In the Minds of Monkeys What do they know--and do they know they know it? It was early morning, and the vervet monkeys had moved out of their yellow-barked acacia sleeping trees to forage on the open plains of the East African savanna. While the adults fed, the juveniles played in a nearby bush. Macaulay, the rambunctious son of a low-ranking female, wrestled Carlyle, the juvenile daughter of the highest-ranking female in the group, to the ground. Carlyle screamed, chased Macaulay away, and went to forage next to her mother. The fight had lasted no more than a few seconds, but it had not gone unnoticed: twenty minutes later, Shelley, Carlyle's sister, approached Austen, Macaulay's sister, and without provocation bit her on the tail. This kind of anecdote sets the stage for the typical article on nonhuman primates. Read any description of a long-term study of monkeys or apes and you will find an account of complex kinship networks, friendships, struggles for dominance, and shifting alliances. For most human observers, what makes these animals so fascinating is their social structure, which often seems as rich and complex as our own. When we read Shakespeare's account of the blood feud between the Capulets and the Montagues, we take it for granted that the members of these two families had a well-developed sense of their own and other peoples' social relationships. If they didn't, there would have been no feud and no ironic or tragic elements to Romeo and Juliet's romance. Monkeys, like Shelley in the anecdote above, apparently also recognize relationships in families other than their own, and they use this knowledge to retaliate against their opponents. For monkeys, as for humans, the enemy of my kin and the kin of my enemy are my enemies too. Highly social creatures, monkeys and apes have often impressed observers with their ability to predict the behavior of other animals and to recognize their relatives and allies. This has led some scientists to speculate that primate, including human, intelligence originally evolved to solve social problems. According to this theory, natural selection has acted with particular force in the social domain, making monkeys and apes especially sensitive to the behavior and relations of others. But what sort of social knowledge really exists in the minds of monkeys? How is their intelligence similar to our own, and how is it different? For the past thirteen years, we and our colleagues have attempted to tackle some of these questions by studying the East African vervet monkey in Kenya's Amboseli National Park. Vervets are members of the largest family of Old World monkeys, which includes baboons, macaques, and many forest-dwelling monkeys, and they are among the most common primates in sub-Saharan Africa. As primates, they are relatives of ours, but they are by no means our closest relatives. Humans and chimpanzees, for example, seem to have shared a common ancestor only 5 million years ago, while the common an ...

1. In the Minds of Monkeys
What do they know--and do they know they know it?
It was early morning, and the vervet monkeys had moved out of
their yellow-barked acacia sleeping trees to forage on the open
plains of the East African savanna. While the adults fed, the
juveniles played in a nearby bush. Macaulay, the rambunctious
son of a low-ranking female, wrestled Carlyle, the juvenile
daughter of the highest-ranking female in the group, to the
ground. Carlyle screamed, chased Macaulay away, and went to
forage next to her mother. The fight had lasted no more than a
few seconds, but it had not gone unnoticed: twenty minutes
later, Shelley, Carlyle's sister, approached Austen, Macaulay's
sister, and without provocation bit her on the tail.
This kind of anecdote sets the stage for the typical article on
nonhuman primates. Read any description of a long-term study
of monkeys or apes and you will find an account of complex
kinship networks, friendships, struggles for dominance, and
shifting alliances. For most human observers, what makes these
animals so fascinating is their social structure, which often
seems as rich and complex as our own. When we read
Shakespeare's account of the blood feud between the Capulets
and the Montagues, we take it for granted that the members of
these two families had a well-developed sense of their own and
other peoples' social relationships. If they didn't, there would
have been no feud and no ironic or tragic elements to Romeo
and Juliet's romance. Monkeys, like Shelley in the anecdote
above, apparently also recognize relationships in families other
than their own, and they use this knowledge to retaliate against
their opponents. For monkeys, as for humans, the enemy of my
kin and the kin of my enemy are my enemies too.
Highly social creatures, monkeys and apes have often impressed
observers with their ability to predict the behavior of other
animals and to recognize their relatives and allies. This has led

2. some scientists to speculate that primate, including human,
intelligence originally evolved to solve social problems.
According to this theory, natural selection has acted with
particular force in the social domain, making monkeys and apes
especially sensitive to the behavior and relations of others.
But what sort of social knowledge really exists in the minds of
monkeys? How is their intelligence similar to our own, and how
is it different? For the past thirteen years, we and our
colleagues have attempted to tackle some of these questions by
studying the East African vervet monkey in Kenya's Amboseli
National Park. Vervets are members of the largest family of Old
World monkeys, which includes baboons, macaques, and many
forest-dwelling monkeys, and they are among the most common
primates in sub-Saharan Africa. As primates, they are relatives
of ours, but they are by no means our closest relatives. Humans
and chimpanzees, for example, seem to have shared a common
ancestor only 5 million years ago, while the common ancestor
of Old World monkeys and humans lived roughly 20 million
years ago.
In Amboseli--an arid savanna woodland punctuated by swamps
at the foot of Kilimanjaro--vervets live in groups of ten to thirty
monkeys that include anywhere from one to eight adult males
and two to eight adult females. As in other Old World monkey
societies, females remain in their natal groups throughout their
lives, maintaining close bonds with their matrilineal kin; males
transfer to neighboring groups at sexual maturity. Social life in
the group is far from democratic. Each male and female
occupies a specific rank, dominating all those further down the
ladder. Offspring assume their mother's rank, so the dominance
hierarchy is in fact a hierarchy of families, with all the members
of family A outranking all the members of family B, and so on
down the line. Even a male assumes his mother's rank until he
migrates to another group. After that, a male's rank depends on
more subtle factors, including fighting ability, age, and his
acceptance by his adopted group's adult females.
While each vervet female inherits her high or low status, this

3. does not mean that she accepts her lot in life without protest.
Quite the contrary. Vervets, macaques, and baboons are--it must
be said--dreadful social climbers. They constantly compete for
the opportunity to groom highranking females, sit near them,
and play or groom with their infants. Animals that groom
together also tend to feed together and form alliances, and high-
ranking females have access to the best food,the best resting
places, and win almost all the disputes they enter. By
establishing a close bond with a high-ranking female, low- and
middle-ranking females may be able to enjoy some of the
benefits of high rank, even if they never actually increase their
status. In sum, vervet monkeys--like characters in a Jane Austen
novel--organize their lives around two principles: to maintain
close bonds with kin and to establish good relations with the
members of high-ranking families.
Time and time again, we have seen the practical value of
alliances. In a typical encounter, one female, Newton, may
lunge at another, Tycho, while competing for a fruit. As Tycho
moves off, Newton's sister Charing Cross runs up to aid in the
chase. In the meantime, Wormwood Scrubs, another of Newton's
sisters, runs over to Tycho's sister Holborn, who is feeding sixty
feet away, and hits her on the head. Hostility between two
animals often expands to include whole families, so not only
must monkeys predict one another's behavior but they must also
assess one another's relationships. A monkey confronted with
all this nonrandom turmoil cannot be content with learning
simply who is dominant or subordinate to herself; she must also
know who is allied to whom and who is likely to aid an
opponent.
We tested the vervets' ability to recognize the kin relations of
others by playing the scream of a two-year-old juvenile through
a concealed loudspeaker. The subjects for each experiment were
three females, one of whom was the juvenile's mother. In a
typical experiment, we would play the scream of Emerson to
three females: Teapot Dome (Emerson's mother), Profumo, and
Suez. Our original purpose was simply to determine whether or

4. not mothers recognized their offspring's screams. But when we
analyzed the films of the playback experiments, we found that
the screams often caused the other two females to look at the
mother. It was as if they were thinking, "That scream goes with
Emerson, and Emerson goes with Teapot Dome. What's she
going to do about it?"
Humans, obviously, do more than simply recognize the
relationships of others; we also compare different sorts of
relationships, classifying them and giving them labels that are
independent of the particular individuals involved. When a
friend mentions a sister or a lover, images of a particular type
of relationship are conjured up in our minds, even if we have
never met the person being discussed. Monkeys don't have
words for particular types of relationships, but they do seem to
evaluate and compare one another's social relationships. Vervets
apparently recognize parallels between their own kinship bonds
and those of others. A fight between Carlyle and Macaulay
increases the probability that Carlyle's relative will later
threaten Macaulay's relative.
While monkeys may know a lot about one another's social
relationships, they seem to know much less about one another's
minds. Consider deception, for example. Among humans,
successful deception demands that the liar identify what another
person believes to be true and then attempt to hide or falsify
relevant information. In other words, the liar must recognize the
distinction between his or her own beliefs and the beliefs of
others. Many animal species, including insects
occasionally give false signals to others, but these signals are
typically inflexible and occur only in a narrow range of
contexts. Male scorpion flies, for instance, sometimes steal dead
insects from other males by mimicking the behavior of a female,
but as far as we know, they never attempt to deceive one
another in any other context or in any other way.
Monkeys and apes, in contrast, attempt to hide or falsify a
variety of signals and patterns of behavior, and they do so in a
variety of contexts. For example, dominant male vervet

5. monkeys often chase subordinate males from sexually receptive
females. To counteract this tactic, a subordinate male will lead
a female behind a bush or tree, out of sight of more dominant
males, before attempting to copulate with her. Nevertheless,
monkeys' lies often seem oddly incomplete. To cite one
example, when vervet males spot a leopard, one of their primary
predators, they give loud barking alarm calls that cause other
vervets to run up into trees for safety. Most of the monkeys'
alarm calls are reliable, signaling the true presence of a
predator. Over the years, though, we have observed cases in
which a male gave apparently false alarm calls just as a new
male was attempting to transfer into his group. Normally, males
are hostile to solitary males that approach their groups, since
such males are almost invariably migrants in search of a group
to join. Resident males are not always successful, however, in
driving away these migrants, particularly when the migrants are
younger and stronger than themselves. The primary perpetrator
of false alarm calls during our study was Kitui, a perpetually
low-ranking male that could reasonably have expected to
become subordinate to any rival that successfully transferred
into the group. Kitui's false alarms were effective because they
caused his rival to run up into a tree and prevented him from
approaching the group.
So far, so good. The alarm calls appeared to be deceitful,
signaling a danger that Kitui, but not the rival, knew to be false,
and they kept the rival temporarily at bay. But was Kitui
actually trying to make his rival believe a leopard was nearby?
We can never know for certain what goes on in the mind of a
monkey when he gives an incorrect alarm call. Even if the call
functions to mislead, it may not be at all appropriate to
conclude that the signaler attributes mental states to others.
Here the issue becomes murky, because Kitui's subsequent
behavior was often puzzling. As if to convince his rival of the
importance of his calls, on three occasions Kitui left his own
tree, walked across the plain in full view of the imaginary
leopard, and entered a tree next to his rival's, alarm calling all

6. the while. He seemed to have gotten only half the story right: he
acted as if he knew that his alarm calls caused others to believe
there was a leopard nearby, but he didn't seem to realize that he
should behave as if he also believed in the leopard.
Numerous psychological studies have demonstrated that, like
Kitui, young children also have difficulty in distinguishing their
own knowledge from that of others. As any parent of a small
child will readily attest, children cannot easily recognize or
create false beliefs in others. Perhaps this iswhat makes them
such poor liars. A child of three will deny having been to the
cookie jar when there are still telltale crumbs on his or her face;
only later do children learn to wipe the crumbs off before
pleading innocence.
Other anecdotes are equally difficult to interpret. Subordinate
female baboons often raise their tails when approaching or
interacting with more dominant animals. Raised tails seem to
reflect anxiety and are usually accompanied by other signs of
subordination, such as grimacing or presenting the hindquarters.
In an earlier study of baboons, we once watched a female
attempt to suppress this sign of subordination. The female,
known to us as the Lady from Philadelphia, was attempting to
follow her daughter on a narrow rock ledge, and the path led her
within two feet of the resting place of the group's dominant
male, Rocky. As she approached Rocky, the Lady from
Philadelphia's tail began to rise. Looking back at her tail, she
pressed it down and held it until she had passed him, as if she
recognized that her raised tail would reveal an anxiety she
wanted to conceal.
Watching this behavior, we were tempted to conclude that the
Lady from Philadelphia was aware of the distinction between
her actual state of mind and the state of mind she wished to
convey to Rocky. Even if her actions represented a true
deceptive tactic, her behavior was difficult to interpret, at least
for human observers. Didn't she realize that by pushing her tail
down in full view of Rocky, she was less likely to fool him? Or
was Rocky's ability to detect deception also so incomplete that

7. it didn't matter how conspicuous her act of deception was?
Many anecdotes suggest that apes may be better than monkeys
at attributing beliefs to others and at recognizing the effects of
their own behavior on others. To give one example, Luit and
Nikki, two adult males in a captive group of chimpanzees
studied by Frans de Waal, were engaged in a prolonged struggle
for dominance. During one fight, Luit chased Nikki into a tree
and then took up a position of vigilance at its base. As he sat,
Luit began to bare his teeth in a nervous "fear grin"--a sign of
anxiety. Quickly, Luit turned his back to Nikki, put his hand
over his mouth, and pressed his lips together, apparently to hide
this sign of submission. Only after three attempts, when he had
succeeded in wiping the fear grin from his face, did Luit turn to
face Nikki again. Luit's actions suggested that he was aware of
his nervousness, of the external manifestation of his fear, and of
the need to hide this sign from his rival. Luit appeared to be
attempting to manipulate Nikki's beliefs, but until definitive
experiments are designed to test this hypothesis, simpler
explanations are also possible. For example, Luit might have
learned that whenever he showed a particular facial expression,
Nikki chased him.
Many observers have suggested that nonhuman primates seem to
show much greater intelligence when manipulating one another
than when manipulating objects. According to this "social
intelligence" hypothesis, the reason that monkeys in the
laboratory can be taught to classify objects according to some
criterion, such as color or shape, is that they do this sort of
thingnaturally in the context of social interactions: placing
objects X, Y, and Z into a particular class comes easily to
animals used to classifying one another as members of different
matrilines. Similarly, when monkeys solve problems of
transitive inference in the laboratory (if A is bigger than B, and
B is bigger than C, then A must be bigger than C), they are
merely duplicating an ability they use daily in assessing other
animals' dominance ranks.
The idea that a given ability may be manifested more in one

8. context than in another is not new. Many food-caching birds,
for instance, exhibit striking spatial memory when it comes to
finding seeds, but it is not clear whether they extend this ability
to nonforaging contexts. Similarly, although the honeybee's
dance conveys extraordinarily precise information about the
location, direction, and quality of food, honeybees do not seem
to use their dance to communicate, for example, about their nest
mates.
Do monkeys in fact exhibit more skills in social interactions
than in nonsocial contexts? Our investigations are still
preliminary, but they suggest that vervets sometimes show
surprising gaps in their knowledge of the external world.
Consider the monkeys' understanding of their predators. In
Amboseli, predation accounts for more than 70 percent of all
vervet deaths. The monkeys are preyed upon by leopards,
smaller cats, martial eagles, pythons, and baboons. In some
respects, the vervets have an impressive battery of responses to
these many predators. They have at least six acoustically
different alarm calls for these different classes of predators, and
each type of alarm call evokes a different escape response. The
loud, barklike leopard alarm call, for instance, causes monkeys
to run up into trees, while their more gruntlike eagle alarm call
causes them to look up into the air.
Vervets also recognize the various alarm calls of other species.
The superb starling, one of the most common bird species in
Amboseli, has two distinct alarm calls: one for terrestrial
predators (including vervets, which steal their eggs); the other
for hawks and eagles. When we played recordings of starling
alarm calls to vervets, we found that the monkeys responded
appropriately: the starling's terrestrial predator alarm call
caused the monkeys to run toward trees, while the starling's
eagle alarm call caused them to look up into the air.
In contrast to their skill at recognizing the alarm calls of other
species, however, vervets seem remarkably poor at identifying
the many kinds of visual cues left by predators. Leopards, for
example, are the only predators that cache carcasses in trees,

9. and vervets invariably alarm call when they spot a leopard in a
tree with a carcass. Nevertheless, the monkeys show no sign of
anxiety or increased vigilance when they spot a carcass in a tree
in the absence of a leopard; they never seem to realize that a
carcass in a tree may mean that a leopard is nearby.
Vervets are similarly blind to visual evidence of pythons. These
snakes hunt vervets by lying in wait for them in bushes or at the
base of trees. The snakes leave straight, wide tracks(reminiscent
of a wide-wheeled bicycle) that cannot be mistaken for those of
any other species, and humans quickly learn to avoid bushy
areas where there are fresh python tracks that haven't yet been
disturbed by wind or other animal footprints. The vervets,
though, never seem to learn that a python track denotes the
proximity of a python. We have often watched in utter
mystification as a vervet monkey walked calmly into a bush to
feed, ignoring the python track that led directly into it, only to
leap away in shocked horror when it encountered the snake
there.
Finally, vervet monkeys flee from Masai herdsmen and their
cattle, and they also respond to the mooing of cows and the
ringing of cowbells with vigilance and flight. Nevertheless, they
don't seem to recognize the distinctive clouds of dust that herald
the approach of cattle and Masai. Livestock herds produce
thick, dense clouds of dust that are readily distinguished (at
least by humans) from the more diffuse dust clouds produced by
zebras, wildebeest, and elephants. Day after day, however, the
monkeys will sit impassively in the midst of the livestock dust
clouds, only to give surprised alarm calls when the cows
invariably emerge.
Why should vervets fail to recognize the visual evidence of
predators? One possible explanation may be that visual and
auditory cues first evolved to deal with social problems.
Vervets do use visual signals in face-to-face interactions with
other monkeys but do not respond to visual evidence of an
absent object or individual. They do not, for example, follow
one another's tracks when foraging, look for the tracks made by

10. other groups when patrolling a territorial boundary, or visually
alter aspects of their physical environment to denote rank or
group membership. Auditory cues, in the form of their many
vocalizations, however, are abundant in these sorts of
situations. Monkeys frequently call when out of sight of one
another. If monkeys are foraging in dense brush, a vocalization
is enough to signal that a dominant animal is approaching or
another group has been spotted. In the social context, vervets
may never have needed to recognize that a visual cue can denote
some absent object or individual. Perhaps as a result, when they
confront a python's tracks or a carcass in a tree, the monkeys do
not make the connection between these objects and the
predators that put them there.
Apes may be better than vervet monkeys at recognizing the
visual cues left by other animals. In the wild, for instance,
chimpanzees make sleeping nests each night. When the members
of one group make raiding patrols into the range of another
group, they sometimes give aggressive displays upon
encountering their neighbors' empty nests. It would be
interesting to determine if chimpanzees were better than vervets
at recognizing the visual clues left by predators. The superior
performance of chimpanzees in many laboratory tests does
suggest that their intelligence may be less constrained and less
context specific than that of monkeys.
One of the most important features of human intelligence is our
ability to take a skill we have acquired in one context and
extend, or generalize, it to another. Humans can use analogical
reasoning not just to evaluate the similarity between our own
and other people's familiarelationships but also to recognize, for
example, that cat doors and the valves of a heart operate
according to the same general principles. One of the primary
distinctions between our intelligence and that of other primates
may lie not so much in any specific skill as in our ability to
extend knowledge gained in one context to new and different
ones.

11. 7 questions.
1. What is the dental formula of vervet monkeys (hint: what
kind of primate are they)?
2.Since vervet monkeys and humans last shared a common
ancestor 20 million years ago, do you think primatologists can
learn useful information about human behavior and intelligence
from studying them?
3.Describe vervet monkey social structures. Why do vervet
monkeys need to keep track of so many other individuals and
their relationships? How do they use vocalizations to do this?
4.What are several ways primates use deception?
5.Define the social intelligence hypothesis. Why are monkeys
better at manipulating each other than objects?
6.What are vervets better at – interpreting visual information
about predators, or auditory information about predators? Why?
7.What distinctions do the authors draw between human and
non-human primate intelligence?