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Review of  The Design of Animal Communication

Reviewer: Anne Reboul
Book Title: The Design of Animal Communication
Book Author: Marc D. Hauser Mark Konishi
Publisher: MIT Press
Linguistic Field(s): Cognitive Science
Book Announcement: 14.3088

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Hauser, Marc D. and Mark Konishi, ed. (2003) The Design of Animal
Communication, MIT Press. (Paperback reprint of 1999 hardback edition)

Announced at

Anne Reboul, Institute for Cognitive Sciences, CNRS, Lyon


This book is the result of a symposium on animal communication
organized in honor of Peter Marler in 1997 at UC Davis. Papers deal
with mechanisms, ontogeny and evolution of communication among such
diverse species as frogs, birds, bees, crickets, bats, non-human and
human primates. Though it is not an easy read, it still is quite
accessible to non-specialists, including linguists. One of its
interests for linguists is that it enlightens the specificities and
commonalities of animal communicative systems with the human language,
thus laying a basis of knowledge on which it is possible to assess
what is specific to language. In other words, it should be relevant to
any linguist with at least an intellectual interest in the complex
question of language evolution. One should not be daunted by the sheer
size of the book (701 pages including the index and TOC): the
fascinating insights provided in the quite real complexity of animal
communication systems as well as the physiological mechanisms which
sustain them are more than enough to balance the effort involved.


The book has three main subdivisions, each with a short
introduction. These three parts are ''Mechanisms of communication'',
''Ontogeny of communication'', and ''Evolution of communication''.

The ''Preface'' to the book, written by Konishi, highlights Marler's
contributions to ethology of communication. Konishi also writes the
introduction to the first part, ''Mechanisms of communication'',
insisting on the wide range of methods used by animals to communicate
and introducing the papers which follows.

The first paper of the first part, by Kelley and Tobias, ''Vocal
communication in Xenopus laevis'', studies vocal communication among
one variety of South African clawed frog. Vocal communication is used
both intersexually to promote reproduction and intrasexually among
males for sexual competition and territorial defense. Thus vocal
communication is different among the sexes, and these differences
''have been traced to the action of gonadal steroid hormones, which
act during development to control the morphogenesis of the vocal organ
and during adulthood to control how the system produces male- and
female- specific songs'' (9). The vocal repertoire of this species is
based on clicks produced by the larynx, with modulation of frequencies
accounting for the different types of calls, with different
functions. Sexual differences in calls are reflected in differences
between the vocal organs of males and females as well as differences
in the neural circuitry used in vocal production, reflecting the
action of gonadal steroids. Though the production of calls is now
well- understood, their perception is less well-known and deserves
more attention.

The second paper, ''The Motor Basis of Vocal Performance in
Songbirds'', by Suthers, deals with oscine birdsong and its diversity,
made more surprising by the relative similarity of the vocal organ,
the syrinx, among the different species. This diversity is due to the
exploitation of two independent and laterally specialized sound
sources in the syrinx, which gives oscine songs its versatility. More
specifically, ''the two sides of the brain can deliver different motor
programs to the left and the right sides of the syrinx, giving each
side an ability to generate sound independently'' (40). This means
that a note can be produced on one side only, on both sides or be
switched from one side to the other during a syllable. Respiration
during the song is typically made through both minibreaths (very short
inspirations) and pulsatile expirations producing each sound. In some
species there is a lateralization of syringeal function. Questions
remaining concern which motor strategies a given species adopts, and
whether they are immutable or subject to tutoring.

The third paper, by Nottebohm, deals with ''The anatomy and timing of
vocal learning in birds''. Vocal learning in songbirds has been
hypothesized to depend on a ''sensitive period'' during which learning
would occur more easily. Vocal learning seems to depend in general on
two steps, the acquisition of an auditory model, followed by the
acquisition of the motor skill necessary to faithfully reproduce the
model. This suggests that there could be more than one sensitive
period. All oscine songbirds are vocal learners though it seems that
there are two main categories among them: age-limited learners, in
which vocal learning only occurs during the juvenile stage and ends
with sexual maturity and open-ended learners who add to the song
repertoire acquired as juveniles during adulthood.

Deafening has a different effect on age-limited learners who usually
retain their songs, while open-ended learners generally loose
them. Brain pathways seem however to be pretty similar among
songbirds, with a distinction between two pathways, one developing
early in ontogeny for the production of unlearned sounds
(e.g. food-begging calls), the other developing at the time when song
is necessary, is found only in vocal learners seem specialized for the
control and performance of learned sounds, i.e. songs. There is a
sexual difference in some species relative to the development of this
second pathway, which is more developed in males than females. Without
going into anatomical details, there are four feedback loops used in
the acquisition and production of songs. Some of this brain circuitry
is in place before the sensitive period, though other parts develop,
both in volume and connectivity at the onset of song development, in
which the typical sequence of food-begging calls, subsong, plastic
song and song crystallization depends, at least in part, on the timing
and order of such anatomical changes. In the same way, the end of the
sensitive period may depend on the reduction of synapses in some part
of the brain. In open-ended learners, brain parts relevant to the
acquisition of new songs will change in volume, such changes being
associated to the seasonal occurrence of song learning. However, even
age- limited learners acquire song memories in adulthood and can
discriminate between the songs of strangers. There is also evidence of
brain lateralization, though a reversion of dominance seems possible
in open-ended learners (but not in age-limited learners). Song is
mainly a male behavior and the development of the song system has been
shown to be due to male hormones in some species. Nottebohm also
reviews social effects on song acquisition. What is more, hearing and
producing song induces changes in gene expression relevant for the
development of brain song learning circuitry.

Michelsen addresses ''The dance language of honeybees: recent findings
and problems'' in the fourth chapter, coming back to one of the first
systems of animal communication precisely described. The dance
language of bees has two unusual features: it is used to communicate
about a remote event (the location of a source of food) and it is an
abstract code. The dance occurs in the hive, the dancing bee walking
in a waggling way (the bee wags her body from side to side) on the
comb and circling back, alternating her return path between left and
right. The problems Michelsen addresses are the following: how can the
follower bees (the ''adressees'') perceive the message in the darkness
of the hive? Which components of the dance do the follower bees
perceive as signals? Three hypotheses have been proposed relative to
the first question: (tactile) perception of dance sounds through the
vibrations of the comb, physical contact between the dancer and
follower bees, perception of the air currents triggered by the
movements of the dancer. Michelsen reviews all three hypotheses,
relating them to the second problem, by examining whether the
information transmitted in these three ways could be precise enough
relative to the distance and location of the source of food. He
concludes that none of these hypotheses is quite satisfactory and
reviews one of his own experiment using a mechanical model of a
dancing bee, producing airflows similar to those of dancing bees and
succeeding in recruiting bees to the location indicated (though
distance was not always successfully transmitted). The wagging run
appears to be the major component for conveying distance. These
results however are far from answering all the questions raised by the
dance of bees and further experiments will be necessary.

The fifth chapter is dedicated to ''Processing species- specific calls
by combination-sensitive neurons in an echolocating bat'' and is by
Kanwal. In addition to echolocation signals, bats have ''a complex
repertoire of communication sounds or 'calls' that rival in variety
and complexity of spectral structure those emitted by the most vocal
primate species'' (133). He quickly reviews call processing in human
and non-human animals, concluding that ''neural specialization can be
based on facilitation of the response to combinations of call
components'' (136). Such specialized neurons have been found in the
processing of echolocation signals in bats and are also involved in
call processing. The calls of bats are produced from a simple
syllables combined to produce a given calls. These combinations,
however, are strictly constrained, as shown by the fact that only 15
out of a possible total of 342 disyllabic combinations are actually
produced. Different species of bats have different dialects,
indicating neural plasticity and audiovocal learning.

Perret authors chapter 6 on ''A cellular basis for reading minds from
faces and actions'', centering on primates abilities in this domain,
and more precisely on visual processing. In this instance, ''visual
recognition involves both the analysis of the visual image and the
associations between what we see, what we feel and what we do''
(159). He approaches the question through a study of ''the response
properties of single cells in the temporal cortex of macaques''
(159).Three types of cells are relevant: cells which encode the visual
appearance of body and face both static and mobile; cells which encode
specific bodily or facial movements; cells which respond to particular
face and body movements as goal-directed actions. The first type of
cells show generalization in as much as they respond irrespectively of
the species of the perceived animal. They subdivide in cells
selectively responsive to different parts of the body and are
sensitive to orientation and perspective. Generalization for the same
posture is achieved by combining the outputs of view specific cells.
There is evidence for hierarchical combinations (e.g. eyes >> head >>
body). The sensitivity to orientation is necessary for gaze following
and for directing attention to a target. The second type of cells
include cells which react to certain facial expressions and it is
well-known that some neuropathological conditions (e.g. relative to
amygdala) can disrupt the recognition of particular emotional
expressions (notably fear) in humans. This capacity is lateralized in
humans. The third type of cells responds selectively to particular
body movements, interpreted as goal-directed, through the relation of
the movements to other aspects of the visual environment. However,
''visual information about motor acts is also encoded in particular
premotor areas'' (174). Thus, some prefrontal cells code both the
motor component and the visual appearance of specific movements. They
seem to code the ''general concept'' of the action. A two-steps
scenario could be proposed, with temporal cells recognizing the
movement and alerting prefrontal motor cells. These prefrontal cells
''share some features of visual selectivity'' (174) with temporal
cells, which can be interpreted as supporting the hypothesis that
''substrates of perception and action overlap, at least to some
extent'' (174). These temporal populations of neurons seem to have
homologues in the human brain. There is a fourth type of cells in the
temporal area which seem to distinguish between self-generated and
other-generated dimensions of visual stimuli, maybe relying
(respectively) on predictability and unpredictability of change. In
conclusion, Perret points out that this sophisticated visual system
may be sufficient for a complex social life without needing an
additional mind reading capacity.

Adolphs signs chapter 7 on ''Neural systems for recognizing emotions
in humans''. The chapter is mostly dedicated to fear, as an emotion
that has received the most attention in animal studies and, hence,
offers a good ground for an evolutionary approach. There are three
domains of study regarding emotion: knowledge about emotion,
experience of emotion, and expression of emotion. The paper focuses on
''the retrieval of knowledge about an emotion, on the basis of a
stimulus that denoted or signals the emotion'' (188). The lesion
method is applied, i.e. the performance of brain damaged patients is
compared to that of healthy subjects with a view to establishing
correlations between specific brain regions and specific tasks. Such
factors as age and IQ are controlled. The stimuli have been facial
expressions. There are six basic emotional expressions, recognized
easily by normal subjects across cultural differences (with some
overlap, however) corresponding to six basic emotions, i.e. happiness,
surprise, fear, anger, disgust and sadness. Valence and arousal are
two attributes that play a role in the recognition of
emotions. ''Emotion concerns the continual changes of body and brain
states that occur in an organism as it interacts with its
environment'' (192). Thus the neural structures involved in processing
emotions are both structures that represent body states and structures
that link perception to body states. One such structure is the
amygdala though its role seems more complex than was once
thought. However, it does appear to play a major role in
fear-conditioning in animals. Adolphs reports experiments similar to
fear-conditioning in animals, involving one patient with selective
bilateral damage to the amygdala, with similar results. The same
subject was unable to recognize or draw facial expression of fear and
showed impaired conceptual knowledge of emotions. The suggestion is
that ''the amygdala may connect percepts of sensory stimuli (...) with
a variety of neural systems involved in response to and knowledge of
such stimuli'' (198). This would mean that the amygdala is involved in
encoding rather in retrieval, an interpretation supported by recent
findings. More generally, there is evidence of brain lateralization
for emotional cognition (with right hemisphere involved in negative
emotions and left hemisphere in positive ones in the human brain),
which also seems the case for non-human primates. As lateralization
also occurs for language, a suggestion is that, as processes involved
in communication, both language and emotion have to be processed
fairly quickly, lateralization being a premium because it reduces
physical distance between the neural systems involved in,
respectively, language and emotion. Adolph ends his paper with the
hypothesis that expression and recognition of social signals,
including emotional ones, have coevolved.

The 8th paper comes back to songbirds, Ball writing on ''The
neuroendocrine basis of seasonal changes in vocal behavior among
songbirds''. In temperate-zone birds, behavioral changes occur over
the course of the year, notably in song. Oscine songbirds produce
song more frequently in late winter and early spring, through
endocrine and neural mechanisms. This is of course linked to
reproduction that occurs in favorable circumstances climate wise. The
cues most prominently involved in triggering the reproductive period,
and hence the singing period for males, are changes in
photoperiod. Over a certain treshold, birds are photostimulated, a
process inducing ''a physiological cascade that includes increases in
gonadotropin secretion, gonadal growth, and a range of
hormone-dependent reproductive processes, including behavior''
(215). This photosensitivity in birds decreases over time leading to
photorefractoriness, ensuring that birds stop breeding at an
appropriate time. Short days then dissipate photorefractoriness and
the cycle can begin again. Side by side with this ''absolute''
photorefractoriness, some species exhibit ''relative''
photorefractoriness, continuing breeding as long as long days
persist. ''There may be a difference between the neuroendocrine
mechanisms underlying the two forms of photorefractoriness'' (217). In
the brain song control circuit of song birds, there are cells
possessing receptors for gonadal steroid hormones leading to changes
in the volume of particular nuclei of the song circuit and controlling
survival and migration of new neurons. However, testosterone is not
equally effective at all times of the year and ''plasticity in the
starling song system appears to require the coordination of the
appropriate hormonal milieu with a permissive photoperiodic
condition'' (237). Photosensitivity may also have effects independent
of testosterone. This suggest ''photoperiodic differences in steroid
receptors or in steroid metabolism'' (239).

Wingfield et al. sign the last chapter (9) of the first part, on
''Testosterone, aggression, and communication: ecological bases of
endocrine phenomena''. Agonistic communication, as manifested, for
instance, in territorial aggression, is an important part of
communication and seems regulated by androgens. However, though
aggressive behavior seems similar at different seasons, it is not
clear that it is and neither is it obvious that the contexts and
hormonal bases for it are similar. Wingfield et al. introduce Jacobs'
finite-state machine theory to descrobe different life-history stages
where aggression may occur. Each stage has environmental input signals
and yields a fixed set of predictable outputs, this being regulated by
neuroendocrine systems. Just as different environmental factors can
yield superficially similar behaviors, there is no reason to think
that internal mechanisms will be identical in each
case. History-stages are pre-determined by environmental cues such as
day length, temperature, etc. though some unpredictable factors may
trigger ''facultative'' life- history stages. The authors' view is
that, while testosterone may control aggression during the breeding
season, other factors, or testosterone but with different mechanisms
involved, may operate at other stages and in facultative stages. Thus
the general picture of the biological control of aggression may be
much more complex than has generally been thought.

The second part of the book, on the ''ontogeny of communication''
opens with an introduction by Hauser, which should be of interest to
anyone interested in the nature/nurture debate. Hauser points out that
the debate stems from a predilection for dichotomies and that a
reasonable position is to posit an interaction between gene and
experience. He contrasts possible ontogenic trajectories and their
underlying causes, advocating the view that ''the genome sets up what
is possible, allowing experience to guide the organism to a stylized
phenotypic outcome'' (286). He then introduce the different papers in
this second part.

The first paper of this second part, chapter 10, is signed by Peter
Marler and speaks ''On innateness: are sparrow songs 'learned' or
'innate'''. Marler points out that the use of dichotomous pairs such
as instinctive/acquired, learned/innate, learned/unlearned are more of
a hindrance than an help in the study of behavioral
development. Taking oscine songbirds as an example, he points out that
though some bird calls and songs are innate, oscine birds are learner
species with a specific specialized network of brain nuclei, which
lacks both in the brain of non-singing birds AND in the brain of birds
with innate songs. Learned songs can be very simple (as innate songs)
or very complex. There are three stages in the learning of a song:
memorizing a song, storing it and producing it. ''During the
memorization phase, there are sensory constraints that take the form
of learning preferences'' (296-297), and ''predispositions are also
manifest in the motor phase'' (297). These last are pan-specific but
other predispositions are species-specific and Marler concentrates on
these. Experiments regarding the role of innateness and experience in
song learning have concentrated on isolates of different species. Such
birds produce simpler songs and seemed influenced in the same way by
isolation, suggesting a major role for experience. However, songs
from isolates of different species were still recognizably different,
indicating species-specific innateness. ''So, we have a paradox''
(300). ''Neither conclusion is satisfactory'' (302). Marler then
reviews experiments focusing on early-deafened songbirds, ending with
just as contradictory results as isolates experiments. He suggests
that ''auditory input is significant, not only for the memorization
and production of learned songs, but also for the activation of latent
central mechanisms that actually encode more information about normal
species- specific song structure than is usually evident in the
amorphous morphology of deaf songs'' (308). Marler then insists on the
fact that ''the potential for varying degrees of what evolutionary
biologists call phenotypic plasticity (...) with the same genotype
giving rise to more than one phenotype in different environmental
circumstances, is extremely widespread if not universal'' (313). Thus,
variability is not an absolute indicator of learning, any more than
homogeneity would be an absolute indicator of innateness. Indeed, ''to
achieve a full understanding of the evolutionary process, neither
genetic nor environmental contributions to this interactive process
can ever be ignored, a position which becomes self-evident if we
approach the nature-nurture problem in developmental terms rather than
as an issue of phenotypic typology'' (314).

The 11th chapter, by Kroodsma, is devoted to ''Making ecological sense
of song development by songbirds''. Kroodsma begins by noting that
songs are used to manipulate conspecific individuals, of which there
are two sorts, males and females. This means that there may be a
divergent evolution inside a given species regarding intersexual and
intrasexual songs. This is the case of male chestnut-sided warblers,
who not only have strikingly different kinds of songs for addressing
males and females conspecifics, but also have different song-learning
programs. Intersexual songs, used for matting, are of four different
types, of which one is usually favored by a given male, though his
ability to sing the other types is preserved. Thus intersexual songs
are fairly stereotyped and it seems that ''it is the female that
selects for this stereotypy'' (322).

Intrasexual songs have a small repertoire of four or five songs, which
are shared among neighbours, but which changes with geographic
distances. Of these four ''neighborhood'' songs, a given male usually
favors the one which is rarely used by his neighbors. Inter- and
intrasexual songs are not learned in the same way, neither do their
respective learning program obey the same constraints. Given the
homogeneity of intersexual songs, they can be learned anywhere and are
typically learned during the hatching year. Intrasexual songs, by
contrast, must be learned just after migration ''when and where the
male acquires both his breeding territory and his singing neighbors''
(323). The uniformity of intersexual songs suggest that they are
learned from many males to average individual differences (and
learning may be innately constrained), while the variety of
intrasexual songs suggest that they must be learned in situ, from the
neighbors (and learning may not be as strongly innately
constrained). Kroodsma then reviews a few scenarios for achieving both
uniformity and variability, highlighting genetic constraints, learning
from a single individual or from multiple conspecifics, improvising,
as well as other ecological and social factors. He concludes that
''strategies of development, such as whether songs are imitated or
improvised, should also be influenced by the probability of
interacting with the same individuals throughout life'' (337).

The 12th chapter, by Doupe and Solis, is ''Song- and order-selective
auditory responses emerge in neurons of the songbird anterior
forebrain during vocal learning''. As said above, there are two
phases in song learning, the first one for the memorization of a song
(where it is crucial that the bird listen to a tutor's song) and the
sensorimotor phase where birds begin to produce song, but do not need
to listen to a model anymore. ''These observations indicate that song
learning must involve memorization of the tutor song during the
critical period'' (343), i.e. during the first phase. However, during
the sensorimotor phase, birds need acoustic feedback (birds deafened
before the singing phase produce abnormal songs). Thus, both phases
crucially depend on hearing. During song learning, in addition to
auditory brain areas, the brain song system is involved. This is the
case for the anterior forebrain pathway of the song system, which
''contains auditory neurons, which change dramatically during
learning'' (345), establishing a spectral and temporal selectivity for
the bird's own song. This suggests that ''the development of this
selectivity is an experience- dependent process'' (352). During the
sensorimotor phase of song learning, some of these neurons will show
preference for the bird's own song, while others will show preference
for tutor's song, and still others respond equally well to both. There
is, however, a correlation between the preference for bird's own song
over tutor's song and the similarity between these two songs. This
''suggests that a bird's neural selectivity is related to its
particular stage or accuracy of song development'' (357).

In chapter 13, Mundinger examines the ''Genetics of canary song
learning: innate mechanisms and other neurobiological
considerations''. Canaries have the advantage ''that several
genetically different strains were produced by artificial selection''
(369). Some strains were selected for their appearance while others
were selected for their songs. In the first ones, the songs are still
similar to those of wild canaries while there are important
differences in the second ones. Among the second type of strains, a
strain is partially deaf. The goal of Mundinger's paper is to unravel
the effect of genetic differences on ''interstrain differences in song
learning preferences and production'' (370). More specifically, the
question addressed was: ''are there interstrain differences in
learning wild canary patterns, and if so, how do they differ?''
(371). The method was to compare the learning performances of the
different strains of canaries as well as crossbreed individuals in
several successive experiments. The results plead in favor of
interstrain differences in learning wild canary song patterns, though
the differences do not appear to be due to syringeal
constraints. Regarding genetics, the following conclusions were
reached: ''(1) [the genetic system] is polygenic; (2) the genes are on
several chromosomes; (3) one of these is the sex chromosome; and (4)
other genes (...) are autosomal [i.e. not sex-linked]'' (376).

Seyfarth and Cheney devote chapter 14 to the ''Production, usage, and
response in nonhuman primate vocal development''. Though vocal
production in primates seems to be innate and hardwired, vocal usages
(the appropriate use of calls) and responses to vocalization may not
be. Indeed, this is where parallels with human language learning could
be found. In vervet monkeys, there are three main types of
vocalizations: alarm calls, social grunts and a ''wrr'' signal
indicating the presence of another vervet group. While the production
of alarm calls seems innate (infant calls are indistinguishable from
adult calls), grunts and ''wrr'', though partially innate, do change
with age. Alarm calls are used to signal the presence of five
different types of predators and are often misused by infants who use
them in the presence of non-predators, while preserving the overall
categories (i.e. harmless warthogs will induce leopard calls, but not
eagle or snake alarms). Thus part of calls usage is innate, but part
is acquired. The same is true of grunts and ''wrr''. In the same way,
the acquisition of adult responses to calls develops with age.

An interesting case is the acquisition of response to another species'
calls. There, again, ''auditory experience seem[s] the crucial
variable'' (396), given that there is no question of innateness
here. In the second part of their paper, Seyfarth and Cheney describe
a cross-fostering experiment with rhesus and Japanese macaques, two
species with the same types of vocalizations, but who use these
differently, i.e. ''normally raised one- and two-year-old rhesus and
Japanese macaques display a striking species difference in call
usage'' (399). ''Cross-fostered subjects generally adhered to their
own rather than their adopted species' call usage'' (400), which
suggests ''a substantial innate component to the development of vocal
usage and that vocal usage is only partially affected by auditory or
social experience'' (400). Nevertheless, cross-fostered juveniles did
not respond preferentially to calls of their own over their adopted
species and both juveniles and adults learned ''to recognize and
respond selectively to individual idiosyncrasies in the calls of
animals from another species'' (404). Thus, the three aspects of
primate vocalizations, production, usage and response to calls are the
result of three different developmental processes, each with its own
causal mechanisms and rates. Though primate vocalizations differ in
certain major ways from human language (absence of generative grammar,
rigid development of production and usage), there are some
similarities in the existence of different developmental trajectories
for production, usage and response, as well as overgeneralization and
the ability to associate a sound an a referent. This raises two
questions: is association a general learning mechanism? And are the
same cognitive processes involved in human and non-human primates?

The next paper, by Kuhl, centered on ''Speech language and the brain:
innate preparation for learning'' takes us straight to human language
acquisition. Perhaps more than any other cognitive system, language
has been the object of a heated innate/acquired controversy. Kuhl
addresses the question through tests of phonetic perception in
infancy. Though an interactionist view of the relation between
development and learning is now generally accepted, ''at issue (...)
is exactly how the two systems interact, and particularly whether the
interaction between development and learning is bidirectional''
(422). Regarding language acquisition, one of the puzzles is the
explanation of universal and orderly transitions in infants. Regarding
phonetic perception, a dramatic change occurs during the first year,
with new-born infants distinguishing phonetic units of any language
and one-year-olds failing to discriminate foreign-languages
contrasts. The crucial period seems to be between 7 and 10 months. ''A
similar transition occurs in speech production'' (424). These
transitions are not purely developmental (linguistic input is
necessary). The suggestion is that ''language input alters the brain's
processing of the signal, resulting in the creation of complex mental
maps. The mapping 'warps' underlying dimensions, altering perception
in a way that highlights distinctive categories'' (424). This is
supported by the ''perceptual magnet effect'', i.e. the existence of
phonetic prototypes. It occurs prior to word learning and ''the change
in phonetic perception (...) assists word learning, rather than the
reverse'' (427). Kuhl outlines the ''native language magnet'' (NLM)
model, which ''argues that early experience establishes a complex
perceptual network through which language passes'' (432).

Kuhl then turns to the notion of ''critical/sensitive period'', or
''windows of opportunity'' for learning. The explanation for such a
period in speech learning could be explained in NLM not by an
alteration of learning mechanisms in themselves, but by the fact that
''the learned structure may interfere with the processing of
information that does not conform to the learned pattern'' (433). The
same stored representations would account for the reduction of infant
phonetic perception as well as for the reduction of infant phonetic
production on this interference account. The visuo-motor system and
parental hyperarticulation in agreement with phonetic prototypes when
addressing infants contribute to the process. Finally, though there is
strong evidence of left hemisphere specialization for language in
adults, speech does not seem as strongly lateralized in infants of
less than four months.

This leads us to the third part of the book, on the ''Evolution of
communication'', with an introduction by Hauser. He briefly reviews
Darwinian natural selection theory, highlighting the difference
between ''homologies'' (features shared by different species through
inheritance) and ''homoplasies'' (features shared by different species
through convergence). Homoplasies are important because they ''show
how and why adaptive design characteristics spring up in quite
distantly related species, because for any given problem, the solution
set will be limited'' (451). He then introduces the genetic twist to
natural selection, according to which ''selection favors gene
replication'' (452). This leads to two consequences for communication:
first the idea that ''the function of communication is to manipulate
receivers for personal fitness gains'' (451), leading to the selection
of receivers by their mind-reading abilities; the second is the
problem ''of working out the veridicality of the signal'' (451), which
is done through the ''handicap principle'' (''signals are honest if
and only if they are costly to produce relative to current conditions
and if the capacity to carry such costs is heritable'', 451). Hauser
then introduces the following chapters.

Hopkins devotes the 16th chapter to ''Signal evolution in electric
communication'', i.e. electrosensory modality and electric signals
among fishes. Electroreception, rare among aquatic organisms, was
widespread among ancestral aquatic vertebrates, was lost among modern
fishes and reappeared ''independently in two distantly related
groups'' (462). Hopkins describes these two groups, mormyriformes and
gymnotiforms. The range of electric signals is limited (one meter or
less), though they are not affected by reflection, refraction or
reverberation and there is no alteration of the temporal
structure. This suggests that the pulse waveform may be
significant. There are species, sex and individual differences in
electric organ discharge (EOD) and the diversity concerns three
features: wave shape, wave duration and wave polarity. Sexually
dimorphic traits are often selected through female preference, an
expression of the handicap principle. Another effective factor of EOD
diversity may be the density of population. The structure of the
electric organ in different species, as well as genetic analyses,
allows studies of the phylogenetic relationships between the two
groups, enlightening the evolution of the electric organ as well as

The 17th chapter, by Bass et al., proposes ''Complementary
explanations for existing phenotypes in an acoustic communication
system''. The goal of biology is giving explanation for the existence
of individual phenotypes, which can be done at several levels:
functional consequences, evolutionary origins, ontogenetic processes,
mechanisms as well as ontogenetic processes and life history. These
can be combined, yielding multiple explanations. ''An existing
phenotype can be operationally defined by behavioral and structural
characters that exist within an ecological environment''
(493). Complementary explanations ''are specified as mechanisms, life
history, fitness, and evolutionary history'' (494) with three
potential ranges of variation, i.e. behavioral or structural
characters and ecological environment. ''Mechanisms either correlate
or causally link characters with each other or with an ecological
environment and are specified as structural-behavioral,
behavioral-ecological, and ecological-structural'' (494). These are
repeated along the temporal axis of time of an individual's entire
life history, while evolutionary history would be represented a
sequence of explanations in terms of past present and future
interactions. The authors take as an example the existence of an
acoustic communication mechanism in midshipman fish, influencing mate
choice by females. They conclude that ''the final mate-preference of
any single individual depends on all three mechanisms, and hence
variation within the population can arise from variation in one or
more characters or mechanisms'' (511).

Gerhardt signs the 18th chapter on ''Reproductive character
displacement and other sources of selection on acoustic communication
systems''. The focus of the paper is on ''some environmental factors
that account, at least in part, for evolutionary change in
communication systems'' (515). ''These external factors interact with
sexual selection: senders whose signals most effectively propagate in
a given environment (...) have an advantage over their sexual
competitors'' (515). Gerhardt studies the calls of four related
species of Australian frogs, among which call differences occur at
very small geographic distances. His hypothesis is that ''after
establishment of the isolated populations that gave rise to the four
recognized species, their calls diverged gradually by random mutation
and drift'' (517), subject to sexual selection. There are two
ecological pressures on vocal communication: physical conditions may
influence the propagation of the call; predators can detect the
callers. These two factors may act as selective mechanisms on the
nature of the call. Another constraint is that the call must be
recognized as either conspecific or not. This means that frogs living
in areas where two different species or more overlap should be more
inclined to differences in calls. This is called ''reproductive
character displacement''. Its relevance to selection is however in
dispute though there are a few examples of it.

The next and 19th chapter, by Ryan and Rand, is still concerned with
frogs, dealing with ''Phylogenetic inference and the evolution of
communication in tungara frogs''. The tungara frog is a small central
American species, with a variable, two-components, call. The wine
initiates the call and may be followed by one or more chucks. Calls
composed of a single wine are simple while combinations of a wine and
chuck(s) are complex. ''Females are responsive to variation in call
complexity'' (535). ''Males vary call complexity (...) in response to
vocal stimulation from other males'' (538). There is a predation risk
represented by a bat which ''respond[s] to call variation in a manner
similar to the female'' (538). ''Thus the countervailing forces of
sexual selection and bat predation appear to have been responsible for
the evolution of the variably complex call of the tungara frog''
(538). In addition to preferring more complex calls, females prefer
lower-frequency chucks, frequency being negatively correlated with
male body size. The auditory organ of the female matches these
behavioral preferences. There are two explanations for these findings:
the coevolutionary hypothesis (''signals and receivers coevolve''
(540)); and the sensory exploitation hypothesis (''females had a
preexisting preference for chucks that was exploited by males''
(541)). Evidence seems to support the second hypothesis.

Wittenbach and Hoy devote the 20th chapter to ''Categorical perception
of behaviorally relevant stimuli by crickets''. There are two ways
that animals may differentiate physically similar stimuli and class
them in different response categories: the perception may guide the
categorization process or the categorization may guide the perception
process. The authors are concerned with evidence of the second
strategy (called ''categorical perception'') in a Polynesian field
cricket, i.e. an invertebrate. These insects have to discriminate
between the calls of conspecific and the ecolocation calls of
predatory bats. There are four operational criteria for
caractegorical perception of sound: distinct categories with sharp
boundaries; no discrimination inside a category; a peak in
discrimination at category boundaries; close agreement between
categorization performance and the predictions made on the basis of
absolute categorization. The authors were able to show through a
variety of experiments, including the more and more popular
dishabituation paradigm, that crickets did indeed use categorical
perception. Categorical perception seems widespread among a variety of
animals (including humans). Its main benefits are speed and accuracy.

In the 21rst chapter, Searcy and Nowicki describe the ''Functions of
song variation in song sparrows''. They address the question at three
levels: within individuals, between individuals within populations,
and between populations. They make two basic assumptions: ''signal
variation must benefit the signaler (...); song variation at some
levels may not be functional at all'' (577). The functions of song are
to attract females and to defend the singer's territory. This entails
the necessity of producing a song recognizable by conspecifics of both
sexes. The features common to a species song thus ''define a volume in
a 'signal space''' (578). Male singers have several song types which
allow for variants, commonality or not of minimal units of production
(MUPs) determining the degree of similarity between songs. ''Song
sparrows regard song types as being more distinctive than variants''
(581). ''Male song sparrows use switching between song types to signal
level of aggressive motivation'' (581) suggesting a first function for
song variation. Repertoire size seems correlated to overall fitness,
as well as with lifetime and annual reproductive success and years of
territory tenure. Within-type variation remains a
puzzle. Between-individual variation clearly favors individual
recognition and may be advantageous for neighbor recognition among
territorial males. Geographic variations seem the product of
historical factors than due to any specific functionality.

Hauser writes chapter 22 on ''The evolution of a lopsided brain:
asymmetries underlying facial and vocal expressions in
primates''. Lateralization is well-known in humans, but understanding
its evolution may be done comparatively, through the study of
hemispheric asymmetries in nonhuman primates. Thus, Hauser
concentrates on hemispheric asymmetries in processing and producing
facial expressions and vocalizations in rhesus monkeys. In humans, the
left hemisphere is dominant for language, while the right hemisphere
is dominant for facial expressions. After reviewing some of the
(controversial) literature on asymmetry in nonhuman primates, Hauser
describes very elegant fieldwork. The conclusions are that ''it
appears that at least some nonhuman primates evidence cerebral
asymmetries during communication, either sending a signal or
perceiving one'' (618), though infant do not show asymmetries. Hauser
also outlines the difference between fieldwork and laboratory
experiments, which are complementary: ''Specifically, the field
studies have been designed to assess biases in sound localization,
whereas the laboratory work assesses asymmetries in response
specificity and discrimination'' (621).

Cheney and Seyfarth describe the ''Mechanisms underlying the
vocalizations of nonhuman primates'' in the 23rd chapter. They begin
by reminding the reader that ''at least some nonhuman primate
vocalizations function to designate objects or events in the external
world'' (629). In other words, they have a referential function, but
this does not mean that they are words in the linguistic sense. For
instance, words are judged as similar not only on the basis of their
acoustic features but on the basis of meaning. The authors report
habituation studies that indicate generalization by meaning in vervet
monkeys. There is more however to meaning than this, as words are
taken by humans ''not just as signs for things, but also as
representation of the speaker's knowledge'' (632) and that, though the
case for chimpanzees may be more complex, it seems clear that monkeys
do not attribute mental states. Nevertheless, quite a lot of monkey
calls have a social function: they ''initiate and facilitate social
interactions'' (632). To test whether monkeys can be said to
communicate in the Gricean way outlined above, Cheney and Seyfarth
examine the use of social calls: are or are they not intended by their
producers to influence the receivers' mental states? The conclusion
seems to be largely negative: calls ''mirror the intent and state of
the signaler, and they fail to take into account their audience's
knowledge or ignorance'' (636). This seems true even in nonhuman
primates. Thus, ''from the listener's perspective, (...) nonhuman
primate vocalizations share many similarities with human semantic
signals'' (640). ''From the signaler's perspective, however, there are
striking discontinuities between nonhuman primate vocalizations and
human language'' (640).

Matsuzawa signs the final chapter of the book on ''Communication and
tool use in chimpanzees: cultural and social contexts''. He begins by
noting that ''the cognitive functions of humans should be considered
in the light of an evolutionary background, and thus as sharing some
aspects with living nonhuman primates'' (645). There are three aspects
to intelligence, defined as ''a way of modulating behavior to adapt to
an everchanging environment'' (645): ''social intelligence, material
intelligence and intelligence about the intelligence of other
individuals'' (645). The first one has to do with establishment and
maintenance of social relationships in the group, the second one with,
e.g. tool manufacture and tool use, the last has been called ''theory
of mind''. The chapter will be mainly devoted on tool use in specific
groups of chimpanzees and on its cultural aspects. ''Communities [of
chimpanzees] may differ from each other in a variety of ways,
including communication (...), tool use, feeding habits, and so on''
(649). This means that ''chimpanzees must individually learn the
unique cultural traditions of their community, thereby maintaining the
continuity as well as the distinctiveness of the latter'' (649).

Matsuzawa focuses on tool use in the community of Bossou (Republic of
Guinea, W-Africa), reporting field-experiments. He concludes that
tool use is flexible, shows individual hand preference, that metatool
use (using a tool on another tool to modify to achieve a goal) exists,
that there are developmental change in tool use, that observational
learning plays a role in the acquisition of skills, that transmission
may not be vertical (from mother to offspring), that a rudimentary
form of possession may exist. In addition, the field experiments
evidenced tactical deception among chimpanzees, rudimentary
manufacture of tools and comparison with human children showed that
''the developmental course of nut/stone manipulation and stone tool
use was fundamentally similar in the two species'' (662). Finally,
geographically close communities of chimpanzees show different tool
use traditions, enforcing the notion of cultural transmission. This
leads Matsuzawa to the general conclusion that studies of tool use in
chimpanzees cannot be restricted to material intelligence but must
take into account social intelligence in cultural transmission.


The question of language evolution has come back to the fore in the
past few years, though linguists have not in general been the most
numerous protagonists in the ongoing debate. Several of the authors in
the present book insist that no evolutionary question can be settled,
or even discussed, in ignorance of what exists in comparable
species. This may be especially the case for language for which there
obviously are no fossils. No matter which way language appeared,
whether it evolved or was a by product of other evolutions or the
result of a saltationist process, no direct physical evidence will be
found for it (though genetics presumably should play a role). The
evidence is of an ethological nature and what should be compared are
communicative behaviors of different kinds. This is of course all the
more true for species known to be near, such as nonhuman
primates. This book is a major tool for linguists who, without
forgetting that their main aim is to investigate the structure and the
cognitive mechanisms of language and language use, think that, though
language is unique in the biological world, it nonetheless is a part
of it and that its place in it should be properly investigated (see
e.g. Hauser, Chomsky and Fitch 2002). In other words, the time may
have come for linguists to take a walk on the wild side and this book
is a good incentive to... just do it.


Hauser, M, Chomsky, N. & Fitch, W. T. (2002). The language faculty:
what it is, who has it, and how did it evolve? Science 298:

NB: A good companion to the present book with papers by Pinker,
Newmeyer and Bickerton is: Christiansen, M. H. & Kirby, S. (eds)
(2003). Language Evolution, Oxford, Oxford University Press.
Anne Reboul is a First Class Research Fellow at the French Center for Scientific Research (CNRS) in France. She has a Ph.D. in Linguistics (EHESS, Paris) and a Ph.D. in philosophy (University of Geneva, Switzerland). She has written some books, among which an Encyclopaedic
Dictionary of Pragmatics and quite a few papers in French and English, on pragmatics and/or philosophic subjects. She is currently involved in a research project on language evolution.

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