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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.
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DESIGN NOTE: IMPORTANT POINT
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.
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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. Bird
brains, which have an anatomy less like our own, can perform prodigious feats
of memory and carry out a variety of cognitive tasks. 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]").
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. 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 and
the astounding array of human-like emotional behaviors that have been documented
for chimpanzees. 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.
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DESIGN NOTE: IMPORTANT POINT
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.
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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. 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?"
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. (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. 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.
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DESIGN NOTE: SELF-EXPERIMENT
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.
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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.
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). 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. 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.
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DESIGN NOTE: LONG IMPORTANT POINT
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.
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Figure 4-2
Changes in the skeleton accompanying
the transition to an upright posture. (a) Chimpanzee. (b) Australopithecus
afarensis. (c) Modern human.
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DESIGN NOTE: SELF-EXPERIMENT BEGINS
HERE
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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.
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DESIGN NOTE: SELF-EXERCISE ENDS
HERE
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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.
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.
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. 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.
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DESIGN NOTE: IMPORTANT POINT
Early hominids may have been scavengers
more often than hunters, and predators less often than prey.
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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. 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. 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.
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. 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.
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. 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. 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). 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). 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.
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. 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.
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DESIGN NOTE: IMPORTANT POINT
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.
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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. 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. 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.
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DESIGN NOTE: SELF-EXPERIMENT
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.
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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. 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.
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.
************
DESIGN NOTE: IMPORTANT POINT
Groups of chimps geographically
isolated from each other develop different tools and grooming rituals and pass
these on through teaching and imitation.
****************
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. 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. They
can classify objects into types and sets 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. 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. 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.
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.)
************
DESIGN NOTE: IMPORTANT POINT
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.
Summary
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.
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