Cover image for Sensory exotica : a world beyond human experience
Sensory exotica : a world beyond human experience
Hughes, Howard C.
Personal Author:
Publication Information:
Cambridge, Mass. : MIT Press, [1999]

Physical Description:
xi, 345 pages : illustrations ; 24 cm
General Note:
"A Bradford book."
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QP435 .H84 1999 Adult Non-Fiction Non-Fiction Area
QP435 .H84 1999 Adult Non-Fiction Open Shelf

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Winner, category of Biological Sciences, 1999 Professional/Scholarly Publishing Annual Awards Competition presented by the Association of American Publishers, Inc. Certain insects and animals such as bees, birds, bats, fish, and dolphins possess senses that lie far beyond the realm of human experience. Examples include echolocation, internal navigation systems, and systems based on bioelectricity. In this book Howard C. Hughes tells the story of these "exotic" senses. He tells not only what has been discovered but how it was discovered--including historical misinterpretations of animal perception that we now view with amusement. The book is divided into four parts: biosonar, biological compasses, electroperception, and chemical communication. Although it is filled with fascinating descriptions of animal sensitivities--the sonar system of a bat, for example, rivals that of the most sophisticated human-made devices--the author's goal is to explain the anatomical and physiological principles that underlie them. Knowledge of these mechanisms has practical applications in areas as diverse as marine navigation, the biomedical sciences, and nontoxic pest control. It can also help us to obtain a deeper understanding of more familiar sensory systems and the brain in general. Written in an entertaining, accessible style, the book recounts a tale of wonder that continues today--for who knows what sensory marvels still await discovery or what kind of creatures will provide the insights? Winner of the 1999 AAP/PSP award in the category of Biological Sciences, granted by the Professional/Scholary Reference Division of the Association of American Publishers.

Reviews 2

Publisher's Weekly Review

What's it like to be a bat or a bee? In one sense, we can never know; in another, we can find out by studying the extraordinary perceptual systems by which these and other animals process the world. Bats' sonar lets them discover their prey, their cave-mates and their caves in the pitch-dark. Dolphins use similar sonar systems to discover obstacles, food and one another in the nearly lightless ocean: they even alter their frequencies (like cell phone users) to avoid interference. And chemical communication systems regulate sex in moths, rats, pigs and, probably, people: pigs hunt truffles so well because the valuable fungus contains a pig sex hormone. Hughes, a professor of psychology at Dartmouth, describes not only how these sixth and seventh senses work, but how scientists found out about them. An Italian in the 1790s struck out the eyes of bats (who navigated just fine afterwards); a Swiss surgeon plugged their ears (they got lost). Despite these tests, zoologists until the 1930s believed that bats used not hearing, but some special sense of touch. Most dolphin sonar research, by contrast, requires some measure of dolphin cooperation. Hughes's forays into animal sensoria require that he explain concepts from acoustics, anatomy, neurology, physiology and animal behavior; he does so cleanly and well, though his style can get condescending or gee-whizzish. ("What did [a researcher] see? Well, as already indicated, he saw... ") Nevertheless, readers with any interest in animal biology will want to track this book down--even if they have to use sonar. 124 b&w photos and illustrations. (Jan.) (c) Copyright PWxyz, LLC. All rights reserved

Library Journal Review

Bats use their own sonar systems to navigate and to catch prey while in flight; so do dolphins and other marine mammals. Hughes (psychology, Dartmouth Coll.) has written a clear and well-illustratedÄbut sometimes overly chattyÄbook, aimed at a general audience, about these and other sensory systems. He thoroughly and clearly covers biosonar (a.k.a. echolocation) and electroreception in various species of fish, and he touches on the magnetic and solar biological compasses found in some birds and insects. And although the last four short chapters (on pheromones and chemoreception) seem to have been added later, this is, overall, a well-written and informative introduction to these systems; recommended for public libraries.ÄPatrick J. Wall, University City P.L., MO (c) Copyright 2010. Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.



Chapter One Prologue: Perceptions, Misperceptions, and Egocentrism As a child, I read an old parable whose message has periodically come to mind ever since. I frequently have occasion to tell it to students in classes, and find I need an occasional reminder myself. It's a story about four blind Hindus who had never seen an elephant. One day, they went to visit an elephant for the first time. The first stepped toward the animal, and happened to touch its ear. "The elephant is much like a fan," he concluded. The second touched the leg and thought the first a fool. "Elephants are nothing like fan," he said. "They are more like a tree trunk." The third felt the animal's side, and concluded that elephants are like walls. The fourth touched the trunk, and decided elephants are like large snakes. The message, of course, is that we should not mistake the way things seem to us for the way they really are. We all need to be reminded that our limited perspective can lead to gross misperceptions of the nature of things. Despite the wisdom acquired through age and education, most of us are quite capable of mistaking partial information for conclusive evidence. Few of us can run a marathon, but we are all plenty fit enough to jump to an erroneous conclusion!     People can be paradoxical. We seem to have a real need to explain the phenomena we see. But often we seem curiously insensitive to the fundamental difference between a description and an explanation of natural events. If a child sees the aurora borealis, she might naturally ask, "What's that?" The parent might respond, "Oh, that's the aurora borealis." Many children will be unsatisfied by that answer. Knowing a name is not an explanation, the exceptional child replies, "What is the aurora borealis?" The parent now mumbles something about how the atmosphere creates these nighttime lights, and that a similar effect occurs near the South Pole. Many children (and adults) would find that "explanation" satisfactory.     Notice, however, that nothing has really been explained. The phenomenon has just been described in more elaborate terms. A real explanation would include why the lights are seen only near the poles and not the equator, and how they relate to sunspots. A real explanation must provide an understanding of electromagnetic radiation, Earth's magnetic field, and how these two interact to ionize gas molecules in the upper atmosphere. This in turn requires an understanding of exactly what "ionization of gases" means, and how ionized gases can produce light. The real explanation is pretty elaborate, and it takes a little more effort to grasp. But it does provide us with a much deeper understanding. That deeper understanding is often accompanied by a much more profound appreciation of the nature and beauty of the aurora. I hope this book serves that purpose for a small subgroup of nature's mysteries: sensory modalities beyond the realm of ordinary human experience.     So our concern is with the perceptual world of other creatures, and our understanding is made more difficult because we have no direct way to measure such things. It is hard enough for humans to try to understand the mental life of other humans. We spend a great deal of effort trying to communicate with one another, often with very limited success. It's difficult enough to formulate your ideas or feelings, and try to communicate them accurately to another. A listener might think he understands, and may assure you that he really does. But how do you know? How can you be sure? Our mental lives are private, and it's hard to make them public, even when we want to. We do have one ability that contributes immeasurably to our attempts at communication. That, of course is language. Dr. Doolittle not withstanding, that advantage is not available in our attempt to understand other animals, and as a result, misperceptions of even our closest relatives on the tree of life are common.     So if you wanted to know whether birds can sense when a storm is approaching, or whether cats can "feel" that an earthquake is imminent, how would you find out? Clearly, you would have to make such determinations by some aspect of their behavior, and that can be a very tricky business.     Consider, for instance, the case of Clever Hans. Hans was a horse who lived in the late nineteenth century. Reportedly, Hans could count. He not only could indicate his age, or the age of his owner, but he also could perform simple arithmetic operations like addition and subtraction. Billed as the horse that knew simple mathematics, Hans become quite a celebrity. He and his owner toured extensively in Europe, demonstrating these remarkable equine computational abilities to appreciative audiences--for a fee. When asked to perform a certain calculation, Hans would tap out the answer with a front hoof (figure 1.1).     A psychologist named Oskar Pfungst eventually was able to provide some insight as to how this done. Although Pfungst established that anyone could ask Hans the question, he discovered that Hans could provide the right answer only if he could see his owner. Apparently, the owner provided subtle visual cues: Hans would simply continue to tap until cued to stop by his owner. A cheap trick perpetrated by a common charlatan? The work of a con artist? Well, the situation was a little more complex and interesting than that. It appears that the owner was completely unaware that he was providing Hans with any cue. He did not know exactly what he did that told Hans the answer. Whatever cue Hans had learned, it was so subtle that determined human observers could not figure out exactly what it was.     Clever Bertrand provides an even more dramatic example. Bertrand was a contemporary of Hans who also could perform arithmetic calculations (apparently, horses were smarter back then). But unlike Hans, Bertrand was blind! Most experts agreed that the horse must have used subtle auditory cues, although once again the exact nature of these cues were never established (Grier and Burk, 1996).     Other entertaining tales of misperception and misinterpretation of animal behavior and animal intelligence abound. In an article titled "Myths of Animal Psychology," C. O. Whitman adds some interesting cases to what is quite a lengthy list. He describes a vicious attack by a large boar on a 19-year-old boy outside of Rochester, New York. The young man, a Mr. George Howard, was grooming his favorite steed when a large hog broke out of its pen. The boar fiercely attacked young Mr. Howard, who fell to the ground near the horse's feet. Just as the hog was about to inflict the death blow, the horse kicked the hog away. Surely the horse had saved the boy's life!     The story appeared in the Rochester Union and Advertiser , and, consistent with the highest standards of journalism, was corroborated by an eyewitness. The headline read, "A Horse Protects His Master from the Tusks of a Savage Boar." Whitman points out, however, that the actual circumstance do not justify the conclusion that the horse was trying to save its master. Rather, Whitman suggests that it was a simple act of self-defense on the part of the horse that was misinterpreted by both the victim and the witness. Whitman's article was printed in 1899.     Now you might think that much has changed in the last 100 years. We are more sophisticated than people were way back then. But in many ways, little has changed. Many people are still quite willing to resort to the mystical or the supernatural in search of their explanations. Take, for example, an article in a Sunday edition of the San Francisco Chronicle (April 1996), which describes the curious (and perhaps dismaying) resurgence of dowsing in America. Dowsing is that method of finding water, oil, or gold using a rod. As the dowser approaches an underground spring or vein of gold, the dowsing rod begins to point downward--apparently on its own. Something like a Ouija board. One part of the article describes a man who uses a dowsing rod to communicate with whales. He stands on the high cliffs along the California coastline, and claims to communicate with unseen whales over remarkable distances. Well, you might think this exceedingly unlikely, even absurd. And I agree. By what physical means could such communications possibly take place? Still, many people wish to adhere to beliefs that appear to defy the laws of physics.     There is something about our nature that longs to believe in magic, in things that appear supernatural. But what if I told you that it is very likely that whales can probably communicate with other whales over miles of open ocean? Or that many animals have an internal compass that they use as a navigational tool that permits them to migrate over long distances? Or that some fish communicate using coded messages that are sent through the water via electrical fields, and that bees and other insects see things that are completely invisible to our eyes? Sometimes the facts are stranger than any fiction, and, as I hope to show, more remarkable than any magic trick or illusion--because they are true, and because their explanations rely on natural laws.     We know a great deal about how many of these exotic senses work. We understand them in mechanistic terms. Such a mechanistic understanding doesn't diminish the sense of wonder we can have about these elegant systems. Rather, it enhances it.     When we consider sensory perception, we naturally focus on the five "special" senses: vision, hearing, touch, taste, and smell. It is through these senses that we experience the world outside our bodies. There is also the world inside our bodies, and there are sensory organs that provide information crucial to internal body states. Our senses of balance, of body motion, and of posture, depend on sensory organs in the inner ear, in our joints, and in muscles. There are even organs that monitor such things as the levels of carbon dioxide in the blood, blood pressure, and blood glucose levels. These organs provide the brain with information essential to life, but they do not produce conscious sensory experiences (otherwise, people would be aware of the onset of hypertension, and it would less frequently go untreated).     Rather than ESP, perhaps we should call these internal sensory systems our sixth sense--a sense beyond the more familiar modalities of vision, hearing, touch, taste, and smell. If so, then this book is about the seventh, eighth, ninth and tenth senses. What are these new sensory modalities? Well, first of all, they are not new. Their possessors have been relying on them for millions of years. It's just that we've "discovered" them only since the 1970s and 1980s. But newness aside, they include such hi-tech systems as biological sonar systems, sophisticated navigational systems, and senses based on electrical fields.     These systems initially seemed so unlikely, so incredible, that many were reluctant to believe they existed. But they do. And in just a couple of decades we have learned a great deal about the detailed working of these remarkable sensory systems. In some respects, the mechanisms are not very different from the more familiar mechanisms of vision, hearing, or touch. In other ways, the differences are quite dramatic. They have one thing in common, however: they all provide vivid illustrations of the creative genius inherent in the process of evolution.     When we speak of sensory experiences beyond the realm of our five special senses, many may think of supernatural things like extrasensory perception: clairvoyance (the ability to see that which is not visible) or telepathy (the ability to sense the "thought waves" of others). Some have suggested that there may be a resurgence of mysticism in modern society, which is curious because there is not a single case of extrasensory perception that has withstood the tests of rational analysis and rigorous experimental control. But, as we shall soon see, the workings of biosonar, electroreception, and other exotic senses are far more interesting than bending spoons and reading unseen numbers on a stranger's driver's license.     Imagine a sonar system more sophisticated than that found in our most advanced submarines. Now imagine that system is used by a small bat that easily fits in the palm of your hand. All the computations that permit the bat to identify the distance, the speed, and even the particular species of insect target are performed by a brain that is smaller than your thumbnail! That is a truly remarkable device. But it is a device. It can be understood in mechanistic terms. Despite all the folklore associated with bats, no appeal to forces beyond natural laws is necessary. And that is what is truly remarkable about these most interesting creatures.     Each of our senses is a wondrous system of information processing. The events that culminate in perception begin with specialized receptor cells that convert a particular form of physical energy into bioelectric currents. Different receptors are sensitive to different types of energy, so the properties of the receptor cells determine the modality of a sensory system. Ionic currents are the currency of neural information processing, and current flows that begin in the receptors are transmitted through complex networks of interconnected neurons and, in the end, result in a pattern of brain activity we call perception. We can distinguish a red 1957 Chevy from a blue 1956 Ford because each car produces a different pattern of neural activity.     The percepts that result from all this brain activity usually provide us with an astonishingly accurate window through which we view the outside world. If that were not so, we couldn't hit a curve ball, or teach kids how to catch one (you've probably noticed they invariably need instruction). In short, our interactions with the world would not be possible. We interact with our environments so effectively and so effortlessly, it is difficult to appreciate the extensive computations that underlie even the simplest sensory experience. We become convinced that we see "what is really out there." But there are some refractive errors in our sensory windows to the world, some distortions. And our perceptual windows are not as transparent as we think.     For instance, our sense of vision depends upon wavelengths of light that range from about 430 to 700 billionths of a meter. But the entire electromagnetic spectrum covers a range that is approximately 300,000,000,000,000,000,000,000,000,000,000,000 times larger than what we call the visible spectrum! Clearly, there is a (very large) portion of the electromagnetic spectrum that we cannot detect. That doesn't mean the energy isn't there, and it doesn't mean that other creatures cannot detect portions of it that to us are not visible. Our visual receptor cells are sensitive to an incredibly small range of wavelengths. Other animals are endowed with different types of receptors that render them sensitive to portions of the spectrum that we cannot see. Those wavelengths that are a little shorter than what we call blue light are called ultraviolet wavelengths, or UV light. We can't see UV light, but some insects can, and they use their UV sensitivity as an aid to navigation. In contrast, wavelengths that are a little longer than what we call red light are called the infrared wavelengths. Infrared (IR) radiation is emitted by warm objects. Have you seen the special night goggles that allow people to see in the dark? They work because they have detectors that are sensitive to the infrared part of the spectrum. Any object that is warmer than its surroundings will produce an IR "signature," and the goggles convert those infrared emissions to wavelengths of light that we are able to detect.     Certain snakes evolved their own form of IR night goggles: little pits that act like pinhole cameras for infrared radiation. Snakes use their infrared system to detect and localize their warm-blooded prey. The system was discovered when it was recognized that an agitated rattlesnake will produce accurate strikes at a warm soldering iron, even if its eyes are covered. All members of the family of venomous snakes known as pit vipers have these infrared detectors--it is the infrared-sensitive pits that give them their name. As far as we know, only two types of snakes have this infrared sensitivity--the pit vipers and some boid snakes (constrictors like the boa constrictor). It would probably be of no use to warm-blooded creatures. Their own body heat would produce so much noise in the system that detection of other objects would not be possible. For this system to work, the animal has to be a cold-blooded hunter ... as cold as the desert night. Rattlesnakes have been tracking their prey by the heat trail they leave behind for millions of years.     Analogous differences in the range of hearing exist for different animals. Dog whistles are one familiar example: we can't hear the whistle, but dogs can. The reason is that they are sensitive to a higher range of sound frequencies than humans are. Yet the auditory abilities of dogs pales in comparison with that of bats or dolphins. Some bats can actually hear the footsteps of their insect prey!     Although dogs can hear higher auditory frequencies than humans, they are most notable for their sense of smell. U.S. News & World Report recently had a story of a dog that apparently can detect the onset of its owner's epileptic seizures--45 minutes before they occur! The pet's early warnings allow the victim to prepare for the impending attack, for instance, by avoiding hazardous activities like driving. Family members say the accuracy rate is as high as 97 percent. Clairvoyance? A case of canine precognition? Probably not. It is much more likely that the dog can detect certain chemicals that may be associated with the onset of an epileptic seizure.     Descriptive accounts of these remarkable feats of sensory perception may be entertaining, but they are just the beginning of the story we wish to tell. Our ultimate goal is and ought to be an understanding of the mechanisms that underlie these abilities. What anatomical and physiological principles permit the astonishing levels of sensitivity displayed by these sensory receptors? How do these systems avoid the many sources of noise that would otherwise degrade perceptual performance? How do the animals' brains process the receptor responses, and how are these exotic modalities integrated with inputs from more conventional sensory systems? What conditions lead to the evolution of such systems, and what advantages are gained by having them? These are the questions we hope to address in the following pages.     In every case, the initial evidence for a new sensory modality came from behavioral experiments: from observations of what the animals actually do . The animal's behavior suggested they must possess some way of sensing environmental events that is different from our own. As early as the 18th century, the bat's ability to avoid obstacles in complete darkness was a subject of scientific investigation, although the fact that they do this by using echoes of calls they produce was not understood until the 1940s. Soon thereafter, a similar system was discovered in dolphins. The auditory modality of these animals thus has two operating modes: a passive mode by which they detect externally produced sounds, and the active, biosonar mode that relies on reflections of self-produced sonar signals.     The sensory modality of electroreception also operates in an active mode and a passive mode: some fish passively sense electrical fields produced by potential prey, while others detect prey by analyzing the disturbances in an "electric halo" that they themselves produce. We hope to do more than produce a compendium of interesting facts that modern science has discovered about a variety of odd and curious creatures, however. These exotic senses illustrate alternative ways of experiencing our planet--ways that, without science and technology, would have forever remained invisible to us. We'll get a brief glimpse of the incredible creativity and ingenuity of life on this planet. We'll celebrate that creativity, and we'll salute the ingenuity of the many people who helped unravel these marvels of the evolutionary process.     The book is a story about what has been discovered, and also of how it was discovered. And it is indeed a story, a story that has many of the elements of a good mystery. We will encounter vague and sometimes misleading clues, and find out how the true meaning of those clues was eventually deciphered by clever detectives. Often those clues were misinterpreted for hundreds of years, and those misinterpretations led to wildly unrealistic claims about what animals could and could not do. Today those old ideas seem quaint, provincial, unsophisticated, and maybe even silly. We shouldn't be too harsh or glib, however. There are no road maps to guide our search for understanding. Sometimes it is our own parochialism, our own narrow frame of reference, that provides the biggest obstacle.     How else can we explain that as late as 1912, bats were thought to navigate in complete darkness by using an elaborate sense of touch? How could so many learned people view the incredible, elaborate ears possessed by bats, and yet discount any role for hearing? The answer is simple. People found it difficult to believe that hearing was involved because they couldn't hear the bats making any sounds! And there were no instruments that could detect the acoustic emissions the bats were in fact producing. The critical demonstrations invariably depended upon the availability of an appropriate technology.     So we are about to begin several stories of discovery. The main characters are bats, dolphins, birds, bees, fish, and other assorted creatures. Humans play a fairly peripheral role in these tales--supporting members of the cast at best. Parts of the stories are very old. Indeed, from the perspective of the characters themselves, the plots go back millions of years. And like any good story, our characters have a motive--the most fundamental motive of all life: survival. The survival of their species, pure and simple. In their quest for survival, animals have evolved some truly astonishing abilities that we shall explore and attempt to understand.     We didn't write these tales, we are simply trying to understand the plot. In many instances, our attempts go back to the beginnings of civilization. Consider, for a moment, the case of electric fish. They represent some of the oldest living vertebrates. Our first encounter was no doubt by accident. Can you imagine the reaction, the complete and utter astonishment, that gripped the first person who touched the animal we now call a torpedo ray? It can deliver an electric shock of 350 volts! Zap! Now there's a sensory experience you'll not likely forget, but we might not characterize it as exotic. Stunning, perhaps, but not exotic.     The explanations given for the remarkable powers of the torpedo ray--now they were exotic. That shouldn't surprise us. What could some poor ancient mariner make of such a thing? How would it fit his philosophy of life? He didn't know anything about electricity, about how it's made, or about how it affects nerves or muscles. He certainly had no appreciation whatsoever that electricity is a form of energy essential to all life.     In an interesting and entertaining account, Chau Wu (1984) tells us of the early attempts to understand the nature of the shocks produced by the torpedo ray. The first written descriptions of the shocks delivered by the Mediterranean black torpedo came from the ancient Greeks, who knew that the shocks could cause numbness and a stuporous state in anything that touched the ray. They also knew that these effects could be transmitted through seawater, iron spears, and reeds. So they were doing primitive experiments on these creatures. They were trying to explain a curious natural phenomenon.     The generally offered explanation was that the ray emitted some microscopic venom, or a substance referred to as "effluviums of their nature," which was transmitted like darts or arrows to the victim. The soporific effects were of great interest. Galen, the greatest physician of ancient times (Greece, A.D. 130-200), theorized these effects were due to a "frigidity" of the nerves, and likened the transmissions from the ray to extreme cold. This idea that the shocks were a form of cold transmitted through water and other media held sway for over a thousand years, for it was not until the late 1700s that the electric nature of the shocks was firmly established.     The rays were considered to have significant medicinal value. The official cure for headache in first-century Rome was to place a torpedo ray on the head until the pain vanished! For gout, the prescription was to stand on a ray until the numbness reached the knees (Wu, 1984). What we now call strongly electric fish may have provided the earliest treatments for the relief of pain. Interestingly, the natives of Amazonia found similar uses for electric eels. In China, electric catfish were used to treat certain nerve disorders.     Although these early uses of electrotherapy may have done more to alleviate symptoms than to cure, the scientific studies of the torpedo ray performed during the 18th century played a prominent role in our early understanding of bioelectric phenomena in general. This spawned a branch of biological science we now call electrophysiology. Of course today we know that all major body systems--the circulatory system, hormonal systems, muscle systems, and the nervous system, are powered by "electrical batteries" that are an inherent property of living cells. The ray may not be the best cure for gout, but it has contributed mightily to medical science. Indeed, the similarities between muscle cells and the ray's electric organ, in conjunction with its unique anatomy, have made electric organs a favored model system in studies of the chemical interactions between nerves and muscles--studies that it is hoped will some day provide cures for a variety of neuromuscular diseases, such as myasthenia gravis.     Understanding some other exotic sensory systems has led to practical applications that range from the control of insect pests through the development of more sophisticated sonar and radar systems to new types of effective shark repellents. We are all familiar with new devices that have become an essential part of our everyday lives--devices that would not have been invented without essential discoveries in basic science research of all types, in all disciplines. Who knows at what stage of development the computer industry might find itself were it not for the American space program of the 1960s and 1970s? And basic science will no doubt continue to make important practical contributions. You can be assured, for example, that the U.S. Navy will continue its longtime interest in animal sonar systems. The reason is simple. The sonar system of a bat rivals that of the most sophisticated man-made devices available. And the bat does it all using a brain that is the size of your thumbnail. Surely we still have much to learn in terms of processing efficiency and elegance from these mammals that "fly with their hands"!     The search for insect sex and alarm pheromones--chemicals that have incredible powers of attraction or dispersal--will continue as we attempt to add new, natural, nontoxic weapons to our arsenal against insect pests. Despite these potential benefits, the ultimate justification for scientific research cannot be measured in terms of national defense, the gross national product, or the Index of Economic Indicators. It comes from a deeper source. It comes from the inquiring nature of the human spirit.     Science is a process. It continues today and will continue into the uncharted future. This book tells a story that is not yet complete. While we may look at early attempts to understand nature with amusement, who knows how the views we hold today will appear in the light of another 100 years of scientific progress? Who can foretell what kinds of new marvels await discovery, what important lessons we will learn, or what kind of creature will provide the instruction?

Table of Contents

1 Prologue: Perceptions, Misperceptions, and Egocentrism
I Biosonar: Echoes In The Night
2 The Discovery
3 The Bat Call
4 Processing the Echo -- The Sonar Receiver A Biosonar Receiver: The Auditory System of the Mustache Bat
5 Variations on a Theme: Sonar Beneath the Seas
6 A Different Kind of Sonar Transmitter: The Dolphin Call
7 The Dolphin's Sonar Receiver
II Biological Compasses
8 Maps, Mobility, and the Need for a Compass
9 Animal Migration: A Compass in the Head?
The Discovery of a Solar Compass
A Celestial Compass
The Discovery of Magnetoreception
The Human Compass Revisited
10 The Search for the Magnetoreceptor
Little Magnets in the Head?
A Compass in the Eye?
11 The Sun Compass of Bees and Ants
III Electroreception: An Ancient Sense
12 The Discovery of Electroreception
13 The Electoreceptor
14 The Nature of Electroreceptors
15 The Electric Organ
16 Electroreception in the Social Context: Better Living through Electricity
IV The Scents Of Attraction
17 Chemical Communication via Pheromones
18 Mammalian Pheromones
19 Human Pheromones?
20 Epilogue
Source Notes