Speaking in Tongues:Theories on the Origins of Language

Sharon N. Solomon xerexes@yahoo.com

M. A. Thesis

Department of Anthropology

University of Toronto May 2001

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Conclusion

Most approaches to the study of the origin of human language tend to focus on the ‘best case’ end result of several thousand years of human cultural evolution. As such, most definitions of language wax poetically about the uniqueness of human language. Some definitions go so far as to state confidently that language is what separates humans from all other animal life forms. However, if humans were the only creature to have tentacles, we would just as confidently state that having suckers on the end of our appendages was what elevated us from all other creatures. This need to see ourselves as separate and ‘above’ mere animal existence defines most areas of research. let us examine at some of the assumptions regarding human language. First, there is an innate mechanism/module/hierarchical structure in the (unique) human brain which allows for both the acquisition and processing of language. Second, the ability to physically produce vowel sounds separates modern humans from both extinct hominid species and extant nonhuman primate species. Third, all languages are composed of phonetic syntax, arranged into a specific rule based grammar. Fourth, this grammar is innate and generalized enough to fit any and all possible languages. Fifth, syntax has ‘meaning’ and ‘context’ which is not limited to phonetic pronunciation (in nontonal languages at least). Finally, syntax and grammar are employed in such a way that they are not restricted in either space or time.

All of the above assumptions seem reasonable at first glance. If one assumes that the capacity for modern language originated in earlier forms of nonhuman primate vocal communication, then it seems highly likely that there is some area of the brain which was preadapted for this later task. However, the next five assumptions need closer examination. Why should the ability to produce ‘vowel’ sounds and construct grammatical sentences be innately human? As for the notion that syntax has meaning and is not bound spatio-temporally, we have no real way of determining whether or not other animals also posses this ability. The waggle dance of bees, and the various species specific songs of whales and dolphins seem to indicate that this is a very tenuous assumption.

Why are these assumptions so tenuous? The answer lies in the fact that the disciplines involved in addressing the language origin question tend to focus on two specific areas: brain area specialization (i.e. left hemispheric dominance for language function), and theoretical models of grammar acquisition. All of these areas of research are within the broader discipline of psychology. The linguists within anthropology are not interested in language origins in the human species, rather they study the spread of languages throughout history or create ethnographic dictionaries. Within paleoanthropology, there is little interest in the daily life of hominid ancestors, other than dietary and technological assessments. Primatologists tend to focus upon how a particular nonhuman primate species interacts within its current environment, while the animal behaviouralists within psychology, tend to study nonhuman primate species within the artificial environment of a lab or research centre, to examine specific aspects of behaviour.

There are many assumptions regarding the significance of the lineage Homo sapiens sapiens. Amongst its various characteristics, language is deemed to be the one factor which separates modern hominids from all other animal species. While it is true that our ability to transmit complex ideologies, both vocally and symbolically, has allowed the development of ‘higher’ societies, we tend to play down the use of communication in other animals. The main point of contention seems to be based solely in semantics. The calls and physical interactions amongst animals are deemed to be somehow less evolved than those of Homo sapiens sapiens because there is no ‘intention’ or ‘representation’ in their communication.

But is this true? Can one confidently state that all of modern hominid behaviours are merely advanced expressions of previous adaptations? This would seem to point to directed evolution at first glance. However, it may be an expression of a preadaptation which just happened to benefit the organism outside of the realm of nature. If this is true, then the vocalizations which classify as ‘language’ may be nothing more than a psychopathology caused as a result of increased neural complexity.

One cannot separate brain evolution from physiological changes when examining the appearance of language in the hominid lineage. There seems to be a general agreement that human language is a recent evolutionary adaptation. As such, one would expect to find that the human brain has undergone some sort of task reorganization to accommodate this new function. The consensus of the research indicates that the left hemisphere (LH) is specialized for most aspects of language. Specifically, the left frontal area shows specialization for expressive language (Broca’s hypothesis), and the left temporal area appears to be specialized for receptive language (Wernicke hypothesis).However, the right hemisphere (RH) appears to regulate the comprehension and production of humor, metaphor and idioms, and controls the cohesion and coherence in narratives. In addition, studies of children with left and right hemispheric lesions indicate that: 1) there is plasticity in the location of ‘language areas’; and 20 the brains of children show slight differences in functional areas when compared to those of adults.

So what is the difference between (spoken human) language and (other animal) communication? How are they defined? Interestingly enough, none of the articles or books referenced for this paper concisely define what is meant by the word language. It is assumed to be self-evident, just as ‘culture’ used to be (and now anthropologists are loathe to employ that term without a full paragraph or two defining what they mean by ‘culture’ and supporting that with a plethora of references which all hold similar definitions). Spoken language consists of words, which have attributed (‘cultural’) meanings; follows a set of conventionally determined rules of syntax and grammar (also ‘cultural’); is not stagnant, as meanings and context can change over time; new words can form spontaneously (based upon old word forms or completely new combinations). A lot of emphasis has been placed upon the importance of the spoken word in modern human communication (citations of Shakespeare abound), however, the majority of our daily lives are spent listening (trying to decipher the world around us) or communicating in the familiar shorthand of grunts, snorts, barks of laughter, murmurs, and a general mangling of linguistic rules.

What is a word? Consists of syllables (formations of vowels and consonants); more specifically, a word is the controlled modulation of exhaled air. Alterations in pitch and tone, due to voluntary, physical (mechanical) manipulations of the lips, tongue, and vocal chords. How is this different from the communication of any other animal species? The trump card in linguistics and the study of language: modern humans can express an infinite variety of meaning (aka symbolic thought) from one generation to the next, thereby creating an information reservoir which allowed the human species to attain domination of the entire planet. Overstating the point, perhaps.

Research into language origins, be it the evolution of languages in the hominid lineage or the spread of languages throughout time (specifically European languages), rests upon all of the above assumptions of language. Most researchers seem to make the, unconscious, assumption of focusing on the adult forms of communication. Although some researchers focus upon child development of language, the goal for paleoanthropology is to show a timetable (the moment of acquisition) for the emergence of language.

Perhaps, the focus should shift from looking at what the adult human form can do, to examining the capabilities of the younger form. From an evolutionary perspective, ontogeny will provide clues to past adaptations, thus the expressive development in the human child should illustrate how communication in our lineage developed. It is assumed that infants are born with the innate ability for modern human languages. This does not make sense for the following reasons: there is no universal syntax or grammar; languages are dynamic; there are an unknown number of ‘lost’ or ‘dead’ languages (which questions the assumption that languages serve as information storage and transmission mechanisms); and there must be a consensus, among the speakers of a language, of meanings and context (which has to transcend regional variations in speech).

The human infant undergoes many physiological and cognitive changes during its development. During the first few months after birth, the infant is physiologically constrained with regards to the types of vocalizations it can produce. With regard to language acquisition in children it is important to remember that: 1) children require models on which to base their early attempts at language; and 2) it takes years before children are aware of all of the possibilities afforded by their linguistic capabilities (i.e. separating emotive clues from the content of vocal speech).

Human specific abilities such as memory and information representation regarding sequences of sound and behaviour no doubt contribute to language acquisition. However, while this may enable grammatical analysis, and may be requisite for learning human languages, it is not an ability specific to grammar. You cannot hold a conversation with someone who does not understand what you are saying. However, you can still exchange information through other means (symbolic - i.e. drawing a picture; using exaggerated physical gestures). Did australopithecines communicate with one another. Yes. Did they have a fully developed language? Why not? Language is not dependent upon the written word. Most cultures did not possess a written language. The earliest form of (surviving) written language did not appear until roughly 5,000 BC (and how many people can read it today?). Most importantly, mass education for ‘grammatical correctness’ has only occurred within the last few centuries in Western civilization. One can assume that before that point in time, communicating ones thoughts and intentions were more relevant to ones survival than the ‘correct’ placement of arbitrary nouns, verbs and articles within spoken language.

Social Grooming

Using modern nonhuman primates as a model, Dunbar (1998, 1996) has argued that social grooming was an evolutionary precursor to speech in our species. Dunbar (1998:95) believes that there is a linear relationship between group size and the amount of time devoted to grooming among Old World monkeys and apes. According to the social grooming theory, ancestral hominids faced a dilemma (Dunbar 1998:96): while increased group size was being demanded by ecological pressures, time budget and energy constraints were preventing them from evolving these large groups.

Dunbar (ibid., 1996:121) states that language (gossip) was an effective solution because: 1) it allows more efficient use of time because an individual can ‘groom’ up to three individuals at the same time; and 2) it allows for the direct transfer of information that can be used to build and service relationships without the need for direct physical contact. According to Aitchison (1998: 21), neoteny, the extended childhood of humans, ties in with this grooming theory. She (ibid.) has proposed that soothing noises made to infants during this extended infancy probably encouraged vocal interaction at a time when vocal grooming was becoming widespread (ibid.). A related suggestion is that this type of nonhuman primate social behaviour has evolved into singing, music and dancing (Beaken 1996:103).

Dunbar (1996:150) suggests that Homo erectus would have employed as ‘sing-song’ vocal grooming rather than speech. He (ibid.) states that vocal grooming needs to be song-like if it is to provide the reinforcing mechanisms of opiate stimulation that make it pleasurable to be groomed. With the implementation of gossip, a different kind of benefit, social information would be introduced. The sounds used in gossip need not be to the same extent intrinsically pleasurable, provided relevant information is conveyed (Power 1998).

However, if grooming among nonhuman primates operates as a signal of commitment precisely because it is costly, then the relative ‘cheapness’ of vocal grooming would tend to undermines its value as an index of commitment (Power 1998:113). Language may enable modern humans to service three times as many relationships for the same amount of social effort as chimps can with manual grooming but the fact that you can chatter to three people at once reduces the indication of commitment to each grooming partner to a third (ibid.).

In modern humans, talking is socially oriented and has little to do with thoughts, and taps into the most superficial levels of language. According to Locke (1998:192), the dissociation between talking and language suggest that there are mechanisms that are specialized for sound making and talking. For example, human infants engage in sound making and talking long before they know that others have mental lives that differ from their own, and presumably are unaware that the talkers to whom they are exposed are exchanging information with arbitrary sounds.

Gesture

Communication starts when two or more individuals coordinate their separate activities to produce a single social act. The earliest version of communication takes the form of an iconic version of the joint activity, a gestural sign (Armstrong 1999; Hadar et. al. 1998; Studdert-Kennedy 1998; Lock 1978). The establishment of the sign in social life depends from the start on agreement between two or more individuals, a convention (Beaken 1996:60-61). This occurs when the response to the gesture is as important as the gesture itself. From initially iconic forms, a variety of forms can develop into arbitrary or conventional signs (ibid.). The context of general sign use is initially limited to a few social activities. Over time, more activities are organized with gesture, and something like grammatical forms start to develop. However, this does not imply that early hominids did not use sound in a variety of social functions. In general, gesture can be used in any situation where speech is not possible or permissible (Beaken 1996).

According to Englefield (1977:87), a gestural sign system can function with a small number of multifunctional iconic signs, however a functioning vocal language requires a large number of words to be learnt by all members of a group. Assuming that early hominids had a shorter learning time than modern humans, but longer than chimpanzees, this may have placed a limit on what could be acquired (ibid.). Beaken (1996:64) proposes that, in this situation, natural gestural signs would be easy to learn and to remember, and would “appear to be the original communication medium”.

Gestures are based on physical properties of the world (Bonvillian 1999; Nöth 1994). The meanings of natural gestures depend on the immediate context in which they are used (ibid.; Kendon 1989). Since interpretation depends on context, meaning is relatively easily recovered and the signer can use contextual features to elucidate meaning. Gesture meaning my be complex or simple, according to the situation. Since each gestural sign has a wide range of meanings, the load on memory is light, though ambiguity and misunderstanding may be frequent (Beaken 1996; Armstrong et. al. 1995, 1994). Gesture is possible at a distance and can also reach a large number of people at once, provided they are attentive. It is possible in noisy conditions and conditions requiring silence. Interestingly, there are still some things, today, that can be better expressed through gesture than speech: dimensions, shapes, directions and specifying objects/people in the immediate context.

Armstrong et. al. (1994:356) propose that the origins of syntax can be found in gesture. Gestures develop over time, as the signers analyze the gesture and gradually decompose it into separate semantic roles or meanings contained in the original sign. Rather than dividing language into two separate forms (spoken and gestured), Armstrong et. al. (1994:352) view spoken words as “complexes of temporally ordered muscular gestures.” They (Armstrong et. al. 1994:354) state that syntax “transformed naming into language by enhancing the ability of hominids to articulate and communicate complex thoughts.”

It is often that language developed through pointing, specifying objects and individuals, which leads eventually to naming them. It is also claimed that early language must have been dominated by actions, at the expense of attention to objects (Beaken 1996). Studies of child development indicate that children become aware of their own activity before they are aware of objects around them (Beaken 1996:69). Their first act of meaning is the action of pointing rather than reference to objects. It is the response of adults to this action, that learning of names proceeds (ibid.).

According to MacNeilage (1998:232), sign language may have gained an impetus from pantomiming acts that the hands themselves performed. He (ibid.) believes that the reasons usually given for sign being superseded by language (lack of omnidirectionality, lack of utility in the dark, inhibits other manual functions) are also reasons why it would not have gained preeminence in the first place. It has been proposed that gesture is more suitable for concrete notions, and speech for abstract (Armstrong 1999). However, abstract notions are not the result of the medium of speech, they are the result of a certain level of social and technical development. Modern deaf signing can cope quite well with abstract and general concepts.

Additionally, it has been proposed that the speed of processing of information is both faster and more efficient with vocal speech (Lieberman 1998). However, modern deaf signers are quite capable of translating spoken language into sign at the same pace of the speaker. This is possible because they are not processing distinct phonetic segments, but information contained in word meanings or propositions (Armstrong 1999; Beaken 1996). It is important to note that spoken language alone, today, is not adequate for all communication needs, as evidenced from our reliance the written word.

Gestural languages have a long history and widespread usage around the world. For example, the American Plains Indians developed a system of gestural language which served as a lingua franca between North American tribes over thousands of years (Skelly 1979). Kendon (1989) identified the widespread usage of gestural languages among Australian aboriginals. Luria and Vygotsky (1992) suggest that every foraging society used both gestural and spoken languages. Within the context of language origins, it is not necessary to promote spoken language over manual language. The mere fact that the human brain is capable of processing both types of language, through similar yet very different means, provides a clue as to the evolution of language. Since sign/gestural languages do not rely upon Chomskian grammatical rules, it seems as though the main impetus for language development was the expression of contextual information.

Part V: Other Theories of Language Origins in Hominids

While the discontinuity or innate theories of language origins tend to predominant in linguistic and psychological studies, there are several continuity or neoDarwinian theories which also deserve attention. These theories fall into three broad categories: cognitive enhancement, social intelligence, and manual gestures. As opposed to the theories which follow Chomsky’s model of identifying universal grammar and defining how a language acquisition device operates, and where it would be located, these continuity theories attempt to synthesize behavioural and environmental information to provide hypotheses of language origins. While the hypotheses of the discontinuity theory are tested using modern human children (i.e. Carstairs-McCarthy 1999; Dromi 1999; Berwick 1998) , continuity hypotheses tend to draw upon research conducted upon nonhuman primates (i.e. Dunbar 1998, 1996; Power 1998; Locke 1978).

Cognitive Enhancement

Dunbar’s (1998:94) social brain hypothesis proposes that the need to hold large highly structured hominid groups together was more important than the need to solve ecological problems. He (ibid.) proposes that in response to ecological pressures, hominid species were forced to evolve proportionately larger brains in order to allow large groups to remain stable. According to Donald (1998:57), modern human speakers often carry out several complex operations at once, in order to maintain “parity with the recipients of their communications”. Human language is thus characterized by its complexity, speed, and demands upon attention and working memory (ibid.). Cognitive enhancement theories state that as the brain evolved, it became capable of performing more complex tasks (Loritz 1999; Müller 1996; MacNeilage 1998; Locke 1997; Bradley 1995). These tasks were not necessarily ‘intentional’ but merely and offshoot of existing mental faculties incorporated into a new task. For example, the mental ‘lexicon’ of modern humans may simply be an enhanced ‘sound contex’ memory area, which would be found in nonhuman animals.

While most theories propose that a ‘protolanguage’ arose within the Homo erectus lineage (i.e. Locke 1998; Worden 1998; Arensburg 1994), a few assume that language is unique to modern humans (i.e. Lieberman and McCarthy 1999; Lieberman 1998; Noble and Davidson 1993). It has been proposed that a significant increment in human cognition resulted from the emergence of language (Mithen 1996; Noble 1996; Noble and Davidson 1989). This position lends itself to the assumption that it is implausible to suppose that cognition grew gradually over the approximately 2 mya of hominid development, but had virtually no effect on behaviour or technology. According to proponents of the discontinuity theories, if human cognition had gradually increased over time, we would expect to find that a slow but steady increase in the rate of technological and behavioural change left marks in the fossil record over the last million and a half years (Bickerton 1998; Mithen 1996, Noble 1996). Instead a long period of ‘stagnation’ was followed by a cognitive explosion occurring only after the appearance of anatomically modern humans in Europe approximately 50 kya (ibid.).

While it is tempting to point to Homo sapiens as being the intellectual giants of the hominid lineage, it is important to remember the following: 1) the fossil record is incomplete; and 2) due to taphonomic process, items such as stone tools tend to preserve for millions of years, whereas organic materials will decompose. These periods of intellectual ‘stagnation’ are due more to the lack of creative thinking on the part of those who study human evolution. It is akin to stating that there have been no technological, behavioural or intellectual changes in Homo sapiens based upon the production of ‘mud’ bricks, which hasn’t altered in over 8,000 years (Cavalli-Sforza 2000). A recent study by McBrearty and Brooks (2000) provides evidence that there was a gradual shift in both technology and behaviour during the Middle Stone Age period (approximately 300 kya) in Africa, which then spread to other parts of the Old World. According to McBrearty and Brooks (2000:4), the view that European Homo sapiens were responsible for ‘revolutionary’ advances in behaviour and technology is due to both Eurocentric bias and the lack of relevant fieldwork outside of Africa.

Social Intelligence: Theory of Mind

According to Locke (1998:197), the social sound making, talking and language evolved to serve the needs of individuals who were alike and knew each other. Thus the pressure to speak elaborately would have come from the need to monitor and share with others, the perceived intentions and actions of fellow members of the group (ibid.). Tomasello et. al. (1993:496-496) have proposed that language could only have emerged after hominids had evolved the social skills that are evident very early in modern human development, and that are the precursors of language. These skills include: theory of mind (understanding the intentionality of other minds), imitation and intentional expression.

It should be noted that: 1) intelligence is not one general ability that assists an organism in all situations (Gigerenzer 1997:271); 2) complex intellectual processes seem to be necessary for many social interactions (Tomasello and Call 1997:351); and 3) primates have a domain specific knowledge of the world. However this knowledge can be transferred or exchanged when there are changes in the environment (Gigerenzer 1997:274-275; Tomasello and Call 1997:353). Field observations of specific primate groups seems to indicate that they possess a complicated, social, intelligence for interacting with other group members (ibid.). Tomasello and Call (1997) suggest that in the wild nonhuman primates have the ability to understand the mental states of others, even though they have failed experimental studies of metacognition. The failure in the lab setting may be due to the fact that the experimental design was originally intended to test theory of mind in human children, and therefore rests upon verbal competence in order to succeed (Tomasello and Call 1997:362). With regard to language and theory of mind in modern humans, most communication does not necessitate any knowledge of the mental states or beliefs of others. For example, the observed behavioural response of a group of individuals to an ‘alarm’ call (i.e. someone yelling “Fire”) is not depended upon the caller having any awareness of the mental states of the other individuals.

Discussion

As demonstrated by the above examples of nonhuman primate communication, one could postulate that there are certain aspects of human vocal production which are similar. Additionally, one can hypothesize that the ability to vary the arrangement of vocal elements, and to produce meaning differences, as found in gibbon duets, chimpanzee long calls and vervet alarm calls, may be the source of language origins. However, it is important to remember that nonhuman primates are not ‘unevolved’ human beings. Humans and nonhuman primates are completely different species. Behavioural and physiological traits from one may be used as an analogy for the other species. However, it makes no sense to state that chimpanzees are more evolved than macaques, nor that the vocal capabilities of humans are ‘more complex’ than that of other nonhuman primates.

Instead, one can examine which fundamental traits define the communication of nonhuman primates, and other animals: 1) the ability to recognize the vocalizations of its particular species, as distinct from other environmental noises; 2) the ability to recognize the vocalizations of kin; 3) the ability to recognize the vocalizations of allies and ‘strangers’; 3) the capacity to learn new vocalizations; 4) the capacity to discern ‘referential meaning’ contained within a species specific vocalization (i.e. the difference between a mating call and an eagle alarm call); and 5) the capacity to alter vocalizations without altering the initial referential meaning.

It is important to remember that human beings are not born as adults. We have a long, steep learning curve which takes years to master. Secondly, vocal communication is only one form of communication. Both humans and nonhuman animals rely upon visual and gestural communication, as much, if not more, than upon vocal communication. Additionally, the majority of human language is little more than ‘grunts’ of acknowledgment or other noises (umm) which fill conversational silences. Although Bickerton (1990) would say that these ‘words’ fulfill a grammatical function by occupying a ‘position’ in a sentence, one could just as simply state that it is no more complex than a chimpanzee long call response. Finally, defining human language as ‘complex’, since it is not bounded in space or time, is a bit of a stretch. Languages are fluid, their complexity arises once their vocabularies increase, which has more to do with the consensus regarding novel acoustic sounds than the so called grammatical rules of a language. In other words, if the constraints of the hypotheses fail when applied to humans, why are they employed on nonhuman primates?

Vocal Responsiveness

In human conversation, individuals appear to take turns in language production, which is characterized by acoustically distinct sounds (Arcadi 2000:206). In contrast, although simple vocal exchanges involving distinct calls have been documented in some primate species, these calls appear to be acoustically similar (ibid.). Mitani and Brandt (1994:250) concluded that there is no evidence that chimpanzee vocal behaviour is different from that of any other primate. However, others (i.e. Burling 1993; Ujhelyi 1998) have stated that chimpanzee vocal behaviour is more ‘sophisticated’ than that of other primates, and therefore may provide insights into the origins of language. However, acoustic analysis has revealed that some primate calls which sound the same to human observers are in fact distinct vocalizations that are employed in different contexts and elicit different behavioural responses (Arcadi 2000: 218; Zuberbühler et. al. 1997:601; Cheney and Seyfarth 1982:748).

Seyfarth and Cheney (1997) found that the ‘grunts’ of female baboons served as a reconciliatory signal because they reduced the anxiety of lower ranking females’ after aggression. In vervet monkeys, Cheney and Seyfarth (1982) have identified four different social situational ‘grunts’: upon encountering a dominant conspecific, upon encountering a subordinate conspecific, to a conspecific moving to an open area and to vervets who are not members of the group. Seyfarth and Cheney (1997) also observed that vervet ‘wrr’ calls were used to indicate that a neighbouring group had been seen and ‘chutter’ calls indicated that an intergroup encounter had become aggressive.

In 1996, Arcadi spent 53 days observing a small group of chimpanzees (10 adult males, 8 central adult females and 9 peripheral adult females) which had never been provisioned, in Kibale National Park, Uganda. Arcadi (2000:213) found that wild chimpanzees vocalize at low rates, tend not to respond to calls that they hear, and when they do respond, they tend to give calls that are similar to the ones they have just heard. She noted that calling rates were higher when other calls were audible, and temporally clumped calling within and between subgroups typically involved either chorusing or counter calling with calls of the same type as those just heard (Arcadi 2000:217).

Social Learning

Learned vocalizations function as an indicator of group membership. Chimpanzees and modern humans live in social groups characterized by within group cooperation and competition between groups. Such social systems put a premium on reliable indicators of group membership, vocal or otherwise (Tomasello and Call 1997). An alternate possibility is that vocal learning is just one example of a domain general mimetic ability in modern humans (Fitch 2000).

Janik and Slater (2000:8) define three different types of social learning: contextual, production and vocal. Contextual learning affects the behavioural context, both usage and comprehension, of a signal. Production learning refers to instances where the signals themselves are modified in form as a result of experience with those of other individuals. Vocal learning is defined as production learning in the vocal domain. It can affect one or more three systems which involve different levels of control over sound production (ibid.): respiratory, phonatory and filter. According to Janik and Slater (2000), contextual learning and respiratory production both preceded the evolution of phonatory and filter production learning.

At the same time, the most important primate specific tool for expressing emotions is the facial gesture. Producing modifiable facial gestures has an immediate communicative function” (Ujhelyi 1998:180). As secondary result, acoustic variations, arise if an animal changes its facial gesture during vocalization. Primates have mobile, nonattached upper lips, which enable them to produce different facial expressions. Different facial expressions include lip configurations which form barriers to the passage of air (Burling 1993:30). Thus they may result in different acoustic outcomes. Although a human like vocal tract is absent, the face will be the main tool for producing articulatory variants (ibid.).

Since most vertebrates can distinguish the vocalizations of different individuals (parent/offspring, conspecifics, strangers), formants, the ‘shaping’ of sound due to physiological constraints, plays an important role in individual identification (Firth 2000:263; Burling 1993). Nonhuman primates also have formants in their calls, which vary with context (Janik and Slater 2000:9). Formants might also provide an indication of the body size of the vocalizer. Firth (2000:263) has proposed that there is correlation between vocal tract length and body size in humans and monkeys. However, formant cues are different than that of vocal pitch, which is not correlated with body size in humans (Lieberman and McCarthy 1999:488).

One could presume that early sound making would have been accompanied by rudimentary vocal facial displays such as those produced by modern nonhuman primates. Later changes, building upon inherent preadaptations, expanded from the strictly prosodic domain into the articulatory domain, and subsequently, the discovery that these sound making movements could be combined in various ways to produce a range of distinctive phonetic forms (words).

Duets

A duet is defined as long calls or songs in which both sexes of a monogamous pair produce loud sounds in an interactive manner, performing a mutually cooperative and coordinated display (Arcadi 2000; Ujhelyi 1998). In some primate species, mated pairs sing ‘duets’ and neighbours ‘counter sing, in an alternating but apparently timed manner. For example, chimpanzee long calls are thought to maintain connections with group members, gibbon duet songs are performed at given times of the day, and indris duets are produced only during the breeding season (ibid.). In gibbon duets, the contribution of males and females to song display show a rather rigid and uniform pattern (Arcadi 2000). Although there are some instances in which song transfer may occur: for example, when a female becomes widowed, she may adopt and perform the male song and so produce a pseudo duet the strong sexual differences in song structure are likely to be genetically programmed (Ujhelyi 1998).

Despite the strong correlation between the duet performance and monogamy, coordinated call display does exist in great apes. The common chimpanzee males often call together, while in bonobos, a male-female pair duet occurs (Ujhelyi 1996, 1998). In both chimpanzee species, duetting or chorusing can be heard all day in relation to different activities (Ujhelyi 1998:184). It has been proposed that duetting is a definitive feature of stable monogamous and territorial primate species, and that the function of duetting may be the maintenance and reinforcement of the pair bond (Ujhelyi 1998:185). Differences in partner preferences are due to differences in group structures between the two chimpanzee species. Ujhelyi (1998) observed that bonobos show a high degree of synchronization between vocalization of different individuals. Ujhelyi (1996, 1998) further postulates that the capacity of duet performance might be a remnant of the earlier monogamous stage, and altered to fit in the current way of life.

Mitani and Brandt (1994:250) observed that chimpanzee males attempt to match the acoustic characteristics of each other’s vocalizations when calling together. Single males appear to alter the acoustic structure of their calls when chorusing with different partners. This tendency results in large variability in call types on the one hand, but homogenization in call repertoire of the group on the other hand (ibid.). According to Marshall et. al. (1999:826), the call repertoire being acquired by a single male may contain a large number of variants mostly acquired via social learning, while the call repertoire itself is not exclusive to a specific individual.

Long calls

Territorial song marks the territory of a group and serves to maintain spacing between members of neighbouring groups. Due to its acoustic nature, it is impossible to mark territory directly, instead the presence, identity and location of the territory owner are broadcast (Ujhelyi 1998:184). Ujhelyi (1998:185) considers this to be a representational function. According to Ujhelyi (1998:180) this territorial behaviour establishes lexical syntactic capacity. If the labeling channel is an acoustic one, and the primary sounds are limited and genetically fixed, then differences in signs “can only be achieved by compositions of the invariant elementary sounds and by varying their arrangement.” In contrast, species capable of producing within call acoustic variants live in large groups with complex social interactions (ibid.).

All the primate species, excluding African apes, which long, variable calls share a common feature in their social behaviour, namely monogamous territoriality (Arcadi 2000:216; Ujhelyi 1996:74). In contrast to other territorial mammals that rely upon olfactory marking, most nonhuman primate species mark and defend individual territory by acoustic signs (ibid.). These distinctive loud calls are given by males as territorial displays, and these can elicit similar calls from one or more conspecific (Ujhelyi 1996, 1998; Tomasello and Call 1997). These long calls or “songs” are displayed without any overt external stimulus and have some musicality in nature. It has been proposed that the songs of different species represent different degrees of complexity (Burling 1993).

Long calls are built from smaller, stable, clearly distinguishable units, and exhibit individual variation over time (Burling 1993; Ujhelyi 1996, 1998). The units of these long calls are ‘traditional’ communicative signals (i.e. alarm or contact call) which are combined in different arrangements in different compound calls. The number of elementary units in long calls differs across species, and acoustically different songs can be created by changing the number, type and position of elements (Ujhelyi 1998:179). According to Mitani and Marler (1989:43) the gibbon song may be divided into distinct vocal elements. Based upon seven variables (duration, maximum frequency, minimum frequency, frequency range, start frequency, end frequency and number of frequency inflections), 13 basic note types can be distinguished (ibid.) The songs are then built up from these notes. The songs can be varied using different type, number and positions of elements, segments or notes. Hence, the song repertoire of an individual male may be rather large.

Both the common chimpanzees and bonobos have long calls, which can be divided into some acoustically distinct segments, similar to gibbon songs (Mitani and Marler 1989; Clark and Wrangham 1994). Chimpanzee vocalizations are highly graded with many variants used in a wide range of contexts (Arcadi 2000:205). It has been noted that these vocal sequences can be long and involve many call types (ibid.; Ujhelyi 1998). Additionally, extended vocal exchanges between individuals out of visual contact are common (Arcadi 2000:206). Chimpanzees and bonobos also emit long, compound calls (pant hoot and high hoot, respectively) which can be divided into acoustically distinct segments (ibid.). Although chimpanzees do not change the order of the four fundamental units of the long call, they insert individually selected vocal elements into different positions of the call (Burling 1993). Chimpanzee males often give the long call together, during which they attempt to match the acoustic characteristics of each other’s vocalizations. The matching tendency shows that call variants can be learned (Arcadi 2000:206; Ujhelyi 1998:185-186).

Ujhelyi (1998:179) has proposed that this type of call variant production “may represent phonological syntax since the altered parts of the call do not possess their own meaning independent of the call”. In other words, this type of call production may represent an intermediate stage between animal communication and language. As a result of living in a large social group, the ability to create syntactically different calls was enhanced. A call repertoire emerged which contained a large number of call variants at group level available for each group member via social learning. Ujhelyi (1996, 1998) believes that this type of animal call is different from ordinary animal communication since it apparently demonstrates some features of human language.

Zuberbühler et. al. (1997:601) found that the long distance calls of diana monkeys function in perception advertisement as well as within group semantic signals that denote different types of predators. Subjects were a group of 20-25 individuals (1 male, 5-7 adult females, subadults and infants) in the Taï National Park, Côte d’Ivoire. It was observed that diana monkeys show age/sex dimorphism in the vocal repertoire (Zuberbühler et. al. 1997:591). Adult females, subadults and juveniles accounted for most of the vocal activity in the group, and are responsible for the following vocalizations (ibid.): contact call, trill, alert calls (leopard, eagle) and agonistic calls directed in both intra and intergroup interactions. Male diana monkeys tended to restrict their vocal communication to long distance calling to which females responded with they own, acoustically different, alarm calls (ibid.). According to Zuberbühler et. al. (1997:601), the long distance calls in nonhuman primates show acoustic specialization. Calls are structurally stereotyped and are given repeatedly (ibid.).

It seems that it is just this territorial behaviour which first established the linguistic capacity. If the labeling channel is an acoustic one, and the primary sounds are genetically fixed. Then only by varying the elementary sounds can sign differences be achieved. Consequently, those individuals who are capable of linking, repeating, and combining these elements get selective advantages. It can be shown that some of the notes of gibbon song occur independently of song, in another context reaction to encounters (Mitani and Marler 1989). These simple elements function in ordinary communicative situations. The combination of available elements resulted in a variable set of songs which became suitable for territorial marking.

According to Zuberbühler et. al. (1997:601), in rain forest habitats, where visibility is generally poor, the acoustic domain may provide the most efficient means by which a prey animal can communicate to a predator. In the case of diana monkeys, calls are given only to hunters which surprise their prey (leopards, eagles) and not to hunters that pursue their prey (chimpanzees, humans) (Zuberbühler et. al. 1997:602). Secondly, calls given in the this contexts are regularly combined with approaching the predators both under experimental and natural conditions (ibid.).

Alarm Calls

Many nonhuman primate species employ various types of ‘referential’ calls to conspecifics. These calls can be classified as food calls, predator alarm calls, and calls for aid (recruitment calls) (Tomasello and Call 1997). Gouzoules et. al. (1984:182) observed that juvenile rhesus macaques, while being attacked by another individual, used one of five different calls to recruit support from relatives. Gouzoules et. al. (1984:183) further grouped these calls as ‘noisy screams’, which are employed by high ranking individuals when there is physical contact, and ‘pulsed screams’ which are used when the attacker is a relative. When recordings of these calls were played during experimental testing, it appeared that individuals were responding to the acoustic properties of the calls, and not the behaviour or emotional arousal of the caller (Gouzoules et. al. 1984:190).

Gouzoules et. al. (1984:190) proposed that the ‘responder’ employed these acoustic properties to determine both the identity of the aggressor and what type of aggression was occurring. Gouzoules and Gouzoules (1995) later repeated this playback experiment with pigtail macaques, since they also appear to employ recruitment screams during agonistic contexts. They observed that the acoustic properties of these calls and the aspects of the agonistic situation differed from that of rhesus macaques (Gouzoules and Gouzoules 1995:449). However, they believed that there is no evidence that the calls of pigtail macaques encode the kinship status of the aggressor (ibid.).

The alarm calls of vervet and diana monkeys have been thought to ‘refer’ to features of the environment (Cheney and Seyfarth 1980, 1990, 1990a). Cheney and Seyfarth (ibid.) state that vervet monkeys employ three distinct predator specific alarm calls (leopard, eagle, snake). A loud barking call is given for leopards; a short, ‘cough like’ call is given for eagles; and a ‘chutter’ call is given for snakes (Cheney and Seyfarth 1990; Hauser 1996). Each call (stimulus) elicits a different escape (behavioural) response on the part of the receiving conspecifics (leopard alarm calls - run up the nearest tree; eagle alarm calls - look up, run into the bushes; snake alarm - stand on hind legs and look down at the ground) (ibid.).

However, it is assumed that this type of referential acoustic behaviour differs from the human usage of words for the following reasons (Seyfarth and Cheney 1997:252): 1) alarm call meaning appears to be limited to the connection between referent and sound; 2) alarm calls are difficult to specify; and 3) may be the result of simple conditioning. Seyfarth and Cheney (1997:252) state that although vervet calls function in a rudimentary semantic manner, it is uncertain whether vervets recognize the referential relation that exists between their calls and features of the environment. Additionally, it is uncertain whether or not this vocalization is interpreted as a representation of the caller’s knowledge of conspecifics (ibid.; Hauser 1996:413).

The alarm calls of male diana monkeys show consistent differences in acoustic and temporal structure depending on whether they are given to leopards or eagles (Zuberbühler et. al. 1997:602). According to Zuberbühler et. al. (1997:602), the most salient feature of these alarm calls, the number of syllables, did not seem to be sufficient for an unambiguous identification (for the human observers). The alarm call for leopards seemed to have fewer syllables than the alarm call for eagles, although there appeared to be some overlap (ibid.). The female and juvenile diana monkeys responded in qualitatively and quantitatively similar ways to both the male’s call to a predator and to the predator that typically caused that call, in both playback experiments and natural conditions (ibid.). Zuberbühler et. al. (1997:602) concluded from this observation that that these calls contain semantic information. Like vervets and diana monkeys, playback experiments with ring tail and ruffed lemurs indicate that they employ referential calls in specific, aerial or terrestrial, predator situations (Macedonia 1990).

In the case of the great apes, there have been no systematic studies with regard to how individuals understand or employ alarm or recruitment calls (Tomasello and Call 1997). Almost all of the systematic research concerns the food calls of chimpanzees: pant hoot, food grunt and ‘food-aaa’; but only the first two have been systematically studied (ibid.). Clark and Wrangham (1994:199) found that pant hoots given by food discoverers did not increase the frequency with which conspecifics arrived at the food site. Hauser et. al. (1993:818) found that chimpanzees used pant hoots in addition to food grunts when the amount of food was large. However, the function of pant hoots is uncertain, since it has been observed in other social situations, such as excitement or the announcement of an individual’s location (Mitani and Nishida 1993; Tomasello and Call 1997). According to Tomasello and Call (1997:257), pant hoots do not indicate the discovery of food since captive chimpanzees pant hoot in full view of conspecifics, even though all individuals are aware of the food source.

According to Hauser (1996) and Tomasello and Call (1997), the type of referential behaviour described in the preceding paragraphs, may be due to an innate mechanism, and does not necessitate any understanding of ones conspecifics. This mechanism enables these particular animals to generate specific noises in the presence of particular visual or emotional stimuli and to respond in certain ways to particular acoustic or visual stimuli (ibid.). However, this would be true of any type of behaviour, once it is broken down into components and taken out of context. One of the problems with this type of reasoning is that it ignores the overall picture (referential communication) in favor of a behavioural model.

Girneys

Most of the research conducted on free ranging nonhuman primates has addressed alarm calls. However, Locke (1998:194) has suggested that a more interesting class of vocalizations would be produced by contented animals, vocalizing quietly among themselves in a family or small group situation. One type of vocalization that is not screamed, but uttered by various species of monkeys is the girney. Girneys are most frequently produced by mothers who are interacting with other mothers or juvenile females. Girneys seem to be “produced behind closed lips and resemble the sound of an individual who is talking with food in his mouth” (ibid.). Girneys may be issued interchangeably with lip smacking, and are common among animals which live in small, intimate groups. From a physical standpoint, they lack the “rhythm of lip or tongue smacking, but are typically phonated” (Locke 1998:195). Locke (1998) has proposed that if the phonatory aspect of girneys were combined with the pulsatile character of lip and tongue smacking, a human like type of sound making could have been achieved.

Part IV: Nonhuman Primate Communication

It is thought that animal communication and human language(s) have fundamental differences in their structures and functions (Fitch 2000; Janik and Slater 2000; MacNeilage 1998; Beaken 1996:103; Hauser 1996; Ujhelyi 1996). According to Tomasello and Call (1997:232) animal communication is a “ritualized social act designed to induce others to act via their own self directed powers”. These signals are thought to express the animal’s emotional states, which in turn motivates the resultant behavioural actions of conspecifics in given circumstances (Hauser 1996; Tomasello and Call 1997). Furthermore, in animal communication, a rather limited set of messages appears to be transmitted, which are in general, genetically fixed (ibid.). However, there seem to be several exceptions, for example, the existence of different vocal signs for different predators in vervet monkeys (Cheney and Seyfarth 1990, 1997; Hauser 1996; Tomasello and Call 1997).

Although some researchers believe that symbolism is found among primates, it is not thought to be necessarily found in their natural communication system (Aitchison 1998:20). It has been proposed that the alarm calls of vervet and squirrel monkeys may represent an intermediate stage en route to symbolization (Tomasello and Call 1997; Hauser 1996). Human raised chimpanzees, who have been taught language like systems, can use signs as symbols, yet do so mainly when they require something (ibid.). However, the realization of the potential power of names, and the subsequent desire to label everything, has not been found in these experiments, although it occurs in human children between the ages of one and two (Aitchison 1998:21; Tomasello and Call 1997).

Human speech has also been distinguished from nonhuman primate gesture call systems by virtue of its representational level. According to Knight (1998:69), linguistic reference is not a direct mapping from linguistic terms either to perceptible things or to intentional states. Instead the mapping is from linguistic terms to communal constructs and representations established in a structured discourse (ibid.). Human vocal activity may have evolved from instinctive animal vocalizations (Beaken 1996:103). Specifically those of social interaction and emotional expression (akin to those of infants). However, the early vocalizations of infants are quite different from the speech patterns of adult human beings.

Ulbaek (1998:33) believes that language evolved from animal cognition, not communication. Ulbaek (1998:34-46) claims that the following are examples of cognitive abilities in nonhuman animals specifically, primates (Ulbaek 1998:34-36). : 1) tool making and usage (termite ‘fishing sticks’, ‘hammer and anvil’ stones for cracking nuts); 2) cognitive maps (knowledge of their territory to plan routes to food areas); 3) learning through imitation; 4) social knowledge (dominance hierarchies); 5) deception; 6) theory of mind (knowledge of the intentions of others); and 7) ability to learn language like systems (based on experimentation).

The main argument against nonhuman primate communication as a precursor of modern human language is the lack of conclusive evidence that nonhuman primates possess a theory of mind. The theory of mind hypothesis states that humans attribute mental states, such as knowledge and beliefs, to others, and that there is a recognition of the causal relationship between mental states and behaviour (Dunbar 1998; Worden 1998, Tomasello and Call 1997; Seyfarth and Cheney 1997:250; Gibson and Ingold 1993). Nonhuman primates appear to recognize one another as individuals, know all about each others’ kin and alliance relations, and can rapidly learn simple rules about who will do what in specific circumstances (Worden 1998:151; Tomasello and Call 1997, 1993). To have social intelligence, primates need to do three things (ibid.): 1) represent in their minds information about social situations, past and present; 2) to learn and represent internally, the causal regularities whereby one social situation leads to another; and 3) to combine knowledge of the present social situation with knowledge of causal regularities to predict what may happen next.

Based upon the criteria for theory of mind, nonhuman primates may have communication systems which are semantic, but do not qualify as a ‘language’ since they are not ‘intentional’ (Tomasello and Call 1997; Hauser 1996). While it appears that most primates do not possess a theory of mind, the picture in great apes is unclear. Some evidence from field studies suggests that they do, while laboratory studies are more negative (ibid.). However, since these laboratory studies are modeled upon similar experiments with preschool human children, and require a verbal response to correlate observed behaviours, the lack of evidence for theory of mind in nonhuman primates is questionable (Aitchison 1998; Tomasello and Call 1997). Since it is known that it takes several years before human children ‘acquire’ a theory of mind, and there is, as yet, no way to know with any certainty what nonhuman animals ‘intend’ or ‘mean’ when they vocalize, this section will focus upon the interpretations of observed and playback experiments of nonhuman primate vocalizations.

It has been suggested that there is no living species which demonstrates an intermediate stage of language evolution (Ujhelyi 1996:74). This should not be a surprising observation, since the intermediate stage of language origins should, theoretically, lay within the early hominid lineage. According to evolutionary theory, the nonhuman primate and hominid lineages ‘split’ approximately six to eight million years ago (Tattersall and Schwartz 2000). For instance, it has been proposed that chimpanzees have remained physiologically unaltered for the last five million years, while the hominid lineage has undergone at least 17 ‘speciations’ with associated physiological changes during that same period of time (ibid.). All of following lines of inquiry of nonhuman primate communication should be viewed as possible modes by which later hominids incorporated into early linguistic forms.

The homologies between language and animal communication have been questioned by a variety of researchers (Burling 1993; Tomasello and Call 1997; Cheney and Seyfarth 1990a). It is generally agreed that most aspects of human vocal production are shared with a variety of other animals, thus it can be examined from the perspective of comparative evolution (Fitch 2000:258). One can hypothesize that the ability to vary the arrangement of vocal elements, and to produce meaning differences, may be the source of language origins (Ujhelyi 1996:71).

There are three main problems with research concerning nonhuman primate communication: 1) it has tended to focus upon the following specific types of communication: alarm calls, long (distance) calls, response calls, and duetting; 2) very few nonhuman primates have been intensively studied (i.e. vervet monkeys, diana monkeys, macaques, chimpanzees, gibbons); and 3) there is a sharp division between the interpretation of observational field reports of wild nonhuman primates, and the analysis of playback experimental studies conducted upon both wild and captive nonhuman primates. Specifically, the anecdotal evidence seems to imply that nonhuman primates have a rich social life inclusive of specific referential communication among conspecifics, whereas playback studies point to simpler, behavioural mechanisms.

Language Areas of the Brain

There seems to be a general agreement that human language is a recent evolutionary adaptation. As such, one would expect to find that the human brain has undergone some sort of task reorganization to accommodate this new function (Worden 1998:150). While some researchers state that brain reorganization would have been a slow process (i.e. Aitchison 1998:22; Worden 1998:148), others have argued that language emerged when humans suddenly discovered an extra use for their increasingly complex brains (i.e. Bickerton 1998; Gould 1987; Chomsky 1968). According to Müller (1996:629), the human brain is larger than that of other primates and so has more interconnections, however some qualitative adaptations have taken place. For example, Broca’s area, traditionally associated with speech production, is now regarded as a cover term for several overlapping areas which involve different abilities (ibid.).

Most studies and theories of language origin focus upon specific language ‘areas’ of the brain which appear to control grammar and syntax (Kim et. al. 1997; Locke 1997; Stiles et. al. 1981). The consensus in this research indicates that the left hemisphere (LH) is specialized for most aspects of language (ibid.). Specifically, the left frontal area shows specialization for expressive language (Broca’s hypothesis), and the left temporal area appears to be specialized for receptive language (Wernicke hypothesis) (Loritz 1999; Locke 1997; Müller 1996). However, the right hemisphere (RH) appears to regulate the comprehension and production of humor, metaphor and idioms (ibid.). Additionally, the RH seems to control the cohesion and coherence in narratives (Stiles et. al. 1981).

It is often assumed that the (adult) pattern of brain organization, for higher cognitive functions, is a result of ‘innate’ properties (Müller 1996; Stiles et. al. 1981). While the basic auditory/vocal production mechanisms employed by speech can be ‘mapped’ through evolutionary history, the evolution of the language ‘area’ is still questionable (Loritz 1999). There is some evidence that this language area may have emerged from both the perceptual and motor systems (Barton 2000; Worden 1998). For example, the various ‘subdivisions’ of Broca’s area and Wernicke’s area, in addition to carrying out linguistic functions, appear to participate in the planning and execution of one or more non-speech specific task (Loritz 1999; Tirassa 1999).

However, there are several instances of functional plasticity (Loritz 1999; Pinker 1999, 1994; Stiles et. al. 1981): 1) while it is estimated that the LH plays a dominant role in the mediation of language in 95-98% of normal individuals, 19% of left-handers have RH language control; 2) normal adults have homologous areas of activation on both sides of the brain in many language tasks, although activation is typically greater in the LH; 3) this pattern can appear in either hemisphere after an early brain injury; and 4) children with various hemispheric brain lesions outperform adults with homologous injuries.

It appears that in the acquisition and development of the linguistic system, children draw on a broader array of brain structures. However, the brain mechanisms responsible for language learning are not the same mechanisms which govern the maintenance and fluent use of language in normal adults (Stiles et. al. 1981:142). Learning what a word means for the first time requires that the child to put together information from many different sources (i.e. auditory signal, the visual and tactile properties of the object, social emotional cues). This learning process may recruit brain areas which are no longer needed once the learning itself is complete. Regardless, the majority of research indicates that the left temporal lobe is of major importance to the emergence of the LH specialization for language, under normal conditions.

In contrast, one would assume that the ability to perform spatial tasks would be a much older evolutionary adaptation. Studies of children with RH and LH lesions indicate that they make the same types of spatial errors as adults with similar lesions (Stiles et. al. 1981:146). Thus, it appears that these spatial mechanisms are ‘hardwired’ in specific brain regions. In general, researchers tend to separate visual, spatial and affect recognition (and production) from language development. It would seem that living in large social groups, coupled with a long period of development to the adult stage, enabled the development of linguistic manipulation, above and beyond that of simple verbal communication. As the individual gains social experience over time, specific areas of the brain, predominantly in the LH, become specialized for processing linguistic functions. However, it must be noted that these are not simply ‘fixed’ locations, since there is evidence of plasticity to compensate for early, developmental, injuries to either brain hemisphere.

Part III Biological Mechanisms of Human Language

Vocal Anatomy

In general, human language involves three main components: auditory mechanisms, articulatory mechanisms, and a brain which coordinates the proceedings (Aitchison 1998:19). The basic properties of the ear are common to humans and nonhuman animals (Loritz 1999). In addition, humans and nonhuman primates can reliable distinguish more sounds than they can produce (ibid.; Aitchison 1998).

Human speech is the result of the action of three subsystems: respiratory, phonatory and articulatory (MacNeilage 1998:223). In all mammals, the first two of these subsystems operate as modulated cycles. The expiratory phase of the respiratory system is modulated to produce a power source for phonation (ibid.). At the phonatory level, the vocal fold vibration cycle is modulated to produce variations in fundamental frequency, heard as pitch variations (ibid.). From a physical standpoint, sound production involves the production of syllabic vocal material in a repetitive and rhythmic fashion (Locke 1998:191). This is done by raising and lowering the mandible in particular ways while phonating. The lips and tongue may be actively or passively positioned to produce various points of constriction (ibid.). MacNeilage (1998:501) has proposed that the evolutionary precursor of syllabic structure was the mandibular oscillation associated with chewing and sucking, which provides the ‘frame’ onto which the ‘content’ of specific phonemes is superimposed.

The human vocal tract anatomy differs from that of other primates. Around three months of age, the larynx begins a slow descent to its lower (adult) position, which it reaches between the ages of three to seven years (Lieberman 1998; Arensburg 1994:279). A second decent occurs in human males at puberty (ibid.). This change in larynx position enables the tongue to move both vertically and horizontally within the vocal tract, and is credited with expanding the phonetic repertoire of humans (Studdert-Kennedy 1998:208; Lieberman 1998; Lieberman and McCarthy 1999:489).

Lieberman (1998) has suggested that slight laryngeal lowering could be adaptive for “mouth breathing during extreme physical challenge, probably starting with Homo erectus”. The selection of Homo erectus (approximately 1.8 mya - 300 kya) is based upon associated cranial expansion, tool modifications and migration outside of the African continent (Tattersall and Schwartz 2000). However, there is no evidence to suggest that this physiological change could not have occurred in the Australopithecine lineages. Additionally, many mammals mouth breath when under stress or for cooling by panting, without requiring permanent larynx lowering (MacLarnon and Hewitt 1999; Fitch 2000:263).

Lieberman and McCarthy (1999) have also proposed that the lowered larynx was a by-product of upright bipedal locomotion. However, no other bipedal species has a lowered larynx (i.e. kangaroos). Another difference is that the vocal tracts of humans lack of laryngeal air sacs (Fitch 2000:263). All of the great apes, and many other nonhuman primates, have inflatable, soft walled air sacs that extend outward from the larynx and beneath the skin of the neck and thorax (Schôn Ybarra 1995:186). These sacs can hold up to 6 litres of air and are presumed to serve a vocal function, although their acoustic or adaptive significance is uncertain (ibid.).

Humans also have the ability to suppress vocal reactions, which in other primates are largely automatic (Atichison 1998:21). Finally, due to a lowered larynx and associated vocal tract lengthening, modern humans are capable of vocal mimicry (Fitch 2000:263; Atichison 1998; Donald. 1998:47). The ability to mimic other animals or natural sounds has been suggested as a possible source of spoken language (Beaken 1996:104). For an imitation to be a communicative sign, the attention of both a ‘sender’ and ‘receiver’ of the information is necessary (ibid.). According to Fitch (2000:264), the evolution of vocal imitation in the auditory domain is much easier than other forms of imitation. It is presumed that no nonhuman primate is capable of producing sounds outside of their species specific repertoire (Janik and Slater 2000:2; Snowdon 1990:216). An animal with a lowered larynx has the capacity to duplicate the vocalizations of a larger animal, thus exaggerating the impression of size conveyed by its vocalizations (Fitch 2000:263). However, evidence of vocal mimicry/learning exists in aquatic mammals (cetaceans) and certain avian species (Janik and Slater 2000:2; Hauser 1996:310; Snowdon 1990:216). Additionally, many bird species have an elongated trachea, which in turn elongates the vocal tract (Fitch 2000:264). This serves to lower the vocal frequencies and thus, exaggerate the impression of body size (ibid.)

Timing of Language Acquisition

The infant undergoes many physiological and cognitive changes during its development. Since the timing of these advances are variable and independent, it affects which behaviours can be observed during the period of language acquisition. During the first few months after birth, the infant is physiologically constrained with regards to the types of vocalizations it can produce. However, experiments indicate that prelinguistic infants are aware of elements contained within adult speech.

During the first five to seventeen weeks after birth, infants can discriminate phonemes (Werker and Desjardins 1995). At two months of age, the vocal production of Homo sapiens sapiens infants is constrained by both the physiological state and physiology of the vocal tract thus, they are only able to “emit reactional sounds which signal their current state of well being” (de Boysson-Bardies 1999). However, they appear to be attentive to the speech of adults as evidenced by the following lip movements, and are able to distinguish voices, with a preference for that of their mother (ibid.). Research has indicated that they are sensitive to the prosody of the language spoken in their immediate environment, and are able to distinguish foreign languages easily (Nazzi et. al. 2000; Aslin et. al. 1998).

Between two to five months of age, infants tend to vocalize only when lying on their backs (de Boysson-Bardies 1999). These vocalizations are almost uniquely made up of sounds which issue from the larynx and soft palate, and there does not appear to be defined phonation (ibid.). However, between four and five months, infants become capable of voluntarily modulating their vocalizations (ibid.). They seem to develop a series of vocal exercises, which manipulate both the prosodic cues (pitch of voice), sound level, and consonantal features (friction noises, nasal murmuring, rolled labials, uvular trills) (ibid.). On acquiring control of phonation, the infant can modulate the duration, pitch, and intensity of vocal productions, and identifiable ‘vowels’ and ‘consonants’ appear (ibid.). However, these are not characteristic of the syllables of spoken language. It has been suggested that through ‘playing’ with intonation, infants familiarize themselves with a number of routines and become capable of producing varied sound effects (ibid.). This controlled phonation allows infants to employ their vocalizations to communicate their emotions and demands (ibid.). Additionally, during this time of development, infants listen significantly longer to repetitions of their own names than of the names of other people, and appear to perceive and represent some objects and events (Tincoff and Jusczyk 1999).

Between four and seven months of age, infants begin to incorporate gestures which bring the forward part of the articulatory apparatus into play (Armstrong 1999. 1995, 1994; Tomasello and Brooks 1999). At this time, infants begin to lose their “encyclopedic hearing (de Boysson-Bardies 1999). They exhibit a representation of vowel space, which is adapted to the language of their environment, just as adults do (Blake 2000; Aslin et. al. 1998). Additionally, they begin to ignore elements which are generally absent from the phonetic structures of their linguistic environment” (ibid.). Six month olds attach the words ‘mommy’ and ‘daddy’ to their own parents, and not to women and men in general (Tincoff and Jusczyk 1999).

Toward the end of the sixth month, infants are capable of coordinating phonatory and supraglottal adjustments (Blake 2000). This voluntary interruption of vocalization is an essential element of vocal control” (de Boysson-Bardies 1999). Additionally, they can model the pitch of their vocalizations on those of the interacting adult (i.e. their voice is higher with their mother than with their father) and can imitate simple patterns of intonation on the basis of adult examples (ibid.; Tomasello and Brooks 1999).

Between six and ten months infants begin to ‘babble’. Canonical babbling, which is characterized by the production of simple syllables in a consonant-vowel sequence (i.e. [ba]) is quickly followed by rhythmic sequences formed by repeated consonant-vowel combinations (i.e. [baobab]) (Davis et. al. 2000; Locke and Pearson 1990). Consonant sounds tend to be occlusive and nasals, combined with low front and central vowels ([a], [æ]) (ibid.). However, there is great variation amongst infants due to individual, linguistic and cultural differences (de Boysson-Bardies 1999; Aslin et. al. 1998; Locke and Pearson 1990). Congenitally deaf infants vocalize like hearing infants but they do not babble (de Boysson-Bardies 1999; Petitto and Marentette 1991). By seven months, the vocalizations of deaf babies tend to diminish (ibid.). However, hearing impaired infants who grow up in an environment with a sign language, ‘babble’ manually by eight months of age (ibid.).

Around ten months of age, infants begin to lose their capacity to distinguish universal consonantal contrasts (de Boysson-Bardies 1999). This reorganization seems to be tied to the beginnings of word recognition (Tincoff and Jusczyk 1999). By this age, it is presumed that infants have selected a repertoire of consonants that reflect the statistical tendencies of their native language (Davis et. al. 2000; Aslin et. al. 1998).

By eleven months to thirteen months, infants begin to show definitive signs of word comprehension (Tincoff and Jusczyk 1999). While they have better control of their articulation, the majority of their vocal productions remain mono or disyllabic, with occlusives and nasals predominating (Davis et. al. 2000; Locke and Pearson 1990). These initial productions tend to resemble the most frequent context in which the words were modeled by their mothers (Dromi 1999:115). However, the effects of maternal input characteristics decline with time and are much less pronounced once the child has established a sizable vocabulary (ibid.).

In order to learn a word, the child must first learn four things: 1) pronunciation ; 2) the syntactic properties; 3) meaning; and 4) usage (Kuczaj 1999:136). Prior to the emergence of first words, children utilize gestures, facial expressions, intonation patterns, and nonsystematic vocalization for communicating their basic pragmatic intentions (Blake 2000; Dromi 1999). The beginning of the one word stage is marked by the emergence of systematic, repeated productions of phonetically consistent forms (Dromi 1999:99). During the one word stage, children might occasionally produce multiword combinations that do not yet reflect the productive syntactic abilities (Dromi 1999:100).

Researchers propose that during the first phase of the one word stage, functional words constitute the dominant class of words (Blake 2000; Dromi 1999; Tomasello and Brooks 1999). During this early stage, there is an indeterminate usage of the same words to refer either to an object or to an activity that is typically associated with that object, or to both (Dromi 1999:107). It is not important whether or not young children find it easier to learn nouns or verbs. Children may use a word as a noun and as a verb, so even the distinction between words that denote objects and those that denote actions or states is not always an easy on to identify (Kuczaj 1999:143). Word meaning acquisition is thus a comprehension based process. Children will not learn words that they have not heard. However, before children begin to acquire words, they have formed concepts of the world (Kuczaj 1999:153). The early words of young children appear to be based upon aspects of the world that they can directly experience, regardless of whether the words are nouns, verbs or adjectives (ibid.).

In general, by the age of two, a child uses between 50 and 600 words, and adds an average of 10 words per day to its vocabulary, “resulting in a vocabulary of approximately 14,000 words by the age of six” (Kuczaj 1999:133). However, while the child can now communicate simple concepts, ‘mastery’ of language has not yet been attained. By the age of four, language experience begins to affect phoneme perception and children use information about syntactic cues to infer the meaning of words (Kuczaj 1999:153; Werker and Desjardins 1995:78). This process has been called ‘syntactic bootstrapping’, and emphasizes the point that word meaning acquisition does not take place in a vacuum but occurs in a larger context (ibid.).

Children learn the rules governing the regular use of most bound morphemes before the age of five, although learning the exceptions may take many years (de Boysson-Bardies 1999). The acquisition of syntax is largely complete by the age of five (Blake 2000). However, aspects of sound, communicative, morphological and syntactic systems continue to develop (Kuczaj 1999:134). An example of this is the incorporation of paralanguage and propositional content to discern a speaker’s intent.

The paralanguage, or affect, of a speaker is conveyed through subtle vocal cues such as altering the speaking rate, pitch level or contour, and voice quality (Morton and Trehub 2001). Paralinguistic features may unintentionally reveal the speaker’s emotional state or, used intentionally, convey the attitude of the speaker. While paralinguistic cues toward attitude vary across cultures, those linked to basic emotions appear to be ‘universal’ (ibid.). In contrast, speakers can use propositional content to depict their feelings directly or to describe a situation that has positive or negative emotional implications.

While adults consider all available cues, but rely primarily on paralanguage when there is a conflict with propositional cues, children of all ages exhibit response latencies to utterances with conflicting cues, which indicate that they processed both sources of emotional information (Morton and Trehub 2001). When the cues conveyed by propositional content and affective paralanguage conflicted, four to ten year old children rely primarily on content and not on paralinguistic cues (ibid.). However, children were able to accurately label the affective paralanguage when the propositional cues to emotion were obscured by a foreign language, even though they failed the similar task in their native language (ibid.).

A possible explanation for this conflict may be that the communication of young children is more pragmatic than that of adults. Young children are not very successful when producing vocal deception, since adults are able to discern paralinguistic cues. It is not until the late teenage years, that humans begin to attain some semblance of affect management (Blake 2000; Loritz 1999). It is possible that children are unable, developmentally, to master this type of verbal ‘deception’, and they are unaware that adults have this ability. Alternately, it may simply be that adults, in general, do not engage in overt paralinguistic deception with children. If they do, the child may be able to discern paralinguistic cues in association with visual information.