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"A welcome addition to the growing body of work on animal thought." —The New York Times Book Review
In one of Rudyard Kipling's charming short stories, he tells us about an elephant child with insatiable curiosity, an elephant who asked so many questions that his relatives spanked him. Curious minds, like the elephant child's, abhor ambiguities, feelings of ambivalence, and the lack of resolution. But curious minds discover uninhabited terrains of knowledge by questioning dogma and pondering the impossible. In the novelist Edith Wharton's words, if we remain "insatiable in intellectual curiosity, interested in big things, and happy in small ways," we will remain alive. Curiosity exacts a cost, but the returns are great. Although animals may not be as curious as Kipling's elephant child, they are active informavores, digesting and storing relevant information in the service of guiding behavior. Let me illustrate this idea with a few vignettes.
· When a common laboratory rat is placed in a maze, it immediately begins to explore, both with its nose and with its eyes. Waiting for the lunchtime food truck to arrive or for the exit sign to be illuminated won't help. With exploration comes detailed knowledge of the turf, an understanding of which way to go for food and which way to go for the exit. Curiosity allows the rat to create a road map, a directory of spatial coordinates.
· Chimpanzees housed in outdoor enclosures often discover novel escape strategies. They insert sticks into the fencing for footholds. Some are even more creative, placing large logs at an angle against the enclosure wall, creatingfunctional ladders. By assessing the height of the enclosure wall and trying out different logs, the chimpanzees eventually escape, thereby discovering whether the grass is, in fact, greener on the other side.
· In many species of schooling fish, individuals leave the safety of their group to swim by and inspect the behavior of a nearby predator. Rather than wait for the predator's attack, such bold inspectors gain information that can be used to decide whether to stay or flee. In fact, they not only gain information, but relative to those who tag behind, lower their odds of being eaten.
· Whenever you take a dog out on a walk, even on a route that it has taken on every outing, the dog sniffs the ground, trees, and fire hydrants. Dogs are interested in the competition. Sniffing allows them to extract scents that other animals have left behind. And of course, they always sign off with their own unmistakable signature.
The claim that animals are curious is based on the general assumption that by looking at the similarity between animal and human behavior we can make similar inferences about their thoughts and emotions. Although our intuitions may sometimes be correct, behavior can be a misleading guide. It is appropriate to be a healthy skeptic, and this chapter shows why.
ANIMALS R US
A number of popular writers theorize that animals and humans think about the world in the same way. These authors also portray scientists as the enemy, naysayers and skeptics. For example, in her preface to The Hidden Life of Dogs, the essayist Elizabeth Marshall Thomas begins,
This is a book about dog consciousness. To some people, the subject might seem anthropomorphic simply by definition, since in the past even scientists have been led to believe that only human beings have thoughts or emotions. Of course, nothing could be further from the truth.... [W]hile the question of animal consciousness is a perfectly valid field for scientific exploration, the general assumption that creatures lack consciousness is astonishing.... After all, thoughts and emotions have evolutionary value. If they didn't, we wouldn't have them.
Thomas makes two errors here, the first concerning evolutionary continuity, and the second concerning adaptation. Given that humans diverged from their chimpanzee-like ancestors five to six million years ago, it is possible for us to have evolved capacities that other animals lack. No miracles. We cry with tears, blush when we are embarrassed, and walk bipedally. Our primate cousins don't. And although consciousness may be adaptive in humans, we cannot deduce from this conclusion that animals must also be conscious. Further, it is a mistake to argue that anything with apparent "evolutionary value" must be an adaptation and therefore should have evolved in animals. A lion out on the savanna might do well with wheels instead of legs, but such a system cannot evolve due to constraints imposed by the nervous system. Wheels would cause a lion's neurons to wrap up into a tangle of spaghetti.
Jeffrey Masson, another popular writer about animals, is a Sanskrit scholar who is best known for his attack on Freud and the psychoanalytic tradition. He opens his book Dogs Never Lie about Love with a similar comment about scientists, science, and the study of animal behavior:
I am aware that most of the "evidence" I have presented for the reality of emotions of dogs consists of stories—what scientists call, dismissively, anecdotal evidence. With their restricted sense of valid criteria, most scientists want to be able to test, probe, and replicate data. You cannot do that with a single story. Scientists seem to think that whereas a story can be either true or false, something that takes place more than once in a laboratory has to be true. There is no reason to believe this to be the case. Data can be faked, forged, or misrepresented as easily as can a story, and what we learn from some laboratory experiments ... does not tell us anything we could not have known without experiments.
Masson's criticisms are replete with disturbing and confusing assertions. Scientists think that anecdotes are unsatisfying, but not useless. They may provide clues or stimulate hunches, but scientific curiosity ultimately leads to further exploration, additional observations, and experimental tests. And yes, scientists can fake data, which is precisely why replication is so important. For example, in 1989 a team of physicists claimed they had evidence of cold fusion, a process in which the fusion of two heavy hydrogen nuclei generates energy. Subsequent attempts to replicate these findings failed, showing instead that the energy generated from the original experiments was due to stored heat within the general system, rather than heat released from the fusion of two nuclei. Had we invested in a cold fusion mutual fund, we would now be deep in debt. In the remaining chapters of this book, I will show how experiments have enabled scientists to avoid incorrect conclusions and gain revolutionary insights into the animal mind. But first, let me try to convince you that animal stories are unsatisfying.
Chimpanzees Form a Natural Bridge
In 1987 I was in the Kibale Forest of Uganda watching a small family of chimpanzees, a mother, her subadult son, and her one-year-old daughter. After feeding in a fig tree for a while, the subadult male gave a departure call and leaped across a gap in the canopy to a tree some distance away. The mother soon followed, but her daughter stayed behind, screaming. The mother and son waited and watched, but the yearling appeared frozen in place. After a stalemate, the mother went back to her daughter, started swinging the tree back and forth, and then, with a long stretch, reached over and grabbed the branch of the neighboring tree. With her feet grasping one tree and hands grabbing the other, the mother formed a natural bridge, which her daughter used to cross over to safety.
What I witnessed was magical and immediately invoked a suite of questions concerning maternal care. How often do chimpanzees create natural bridges? Do they create a mental image of their body bridging a gap in the trees before actually stretching across the canopy? Do they create bridges for any yearling, juvenile, or adult in need? How does an individual recognize another in need? Does a mother empathize with her daughter when she is stuck behind, screaming? Would she empathize with an unrelated yearling frozen in the same position? To address these questions, we would need to make additional observations. The insistence on replication is not a silly scientific ritual, performed by priests in white lab coats. It is a tool for understanding whether an event is common or rare, and why it occurred. In this case, the mother's actions appear to be intentional and deliberate. But did she actually plan to make a bridge because she knew it would allow her daughter to cross the canopy? If so, did she invent this technique or did she learn it from her mother, who learned from her mother, a tradition passed down through the ages? Perhaps she was merely showing her daughter how to cross. In the midst of the mother's demonstration, however, the yearling seized the opportunity and walked across her mother's back. If the second description is correct, then we must seek a different interpretation. Either the infant hit on an insightful stroke of genius or she was blessed with dumb luck.
Returning to Masson's statement, it is not the case that such "stories" are uninteresting. Indeed, they are fascinating, but limited with respect to what we can learn from them. One observation leads to several intriguing questions and problems. The only way to address them is by collecting additional observations and, if possible, running experiments. Of course, that is not always possible. We can't, for instance, necessarily induce our bridge-forming mother to do so again. We may wait for a long time for another occurrence. Even if we can induce others to form bridges, what would that tell us about the emotions of the bridge makers and the bridge users? How can we understand whether each bridge maker invented the technique on her own or learned the technique by imitating someone else? A second example might help answer some of these questions.
In The Hidden Life of Dogs Elizabeth Marshall Thomas uses observations of dog behavior to make claims about their emotions and thoughts. Her interpretations, however, are overinterpreted and fraught with assumptions. Here is an example:
[M]ost animals, including dogs, constantly evaluate other species by means of empathetic observation. A dog of mine once assessed my mood, which was dark, over a distance of about one hundred yards, and changed his demeanor from cheery to bleak in response.
To tap into your own intuitions about Thomas's observation and interpretation, try the following thought experiment. Substitute another animal for the word "dog" in the passage above and reread it. For example, "A lizard of mine once assessed my mood ..." Play with this thought experiment until you hit on an animal that, when inserted into the sentence, makes it sound absurd. Even if you never come upon such an animal, and my hunch is that you will, what assumptions are you making about these animals' thoughts and feelings? Let's say that you are convinced that a dog can read someone else's mood, while a slug, lizard, or fish cannot. You are making a distinction somewhere in the tree of life, a distinction based on what you can observe. As far as you can tell, zucchinis lack thoughts and emotions. Whatever thoughts and emotions you ascribe to slugs, lizards, and fish, you may not believe that they are capable of creating a bond with their owner. Fine.
Let's return to Thomas's description and analyze what she observed. The dog spots Thomas at a distance and is bouncy, tail wagging. As he approaches and looks at Thomas, his head and tail drop and he loses the bounce in his walk. How are we to interpret what the dog is feeling? Thomas's interpretation assumes that dogs empathize with humans. To empathize, however, the dog must not only understand what human feels, but feel the same as well. Thomas's dog must experience Thomas's dark mood. Alternatively, perhaps the dog is simply responding to Thomas's behavior without feeling what she feels. He has lost his bounce because he correctly anticipates, based on prior experience, a less than affectionate response from Thomas. When she is smiling, the greeting involves play and lots of back scratching. When she is frowning, the greeting is brief and dismissive. The dog's dark mood arises, therefore, out of selfishness rather than empathy. Thomas's dog has lost an opportunity for quality time.
Thomas's example and the interpretation she offers are a classic case of seduction. We are seduced by appearance. If there are familiar cues or signals, we tend to ascribe similar emotional experiences and thoughts. But appearances can be misleading, guiding us down mirrored halls.
Since 1988 I have been studying rhesus monkeys on the island of Cayo Santiago, located just off the coast of Puerto Rico. During the breeding season, males fight a great deal. Dominant males often chase subordinates away from potential mating opportunities. Sometimes the dominant catches a subordinate, pins him down, and rips out one of his testicles. While the testicle is being ripped out, the subordinate is generally quiet and there are no noticeable facial expressions. Even more striking, the injured male is often seen mating or attempting to mate within a few hours of being attacked. From what we observe, how can we determine what the subordinate is feeling? Can we really use our own experiences, imagined or real, to deduce what subordinate rhesus monkeys feel in this situation? Unlikely. Although appearances often provide us with accurate tips for what is going on inside another individual, we must tread cautiously.
Jeffrey Masson describes a case of "compassion" in dogs. It is, on the surface, similar to Thomas's example of empathy and my own example of the chimpanzee bridge.
When one of my three dogs strays too far from the others and I continue walking, oblivious, I will notice that the other two stop and wait for their companion to return.... They do not want to continue until the pack is complete. This act is surely indicative of compassion.... Of course, we could explain it in other ways; there is always another explanation, whether for human or animal compassion.... But even if there is some truth in these explanations, they do not cancel out the element that derives from love and compassion because they cannot explain away the feelings that accompany those actions.
The act of waiting is interpreted as a sign of compassion. From this interpretation, Masson makes the point that even if other factors such as self-interest can account for the act, this doesn't negate the importance of emotion in guiding behavior. What Masson states here is important at one level, and wrong at another. It is important because there are always different ways to explain why something occurred. It is wrong because although all behaviors can be explained in different ways, one kind of explanation need not exclude the others. The explanations are not mutually exclusive.
Why do dogs move in packs? From the perspective of understanding the mechanisms linking cause and effect, we might say that dogs form groups and stay together because they have a desire to affiliate, a desire that is presumably driven by the anticipation of feeling happy or something like it. In many animals there are parts of the brain involved in the regulation of attachment between individuals. Highly social animals, such as dogs, monkeys, and humans, undergo hormonal changes associated with separation that are different from those experienced by less social animals. From a developmental perspective, we can explain grouping as something that is instinctual, a genetic predisposition that is shaped by the experience a puppy obtains from watching siblings and its mother. At an adaptive level, concentrating on traits that promote increased survival and reproduction, we might argue that natural selection favors animals who stay with the pack because those who stray are more likely to be attacked and killed by predators. Although waiting may be costly, it may represent a kind of altruism that is based on reciprocation—I wait for you today, knowing that you will wait for me tomorrow. Using a phylogenetic or historical analysis, we would conclude that staying in packs represents an evolutionarily ancient characteristic, one that is seen in the domestic dog's ancestors, the wolves. Pack formation is a characteristic that domestic dogs inherited from wolves.
We gain a rich understanding of behavior by addressing each of these four causal questions. This approach was developed in the 1950s by one of the founding fathers of the study of animal behavior, the Nobel laureate Nikolaas Tinbergen. To this day, it represents the foundation of modern research in animal behavior.
What's all the fuss about then? Few students of animal behavior would argue that a dog, or any other animal, lacks emotion. Disagreement enters the discussion when we attach a certain level of confidence to the kind of emotion based on anecdotal observations alone. Waiting for a pack member to catch up could be a sign of compassion or it could be a sign of fear, anxiety, the desire to control pack movement, to find out what the stray learned on his brief excursion, and so on. To discover what a dog or any other animal feels and thinks, we must carry out systematic observations and experiments, guided by the theories of evolutionary biology and cognitive science.
PETS ON THE COUCH
Nicholas Dodman, a veterinarian at Tufts University, has spent his career working on pet dogs and cats with behavior problems. He opens his book The Dog Who Loved Too Much with the claim that people may "have vague images of a voodoo-style veterinary psychiatrist who will put their dog on a couch and inquire about its puppyhood. Some owners even fear being psychoanalyzed themselves." But this is no pet quackery. Dodman discusses a growing body of work indicating that many of the behavioral problems that dogs experience can be treated with the same type of pharmacological drugs that work on human psychiatric disorders. In particular, some dogs manifest behavioral symptoms indicative of bipolar disorder, depression, separation anxiety, dominance aggression, rage, and obsessive-compulsive disorder. In some cases, the problems appear to be breed-specific: anxiety-prone Afghans, springer spaniels with rage syndrome. Consider the following case of obsessive-compulsive disorder in a Doberman named Taylor.
Taylor ... like many Dobermans, had a licking problem. Taylor was first noticed to be somewhat orally inclined when he was about one month of age; he would knead cushions and blankets with his paws, mouthing and sucking the items until they were wet.... As a puppy, [he] would also nurse on other dogs' ears, and when there were no blankets or ears around, he would just suck and chew stones or mouth the skin of his flank until it was moist with saliva. Blanket sucking and flank sucking occur almost exclusively in Dobermans, suggesting that the condition may be genetic.... When Taylor was two, he started another oral activity: licking his legs.
There are several intriguing observations and intuitions here. The repetitive licking of one spot in early development, and the migration to other body parts later on, is reminiscent of the many obsessive-compulsive cases reported for humans. In particular, the disorder has a strong genetic component, often expressed at a young age, and most individuals tend to manifest similar behavioral symptoms, usually excessive washing. Later in life, the problem becomes highly stylized and personal, with some patients driven to repeatedly checking that the lights in a room are off, or walking in and out of a door frame until they cross at the precise midpoint. In one famous case, a young man with an extreme hand-washing problem was driven to an attempted suicide. He took a gun and shot himself in the mouth. Rather than ending his life, however, he actually fixed the problem. The bullet went straight through the frontal lobe of his brain—the prefrontal cortex—causing a lesion and ending the obsessive-compulsive disorder from which he suffered. As some researchers suggest, patients with obsessive-compulsive disorder clearly experience difficulties when an action must be inhibited. Several studies of humans and animals indicate that the prefrontal cortex plays a critical role in the process of inhibition. By shooting himself, the patient was lucky enough to remove the troubling area of his brain. As they say, this kind of self-help treatment is not recommended.
Are there other, less invasive techniques for treating obsessive-compulsive disorders? Following recent advances in human medicine, Dodman and other veterinarians are pursuing a course of treatment that involves both behavioral therapy and drug administration. For example, repetitive licking in Dobermans often emerges in response to boredom and stress, and with time becomes highly uncontrolled and repetitive. Behavioral treatment involves increasing the level of exercise, altering the diet, and putting a collar around the neck to prevent licking. Much greater success is achieved when behavior therapy is combined with drugs that directly affect the neurotransmitters, the chemical messengers of the brain. Although there are significant differences in brain anatomy between animals, there are relatively few differences in their neurotransmitters. Consequently, neuropsychological disorders in humans and dogs can be treated with many of the same drugs.
Dodman's work provides one approach to the problem of comparing animal psychologies. Under certain conditions, dogs and humans appear to show similar behavioral responses and manifest the same sorts of neurochemical changes. The work is elegant and sits properly within the tradition of Sherlock Holmes and the scientific method. One observation provides a clue. Additional observations are then collected so that hypotheses can be formed and tested through experimentation, in this case, therapy, drugs, and further observation. Unfortunately, a problem remains. Although the behavior and neurochemistry are similar, this doesn't guarantee that the intervening thoughts or feelings are the same.
Consider the following hypothetical example involving two human patients diagnosed with obsessive-compulsive disorder. Whenever they are presented with an array of objects, they each sort the square ones from the others, then put the objects back in a pile and start over again. At the end of the sorting process, both patients have a pile of square objects and a pile of nonsquare objects. Their behaviors are the same and previous tests reveal that the underlying neurochemical imbalances are the same. The problem is that when we ask them about their sorting rules, one states that he was looking for parallelograms, whereas the other says he was looking for squares. By chance, it turns out that all the parallelograms around are squares. As a result, although their piles look identical, each patient used a different conceptual representation while sorting the squares from the nonsquares. Same behavior, same neurochemistry, but different thoughts.
Serious shoppers want the best deal. They research the field, identify the competitors, list all the pros and cons, and then make a decision based on their priorities. It's a game of compare and contrast. Humans, and many other species, face a similar problem in finding the best mate. In the story of Cyrano de Bergerac, poor Roxanne thinks that she is in love with the handsome Christian. When she finds out that the poetic spirit behind his voice is, in fact, the physically unattractive Cyrano, she is forced to make a choice between physical and poetic beauty. No easy answers here, but there is a choice. Shoppers for mates, just like shoppers for clothes, microwave ovens, or cars, must be able to dig beneath the superficial gloss. There is rarely truth in advertising.
The history of research on animal thinking has, in many ways, been driven by a shopper's mentality: to find out who is the real brain, the whiz of the animal kingdom. And the comparison is, most commonly, between humans and the other animals. As the philosopher Hilary Putnam stated, "Our world is a human world, and what is conscious and not conscious, what has sensations and what doesn't, what is qualitatively similar to what and what is dissimilar, are all dependent ultimately on our human judgments of likeness and difference." Poets, novelists, and scientists have identified us as superior because we are the noble, rational, intelligent, social, successful, creative, tool-making, linguistic, and anxiety-driven species. We are also, as Mark Twain noted, "the only animal that blushes. Or needs to." No one expresses this overall vision of superiority and uniqueness more eloquently than Shakespeare's Hamlet, who called humans "the beauty of the world, the paragon of animals." To admire our species for its qualities is natural. To place us with the gods and angels, above all the others, is both pompous and boring. It is pompous because it places us on top of an intellectual pyramid without articulating the criteria for evaluation. It is boring because it ignores differences in thinking, and fails to search for an understanding of how different shades of mind evolved.
A commonly expressed dichotomy is that animals are driven by their passions whereas humans are guided by reason. We are rational, coolheaded, and thoughtful. They are irrational, hotheaded, instinctual beasts. Whereas we follow the dictum "I think, therefore I am," they adhere to "I feel, therefore I act." The division between the emotions and rationality represents a vestige of Cartesian thinking. As the neuroscientist Antonio Damasio pointed out in his 1994 book Descartes' Error, our emotions often play a critical role in guiding our decisions. When we attack a problem, we often consult our emotions, using them as guides. Although it is clear that our emotions can cloud and overpower our rational minds, we are more often than not making decisions that depend on an understanding of what we feel. In John Le Carre's novel The Taylor of Panama, Marta, an upstart in the student revolution, states the case with precision: "Reason only functions when the emotions are involved.... There's no logic unless the emotions are involved. You want to do something, so you do it. That's logical. You want to do something, and don't do it, that's a breakdown of reason."
The idea that rationality depends on the emotions comes from studies of brain-damaged patients and the use of modern neuroimaging techniques such as petscan (PET) and functional magnetic resonance imaging (fMRI). The capacity to make rational decisions breaks down when the planning area of the brain (prefrontal cortex) is disconnected from a key emotional area of the brain (amygdala). Further, neuroimaging results show that these two areas of the brain are highly active when non-brain-damaged humans make decisions about emotionally salient problems. The conclusion we must then draw from this work is that emotions are necessary for making decisions in humans. What I will argue is that emotions play a central role in animal decisions as well. Many animals, especially the nonhuman primates, have a prefrontal cortex, an amygdala, and the neural circuitry that connects these areas. This neural gear provides them with rich emotions and a foundation for making emotionally relevant decisions. Without delving into the details, I leave this problem for later chapters axed simply claim that Descartes' dichotomy is a nonstarter. We need a better theory for understanding animal minds.
Darwin's theory of natural selection—and the logic of design and engineering that it encompasses—is central to the thesis of this book. Just as a variety of transportation vehicles have been engineered, natural selection has engineered brains with specialized devices, what I call mental tools. Some tools are shared across species, whereas others are unique. Whether the design of a mental tool is good or bad is decided in a competitive arena, one in which only the winners survive, reproduce, and pass on genes into the next generation.
Consider the fact that once the wheel was invented as a transportation tool, its functionality depended on the invention of roads. Once roads were in place, increasingly sophisticated land vehicles emerged, with horse and buggy outpaced by Henry Ford's Model T, followed by the Lamborghini, and rocket-like hot rods that can now break the sound barrier. Travel by air and water presented different challenges, but technology responded with the invention of sailboats, kayaks, windsurfs, jetskis, gliders, airplanes, and rockets that can take us away from our beloved planet Earth. Some of these designs were elegant and relatively efficient. With the march of time and technology, however, the state of the art changes, each generation contributing design improvements as well as new tools.
Like our man-made vehicles, animals also confront problems of locomotion on the ground, in the air, and through the water, and their brains have been built to solve such problems, tracking changes in topographic contours, temperature gradients, and wind and water currents. But animal brains must cope with other problems as well. Brains have been designed to help animals find a meal, avoid becoming one, pick a mate, care for offspring, build friendships, learn from experience, communicate, remember where home is, avoid enemies, collaborate with allies, and much more. Like transportation vehicles, specializations of the animal brain emerge and persist in the face of unique but recurrent problems. Similarities in design arise when the set of possible solutions to a problem is limited. Let me illustrate these points with an example from nature's favorite drama, the epic battle between predator and prey.
The Firefly's Fatal Flash
Tennyson's song "Now Sleeps the Crimson Petal" opens with a stanza about fireflies whose magical light gently awakens the sleeping plants and people. Little did he realize that the flash of the firefly represents both an invitation to mate and a neon advertisement to predators. When females of the predatory Photinus species see the courtship flash of a male from the prey species, Photuris, they respond with a deceptively accurate copy of a flash from a female Photuris. This visual wink from an interested female is sufficient to lure the male in. When he arrives, she calmly devours him. Lust can sometimes kill a male firefly.
There is a fascinating twist to this firefly story, described in 1997 by the biologist Tom Eisner and his colleagues at Cornell University. As in many complex environments, animals often experience life as both predator and prey. Photinus, the predatory firefly, is eaten by thrushes and jumping spiders. Photuris, in contrast, is less vulnerable to thrushes and jumping spiders thanks to a plant it eats that contains a chemical the predators find unpalatable. Following predation on Photuris, the predatory Photinus not only boosts its energetic reserves, but also simultaneously ingests the same chemical that makes Photuris unpalatable to jumping spiders and thrushes.
What does this epic battle tell us about the design of animal minds, and in particular, firefly minds? From these observations, we cannot conclude that females of the predatory firefly species are aware of what they are doing. Presumably, they didn't sit down and calculate the effectiveness of the plant's chemistry and its role as a prophylactic against predators. Rather, natural selection favored the capacity of female Photinus to recognize the mating flash of Photuris, signal a deceptively seductive flash saying, "Yes, I'm interested," and then devour the courting male, thereby obtaining a meal and a vaccine against predation. For this system to have evolved, encounters between firefly prey and their predators—jumping spiders and thrushes—must have been relatively frequent, statistical regularities of their environment.
Does the predatory Photinus deserve a genius award for outwitting its prey, Photuris, as well as the thrushes and jumping spiders? On an evolutionary time scale, Photinus's success may represent a fleeting victory, an eye blink of glory. Most predator-prey battles operate like military arms races. Predators win for one stretch of time, and then prey evolve defenses to evade predation, thereby gaining the upper hand in the evolutionary race. For example, male Photuris capable of recognizing mimics would be favored. Similarly, jumping spiders capable of discriminating Photinus females that have recently eaten Photuris males from those that have not would be favored by natural selection, although there may well be constraints for evolving such abilities; for example, because spiders can't continuously monitor the food intake of Photinus females, they would have to use a secondary cue such as smell to determine what had been eaten. Though Photinus has been equipped with a smart hunting device, it is only smart in a narrow sense. If Photuris changed the signature of its flash, it seems unlikely that Photinus would be able to mimic in kind, at least not over a short period of time. There is no evidence that the mimetic system is flexible, capable of matching any variant that comes its way. The capacity represents a highly specialized skill, one that is radically different from our own capacity to mimic or imitate (see chapter 6).
Fireflies are not the only mimics in the animal kingdom. But when we compare across animal groups, we find that there are differences in the mimetic tricks themselves as well as in their functions. In some species the trick is fixed, part of the animal's body. In other species it's like a Halloween costume, a façade, one that can be put on and then taken off depending on the season. Thus, some songbirds such as the chaffinch and lyrebird can mimic the sounds of other birds and even nonbiological sounds such as the ring of the telephone. One explanation for mimicry in songbirds is that it provides an illusion that a given habitat is saturated—a vocal "No Vacancy" sign. The bird mimics by listening, storing, and then reproducing the sound heard. Mimicry is a capacity that is based on innate mechanisms for learning about particular sounds in the environment.
Some snakes, when confronted by a potential predator, Will mimic the posture of a dead snake, turning their head upside down while keeping their mouth wide open. Since predators typically bypass dead things, the snake's death-feigning performance represents an effective ploy, a functional case of pretense. A similar ploy is used by the burrowing owl. Because burrows are scarce and highly valuable, the owl has evolved a high-fidelity copy of the rattlesnake's rattle in order to fend off potential intruders from its burrows. In contrast with songbird mimicry, which depends on specific experience, the death-feigning performance of the snake and the owl's rattle emerge without practice, experience, or instruction. As we can see from these examples from nature's directory of Marcel Marceau acts, what is similar at one level can be quite different at another.
The following chapters show how evolution has placed specialized mental tools into the toolkits of species as diverse as the Tunisian desert ant, the New Caledonian crow, the Indian rhesus monkey, and the urban human infant. Each chapter, then, represents a piece to an evolutionary puzzle, a puzzle about the construction of animal minds. As Aristotle so elegantly put it, "In all things of nature there is something of the marvelous."
|Prologue: Mental Toolkits||xiii|
|Part I||Universal Knowledge|
|2||The Material World||21|
|Part II||Nature's Psychologists|
|6||Schools of Learning||115|
|7||Tools of Deceit||141|
|Part III||Minds in Society|
|8||Gossip on the Ark||175|
|Epilogue: What It's Like to Be a Spider Monkey||255|