大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
溝通的演化
(The Evolution of Communication)
─動物行為學 (Ethology)
鄭先祐(Ayo)
國立 臺南大學 環境與生態學院
生態科學與技術學系 教授
Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/
Part 3. 個體間的互動
 生殖行為 (Reproductive Behavior)
 親代照顧與交配體系 (Parental Care and Mating




Systems)
溝通：管道與功能 (Communication: Channels and
Functions)
溝通的演化 (The Evolution of Communication)
衝突 (Conflict)
團體生活，利他和合作 (Group Living, Altruism,
and Cooperation)
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15b 溝通的演化
Communication: Evolution
 The changing views of communication


Sharing information
Manipulating others
 Signals and honesty
 The evolutionary origins of signals


Retualization
Receiver-bias mechanisms
By Goodenough, McGuire, and Jakob
 Selective forces that shape signals
 Language and apes


What is language?
Ape language studies
 Communication and animal cognition (認知)
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Views about communication are changing
 We can answer the questions of who, what, where, and
when of the communication process

But it is difficult to answer questions of how and why have
signals taken various forms that they have
 Communication involves the transmission of information
from one animal to others
 A cooperative view of communication: both sender and
receiver benefit from the accurate transfer of information


Selection should make signals efficient, reliable, and
unambiguous
Dishonest or inaccurate signaling was thought to be unlikely
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Animals manipulate other animals
 The cooperative view of communication does not fit
every situation
 A sender might gain by sending an inaccurate signal


In a territorial dispute, the sender might bluff by sending
signals that exaggerate its willingness to escalate the
contest
A male competing for a female’s attention might
exaggerate his qualities
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Dishonesty may benefit an animal
 An animal that gives a dishonest signal gains an
advantage

Over animals that honestly communicate their abilities or
intentions
 So, animals don’t communicate to convey information
 But to manipulate the behavior of others to their own
advantage
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Signals: normally reliable, occasionally
deceptive
 An animal produces a signal when, on average, it
increases its own reproductive success


By influencing the behavior of others
For signals to evolve, they must benefit senders overall
 Senders may not be trustworthy
 If signals are potentially dishonest, why not just
ignore them?


On average, the receiver must benefit from responding
to signals
Even if it is sometimes deceived
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When are honest signals likely?
 Four circumstances under which we expect to see
honest signals:




When senders and receivers share overlapping goals
When signals indicate something about the sender that
cannot be faked
When signals are costly to produce
When dishonest signalers can be identified
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Honest signals: senders and receivers share
goals
 Natural selection favors unambiguous, honest signals for
coordination of mating activities
 The sexes share overlapping goals in the relationship
between parent and offspring

But even this relationship can entail significant conflict
 Altricial baby bird s(幼鳥) beg their parents to feed them

Baby birds stand, gape, flap their wings, and call
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Honest communication
 Begging chicks are obvious to predators
 Begging too much, when food is not needed, is a poor
strategy
 Parents provide food to chicks that beg most vigorously
 Parents respond because their own fitness depends on the
survival of their offspring

Communication between baby birds and parents is honest
 Other examples of similar goals of the sender and receiver
 Belding’s ground squirrels call to warn relatives of a
predator
 Every bee benefits when scouts convey the location of a
patch flowers
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Honest signals: signals cannot be faked
 Signals are honest because they are tightly linked to a
trait of the sender

The sender simply cannot fake the signal
 Size is a good predictor of fighting success
 Displays allow opponents to judge one another’s size
 Combatants(戰鬥人員) enhance their apparent size



Puffing up their feathers
Fluffing out their fur
Assuming an upright posture
 In other species, size is not so easily faked
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Male stalk-eyed flies send honest signals
 During an aggressive display, these flies strike a pose
that


Allows each competitor to compare the length of its
eyestalks
Males with shorter eyestalks usually retreat without a
fight
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Honest signals are linked to an animal’s
health
 Bright red and yellow feathers, scales, or fleshy necks
or combs of some birds


Depend on chemicals called carotenoids
Carotenoids must be obtained in the diet
 These bright colors honest signal of foraging ability
and health

Female house finches prefer brighter, redder males
 Females benefit from their choice
 Brighter males are better parents
 Bringing more food to the nestlings.
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Honest signals: are costly to produce
 What prevents a male from exaggerating his qualities?
 Handicap principle (障礙原則): reliable signals are
favored when signals are costly to the sender

Their very extravagance indicates the owner’s qualities
 These signals are handicaps
 Their owners are perceived as doing well
 In spite of the handicap of investing in the signal
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Criteria for a signal to evolve as a
handicap
 The signal must be costly
 It must relate to the quality of the sender
 The receiver must be interested in the quality of the
sender that is being signaled

And must benefit from attending to an honest signal
 Receivers benefit from correctly assessing the quality
of a signaler

Especially in the context of sexual selection
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Signals may be costly
 Energetic costs are the most common measurements
 Oxygen consumption increases in insects and frogs
 Male red deer lose weight during the rut cost (發情代價)
 Other costs: decreased ability to move, escape, or forage
 Long tail feathers of male birds serve as sexual ornaments
 And impair their ability to fly
 Higher-quality senders can pay the cost of higher-quality
signals


Brighter colors, vigorous displays
Only male red deer in top physical condition can continue
roaring (咆嘯) to win the vocal duel (聲音對抗)
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Honest signaling in the blue-footed booby
 Seabirds with brightly colored feet
 During their courtship ritual, boobies stand facing one
another

The male lifts his feet to display them to the female
 Males in good condition have bright blue-green feet
 Unfed males have dull blue feet
 Females prefer males with brightly colored feet
藍腳鰹鳥
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 blue-footed booby (藍腳鰹鳥)
 blue penguins : Few penguin
interactions end in fighting
because they suffer flesh
wounds and sometimes eye loss
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Signal costs also affect receivers
 In the form of the response of receivers to the signal
 Little blue penguins have aggressive displays that
differ in



Cost (risk of injury)
Effectiveness in deterring an opponent
Ability to predict an attack
 A penguin conveys information about its willingness to
sustain injury while performing the display

And its willingness to fight
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Penguin displays are honest
 Because aggressive encounters are potentially costly
 Attempting to intimidate (威嚇) an opponent into
retreat could be costly

If the rival called the bluff (嚇唬)
 Penguin encounters begin with low-risk displays
 They escalate until one opponent retreats or a fight
occurs
 One “bidder” decides that the territory is not worth the
risk
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Honest signals: dishonest signalers can
be identified
 A stable social unit favors honest communication
 Individuals both send and receive signals at different
time
 The advantages of sending dishonest signals would be
reversed


When the animal is the receiver
So honesty predominates in the population
 Members of social units recognize one another
 And learn whether a particular individual is honest
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Vervet monkeys don’t believe dishonest
signalers
 Members of a social group stop believing an individual
that gives unreliable signals
 Vervet monkeys have two different calls that warn of
another group of monkeys on their territory

Monkeys stopped responding and no longer believed a liar
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 Vervet monkey alarm calls that alert group members
of the approach of a neighboring troop are of two
types. The “chutter” warns that another group is
nearby. The “wrr” is given when another group is
spotted in the distance.
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Dishonest signals: senders and receivers
have different goals
 Different goals set the stage for deception (欺騙)
 A father bird and his chick share the goal of the
chick’s survival


But the chick may want more parental investment than
the father would like to give
At the cost of his other chicks or his future reproduction
 Signals between parents and chicks are essentially
honest

But with some attempt by the chick at manipulation
and deceit
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Some signals are bluffs (嚇唬)
 Honest signals can be corrupted by dishonest bluffs
 Stomatopods (mantis shrimps)蝦蛄 ferociously
defend their burrows
 Stomatopods have two appendages used in prey
capture and territorial defense
 Combatants may be injured or killed during battles
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 Stomatopods
(mantis shrimps)
蝦蛄
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Mantis shrimp (蝦蛄) signal their
readiness to attack
 Readiness to attack is signaled by a threat display
(meral spread)
 A newly molted stomatopod is defenseless


But still gives the meral spread display
Its opponent is deceived and retreats
 A stomatopod can get away with the bluff
 The receiver would pay dearly (付出昂貴代價) if it
tested the honesty of the signal
 The signal is stable because, on average, it is honest
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Honest and dishonest signals coexist
 The costliness of signals can reinforce honesty
 When signals are generally honest
 A low level of deceit is stable and is expected to evolve
 Populations are in flux
 At any time dishonesty may spread
 A signal may be perceived by different receivers
 Some have the same goals as the sender (i.e. prospective
mate)
 Some have different goals (a competitor)
 A mixed signaling strategy, sometimes honest and
sometimes deceptive, may be best
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The evolutionary origins of signals
 Two approaches may explain the evolutionary origins of
signals


Identifying the behaviors of the senders that form the raw
material for signals
 Ritualization
Focusing on how signals exploit the receiver’s sensory
biases
 Ability to detect some information better than others
 These two evolutionary pathways are not mutually
exclusive
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Ritualization
 Many signals get their start as part of another behavior
 Or as a physiological response
 That takes on a signaling function later
 Ritualization: evolution favors modification of the
incipient signal

It becomes more stereotyped and unmistakable
 The three sources of raw material for signals are
1. Intention movements
2. Displacement activities
3. Autonomic responses
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1. Intention movements
 Animals begin behavior patterns with characteristic
movements

That prepare them for action
 It is possible to judge what the animal intends to do
 A wolf pulls back its lips and bares its teeth before
biting
 It improves another wolf’s fitness if he correctly
interprets the bared teeth
 Rather than waiting to get bit
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Avian displays originated with intention movements
 For flight or walking
 A bird about to fly crouches, points its beak, raises its
tail, and spreads its wings
 Components of the takeoff leap have been ritualized
into communicative signals
 The blue-footed booby incorporates “sky pointing”
into its courtship dance


This display originated in flight
But changed during ritualization
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2. Displacement activities
 Irrelevant actions performed in situations in which an
animal has conflicting motivations and is thus
indecisive (無法決斷)
 Faced with an aggressor, an animal may have
conflicting motivations


To fight and to flee
So it may instead preen itself (鳥)用喙理(毛);
 Displacement activities are often incomplete actions
 Courtship is a time of conflicting tendencies
 Sexual partners must come together to mate
 In spite of aggressive tendencies that keep them apart
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Displacement activities in male ducks
 Mock preening of the courtship displays of male ducks
 Originated in displacement preening
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3. Autonomic responses
 The autonomic nervous system (自主神經系統)
regulates many basic body functions

Digestion, circulatory activities, heart rate, diameter of the
blood vessels, thermoregulation
 Displays may have originated from autonomic functions
 At times of stress or conflict
 The naked head or neck skin of turkey, jungle fowl, and
bateleur flush (發紅) and swell (腫脹)during stress
because of vasodilation

These changes are now part of signaling during courtship
and aggressive encounters
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Evolution of signals from the respiratory system
 Modifications of the respiratory system
produce sound signals

And visual signals
 In inflation displays of birds, males fill
pouches with air to attract mates

The male frigate bird’s throat pouch
inflates to an enormous size and brilliant
color to attract females
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Evolution of signals from thermoregulation
 Piloerection (erection of feathers and hair) traps heat
It is also a part of aggressive(攻擊) and appeasement(緩和)
displays
 A zebra finch that cannot escape from a dominant individual
 Fluffs its feathers as an appeasement signal
 Feather position can be part of courtship displays
 Tail-raising courtship display of the peacock (孔雀)
 In mammals the message’s meaning varies with the part of the
body on which hair is erected
 If all the hair is erect on tamarins (狨猴) : attack or be
indecisive
 If only the tail hair is erected: flee (逃走)

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 zebra finch
 tamarins (狨猴)
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Other behaviors as raw materials for displays
 Ritualization is a highly opportunistic evolutionary
process

It can be launched from almost any behavior pattern,
anatomical structure or physiological change
 Predatory behaviors have been ritualized in the male
gray heron (灰鷺)



During courtship, he erects his crest and body feathers
Points his head downward and snaps his mandibles
closed
Movements are similar to those used during fishing
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 Masked lovebirds
 gray heron (灰鷺)
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Food exchange has also been ritualized
 The touching of bills is derived
from the parental feeding
 Is common in courtship and
appeasement display

Establishes or maintains bonds
 Masked lovebirds bill during
greetings and after a spat
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Flight can also be ritualized
 Yellow-headed blackbirds and red-winged blackbirds
perform aerial displays to entice(誘惑) females

Ritualized flight is more conspicuous than normal flight
 Movements are accentuated and reveal plumage patterns
 Courtship displays of the fiddler crab evolved from the
movement of the male while entering his burrow
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 Ritualized flight in blackbirds.
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The ritualization process
 During the evolutionary process of ritualization
 Signaling behaviors become more stereotyped
 They may also change
 Slow down, speed up, become more exaggerated
 Anatomical features (colors, claws) might evolve to draw
attention to the display
 Emancipation (解放): behaviors that become freed from
the internal and external factors that originally caused them


The original triggers no longer cause the behavior to occur
The behavior has only a communicative function
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Evolution of the whistle-shake in ducks
 The body-shake is the evolutionary precursor of the
whistle-shake in ducks

Serves to dry and rearrange the feathers
 Whistle-shakes resemble body shakes
 But are ended by the duck tilting(翹起) back its head and
emitting a trill (顫音)
 And are given in social situations
 Some signals are not completely emancipated from their
original causes

Whistle shakes are still given in response to water
sprays
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Receiver-bias mechanisms
 Ritualization focuses on characteristics of the sender
 Sensory exploitation hypothesis: the receiver has a
preexisting preference for a particular signal

Features of the receiver’s nervous system makes it more
responsive to a particular form of stimulus
 The sender takes advantage of the receiver’s preexisting
sensory biases when new signals are evolving.

Evolution of swordtails (劍尾魚) in fish
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Sensory bias in frogs
 Female túngara frogs prefer males with lower frequency
chuck calls
 Female túngara frogs benefit from their preference


Low-frequency chucks are produced by larger males
Resulting in more fertilized eggs
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Sensory bias in water mites
 Male courtship signals have exploited the females’
sensory adaptations for prey detection

Water mite hunts by ambush
 When a courting male detects a female he moves his
legs


These vibrations mimic prey
Leading the female to grab him
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Sender characteristics shape signals
 Anatomical structures form the foundation for
producing signals

i.e. sensory organs of electric fish
 Body form (i.e. size) influences signal design
 Small species not be visible, so other sensory modalities
are favored for long-distance communication
 Physical characteristics may evolve that enhance visual
signals (i.e. facial expression, erection of hair)
 Smaller species give more acrobatic (特技的) displays
 In vertebrates it influences vocalizations
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Signal evolution does not happen in a vacuum
 Many signals are produced by structures that have other
functions


Body size, hair, beaks, and respiratory tracts are under
selection for other reasons
Besides their role in producing signals
 For example, beak shape in Darwin’s finches is
important in


Feeding behavior
Song production
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Environmental characteristics affect the
choice of communication
 The habitat helps determine which channel of
communication (sound, chemical, visual, etc.) a
species uses
 Visual signals are not much use in the ocean’s depths

So whales rely on sound for long-distance
communication
 The habitat affects sound transmission
 Attenuation (weakening): how far the sound will carry
 Degradation: how distorted the signal becomes during
transmission
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The acoustic adaptation hypothesis
 Acoustic properties of bird song are shaped by habitat structure
 Songs attenuate and degrade differently in different
environments
 Songs are more attenuated and degraded in dense foliage
 Lower frequencies become less distorted in dense foliage
 In habitats with complex vegetation structure
 Songs should have low frequencies, narrow bandwidths
 Whistles and long notes
 In open habitat (i.e. grasslands)
 Songs should have high frequencies and broad bandwidths
 Trills and short notes
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Habitat structures influence bird songs
 Great tits have a large geographic distribution
 Forest dwellers sing songs with a lower pitch
 A narrower range of frequencies
 Fewer notes per phrase than open woodland birds
 No differences were found between other species in
different habitats


But a review of the literature (meta-analysis) shows that
Habitat structure weakly influences acoustic properties
of bird songs
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Displays vary according to the background
 The environment influence transmission of other
channels of communication
 Visual signals differ in visually “noisy” versus plain
environments
 Many lizard species rely on visual displays

Head bobs, push-ups, back arching, extension of the
dewlap and tail flicks
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Lizard displays and background motion
 Jacky lizard species that live in trees display faster and
flick their tails more

When it is windy and the vegetation moves
 Senders of signals may change their behavior when the
environment changes
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 Jacky lizard
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Habitat changes caused by humans
 Human activities alter the environment in which animals
communicate

And alter selection pressures on signal form
 Great tits do well in both urban and rural environments
 Urban birds sing shorter, faster songs with higher
minimum frequencies
 Most likely due to competition with the noise of the urban
background
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Human-induced environmental changes
affect visual signals
 Visual signals can be impeded (阻礙)
 The Baltic Sea has grown turbid (cloudy)
 Making it harder for female stickleback fish to see
males
 Males have to court much more vigorously to get the
female’s attention
 The honesty of male signals is reduced because males
are not as likely to see each other
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Receiver characteristics: sensory drive
 Sensory drive: the environment shapes receiver
characteristics
 Surfperch (海鯽) are marine fish that live in a variety of
habitats

Differing in light intensity and variability
 The retinas of surfperch species differ
 They are good at detecting differences in color contrast
 Or differences in brightness
 But not both
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 Different optical habitats of related surfperch species.
 (left) live in an environment that is highly variable in light intensity.
Striped surfperch (right) live in deeper water in the kelp forest where
the background light is more even.
 Deepwater surfperch are better at detecting brightness differences
 Species living in shallow water can better see color differences
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Language and apes
 Humans are very interested in what separates us from
other species


Tool use was thought to be confined to humans
But this is not the case
 Language seems to clearly be a talent confined to
humans



Which elements of language are unique to humans
Which are more broadly shared?
Are differences a matter of kind or degree?
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True language has four elements
Words or signs must be used as true symbols
 That stand for, or take the place of, a real object, event,
person, action, or relationship
2. Symbols should permit reference to objects or events
 That are not present
3. There should be some elements of grammar (rules)
 That determine the relationship between words
 Changing the order of symbols alters the meaning of the
message
4. Words or signs should be combined to form novel phrases
 Or sentences that are understandable to others
1.
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Early studies taught chimps to talk
 Researchers have studied the ability of great apes
(chimpanzees, western (lowland) gorillas orangutans,
bonobos) to learn language
 A chimp named Viki was taught to say three words

“Mama,” “papa,” and “cup”
 These attempts failed
 Chimpanzees lack the vocal apparatus to make the
range of sounds of human speech
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Studies taught chimps nonverbal languages
 Washoe, a young chimpanzee, was taught American Sign
Language (ASL)
 Washoe and other chimps were reared like human
children


Spoken English was not allowed
Washoe had a vocabulary of 132 signs
 Her signs were not restricted to requests
 She applied them correctly to a wide variety of referents
 She extended the sign for dog from a picture to all pictures
of dogs, living dogs, and even the barking of an unseen dog
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Washoe signs with ASL
Washoe combines signs to denote “water bird” for a
swan
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Stop and think:
 Do you agree that the best way to test whether apes
have linguistic skills is to incorporate them into human
society as much as possible?
 What are the advantages and disadvantages of this
approach?
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Koko, Chantek and Nim Chimpsky
 A gorilla named Koko and an orangutan named Chantek
were taught ASL



Spoken English was permitted
Emphasized the production of language (the use of signs)
Not comprehension (understanding the meaning of signs)
 Nim Chimpsky a young male chimp, was accused of
imitating his trainers


But Nim’s language abilities were stunted(受礙) by the
operant-conditioning procedures used in his training
And Nim’s trainers changed so often that he could not form
the relationships essential for language development
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It was accepted that chimpanzees could
not learn language
 But when other trainers worked with Nim
 His language skills improved
 Chantek’s signs were more spontaneous
 Could not be attributed to imitation
 Washoe and the other language-trained chimps
 Signed to other animals and objects
 And frequently to themselves
 Washoe adopted a ten-month-old infant named Loulis
 Loulis learned his first 55 signs by observing other chimps
 Washoe and her family signed to one another their daily
activities (playing, eating, family fights)
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Sarah used plastic chips as words
 The chimpanzee Sarah used a particular
plastic chip as a word


To complete a preformed statement
She arranged four to five words into a
sentence
 Sarah named many objects and used
complicated relationships

Such as if-then and same-different
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The LANA Project
 A chimpanzee named Lana was trained to use a
computer to communicate

Eliminating social cueing and the difficulty of
interpreting symbols
 Lana communicated in Yerkish, a symbolic language
 Yerkish words (lexigrams) are geometric figures
 Pressing a computer key labeled with the lexigram
selects words
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The LANA Project
 Lexigrams had to be used
in an appropriate order


Lana had to learn syntax rules governing word order
She developed a large
vocabulary and mastered
grammar
 She also coined new words
 She called an orange soda a
“Coke-which-is-orange”
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Apes learn words in various forms
 To refer to objects not present
 Stringing words together in short sequences
 Follow rules of grammar
 They coin new words
 But do apes use words as symbols?
 When a chimp uses a “word” (sign, plastic chip, or
lexigram) to name an object
 Is it used as a symbol that stands for the object
 Or is it a label that is associated with the object through
a reward system?
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Using “words” as true symbols
 Two chimpanzees, Sherman and Austin communicated
with each other symbolically

By pressing computer keys with lexigrams
 The emphasis was on interanimal communication,
 They were not taught to produce strings of lexigrams
 Or to adhere to grammatical rules
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Chimps communicate with each other
 Sherman and Austin specify foods to one another using
lexigrams


They communicate with each other
Regardless of which of them is the observer
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Chimps use symbols in communication
 To inform each other of the appropriate tool to use to
solve a problem

Clearly using words as symbols and not simply labeling
objects
 This shifted the emphasis from demonstrating that apes
can produce language


To showing that they can understand symbols or words
of language
It also showed how important the learning environment
is in developing language comprehension
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Kanzi and Panbanisha
 Bonobo (pygmy) chimpanzees
 Kanzi was adopted and raised by Matata
 And was always present during Matata’s training
sessions
 After Kanzi was separated from Matata
 He used symbols on the keyboard that they had tried to
teach to Matata
 Not only did he know the lexigrams
 He also knew the English words that the lexigrams
represented
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Kanzi has a large vocabulary
 Kanzi learned communication skills by observing his
mother’s training

Much the same way as a child would
 Panbanisha, Kanzi’s half-sister
 Was reared in the same learning environment as Kanzi
 She, too, shows remarkable comprehension of spoken
English
 Reward-based language training was stopped and
replaced with conversation

Kanzi’s human companions served as communicative
models
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Kanzi learned symbols through observation
• Kanzi observed and interacted with humans who used
gestures and lexigrams to communicate
Kanzi communicates using a board with 256 lexigrams
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Kanzi and others understand spoken
English
 Besides being able to produce language
 Kanzi was not trained to vocalize
 But spontaneously makes sounds with different content
 Chimpanzees utter natural sounds when they find food
 Producing distinct grunts when encountering different
foods
 This skill is found in other animals besides apes
 Including vervet monkeys and even chickens
 Ape communication fulfills the four requirements of
language
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Communication and animal cognition
 Do nonhuman animals have thoughts or subjective
feelings?


Are they are aware of other animals’ feelings?
Are they cognitive, conscious, aware beings?
 Tapping animals’ communication lines can indicate
whether animals have conscious thoughts or feelings


If nonhuman animals thoughts and feelings
They probably communicate them to others through
their communication signals
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Evidence of cognition: forming mental
representations
 Of objects or events that are out of sight
 Some animal signals are symbolic
 They refer to things that are not present
 Some animals learn a language that uses symbols
 i.e. apes
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Other species understand symbols
 Alex the parrot could vocally request more than 80 items
 Even if they were out of sight
 He could quantify and categorize these objects
 He understood the concepts of color, shape, and same versus
different for both familiar and novel objects
 Bottlenosed dolphins also understand symbolic languages
 “Words” are gestures or are generated by a computer
 They can refer to objects, actions, and relationships
 Dolphins understand experimenter’s references to objects that
are not present
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Evidence of cognition(認知): natural
communication systems
 Language involves the ability to relate words to
meanings
 In some species, individuals classify signals by their
meaning

Not by some obvious physical property (the way a signal
sounds)
 When a rhesus monkey finds food
 It announces this with one or more of five different food
calls
 A different type of call announces if the item is of high
quality or rare
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Classifying calls by meaning or sound
 Animals habituate (gradually stop responding) to a
stimulus that is repeated many times without
consequence
 If monkeys classify a food call by its sound

After habituating to one type of call they still respond to
any other type of call because it sounds different
 If they classify a food call by its meaning
 They will be unresponsive to a call in the same category
 But remain responsive to a call in a different category
 Rhesus monkeys classify calls by their meaning.
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Evidence of cognition: understanding
mental states of others
 Does a communicating animal understand what
potential receivers know?

Vervet monkeys apparently do not
 Mother vervet monkeys give alarm calls when they
sense a predator

But do not take into account whether their offspring
are ignorant or knowledgeable about the predator
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Langurs call to their audience
 Male Thomas langurs give alarm calls
 But only if there is an audience
 Males call persistently after spotting a predator
 Stopping only when every other member in the group
also gave an alarm call
 Callers seem to keep track of all the other members in
their groups
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Ethical ramifications of cognition in
animals
 The question of animal awareness is difficult to answer
scientifically
 The answer has ethical ramifications




If the line between animals and humans is erased or even
smudged a bit, should we rethink the way we treat animals?
Should we keep them in zoos?
Should great apes be used for language studies?
What about dolphins?
 So what’s your opinion?
 Are animals aware, cognitive beings? All of them?
 Where do we draw the line?
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Summary
 Signals should be honest, unambiguous and informative
 Sometimes the sender of a signal benefits from being dishonest
On average, a sender manipulates the behavior of others to its
own advantage
 Receivers should respond to signals when they benefit from
them, on average, even if they are sometimes deceived
 Conditions for honest signals (1) senders and receivers share
overlapping goals, (2) they cannot be faked, (3) they are costly
to produce, and (4) dishonest signalers can be identified
 Conditions that favor dishonest signals (1) senders and receivers
have different goals, (2) they are costly to assess or to challenge

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Summary
 Honest and dishonest signals can coexist in a population
 Signals originate through ritualization and sensory exploitation
 Evolutionary sources of ritualization (1) intention movements,
(2) displacement activities, and (3) autonomic responses
 The design of the signal may be influenced by the anatomy and
physiology of the sender and the habitat
 Most animal communication signals are not true language
 They do not use symbols that can replace their referent
 They do not string signals together to form novel sentences
 Researchers have attempted to teach apes language
 Some animals understand signals that represent unseen items
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問題與討論
Japalura@hotmail.com
 Ayo 台南 NUTN 站
http://myweb.nutn.edu.tw/~hycheng/
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