is just nature’s clever trick to keep individuals around long enough so that they can reproduce.

Why is it that in many animals the males are the more beautiful sex?

In most animals there are many differences between males and females. But what is the defining character? What makes a male a male and a female a female? It is not the way they act, the way they look, the way they behave. It is not even defined by the individual’s sex organs, penis versus vagina in many types of animals.

The defining characteristic of the sexes is gamete size. Males have many small gametes and females have fewer large gametes.  The maximum number of offspring that an animal can sire will be limited by the number of gametes. Therefore, males could potentially father many more offspring than a female could mother.

But of course males need females to reproduce. So this sets up competition where the many gametes of the males are competing to hook up with the fewer gametes of the females. Thus in many species males are under selection to mate often, they will never run out of gametes, while females are under selection to mate carefully and make good use of the fewer gametes they have. Thus males are competing for females, either through direct combat or by making themselves attractive to females, and females decide which males get to mate. The latter is the topic of this book.

Why is sexual beauty so dangerous?

The first step in communication is being noticed, standing out against the background. This is true whether animals communicate with sound, vision, or smells. It is especially true for sexual communication. The bind that males face is they need to make themselves conspicuous to females but their communication channel is not private, it is open to exploitation by eavesdroppers. These eavesdroppers can make a quick meal out of a sexually advertising male. One famous example, described in this book, involves the túngara frog and its nemesis, the frog-eating bat. Male túngara frogs add syllables, chucks, to their calls to increase their attractiveness to females. But it also makes them more attractive to bats, so when these males become more attractive they also become more likely to become a meal rather than a mate.

The túngara frog is only one example of the survival cost of attractive traits. When crickets call, for example, they can attract a parasitic fly. The fly lands on the calling male and her larvae crawl off of her onto the calling cricket. The larvae then burrow deep inside the cricket where they will develop. As they develop they eat the male from the inside out, and their first meal is the male’s singing muscle. This mutes the male so he will not attract other flies who would deposit their larvae on the male who would then become competitors.

Another cost of being attractive is tied up with the immune system. Many of the elaborate sexual traits of males develop in response to high levels of testosterone. Testosterone can have a negative effect on the immune system. So as males experience higher testosterone levels that might produce more attractive ornaments, but these males are paying the cost with their ability to resist disease.

How did you come to discover that frog eating bats are attracted to the calls of túngara frogs?

The credit for this initial discovery goes to Merlin Tuttle. Merlin is a well-known bat biologist and he was on BCI the year before I was. He captured a bat with a frog in its mouth. Merlin wondered how common this behavior was and whether the bats could hear the calls of the frogs and use those calls to find the frogs.

When Stan Rand and I discovered that túngara frogs become more attractive when they add chucks to their calls, we wondered why they didn’t produce chucks all the time. We were both convinced that there were some cost of producing chucks and we both thought it was likely the ultimate cost imposed by a predator.

Merlin contacted Stan about collaborating on research with the frog-eating bat and frog calls, and Stan then introduced Merlin to me. The rest is history as this research has blossomed into a major research program for a number of people.

Is beauty really in the eye of the beholder?

Yes, but it is also in the ears, the noses, the toes and any other sense organ recruited to check out potential mates. All of these sense organs forward information to the brain where judgements about beauty are made. So it is more accurate to say beauty is in the brain of the beholder. It might be true that the brain is our most important sex organ, but the brain has other things on its mind besides sex. It evolves under selection to perform a number of functions, and adaptations in one function can lead to unintended consequences for another function. For example, studies of some fish show that the color sensitivity of the eyes evolves to facilitate the fish’s ability to find its prey. Once this happens though, males evolve courtship colors to which their females’ eyes are particularly sensitive. This is called sensory exploitation.

A corollary of ‘beauty is in the brain of the beholder’ is that choosers, usually females, define what is beautiful. Females are not under selection to find out which males are attractive, by determining which males are attractive. They are in the driver’s seat when it comes to the evolution of beauty.

What is sensory exploitation?

We have probably all envisioned the perfect sexual partner. And in many cases those visions do not exist in reality. In a sense, the same might be true in animals. Females can have preferences for traits that do not exist. Or at least do not yet exist. When males evolve traits that elicit these otherwise hidden preferences this is called sensory exploitation. We can think of the evolution of sexual beauty as evolutionary attempts to probe the ‘preference landscape’ of the female. When a trait matches one of these previously unexpressed preferences, the male trait is immediately favored by sexual selection because it increases his mating success.

A good example of this occurs in a fish called the swordtail. In these fishes males have sword-like appendages protruding from their tails. Female swordtails prefer males with swords to those without swords, and males with longer swords to males with shorter swords. Swordtails are related to platyfish, the sword of swordtails evolved after the platyfish and swordtails split off from one another thousands of years ago. But when researchers attach a plastic sword to a male platyfish he becomes more attractive to female platyfish. These females have never seen a sworded male but they have a preference for that trait nonetheless. Thus it appears that when the first male swordtail evolved a sword the females already had a preference for this trait.

Do the girls really get prettier at closing time, as Mickey Gilly once sang?

They sure do, and so do the boys. A study showed that both men and women in a bar perceive members of the opposite sex as more attractive as closing time approaches. This classic study was repeated in Australia where they measured blood alcohol levels and showed that the ‘closing time’ effect was not only due to drinking but to the closing time of the bar.

The interpretation is of these results is that if an individual wants to go home with a member of the opposite sex but none of the individuals meet her or his expectations of beauty, the individual has two choices. They can lower their standards of beauty or they can deceive themselves and perceive the same individuals as more attractive. They seem to do the latter.

Although we do not know what goes on in an animal’s head, they show a similar pattern of behavior. Guppies and roaches are much more permissive in accepting otherwise unattractive mates as they get closer to the ultimate closing time, the end of their lives. In a similar example, early in the night female túngara frogs will reject certain calls that are usually unattractive, but later in the night when females become desperate to find a mate they become more than willing to be attracted to these same calls.  It is also noteworthy that middle-aged women think about sex more and have sex more often than do younger women.

Deception seems to be widespread in human courtship. What about animals?

Males have a number of tricks to deceive females for the purpose of mating. One example involves moths in which males make clicking sounds to court females. When males string together these clicks in rapid succession it sounds like the ‘feeding buzz’ of a bat, the sound a bat makes as it zeros in on its prey. At least this is what the female moths think. When they hear these clicks they freeze and the male moth is then able to mount the female and mate with her with little resistance as she appears to be scared to death, not of the male moth but of what she thinks is a bat homing in on her for the kill.

Other animals imitate food to drive female’s attention. Male mites beat their legs on the water surface imitating vibrations caused by copepods, the main source of food for the water mites. When females approach the source of these were vibrations they find a potential mate rather than a potential meal.

What about peer pressure? We know this plays a role in human in interactions, and the influence our perceptions of beauty? What about animals, can they be subjected to peer pressure?

Suppose a woman looks at my picture and is told rate my attractiveness on the scale of 1 to 10. Another woman is asked to do the same but in this picture I am standing next to an attractive woman. Almost certainly I will get a higher score the second time; my attractiveness increases although nothing about my looks have changed, only that I was consorting with a good-looking person.  This is referred to as mate choice and it is widespread in the animal kingdom.

Mate choice copying was first experimentally demonstrated in guppies. Female guppies prefer males who have more orange over those who have less orange. In a classic experiment, females were given a choice between a more than a less colorful male. They preferred the more colorful male and then were returned to the center of the tank for another experiment. In this instance they saw the less colorful and less preferred male courting a female. That female was removed and the test female was tested for her preference for the same two males once again. Now the female changes her preference and prefers what previously had been the less preferred male. She too seems to be employing mate choice copying.

Many animals learn by observing others. Mate choice copying seems to be a type of observational learning that is common in many animals in many domains. It might suggest that we be careful with whom we hang out.

What is the link between sexual attraction in animals and pornography in humans?

Animal sexual beauty is often characterized by being extreme: long tails, complex songs, brilliant colors, and outrageous dances. The same is often true of sexual beauty in humans. Female supermodels, for example, tend to be much longer and thinner than most other women in the population, male supermodels are super-buff—hardly normal. Furthermore, in animals we can create sexual traits that are more extreme than what exists in males of the population, and in experiments females often prefer these artificially exaggerated traits, such as: even longer tales, more complex songs, and more brilliant colors than exhibited by their own males. These are called supernormal stimuli. Pornography also creates supernormal stimuli not only in showcasing individuals with extreme traits but also in creating social settings that hardly exist in most societies, this manufactured social setting is sometimes referred to as Pornotopia.

RyanMichael J. Ryan is the Clark Hubbs Regents Professor in Zoology at the University of Texas and a Senior Research Associate at the Smithsonian Tropical Research Institute in Panama. He is a leading researcher in the fields of sexual selection, mate choice, and animal communication. He lives in Austin, Texas.


Bird Fact Friday – Romancing a mate

From page 146 of Bird Brain:

Food sharing is a behavior at the heart of many avian pair bonds. Some males offer a potential partner a nuptial gift as a display of their ability to provide. In some cases, gift-giving continues throughout the pair’s life as a means of solidifying their bond.

Bird Brain
An Exploration of Avian Intelligence
Nathan Emery
With a foreword by Frans de Waal

EmeryBirds have not been known for their high IQs, which is why a person of questionable intelligence is sometimes called a “birdbrain.” Yet in the past two decades, the study of avian intelligence has witnessed dramatic advances. From a time when birds were seen as simple instinct machines responding only to stimuli in their external worlds, we now know that some birds have complex internal worlds as well. This beautifully illustrated book provides an engaging exploration of the avian mind, revealing how science is exploding one of the most widespread myths about our feathered friends—and changing the way we think about intelligence in other animals as well.

Bird Brain looks at the structures and functions of the avian brain, and describes the extraordinary behaviors that different types of avian intelligence give rise to. It offers insights into crows, jays, magpies, and other corvids—the “masterminds” of the avian world—as well as parrots and some less-studied species from around the world. This lively and accessible book shows how birds have sophisticated brains with abilities previously thought to be uniquely human, such as mental time travel, self-recognition, empathy, problem solving, imagination, and insight.

Written by a leading expert and featuring a foreword by Frans de Waal, renowned for his work on animal intelligence, Bird Brain shines critical new light on the mental lives of birds.

Firefly Fact Friday – Every man for himself

“But we’ve learned that synchrony, or paradoxically cooperative male behavior, is merely the first stage in these [Photinus carolinus] fireflies’ courtship rituals; once a female appears on the scene, males’ cooperation abruptly ends. Now it’s every man for himself as they gear up for competition mode, each male trying to stand out from his rivals… Turning competitive, males crowd around the female, grappling fiercely and shoving one another with their head shields. Even after one victorious male mates successfully with the female, his ever-hopeful rivals remain piled atop the mating pair for hours.” p. 98

Silent Sparks
The Wondrous World of Fireflies
Sara Lewis

LewisFor centuries, the beauty of fireflies has evoked wonder and delight. Yet for most of us, fireflies remain shrouded in mystery: How do fireflies make their light? What are they saying with their flashing? And what do fireflies look for in a mate? In Silent Sparks, noted biologist and firefly expert Sara Lewis dives into the fascinating world of fireflies and reveals the most up-to-date discoveries about these beloved insects. From the meadows of New England and the hills of the Great Smoky Mountains, to the rivers of Japan and mangrove forests of Malaysia, this beautifully illustrated and accessible book uncovers the remarkable, dramatic stories of birth, courtship, romance, sex, deceit, poison, and death among fireflies.

The nearly two thousand species of fireflies worldwide have evolved in different ways—and while most mate through the aerial language of blinking lights, not all do. Lewis introduces us to fireflies that don’t light up at all, relying on wind-borne perfumes to find mates, and we encounter glow-worm fireflies, whose plump, wingless females never fly. We go behind the scenes to meet inquisitive scientists who have dedicated their lives to understanding fireflies, and we learn about various modern threats including light pollution and habitat destruction. In the last section of the book, Lewis provides a field guide for North American fireflies, enabling us to identify them in our own backyards and neighborhoods. This concise, handy guide includes distinguishing features, habits, and range maps for the most commonly encountered fireflies, as well as a gear list.

A passionate exploration of one of the world’s most charismatic and admired insects, Silent Sparks will inspire us to reconnect with the natural world.

For more information, visit Sara Lewis’s website! To check out some cool firefly videos, find her on Vimeo.

Bird Fact Friday – Why do birds hybridize?

From page 26-27 of Waterfowl of North America, Europe & Asia:

Birds mate with other birds of different species in the wild for several reasons. Usually there is genetic closeness, since if the parent genomes’ are too distant offspring will be sterile or unviable. Birds with different courtship rituals, breeding times, or habitats usually won’t mate, unless geographic restrictions are lifted (such as in captivity) when it becomes more common. Sometimes hybridization occurs because of interspecific parasitism, which leads some species of ducks to lay a portion of their eggs in the nests of other species. This can produce an imprinting phenomenon in the female of the host species, affecting the choice of sexual partners later in life. Other causes of hybridization are described in Waterfowl of North America, Europe & Asia.

Waterfowl of North America, Europe, and Asia
An Identification Guide
Sébastien Reeber

ReeberThis is the ultimate guide for anyone who wants to identify the ducks, geese, and swans of North America, Europe, and Asia. With 72 stunning color plates (that include more than 920 drawings), over 650 superb photos, and in-depth descriptions, this book brings together the most current information on 84 species of Eurasian and North American waterfowl, and on more than 100 hybrids. The guide delves into taxonomy, identification features, determination of age and sex, geographic variations, measurements, voice, molt, and hybridization. In addition, the status of each species is treated with up-to-date details on distribution, population size, habitats, and life cycle. Color plates and photos are accompanied by informative captions and 85 distribution maps are also provided. Taken together, this is an unrivaled, must-have reference for any birder with an interest in the world’s waterfowl.

Bird Fact Friday – 50 Shades of Grouse

From page 9 of The Birdwatcher’s Companion to North American Birdlife:

For many species of grouse during courtship rituals, the male will act aggressively towards the female and treat her as a rival before responding to the female’s attempts to gradually encourage a more benign approach by behaving in a way that defuses the male’s attack response.

The Birdwatcher’s Companion to North American Birdlife
Christopher W. Leahy
Illustrations by Gordon Morrison

LeahyThe quintessential A-Z guide, this is a book that anyone interested in birds will want to have close at hand. First published more than twenty years ago, this highly respected reference volume has been fully revised and updated. It captures the fundamental details as well as the immense fascination of North American bird life in a style that is authoritative, yet fresh, witty, and eminently readable.

Both a practical handbook for amateurs and a handy reference for seasoned birders, it provides accounts of the basic elements of birdlife, as well as a wealth of easy-to-access information on such subjects as bird physiology and anatomy, terms and jargon, name definitions and etymology, and ornithological groupings.

Readers will discover everything from the color of a dipper’s eggs (glossy, white, and unmarked) to the number of species of woodpeckers in the world (216). They will also find more than one hundred of the best-known and most colorful colloquial names for birds, alphabetized and briefly defined. Collective nouns relating to birdlife–for example, “an exaltation of larks”–are included in the “Nouns of Assemblage” section. Biographical sketches of persons responsible for describing or naming a significant number of North American species are also included, as well as handsome and accurate illustrations by Gordon Morrison. And for those who want to go beyond reading about their favorite birds and take to the great outdoors, the book offers still more useful information: descriptive entries on a selection of the best-known birdwatching spots of North America.