Future research may well identify characteristics that distinguish various mammalian brains. Some evidence suggests that certain species even differ in the types of cells that constitute the brain. The brains of great apes and humans, for instance, contain a distinct type of large cell that is unusual in other species.14 We are only beginning to unravel the mysteries of brains, so we may hold out for as yet undiscovered features that set human brains critically apart from the rest.
As it stands, however, it is not clear what it is about our brains that causes our minds to be special. The study of the brains of different primates has not clarified what their minds are capable of and what their limits are. To find out about the nature of the gap we need to return to behavior as an indicator of mind. Long-term field studies have increasingly provided details about the ecology and natural behavior of our closest animal relatives. Controlled experimental studies aim to infer their mental capacities. So next we turn to comparative psychology and the tools of studying minds.
1Anatomically, primates are recognizable by a peculiar small bone covering part of the inner ear (the petrosal bulla).
2Barbary macaques also do not have a tail and are therefore sometimes called apes—but they are monkeys.
3Small apes are also often called “lesser apes,” but I shall refer to small apes to avoid unfortunate connotations of inferiority.
4To learn about gibbon conservation, see http://www.gibbonconservation.org
5Humans can be even greater apes: the heaviest recorded specimen reached more than an astonishing 500 kilograms.
6Orangutans are an exception to the social brain hypothesis that links large brains to large group sizes. One reason for this may be that the ecological niche of modern orangutans is quite different from the context in which they evolved. In captivity, orangutans show more social affiliation, so it is also possible that the complexity of their social lives high up in the trees has been underestimated.
7As I write this, fires apparently set by a palm oil company are raging through one of the remaining few Sumatran orangutan habitats, the Tripa Swamp forest. For orangutan conservation, see the Borneo Orangutan Survival Foundation (http://orangutans.or.id) or the Orangutan Project (http://www.orangutan.org.au).
8For protection of the gorillas, see the International Gorilla Conservation Program: http://www.igcp.org.
9When Jane Goodall first documented this tool manufacture in 1964, it caused quite a stir. Curiously, this observation was not as novel as had long been believed. It turns out that a Liberian stamp from 1906 already depicts a chimpanzee using a stick to forage for termites long before any scientist documented such behavior.
10For chimpanzee conservation, see, for example, the Jane Goodall Institute: www.jane-goodall.org.au.
11For bonobo conservation visit, for example, the Bonobo Initiative: http://www.bonobo.org.
12Other schemes have been proposed, such as ratios between different parts of the brain. For example, we have already encountered the ratio between the neocortex and the rest of the brain; Robin Dunbar used it when relating group sizes in primates to cognitive powers. There is some difficulty in demarcating different sections of the brain in different species, so this also has not been universally accepted. Concern has been raised about ignoring absolute brain matter altogether in favor of ratios or quotients. Surely there must be something about absolute neuronal resources that enable or limit cognitive capacities. If you have only one thousand neurons, there is only so much computation that can be done regardless of EQ or relative brain size. Indeed, it has been argued that absolute size is the better predictor of capacities in primates. But given that body size appears to have some effect on brain size, we cannot entirely ignore this factor either.
13One idea is that the primary direction of information flow has reversed in humans from the typical flow from the back to the front of the brain, to one biased toward flow from the front to the back.
14For a while these so-called Von Economo neurons were thought to be unique to great apes and humans, but recent work has documented them in the brains of elephants, whales, and macaques.
THREE
Minds Comparing Minds
MIND IS A TRICKY CONCEPT. I think I know what a mind is because I have one—or because I am one. You might feel the same. But the minds of others are not directly observable. We assume that others have minds somewhat like ours—filled with beliefs and desires—but we can only infer these mental states. We cannot see, feel, or touch them. We largely rely on language to inform each other about what is on our minds. But even when someone says what is on his mind—that he is, say, sorry or happy—you might question whether or not he is telling the truth. Still, when verbal and behavioral indicators point in the same direction, we can generally be confident about another’s mind.
Similarly, we can use behavior to infer the minds of animals. In the absence of verbal self-reports, however, we may be less certain about what goes on in their minds, as they lack the ability to confirm our conclusions or set us straight. So people sometimes maintain opinions about animal minds that are in stark contrast to each other. At one extreme, humans imbue their pets with all manner of mental characteristics, treating them as if they were little people in furry suits. At the other, humans regard animals as mindless bio-machines—consider the ways animals are sometimes treated in the food industry. Many people vacillate between these interpretations from one context to another.
Scientists are supposed to guard against preconceived ideas that bias their research. Nonetheless, the philosopher Daniel Dennett notes that comparative psychologists also gravitate toward opposing positions: the “romantics,” who ascribe complex, humanlike abilities to animals, and the “killjoys,” who are reluctant to do so.1 In other words, some researchers favor what I like to call “rich” interpretations, while others prefer “lean” accounts. One might suspect, as Dennett does, that the truth typically can be found somewhere in the middle. But when scientists themselves have such biases, we have a problem—and a clue why progress on establishing what we share with other animals and what sets us apart has been somewhat slow.
To get to the truth, we need to go beyond preconceptions and apply methods and criteria that can compellingly establish animal mental capacities. In this chapter I will illustrate the approaches of modern comparative psychology by reviewing evidence for some mental faculties apes seem to share with us. Only a prudent and cautious analysis will allow us to make systematic progress on identifying the gap. It is about time that we do. If we can establish scientific consensus about what we share with which other animals, it will have important implications, for instance for establishing the genetic and neurological bases of mental capacities and, arguably, for animal welfare. For us humans, nothing less is at stake than our place in nature.
DARWIN TRIED TO SUPPORT HIS case for continuity with anecdotes of behavior purportedly showing that animals possess the rudiments of many facets of the human mind. He wrote that “the senses and the intuitions, the various emotions and faculties, such as love, memory, attention, curiosity, imitation, reason, &c, of which man boasts, may be found in an incipient, or even sometimes in a well-developed condition, in the lower animals.”
However, anecdotes are difficult to verify and may be biased by preconceived ideas of the person reporting them. For instance, one nineteenth-century scholar cited an anecdote of a dog burying the remains of a duck to argue that the dog was aware that murdering the duck was a crime and that it was trying to conceal the evidence. Maybe so. Yet we can explain why dogs bury bones without having to suppose that they scheme about thwarting law enforcement. Conway Lloyd Morgan, one of T. H. Huxley’s students, argued that we should not interpret animal behavior as the outcome of a higher “psychical” faculty when it can be fairly explained as the result of a lower one. This principle came to be known as Lloyd Morgan’s canon and is a favorite of killjoys.
Even impressive and unusual animal behaviors often have simple explanation
s. A classic cautionary event occurred at the beginning of the twentieth century. A German schoolteacher named Wilhelm von Osten had trained his horse to give apparently intelligent answers to a great variety of questions. The horse became a sensation and was widely known as Clever Hans (Der Kluge Hans). He could answer questions about simple addition (e.g., What is 5 plus 7?) by stomping his foot the right number of times. Hans could also correctly reply to questions about calendar days (If Monday is the eighth, what is Friday’s date?). And it did not stop there. Herr von Osten developed a table that would translate stomps into letters, allowing Clever Hans to answer questions in words. The idea that this horse understood the German language and how calendars work may seem a bit rich. But no one could explain how else the animal might do what it did. A scientific committee, headed by the leading psychologist Carl Stumpf, examined the case and, failing to come up with a leaner alternative explanation, endorsed the equestrian genius.
One of Stumpf’s students, Oskar Pfungst, pursued the issue further. He eventually discovered that Hans could only answer the questions correctly if the person asking the question knew the answer. He also noted that when he made von Osten ask questions from a place where the horse could not see him, performance broke down. Pfungst concluded that the horse stopped stomping in response to subtle cues, such as a jerk of the head. The horse was clever in picking up on these cues and learning the association with reward, but did not understand German or mathematics. There is a long history of people, such as those working in a circus, training animals to respond in particular ways to subtle movements. What is remarkable in this case is that Herr von Osten was apparently unaware that he had cued the animal into acting in the desired way.
Such unintentional cue-giving is a serious problem for those studying animal mental capacities, and this case had a dramatic influence on comparative psychology. It highlighted the need for researchers to actively guard against such cuing, as merely trying not to give cues may not be good enough. One way to achieve an unbiased result is to have the experimenter unaware (“blind”) of what the desired response of the animal is. In addition to enhancing methodological rigor, the Clever Hans effect, as it came to be known, drove home the fact that behavior that looks intelligent can be the result of simpler learning processes. It powerfully illustrated Lloyd Morgan’s canon. When confronted with a rich interpretation, one that supposes complex mental capacities, we should consider carefully whether leaner accounts could do the trick.
Anecdotal approaches and rich interpretations subsequently went out of fashion. Behaviorism became the dominant force in psychology for much of the twentieth century and focused on explaining behavior in terms of general associative learning rules, rather than species-specific mental capacities. For example, Edward Thorndike’s studies on the time it took animals to escape from a puzzle box led to the “Law of Effect”: consequences of an act determine its future probability in similar situations. Lean interpretations were favored, and any attribution of mentality to animals was greeted with suspicion, if not ridicule. The pendulum had swung from the extremes of romantic anthropomorphism to a “mindless” zeitgeist. Despite Morgan’s openness to evidence for it, many behaviorists threw the baby out with the bathwater and seemed to deny mental capacities to animals a priori.
Today, more romantic positions have regained popularity. Comparative psychologists try to establish the mental capacities of animals, and reports of amazing feats once thought to be uniquely human appear frequently. However, academic debates between romantics and killjoys are commonplace. Both can make important contributions to a more precise understanding of animal minds. Romantics challenge lean views by searching for evidence demonstrating rich competences in animals, and killjoys provide lean alternative explanations for claims about rich animal capacities. The hope is that with each of these battles we get a little bit closer to the truth.
Indeed, moderate explanations are beginning to take much clearer shape, as we will see throughout this book. Old dichotomies and extreme positions are sometimes not as far apart as they at first appear. It is quite possible, for instance, that there is a vast gap separating animals and humans and that animals have richer and more diverse mental lives than is often assumed.2 Even the apparently clear-cut distinction between qualitative and quantitative differences, between the belief in a fundamental difference in kind that sets us apart from animals and Darwin’s belief that human and animal minds only differ in degree, can be a bit of a red herring. We know that changes in degree frequently produce distinct attributes that may well be regarded as a difference in kind. When temperature gradually increases, the properties of H2O change radically as ice turns to water and then to gas. By the same token, gradual changes in, say, processing capacity could lead to radically different possibilities of thinking.
Apparently stark disagreements about the gap at times merely reflect differences in opinion about the relevant criteria rather than about matters of fact. For example, to demonstrate language, is it sufficient to show that other animals communicate, or must they be able to tell us a story? As long as we can establish what exactly animals can and cannot do, the rhetoric does not really matter. Throughout this book I shall focus on finding scientific answers rather than on securing human superiority or dispelling human arrogance.3
The question to answer is this: Which characteristics of the human mind, be that distinct traits or gradual differences, enable and motivate us to do the great diversity of things that other animals do not? What makes us human? On the face of it, human behavior differs from animal behavior in countless ways. For instance, we play football, sell insurance, go to school, build bicycles, and have BBQs. What are the fundamental bases for our many peculiar behaviors? The answer should shed light on related questions, such as: what allowed us to dominate this planet, and why do we ponder such questions?
In the chapters to follow I will discuss the domains that are most commonly claimed to be, or to contain, key uniquely human attributes that may have led to a profound shift in human behavior: language, mental time travel, mind reading, intelligence, culture, and morality. Each topic is multifaceted and requires some careful scrutiny. Therefore, about half of each of these chapters deals with what the science of the mind has taught us about the human faculties. In particular, I discuss what mental traits are fundamental in these domains and important to our success. To identify the basic building blocks of our minds, it is useful to consider carefully how infants and children first acquire them.4 I will therefore reflect considerably on development along the way to identifying the gap.
In the other half of each chapter, I examine what is known about animal capacities in these domains that challenge claims of human uniqueness. We will discover many sophisticated parallels to human behavior as well as some strange capacities that are unique to certain species. We are only beginning to scratch the surface of the plethora of colorful mechanisms various animals deploy. The repeated comparison of human abilities with those of other animals will bring into sharper view what it is about the human mind that sets us apart. Before we get into these analyses, however, I will first address how we can infer the presence or absence of mental capacities in animals.
CONSIDER ONE OF THE MOST fundamental aspects of our human mind: we can imagine things other than what is available to the senses. We can picture past, future, and entirely fictional worlds and think about them. William James noted that it is the capacity to conceive of alternatives that allows us to question why things are the way they are. Humans ask big questions like: what are we, where do we come from, and where are we going? Most cultures have elaborate creation myths that children are told when they start raising these questions. Some of the oldest are those of indigenous Australians, who refer to the dreamtime in which the world was molded, for instance, by a gigantic rainbow serpent. These stories, or “dreamings,” belong to specific individuals or tribes and provide them with meaning. Questioning and finding meaning are essential to the human mind. (Why else ar
e you reading this?) But what about animals? Do they ponder past, future, or fictional events? Do they search for the meaning of life? Can they conjure up worlds beyond what they can perceive here and now? Do they have even the most basic imagination? How could we find out?
Darwin argued that various animals dream (in the English rather than Aboriginal sense of the word) and so must possess some imagination. Perhaps Darwin was right: when we are woken out of rapid eye movement (REM) sleep, we typically report having been dreaming, and many animals show REM. However, a killjoy skeptic would argue that REM need not entail dreaming in other animals, and even if it did, dreaming need not entail a capacity to imagine when one is in a waking state.5 So far, animals have not told us their dreams (nor any dreamings).
In human development pretend play is the first obvious behavioral expression of an imagination that goes beyond the here and now. Toddlers typically start to display pretend play in the second year of life, and many subsequently spend much of their waking time enacting their fantasies. When children pretend that one thing is another, they experience two worlds: in addition to perceiving the world around them, they construct an imaginary scene. A block can become a horse, a banana a telephone, and a pen a comb. The hand may turn into a gun, and the cushions become an impenetrable wall. Children do not typically confuse the pretend identity of an object with its real nature and properties, however—they are rarely tempted to eat their mud pies. So they must be able to hold in their minds a representation of reality as well as a representation of a parallel pretend situation. Therefore, if we could demonstrate that other animals also engage in pretend play, we would have good grounds to argue that they, too, have a basic capacity for imagination.
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