Deric Bownds

Chapter 4

Primate Mind

Let's take a few steps back from our discussion of human brains and consider the minds and brains of simpler animals. This will set the stage for describing the transition from monkeys through apes to the hominids of about 2 million years ago (we will save more recent times for later chapters). We can then consider the minds of contemporary monkeys and apes in the search for types of intelligence that might have antedated ours. We share with chimpanzees and some other great apes mental attributes that appear to be unique in the animal kingdom, reflecting the appearance of new brain structures and processes.

The Question of Animal Consciousness

Consciousness is a device for focusing awareness through the linking of emotions and feelings to sensing and acting. It is an emergent level of organization that can coordinate and direct the neuronal assemblies from which it is derived. If we take consciousness to be an increasingly refined evolutionary adaptation, it seems reasonable to grant other animals a kind of consciousness that correlates with the complexity of their brains---to consider it a matter of degree rather than an all-or-nothing phenomenon.



Consciousness is an emergent property that is a product of biological evolution. It confers selective advantage by making it easier to adapt to rapidly changing features of the environment.


The minds of animals very different from ourselves can do some amazing things that may cause us to wonder how special our intelligence really is. The language of humans is impressive indeed, but so is the sonar communication of bats and the celestial navigation of birds. Dolphins not only use sonar but also communicate with vocal calls. These mammals have been aquatic for 60 million years and have brains larger than our own. They exhibit complex social organization and can spontaneously acquire new signals and use them appropriately. 1 Bird brains, which have an anatomy less like our own, can perform prodigious feats of memory and carry out a variety of cognitive tasks. 2 For example, in one study an African Gray parrot named Alex was taught to recognize over 50 objects and could apply same-different distinctions based on color, shape, or size (up to six). If the parrot wanted a cracker and was given a nut, he would say no, implying intentionality, or knowledge that his word for "cracker" was about something: crackers, not nuts. He had very limited abilities to recombine words in new ways to indicate different goals, as in "I want...[object]" and "I wanna go...[place]"). 3

It is tempting to assume that what is going on in these animals' heads is similar to what we think would be going on in our own heads in the same situation. The actual observations of their behaviors, however, don't indicate that these animals are self conscious in the way that we are. For example, we cannot assume that the parrot was thinking about what was going on in the experimenter's mind. A simpler explanation is that he was producing behaviors that had, in the past, resulted in food rewards. In an example drawn from a more natural setting, we cannot assume that a mother bird that feigns a broken wing to distract a predator from her young knows that she is deceiving her foe---only that experience or instinct has instructed her that this behavior has the desired result. To know that she was deceiving the predator, she would need to represent the mental state of the predator. This is the same thing as saying that she would be attributing a mind to the predator and imagining what it was thinking---that it was being fooled by her trick. This process is usually referred to as having a theory of mind.

Although it seems natural to do so, we cannot regard the cleverness of animals---beavers building dams, dolphins saving drowning comrades, ants building nests, or chimps or pigeons noticing a spot of dye painted on their bodies---as evidence of self-awareness. 4 Sophisticated information processing might be accompanied by self awareness or it might not. The problem is that we don't know in most of these cases whether detailed analysis would show that a simpler explanation might account for an observed behavior. Rather than attributing to an animal behavior our notions of believing, wanting, knowing, or seeing, might it be possible to prove that some kind of associative learning explains the behavior? Animals might respond to observable cues, categorize them, form associations among them, make inferences about them, and develop routine behaviors reinforced by rewards, all without any sense of self.

We need to remain open-minded in the face of the elephant that cries after being punished for stupidity 5 and the astounding array of human-like emotional behaviors that have been documented for chimpanzees. 6 We cannot prove that attributing these animal behaviors to human traits such as intentionality is incorrect, and it is a convenient way to organize descriptions. However, we must remember that what is actually going on may not be this complicated. The problem with virtually all of the popular accounts of love, hope, fear, grief, joy, rage, compassion, shame, and so on in animals is that simple hypotheses attributing these behaviors to something like reflexive conditioning have not been tested and ruled out. Rather, we forge an "explanation" by ascribing human traits to animals. This risky practice is referred to as anthropomorphism. The fact that there are strong physiological similarities between the emotional brains of humans and those of other animals does not mean that our emotional experiences feel the same as theirs. Given the empathy we can feel for our pets when they exhibit emotional behaviors that appear to be similar to our own, this point seems a bit alien and hard to accept, but it is true nevertheless.



If a simple model or hypothesis can explain a behavior without reference to higher-order intentionality or a theory of mind, then we should not accept any more complicated explanation without proof.


As a subdiscipline of the field of ethology, the study of animal behavior, cognitive ethology attempts to deal with some of these issues by asking whether mental concepts such as representation and intentionality are useful in our efforts to understand animal behavior. 7 Representation, for example, might be inferred from the behavior of sentries posted to look for predators of a group. The frequency of scanning for predators in some groups of birds depends on the geometry of the group, which suggests that the sentry has some sort of internal representation of this geometry. Play behavior in many animals seems to involve a clear set of signals and intentions. For example, in canines, a bow can signal "I want to play, do you?" 8

A number of techniques developed by cognitive psychologists to study human memory or imagery can be applied to animals, but designing animal experiments to prove unambiguously the existence of such mental experiences as intentionality, awareness, and conscious thinking is very difficult. 9 (It's not easy to do with humans, either!) Looking for objective evidence for a faculty such as self-awareness in animals provides an example. Potential evidence on this comes from experiments with mirrors. Only chimpanzees, gorillas, orangutans, and humans more than about 18 months old consistently show curiosity about their reflection in a mirror or engage in mirror-guided behavior without training. But it turns out that pigeons and monkeys that have had mirror exposure and show no curiosity still recognize a change in themselves if, in a mirror, they observe a part of their body that has been colored by an experimenter. 10 How do we distinguish whether this awareness comes with or without a sense of self?

At least one of the several different kinds of conscious awareness we mentioned in Chapter 1, the direct and unreflective kind of experience (such as what it is like to taste an apple), seems likely to be ubiquitous among higher vertebrates. Direct experimental measurements demonstrate that we also share with many animals the faculties of awareness, perception, attention, orientation, movement, memory, learning, thinking, emotions, energy, and mood. The contents of their consciousness or ours at any given moment consist of the brain's awareness of a small fraction of what these faculties are doing. These contents change continually, depending on demands of the current environment. There may be a sort of consciousness comprising all these elements that we all share, which might not require such things as a sense of self, language, or strategic planning. This consciousness is included in, but simpler than, our fully human version.

In examining the behavior of monkeys and apes, we start to have the uncanny feeling that very kindred spirits are at play. The next section offers a brief review of our primate precursors. We start by tracing the time line of the transitions from monkeys to apes and hominids, and then we review what we have learned from studying present-day monkeys and apes. It seems possible that distinct discontinuities, or cognitive chasms, may distinguish the minds of the great apes from those of monkeys and other vertebrates, and the minds of humans from those of apes. Current experiments suggest that the concept of a self occurs only in the great apes and humans and that the attribution of mental states to others occurs in humans alone.

Transitions from Monkeys to Hominids

Our ancestors of 30--60 million years ago were arboreal (tree-dwelling) creatures rather like lemurs and tarsiers, and we ourselves exhibit many of their most distinctive features. In these animals, who have many representatives in the present, bones and muscles are specialized for swinging between branches, thumbs and big toes are separate from the other digits (this makes grasping possible), and the shoulder girdle and pelvic girdle are looser than in most terrestrial mammals (see Figure 4-1). The gyrations that human joints can go through in modern ballet performances are far greater than other higher vertebrates can perform. Arboreal existence places extreme demands on the nervous system. The coordination required among vision, gravity sensing, and motor actions is intricate. Many arboreal primate societies are socially stratified, and individuals recognize each other and communicate emotions via facial muscles corresponding to those we use. These animals also draw on a large repertoire of nonverbal communication (body language) and of noises and shouts.



You might stop for a moment to compare your own body to that of a pet dog or cat and note the much greater freedom of movement you have in your limbs.


Figure 4-1

Early arboreal mammals. (a) Lemur. (b) Monkeys. (c) Apes. The limbs are specialized for the tension-bearing required to grasp tree branches and move about in them.

The earliest anthropoids, the monkeys and apes, appeared in Africa during the Oligocene epoch about 30 million years ago. They usually have single births, the newborn are largely helpless, and the young depend on parental care during a long period of growth and maturation. There is now general consensus that the hominid and chimpanzee line diverged from a common ancestor about 5 million years ago, whereas the gorilla and the orangutan split off at least 9 million and 12 million years ago, respectively. The evolutionary writer Richard Dawkins has illustrated this process by suggesting that you imagine yourself to be holding your mother's hand, and she your grandmother's, and so on for a chain of generations that stretches in a straight line as far as the eye can see. Alongside this line stretches another one: a line of mother and daughter chimpanzees. If you now let go of your mother's hand and walk for many miles down the aisle between the two lines, the chimp and human faces will become more and more similar. Finally, your walk will be blocked by your joint ancestress who is standing at the fork of the two chains. If we assume 3 feet per generation, this is a walk of about 300 miles, which doesn't seem all that far. 11

Upright Posture

A distinguishing characteristic of the early hominids (australopithecines) that appeared approximately 4 million years ago was the bipedal stance that permits an erect posture---an adaptation that is energy-efficient and enables us to walk long distances. This happened in animals the size of modern chimpanzees, well before the brain began to enlarge (see Figure 4-2). 12 Ideas about what adaptive advantages might have been associated with standing include better dissipating body heat, extending the range beyond forest to open savanna, reaching higher in foraging, seeing farther over tall grasses, and carrying food or infants over long distances. 13 In addition to direct evidence of erect posture and the use of simple stone tools, there is indirect evidence for division of labor (sexual dimorphism), shared food, nuclear family structure, larger numbers of children, and longer weaning periods.



We are built for moving, not for standing. Our body structure has a high center of gravity, and walking is essentially a controlled falling forward. The humanoid frame can move in many more ways than the frames other vertebrates. Some have speculated that the intelligence related to sensing and moving in these new spatial coordinates was a precursor to more advanced analytical capabilities.


Figure 4-2

Changes in the skeleton accompanying the transition to an upright posture. (a) Chimpanzee. (b) Australopithecus afarensis. (c) Modern human.




You can get a direct sense of the difference between the carriage of human skeletons and those of monkeys and apes by trying this simple exercise. (If you are worried about looking silly, you should probably do this when you are alone!) Stand up, and then crouch down by bending at your knee and hip joints. Your behind should stick out as you lower your torso forward and let your head and arms hang down. This may feel strange, because social conventions in Western cultures dictate that we never move the hip joint in isolation (torso and leg muscles are always included) and also require that we lock together movements of the shoulder, head, and neck. In this crouching, simian position, see if you can shake your head and shoulders a bit to let them come loose so that your arms dangle down. Bounce on your knees and let your behind go even further back. If you go ahead and do this, you can feel the stress taken off your back and the tension in the abdominals relieved as your gut hangs down. You're ready to go banana hunting! Note that turning about is a bit more clumsy, because your moment of inertia about the vertical axis is larger than it was when you were upright. Now slowly rise to your normal, upright, standing position and note the difference between this and the ape-like posture in an activity such as turning. The moment of inertia about the vertical axis is smaller in humans than in monkeys and other animals. We use less energy when we turn.

As you stand up, note the following differences that have appeared in the transition from chimpanzee to human skeletons: The human chest is compressed and the head moves back. The tail shrinks to a tailbone that forms a basin for our internal organs, and a curve is introduced in our lower backs. Our shoulder blades are lengthened for a wider range of upper-body movement. Our legs are lengthened and our feet are narrowed to support walking and running. Muscles around the pelvis arrange themselves for striding rather than power lifting. Vertebrae are wedge-shaped rather than square as in monkeys, which permits more flexible movement of the spine. The front of the pelvis in humans, at the center of gravity, is a triangle of weakness. Our front flexors usually do not match the strength of our back extensors. The central role of this weak area at the center of gravity is well recognized by athletes, dancers, and martial artists.




Larger Brains

The upright posture achieved by the australopithecines was not accompanied by an increase in brain size. Larger brains appeared in the various Homo lineages, such as Homo habilis ("handy, or skillful, man"), whose brain size had increased to 600--700 cubic centimeters (cc) by approximately 2 million years later. Stone tools for cutting as well as mashing are found at Homo habilis fossil sites. These are crude tools of the sort created by slamming two rocks together until you get a sharp edge. Between 1.5 and 2.5 million years ago, as Homo erectus ("standing man") was becoming more prominent, brain volume increased to 900--1100 cc (see Figure 4-3) and more elaborate tools were being made, along with fire, shelters, and seasonal base camps. Migration out of Africa began. The second major increase in brain size, to approximately 1400 cc, occurred around 300,000 years ago, with archaic sapient humans, and the vocal tract started to assume its modern form. No later than 100,000 years ago, our fully modern version of Homo sapiens ("wise man") was present. 14

Figure 4-3

Changes in the shape and volume of the skull in the transition from (a) Australopithecus, through (b) Homo erectus, to (c) Homo sapiens.

Lower primates have approximately the same ratio of brain size to body size as hundreds of other mammalian species. If this is assigned a value of 1 for the purpose of comparison with higher primates, the ratio increases from a value of 1 in the lower primates to over 2 in the great apes, to 4 in H. habilis, 5 in H. erectus, and 6--7 in H. sapiens. That is, we have six to seven times as much brain as the average mammal with a similar body weight. The increase in the mass and the energy consumption of the hominid brain is balanced by a reduction in the size of the gastrointestinal tract, made possible, perhaps, by a higher-quality diet. The prevailing idea is that the main cause of this relative increase in brain size in primates was selection for the intellectual ability required to participate in large social groups and for the memory capacity required to handle many different relationships within groups. The increase in brain size correlates with group size in a number of primate species. Extrapolated to humans, the data suggest an ideal group size of slightly over 200. A survey has shown the average size of human hunter-gatherer groups and nomadic societies to be 150--180 individuals. 15

An alternative ecological theory suggests that a larger brain is required for the cognitive skills involved in coping with larger home ranges and seasonal migrations. An implicit assumption here is that bigger is smarter, but we have little firm evidence from other animal species that size correlates strongly with intelligence. Some fish species with brains the size of pinheads are much brighter than others with brains a thousand times larger. Elephants have big brains because elephants are big; they are not strikingly smarter than other animals. Another idea about our big brains, perhaps a bit far-fetched, suggests that they are a consequence of the heat stress on the brain that is caused by our upright posture. Heat that is dissipated from the exposed back of a quadruped or crouching ape rises to the head in hominids. Perhaps the brain got bigger to provide the increased blood flow needed for radiative cooling! The extra nerve cells that went along with this change in plumbing might then have been recruited for other purposes. Perhaps when hair was lost from the rest of the body, it was retained on the head because it reduced radiative heating from the sun. In short, no theory of what drove the explosive evolution of the hominid brain has gained complete acceptance.

Stages in Hominid Emergence

It is commonly supposed that the social behaviors and divisions of labor that we now observe in chimpanzees, such as male hunting groups and limits on female mobility associated with the period before weaning, might have become more pronounced with the transition to bipedal posture. Some available fossils suggest sexual dimorphism in australopithecines. The scenario of "man the hunter" as a driving force in early hominid social evolution has passed from favor as evidence for "man the scavenger" has accumulated. Animal bones found together with hominid remains also suggest that hominids may have been prey as well as predator. One possibility is that a distinctive evolved hominid behavior was cooperative scaring away of predators such as lions (by throwing rocks or using fire), thus making it possible to scavenge their kills. There is evidence that H. erectus tamed fire and thus could have used it both for this purpose and for cooking to counter spoilage. 16 During the development of the genus Homo, many behaviors strikingly different from those of monkeys and chimpanzees appeared. These included feeding children after the age of weaning instead of leaving them to find food on their own, most adult men and women associating in couples, fathers as well as mothers caring for children, living long enough to experience grandchildren, and females undergoing menopause. 17



Early hominids may have been scavengers more often than hunters, and predators less often than prey.


The course of hominid evolution was emphatically not the simple sequence Australopithecus -> H. habilis -> H. erectus -> H. sapiens. Rather, it was more like a pagoda tree with at least five layers of branching limbs representing radiations of australopithecines, habilines, erects, archaic moderns, and moderns. 18 The erects and habilines could have independently derived from different branches of the australopithecine line. Moderns (including the Neanderthals) could have descended from early erects. (This point is taken up further in the next chapter. See Figure 5-3 for an illustration of the hominid evolutionary tree.)

Discontinuities, or pulses, in the evolution of hominids appear to correlate with abrupt cooling periods and contractions of rain forests that occurred in Africa about 5 million, 2.5 million, 1.7 million, and 900,000 years ago. 19 At these times, major changes in the fossil remains of other animals are observed. Antelope horns, used in species-specific mating recognition, have proved to be a useful marker for changes in nonhominid species. One hypothesis is that a cold spell and shrinkage of forested habitat 5 million years ago forced tree-dwelling quadrupeds to forage as bipeds on the savanna. The next major cooling, about 2.5--2.8 million years ago, may have caused a permanent shift to grasslands and a splitting of prehumans into Australopithecus and Homo. The cold spells of 1.7 and 0.9 million years ago may have reinforced the emergence of H. erectus. Definitive proof of the "evolutionary pulse" idea is difficult to obtain, however, and recent work examining in more detail the mammalian fossil record in East Africa has been interpreted to indicate slower, continuous changes. 20

On balance, the observations are consistent with the idea that slow evolution in the Darwinian mold has been "punctuated" when sudden changes in global climate have occurred. An animal species stressed by the disappearance of its accustomed environment will have one of three fates. It will migrate to an environment similar to the old one, adapt to the new environment, or become extinct. 21 The chaotic and uncertain nature of these environmental changes makes it possible that the appearance of fully modern humans, perhaps in response to one of these changes, had a large element of chance and certainly was not foreordained. Forms like ourselves might just as easily never have appeared, or they might have arisen only after several million more years. 22

Origins of Human Intelligence

Having laid out a time line for the evolution of humans from a chimpanzee-like precursor, what can we say about the changes in mental machinery that were going on? Unfortunately, the paleontological record tells us very little about what was going on inside those fossilized skulls as they increased in size in the transitions from australopithecines through H. sapiens, alongside the increasing complexity of tools and artifacts. Cranial endocasts of fossil H. habilis skulls, made by using the skull as a mold for a plaster cast of the brain it once contained, do reveal one interesting feature: Bulges appear over Broca's and Wernicke's areas, which (see Chapter 3) are involved in the generation and comprehension of language, respectively. This observation indicates a relative increase in the sizes of these areas, and perhaps language competence increased along with it. 23 Apart from evidence like this, the best way we can obtain clues to the origins of our modern human intelligence is to study the brains and behaviors of modern monkeys and apes.

Figure 4-4

The brain of modern humans (a) is larger, is more densely folded, and has a more prominent prefrontal cortex (shaded areas) than that of modern apes (b).

Primates have larger frontal cortexes than other mammals, and the prefrontal cortex contains a unique layer of small granular cells. 24 The most striking increase in brain size during the monkey, ape, and hominid transition is in the prefrontal cortex, which occupies about 24% of the cerebral mantle in humans, compared with about 14% in the great apes (see Figure 4-4). 25 PET imaging studies suggest that the left medial frontal lobe is an important locus of theory-of-mind tasks (see the section "Awareness of the Mental States of Others" near the end of this chapter). 26 It is also central to foresight and planning mechanisms that are absent in the apes. Expansion of the cerebellar cortex in humans is also larger than extrapolation from primate trends would predict. A phylogenetically newer part of the human cerebellum called the dentate nucleus makes connections with the frontal lobes and may be correlated with distinctively human language and cognition. 27

Because genetic data make it clear that our closest ancestor is a creature similar to the modern chimpanzee, it is commonly assumed that we can take chimpanzee behaviors as possible precursors of our own. We have to keep in mind, however, that evolution is not like a ladder, with one character always building on a previous, similar one. It is more like a tree, in which similar characters may have appeared independently on several different branches. Thus some present-day behaviors of humans and chimps (such as genocide) may have arisen quite independently, in response to the selective pressures of their separate environments. If we humans had chosen to study bonobos (pygmy chimpanzees) intensively for many years, rather than other species of chimpanzees or baboons, we might have concluded that early hominids lived in societies in which warfare was rare or absent, social life centered on females, and promiscuous sex facilitated a large array of social interactions. 28 Or, to put the point another way, the fact that pygmy chimps are so totally different from other apes in their social structure and sexual, nonaggressive behaviors raises the possibility that we might have turned out that way rather than being genocidal and xenophobic. Thus the undesirable behaviors that we share with chimps may or may not have been our own separate invention.



Evolution is a tree, not a ladder. Human brains did not evolve "from" chimpanzee brains. Rather, hominid and chimpanzee evolution have been proceeding independently in the 5--6 million years since our evolutionary lines diverged.


Episodic Intelligence

Bearing in mind the foregoing cautions, we do see intelligences in monkeys and chimps that would appear to be an appropriate foundation on which to build, in stages, our more complex minds. Merlin Donald, a Canadian psychologist, has proposed a sequence comprising four main stages of cognitive evolution in primates and hominids: the episodic, mimetic, mythic, and theoretic. He suggests that these stages correlate approximately with apes and australopithecines, Homo erectus, archaic moderns, and modern humans. 29 The central idea is that older systems and their associated brain structures are encapsulated by newer ones, all operating in parallel. We can at different times be operating from one or from a combination of these intelligences. There is debate over the validity of these stages, but they offer a useful context and are generally accepted. 30 It is Donald's earliest stage, the episodic intelligence he attributes to monkeys and apes, that is relevant to our current discussion. The other stages are covered in later chapters.

An episodic intelligence lives in the present---in a series of concrete occasions. Single events and sequences of events or episodes can be remembered, and retaining these as well as remembering complex sets of social relationships, requires a large memory capacity. The episodic memory system stores and recalls perceived events. Many animals demonstrate the ability to analyze and recall situations, but they show no evidence of being able to re-present them for reflection. The closest we might come to understanding what is meant by episodic intelligence, when it is suggested as a component of our current brand of human awareness, is to conceive of it as being present in those moments when our minds are momentarily devoid of internal narrative chatter, when we are attentive only to what is happening in the immediate present, having sensations but not reflecting on them, letting memory associations triggered by current perceptions rise spontaneously. In this frame of mind, we might find, for example, that we know (remember) where a purse or comb is, without thinking about it.



Try putting aside this book and your language mind for a moment to test whether the idea of an episodic mind makes sense to you. Pause and see whether you can put yourself in a mental space of "just being," letting your mind feel more quiet and noting only the sensing and acting happening in the immediate present, along with any nonverbal memory associations that are triggered by your current perceptions.


Some of the most thorough studies attempting to define the nature of episodic minds have focused on East African vervet monkeys, which are not as advanced as chimps. 31 These monkeys show complex social interactions, classify relationships into types, and also classify sounds according to the objects and events they denote (such as leopard alarm, snake alarm, and eagle alarm, each associated with specific behaviors). They have a laser beam sort of intelligence focused on a very narrow region. There is no evidence that these monkeys attribute mental states to each other. They are skilled observers of each other's behavior but can't be said to analyze each other's underlying motives. The monkeys exercise subtle and penetrating discrimination in social matters, yet they don't seem to transfer this capacity to other contexts. They do not seem to have knowledge of their knowledge (to know that they know), in the sense of being aware of their own states of mind and using this awareness to explain or predict the behavior either of themselves or of others. The lack of such awareness may be why they can't transfer very specific pieces of knowledge or procedures to similar appropriate occasions (for example, they do not use the "leopard sound" process to invent a sound for a new danger that appears). Even so, we must be cautious in generalizing about the behavior of monkeys, for very intelligent behaviors have been noticed in some exceptional individuals. One Japanese macaque monkey, for instance, devised a variety of physically sophisticated strategies to extract an apple from a transparent tube. 32

The Great Apes: Selves and Others

The chimpanzees and other great apes mark a major increase in cognitive abilities. Chimpanzees are socially the most advanced of the nonhuman primates and have greater than 98% genetic similarity to us. This is more similar than the red-eyed and white-eyed vireo songbirds are to each other. Jared Diamond, a student of human evolution, points out that a zoologist from outer space would classify us along with the two species of chimpanzees as three species of the genus Homo. The genetic differences between humans and chimps, although small, are obviously very important. Detailed explorations of the genetic differences between humans and chimps imply that chimps and humans may be different by only a few hundred genes, and less than 100 genes account for the cognitive differences.

Socialization and Other Skills Among the Chimps

The chimp life cycle starts with a long period of socialization, and loose bonds are maintained between females and their adult offspring. Societies of 30--80 individuals occupy a persistent and defined home range over a period of years. Males cooperate during hunting and sharing of meat in a way that is unique in nonhuman primates. The social organization shows flexibility; different subgroups form on different days for hunting forays. Chimps employ complex visual and auditory communication, and at least 35 different sounds have distinct meanings. When two groups meet, they sometimes share a feeding site. At other times they use exaggerated movements and shouts in a territorial display, then withdraw. Genocide has been documented, as in, for example, one troop of chimps wiping out another in a slow and systematic way. We don't know whether this is a precursor or a separate invention of the same behavior shown by humans. This chimpanzee behavior raises the possibility that one rationale for hominid group living was defense against other hominid groups. Group living would enhance both the effectiveness of defense against other human groups and aggression toward them.

Chimps have highly developed manual skills, can solve problems, can use natural tools, and have elementary tool-making ability. However, their ability to look ahead and plan appears to be very limited. For example, no chimp spends an evening collecting a supply of sticks to use in fishing for termites the next day. It is interesting that species other than ourselves haven't come up with a faculty as useful as foresight. This faculty appears to be correlated with the enlargement of the frontal lobes, which is distinctive to our hominid brains.



Groups of chimps geographically isolated from each other develop different tools and grooming rituals and pass these on through teaching and imitation. 33


Groups of chimps show political and moral behaviors that are strikingly similar to our own. They follow prescriptive social rules and anticipate punishment for infractions. Their rules of reciprocity concern giving, trading, and revenge, and they exhibit moralistic aggression against violators. Groups learn to adjust to, and give special treatment to, disabled and injured individuals. The status hierarchy is modulated by complex alliances, peacemaking, and negotiation. 34 We can also recognize analogs of our entire range of human emotions, as individuals move between moods of being happy, sad, angry, lonely, tired, embarrassed, and so on.

Chimps in captivity have even been trained to do simple addition with Arabic numerals. 35 They can classify objects into types and sets 36 and can arrange differing numbers of objects in correct numerical order. (Rhesus monkeys have also been shown to have this capacity.) Although chimps and monkeys can use simple signs or symbols presented by humans, they do not spontaneously invent them. Some bonobo chimps, upon watching others use a board of symbols, have used the board in simple communication tasks. 37 The animals will perform language-like operations that some investigators claim reveal a grammar equivalent to that of a human infant, showing some sensitivity to word order and syntactical rules, but this is done in response to extensive molding, drilling, and reinforcement by the researcher. They don't seem to have a genuine feel for what language is about. 38 To be sure, it is an anthropocentric distortion to be prompting chimps to try various human-style tasks as though these abilities were a measure of biological worth. Critics of animal language research say that trying to teach chimps language is like trying to teach humans to fly, for they have nothing analogous to the language instinct that humans have.

Developing a Concept of Self

As we have noted, chimps, orangutans, and human infants after about 18 months of age are unique among the primates in their reaction to mirrors. Monkeys and other vertebrates, upon encountering a mirror image of themselves, never move beyond treating the image as another member of the species and frequently make threatening displays. Chimps who look into a mirror act at first as though they have encountered another chimp, but they soon begin to perform simple repetitive movements, like swaying from side to side, while watching their images. Perhaps they are learning that they can control the movement of the other chimp. They then appear to grasp the equivalence between the mirror image and themselves and start to explore body parts such as their genitalia, which they can't ordinarily see (see Figure 4-5). If a spot of dye that can't be smelled or felt is placed on a chimp's eyebrow ridge during anesthesia, the animal will notice the dye when it first encounters a mirror after waking. More telling, the chimp will touch the dyed area and then smell and look at the fingers that have contacted the mark, behaviors that suggest self-recognition---a sense of self.

Figure 4-5

Chimpanzees display active curiosity when encountering a mirror, exploring parts of their body that they cannot otherwise see. Their behavior suggests that they have a sense of "self" somewhat akin to our own.

Awareness of the Mental States of Others

Although chimps show behaviors more consistent with having a sense of self than do monkeys and less complex vertebrates, there is debate on whether they can perform a further operation characteristic of humans: to appreciate others as also having selves to which beliefs can be ascribed. Do chimps, like humans, have a theory of mind? Observations of deceptive behaviors shown by chimps in the wild seem most easily explained by assuming that they are ascribing beliefs to the animals they are deceiving, but the fact that chimps know how to deceive does not prove they know they are doing so. Studies on autistic human children suggest a dissociation between having a sense of self and being able to ascribe beliefs to others. Autistic children begin using a mirror to inspect themselves at the same age as normal children, but they appear to develop only a rudimentary ability to attribute a mental life to others. They appear to suffer a sort of "mind-blindness" with respect to other humans. 39

The most critical experimental tests of whether chimps can attribute mental states to others have involved vision. The effort has been to determine whether for chimps seeing is believing, as it is for humans. The experiments usually involve at least two humans. One, the knower, observes food being placed in one of several cups screened from the chimp's direct vision, while the second, the guesser, has left the room. The guesser returns to the room and points at an empty cup while the knower points at the baited cup. The chimp is allowed to search one cup and keep the food if it finds it there. Animals quickly learn to select the container indicated by the knower more often than that indicated by the guesser. However, because the chimp might not be making an association based on the knower's visual access to the baiting, but rather associating "the one who stayed in the room" with food, more complicated experimental designs are tried. For instance, the guesser remains in the room with a paper bag over his head while a third person enters the room and baits a cup in the view of the knower. Chimps learn to choose the cup subsequently pointed at by the knower, but this could reflect a further associative rule that has nothing to do with seeing as knowing---for example, "pick the cup pointed at by the guy who didn't have a bag over his head."

In another set of experiments, chimps are exposed to two trainers, one able to see and one whose vision is occluded by a blindfold, screen, or food bucket placed over the head. The chimps are rewarded with food for making a begging gesture in front of the trainer that a human would judge able to see the chimp. The fact that the chimps show no disposition, either immediately or during early training, to prefer the person whose vision was unblocked suggests that they may not understand the relationship between seeing and attending. A problem with this experiment is that even if chimps have a learned or unlearned tendency to beg from people with visible eyes, this might reflect the unconscious associative rule "begging from people with visible eyes is more likely to lead to reward," rather than requiring an explanation in mental terms, such as "seeing is knowing." More subtle experiments are needed to determine whether a chimp can have the concept "see." There is no ambiguity about this issue in human infants, who between the ages of 3 and 5 years begin to use their visual experience to attribute real and false beliefs to others. (See "Stages in the Development of Human Selves" at the beginning of Chapter 7.) 40



Humans and chimps display many similar behaviors. However, we cannot know whether these similarities in behavior reflect similar subjective experiences.


Human children seem to understand desires before they understand beliefs, which suggests that chimps might do better when examined for evidence of understanding desires or goals rather than beliefs. Chimps watching actors try to solve a problem are more likely to select photographs depicting achievement of the actors' implicit desires or goals. More interestingly, they can cooperate with a human partner on a task that requires different roles, and they can switch roles. However, we cannot know whether these similarities in behavior between chimps and humans reflect similar subjective experiences. Because humans can do so much without self consciousness (later chapters discuss examples such as blindsight, procedural learning, and cognition outside of awareness), and because our consciousness of self is so labile, an extrapolation to what it is like to be a chimp is not in the cards. We have to remember that the brains and minds of chimps are not simply steps on the ladder to humanity but alternative products of the evolutionary process.


The question of what kind of consciousness animals have is a difficult one, because we don't have the tools to look into those minds and know what it is like to be an insect, a bird, a dog, or a chimpanzee. What we can observe are behaviors and nervous structures that show a continuous thread of increasing complexity throughout vertebrate evolution, leading us to assume that we share fundamental faculties like awareness, attention, memory, and emotion. However, the temptation to attribute our human style of experience and motivation to animals such as our pets must be tempered with the realization that simple associative learning---as when animals learn by trial and error which behaviors produce food reward, affection, or punishment---is sufficient to explain very complex behaviors; there is no need to invoke a "self" such as we experience. It is in the anthropoids that appeared about 30 million years ago and now form our closest link to the rest of the animal world that we observe structures and behaviors that are clearly antecedent to our own. The transition to an upright posture that evolved at some point after the hominid and chimpanzee lines split about 5--6 million years ago was bad for our backs but freed our hands for manipulative use and gave us a greater range of movement than other vertebrates enjoy. The rapid radiation of a series of different lines, such as Australopithecus, Homo habilis, and Homo erectus, tested different hominid designs as brain size steadily increased. Archaeological sites with hominid remains show that simple tools and fire were in use by approximately 2 million years ago.

As a starting point for describing distinctively hominid intelligences, we make the assumption that the minds of monkeys and apes have changed much less rapidly than ours during the past few million years and that they thus represent a base on which further changes are built. We attribute to monkeys, apes, and many other animals a sort of intelligence that is episodic and present-centered, has very little sense of past or future, and is largely unaware of its own state. It is only in the great apes that we see the first compelling evidence of an appreciation of "self" more like our own. A final transition, from the sense of having a self to the attribution of such a self to others, appears to be a distinctively human feature. Experiments with chimpanzees suggest that their ability to attribute beliefs to others, if present at all, is extremely rudimentary. Although we share with animals a host of cognitive abilities---such as perception, memory, and learning---there is no evidence that any animal comes close to humans in generating an internal "I" that fills a mind-space with stories of past and future and imagines the minds of others. Stages in the development of these hominid innovations are the subject of Chapter 5.

Questions for Thought

1. Think of a seemingly quite intelligent behavior that you have observed in a pet animal---a behavior that might well lead you to assume that the animal knew what was going on in your mind. Can you think of ways to explain the pet's behavior in more simple terms that don't rely on its interpreting your mental state? What would lead you to choose the simpler or the more complicated explanation?

2. It is widely believed that humans are the only species that shows foresight---that is, can plan ahead. Do you think this is true? What kind of experiments would you design to look for foresight in an animal?

3. A chimpanzee that is familiar with its face in a mirror is briefly anesthetized, and a small, odorless spot is painted on its face. If the chimp looks in a mirror after waking, it notices the spot in the mirror and points at the spot on its face. This experiment was originally interpreted to suggest that the chimp had a notion of self similar to our own. However, the same sort of experiment can be shown to work with a pigeon, an animal with which we feel much less kinship. Is there an interpretation of these results that does not require postulating the sort of awareness of self that we experience?

4. Genocide and xenophobia are observed between groups of chimpanzees and also between groups of humans. What conclusions can we draw from this about the origins of the human behaviors?

Suggestions for Further General Reading

Gould, J.L., & Gould, C.G. 1994. The Animal Mind. New York: Freeman/Scientific American Library. This book is a well-illustrated survey of animal minds and behavior. It gives many examples of the sort mentioned in the first section of this chapter, describes Pepperberg's experiments with the African Gray parrot named Alex, and reviews attempts to train apes in language use.

de Waal, F.B.M. 1996. Good Natured: The Origins of Right and Wrong in Humans and Other Animals. Cambridge, MA:Harvard University Press. A description of many animal behaviors, particularly those of chimpanzees, that mirror human behaviors. De Waal argues that the gulf between animal and human consciousness is not as wide as some people think.

The next three books discuss changes in cognition and structure that accompanied the transitions from monkeys to hominids. They are equally relevant to the subject matter of Chapter 5.

Diamond, J. 1992. The Third Chimpanzee. New York: Harper Collins.

Donald, M.D. 1991. Origins of the Modern Mind. Cambridge, MA: Harvard University Press.

Kingdon, J. 1993. Self-Made Man---Human Evolution from Eden to Extinction? New York: Wiley.

Reading on More Advanced or Specialized Topics

Deacon, T.W. 1997. The Symbolic Species---The Co-Evolution of Language and the Brain. New York: Norton. A masterful description of mammalian brain evolution and the specializations that might have provided a foundation for the hominid invention of symbols.

Grier, J.W., & Burk, T. 1992. Biology of Animal Behavior. St. Louis: Mosby - Year Book. This comprehensive college text covers many of the points in this chapter.

Povinelli, D.J., & Preuss, T.M. 1995. Theory of mind: Evolutionary history of a cognitive specialization. Trends in Neurosciences 18:418--424. This article provides more information on the question of whether apes can attribute mental states to others.

Seyfarth, R.M., & Cheney, D.L. 1992. Meaning and mind in monkeys. Scientific American 267:122--128. This article provides a description of monkey intelligence and its limits.

1. Reiss and McCowan, 1993.

2. Wasserman, 1995.

3. Pepperberg, 1994.

4. The book by Gould and Gould, 1993, provides a fascinating and well illustrated survey of animal mind and behavior.

5. Masson and McCarthy, 1995.

6. de Waal, 1996.

7. Bekoff, 1993

8. Bekoff, 1995.

9. Yoerg and Kamil, 1990.

10. Hauser et al., 1995; Parker et al. 1994.

11. Wade, N. 1994, quoting Richard Dawkins.

12. Reynolds, 1980, Ch.5; Wessels and Hopson, 1988, Ch. 50

13. Wilford, 1995.

14. Donald, 1991, Ch. 4.

15. Dunbar, 1993; Dunbar, cited in Donald, 1991, Ch. 5.

16. Balter, 1995. It is interesting that we modern humans have a dietary preference for aged (partially spoiled) red meat that is then cooked. Fresh meat is not usually considered to be as palatable.

17. Diamond, 1992, pg. 8

18. Kingdon, 1993.

19. Vrba, 1993; deMenocal, 1995.

20. Kerr, 1996.

21. Shell, 1993; Stevens, W.K. 1993.

22. Kimura, pg 225, in Keller and Lloyd, 1992; also Gould and Eldredge, 1993 on punctuated equilibrium theory.

23. Tobias, 1987.

24. Preuss, 1995. Nimchinsky et al., 1999, have reported an unusual projection neuron in layer Vb of the anterior cingulate cortex which is found only in great apes and humans.

25. Preuss, 1995.

26. Lewin, 1995.

27. Leiner et al., 1993.

28. de Waal, 1995.

29. Donald, 1991.

30. Donald's 1991 book has been the subject of a multiple book review in Behavioral and Brain Sciences (Donald, M. 1993).

31. A good recent summary is found in Cheney and Seyfarth, 1992; and Seyfarth and Cheney, 1992. R. Byrne's book, 1995, is also useful.

32. Lincoln, 1994.

33. A recent study compares seven separate groupg of chimpanzees, isolated from each other, that have culturally transmitted distinctively different patterns in using stick-tools, leaves, and objects, as well as different procedures for pounding food and engaging entertainment and attention. See Whiten et al., 1999.

34. deWaal, 1996.

35. Fishman, 1993

36. Spinozzi, 1996.

37. Savage-Rumbaugh and Lewin, 1994.

38. Pinker, 1994, pg. 340.

39. Byrne, 1995, argues for mindreading in great apes, Baron-Cohen, 1995, suggests that it exists only in humans and evolved alongside language.

40. The material in these paragraphs is taken from Povinelli, 1994; and Povinelli and Preuss, 1995, and Povinelli and Eddy, 1996.

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