Origins of Gestures and Language: Detailed Notes

Introduction

Human language is learned through social interactions, culturally transmitted, and varies across societies. Culture and language are evolutionarily related. Culture-like phenomena are observed in animals like birds, cetaceans, primates, fish, and insects. This review focuses on primates, predominantly great apes for gestures and monkeys for vocalizations.

Group-specific behaviors, such as tool use in chimpanzees (Pan troglodytes), can occur in neighboring groups with genetic differences. Most studies focus on foraging, overlooking communication. Cultural transmission exists in vocal traditions (orangutan nest-building calls, Pongo pygmaeus) and visual signaling (howler monkeys, Alouatta pigra, placing hands in front of their mouths).

A gesture is defined as a limb, head, or body movement directed at a recipient that lacks mechanical force and elicits a voluntary response. Comparative evolutionary approaches can elucidate language acquisition mechanisms. Gestures are crucial in primate communication, sharing characteristics with human language like intentionality, referentiality, and conversational rules. Studying primate gestures can reveal the evolutionary roots of human language.

This review assesses primate gestural communication, suggesting gestures played a key role in language emergence. It discusses the origins of gestures and presents four language origin theories: vocal, gestural, multimodal, and multicausal, proposing an evolutionary scenario.

Gestures: A Key Element in the Emergence of Language

Most primate studies investigate the expressed gestural repertoire, while fewer focus on the understood repertoire. The expressed repertoire is 'the set of gesture types that a signaller deploys,' while the understood repertoire is 'the set of gestures to which a recipient reacts in a way that satisfies the signaller repertoire.'

Studies include great apes such as bonobos, chimpanzees, gorillas, orangutans, small apes (gibbons, siamangs), New World monkeys (spider monkeys, squirrel monkeys, capuchins), and Old World monkeys (Campbell's monkeys, mandrills, baboons, macaques).

These studies report complex and flexible gestural communication systems. Key characteristics are repertoire size and intentionality. Primate gestural repertoire is substantial, including various gestures. For example, gorilla gestural repertoire exceeds their vocal repertoire, 33–102 gesture types versus 5–17 call types. Manual gestures constitute at least 50% of each species' repertoire, with gorillas at 73%.

The described gestures include visual (RAISE ARM, EXTEND HAND), tactile (EMBRACE, TOUCH BODY), auditory (SLAP HAND, BEAT BODY), and object manipulation (SHAKE OBJECT, THROW OBJECT).

A signaller's gesture is considered intentional if it has a social goal, directed towards a recipient via body orientation, gaze alternation, or physical contact and elicits a voluntary response indicated by gazing at the recipient or communication persistence.

Criteria differentiating intentional gestures from innate or conditioned ones include flexibility of gesture use, sensitivity to the recipient’s attentional state, and signaller’s persistence.

Flexibility of Gesture Use

Great apes use gestures flexibly. Chimpanzees use a single gesture in various contexts (play, aggression, appeasement, food, sex, nursing, grooming), and a single context can elicit diverse gestures. Great apes invent or learn new gestures in captivity and the wild.

Sensitivity to the Targeted Recipient’s Attentional State

Apes adjust gestural communication to the recipients’ attentional state, gesturing more when the recipient is oriented towards them. Visual gestures are used mainly when the recipient is looking, whereas auditory and tactile gestures are performed regardless of attention. Chimpanzees and bonobos are more sensitive to the audience effect than gorillas and orangutans.

Communication Persistence to Achieve a Social Goal

A signaller stops communicating after achieving its goal. If the initial gesture fails, the signaller repairs communication by repeating the gesture or elaborating with another gesture. Elaboration is a more reliable marker of intentionality than repetition.

Additional intentionality criteria include:

  1. Using a signal to achieve a social goal.

  2. Waiting for the recipient’s response while maintaining visual contact.

  3. Using attention-getting behaviors.

  4. Apparent satisfaction of the signaller upon achieving the goal.

The Need for a Finer Grained Categorisation of Intentionality

Intentionality and shared intentionality are key to human social cognition, playing a fundamental role in linguistic communication, cooperation, and cultural learning. Multi-criteria methods should reduce uncertainties in qualifying intentional behavior.

A study differentiating between multiple-criteria gestures and single-criterion gestures found that a finer-grained analysis is necessary to understand intentionality development at individual, population, and species levels. Prieur et al. (2018b) proposed an Intentionality Characterisation Index (ICI) to quantify intentionality, helping to compare communication systems.

The factors that should be considered range from sociodemographic characteristics of the signaller and recipient (e.g. age, sex, group, affiliation, kinship and rank status, e.g. Prieur et al., 2016a, 2017c) and socioecological factors of populations and species (e.g. habitat, social structure and dynamics, e.g. Cunningham & Janson, 2007; Bouchet, Blois-Heulin & Lemasson, 2013) to several characteristics related to context (e.g. audience effect and interactional components, e.g. Fröhlich et al., 2017; Coppinger, Cannistraci & Karaman, 2017) and of the communication signals (e.g. ICI and type of sensory modalities involved).

The literature suggests primate gestural communication likely played a role in language emergence, based on communication repertoires and multifaceted intentionality. This has led researchers to formulate hypotheses about the origins of gestures.

The Origins of Gestures

The origins of gestures are still debated with four main hypotheses/mechanisms proposed:

  1. Phylogenetic ritualisation

  2. Ontogenetic ritualisation

  3. Social learning via imitation

  4. Learning via social negotiation

Phylogenetic ritualisation involves communication displays emerging from body movements borrowed from other contexts. Ontogenetic ritualisation involves signals created by individuals shaping each other’s behavior over time. Imitative learning involves observers acquiring gestures by copying others. Social negotiation is based on a shared understanding of gestures by interactants.

Phylogenetic Ritualisation

Studies support biological inheritance of primate gesture acquisition, showing chimpanzee gestures shared among community members and similarities among genera like bonobos, chimpanzees, gorillas, and orangutans.

The repertoire tuning hypothesis suggests an originally large innate repertoire is shaped by experience. Most great ape gestures are innate, exhibiting flexibility in use but not form.

Ontogenetic Ritualisation

Studies support an ontogenetic basis for gestural acquisition, evidenced by idiosyncratic gestures and variability in gestural repertoires between groups. Interactions result in shortening physically effective actions. Gestures exhibit flexibility in use but not form.

Social Learning via Imitation

Individuals learn gestures by observing and replicating behaviors. The social learning via imitation hypothesis predicts that concordance of repertoires would be high within groups but low among groups. However, very few primate data show the presence of group-specific gestures. Although humans learn by observation, it seems that the role of imitation in great ape gestural acquisition is negligible.

Social Negotiation

Studies suggest that neither genetic channeling nor ontogenetic ritualization and social transmission through imitation explain the variability and flexibility of chimpanzee gestural interactions adequately. They proposed a revised version of the social negotiation hypothesis, which states that gestures are the output of social shaping, shared understanding of gestural meaning and mutual construction in real time by interactants.

Longitudinal data emphasize interactional experience and social exposure in gestural acquisition. Social negotiation implies mutual online adjustment and exchange of behaviors. Gestures exhibit flexibility in use and potentially form.

Towards a Consensus on the Origins of Gestures

Some data support phylogenetic ritualisation (species-typical gestures) and family-typical gestures common among genera. Other data support ontogenetic ritualisation (idiosyncratic gestures). Fine-grained analyses support social negotiation (interactional experience). Great ape gestural acquisition can be explained by these non-mutually exclusive processes. These three processes involve different mechanisms of concept learning.

Phylogenetic ritualisation requires perceptual concept learning, where objects/stimuli are categorized based on physical similarity. Ontogenetic ritualisation and social negotiation require associative concepts, where arbitrary stimuli become interchangeable due to association. These learning mechanisms may have played a fundamental role in the acquisition and development of meaningful social behaviors.

We hypothesise a scenario for the evolutionary origins of gestures. First, gestures originate from existing actions, conveying emotional state through physiological changes. Observers benefit by anticipating behavior, progressively evolving into signals. Second, ecological and social complexity shapes communicative properties, acquired through trial-and-error, shortening sequences through ontogenetic ritualisation, and adapting behaviors through social negotiation.

Theories of the Origins of Language

Research on language emergence in great apes includes teaching apes human vocalizations and studying primate gestures without human instruction. Three major theories explain language emergence:

  1. Vocal theory: Language from auditory-vocal modality.

  2. Gestural theory: Language developed from gestures.

  3. Multimodal theory: Gestural, vocal, oro-facial, and eye systems co-evolved.

The multicausal theory posits communicative signaling stems from a cost-benefit trade-off related to species, individual, context, and behavior.

The Vocal Theory of Language Origins

The vocal theory predicts calls represent a precursor of human language. Key characteristics of human language identified in primate vocalizations include:

  1. Referentiality: Alarm calls convey semantic content and urgency. Non-alarm calls convey food quality and quantity or fertile females.

  2. Protogrammar rules: Morpho-syntax is shown by complex calls or vocal sequences enriched information.

  3. Homologies in terms of articulation and acoustics by production and use of proto-vowels and proto-consonants Singly or in relatively simple syllable-like call combinations.

  4. Acoustic rhythmicity: Similar rhythmicity within the 3–8 Hz range.

  5. Conversational rules: Turn-taking, overlap avoidance, and acoustic matching.

  6. Socially determined variations: Vocal convergence based on affiliation and rank.

  7. Social learning: Juveniles learn context of use and meaning of calls.

  8. Intentionality: Changes in call rates and dynamic control over the vocal tract.

  9. Statistical regularities: Patterns consistent with Zipf’s law and Menzerath’s law.

The Gestural Theory of Language Origins

The gestural theory predicts gestures represent a precursor of human language. Arguments include:

  1. Flexibility of gestures: Gestures adapt to social context and rank, leading to variations among individuals and groups.

  2. Mirror neurons: Neurons activate both when performing and observing actions. The hand/mouth command system connects to the premotor cortex.

  3. Hemispheric specialization: Left cerebral hemisphere of Broca’s and Wernicke’s area and homologous areas in great apes. Gestural communication is right-lateralized.

  4. Interrelationships: between human spoken language and laterality in non-verbal communication with predominant use of the right hand for iconic, symbolic, deictic, tactile and auditory gestures

  5. Key Characteristics: Gestural communication in primates shares key characteristics with human language (intentionality, conversational rules, referentiality, a degree of iconicity and linguistic laws)

The Multimodal Theory of Language Origins

Communication systems are multimodal. Vocalizations imply oro-facial expressions, and gestures associate with vocalizations and eye behaviors etc. Human speech rhythm evolved from facial expressions of ancestors. Accumulated empirical and comparative evidence focusing on lip-smacking supports the hypothesis that the bimodal (visual and auditory) human speech rhythm could have evolved from the rhythmic facial expres- sions of ancestral primates.

Eye behaviors are essential for understanding, maintaining, and regulating mutual understanding. Multimodal theory: human language is the result of coevolution of gestural, vocal, oro-facial, and eye signaling.

Neurological studies suggest a dual hand/mouth command system. Gestural communication could be the precursor of the left-lateralized intentional communication system of primates. This system would have gradually incorporated intentional vocalizations and oro-facial expressions to elaborate the multimodal nature of our language.

The Multicausal Theory of Language Origins

Many factors influence primate communication. These include:

  1. Species characteristics Ecological and social lifestyle

  2. A genetic basis for primate communication systems and effects of demographic and social factors

  3. Context-related characteristics Emotional valence and behavioural context, various interactional components

  4. The Behavior (i.e. type of signal such as the gesture SLAP HAND) and its characteristics impact the communication systems of primates. Moreover, various characteristics can influence their signalling behaviour, mainly the use of different types of uni- or multimodal and multicomponent signalling

Similarities and dissimilarities in signaling result from differences in the costs and benefits of signal production and processing. Key factors and associated abilities would have been selected for and developed based on a cost–benefit trade-off. (Fig. 3)

Human language arose from cognitive enrichment with lifestyle changes. Bipedal posture allowed display and refinement of gestures and adaptation of the vocal tract. An intense daily interactions promoted cooperative relationships. The reduction of of human disturbance has shaped our social communication system, particularly of vocal communication.

Language and speech, once thought unique to modern humans, are ancient communication systems shared with Neanderthals. Human communication systems are inevitably still evolving in response to our sociocognitive–communication environment.

Language properties are shared with gestures, vocalizations, oro-facial expressions, and eye behaviors. Similarities and dissimilarities result from costs and benefits of signaling. This is the multicausal theory.

We need comprehensive (multimodal and multifactorial) approach to understand primate social cognition and communication skills.

Future Directions

Empirical evidence on language properties is limited. Important issues for future research:

  1. Signaling behavior based on language properties.

  2. Relationships between emotion and intentional signals.

  3. Expressed and understood repertoires.

  4. Signal asymmetries.

  5. Relationships between communication functions and psychological characteristics.

  6. Language-like properties in primate communication systems.

  7. Statistical and methodological tools.

  8. Fine-grained evolutionary approach.

Conclusions

Research suggests gestures played a key role in language emergence. The origins of gestures involve phylogenetic ritualisation, ontogenetic ritualisation, and social negotiation. In second place, increasing behavioral and neurological evidence supports a multimodal origin of language: gestural, vocal, oro-facial and eye components Multicausal theory: human communicative signaling evolved in response to a cost–benefit trade-off related
to species, individual, context, and behavior.

Further research should deepen our understanding of primate communication systems.