The Evolution of Language

Preface.

Contents.

The Mirror System Hypothesis (MSH) of the evolution of brain mechanisms supporting language distinguishes a monkey-like mirror neuron system from a chimpanzee-like mirror system that supports simple imitation and a human-like mirror system that supports complex imitation and language. This paper briefly reviews the seven evolutionary stages posited by MSH and then focuses on the early stages which precede but are claimed to ground language. It introduces MNS2, a new model of action recognition learning by mirror neurons of the macaque brain to address data on audio-visual mirror neurons. In addition, the paper offers an explicit hypothesis on how to embed a macaque-like mirror system in a larger human-like circuit which has the capacity for imitation by both direct and indirect routes. Implications for the study of speech are briefly noted.

Semiotic dynamics is a fast growing field according to which language can be seen as an evolving and self-organizing system. In this paper we present a simple multi-agent framework able to account for the emergence of shared conventions in a population. Agents perform pairwise games and final consensus is reached without any outside control nor any global knowledge of the system. In particular we discuss how embedding the population in a non trivial interaction topology affects the behavior of the system and forces to carefully consider agents selection strategies. These results cast an interesting framework to address and study more complex issues in semiotic dynamics.

I discuss the ubiquity of power law distributions in language organisation (and elsewhere), and argue against Miller's (2000) argument that large vocabulary size is a consequence of sexual selection. Instead I argue that power law distributions are evidence that languages are best modelled as dynamical systems but raise some issues for models of iterated language learning.

Human languages are characterized by a number of universal patterns of structure and use. Theories differ on whether such linguistic universals are best understood as arbitrary features of an innate language acquisition device or functional features deriving from cognitive and communicative constraints. From the viewpoint of language evolution, it is important to explain how such features may have originated. We use computational simulations to investigate the circumstances under which universal linguistic constraints might get genetically fixed in a population of language learning agents. Specifically, we focus on the Baldwin effect as an evolutionary mechanism by which previously learned linguistic features might become innate through natural selection across many generations of language learners. The results indicate that under assumptions of linguistic change, only functional, but not arbitrary, features of language can become genetically fixed.

Compositionality is a hallmark of human language - words and morphemes can be factorially combined to produce a seemingly limitless number of viable strings. This contrasts with non-human communication systems, which for the most part are holistic - encoding a whole message through a single, gestalt form. We show that compositional language can arise automatically through grounded communication among populations of communicators. The proposed mechanism is the following: if a holistic and a compositional approach are in competition and if both structured (compositional) and atomic meanings need to be communicated, the holistic strategy becomes less successful as it does not recruit already acquired bits of language. We demonstrate the viability of this explanation through computer simulations in which artificial agents perform a communicative task. It is shown that simple reinforcement mechanisms applied during communicative interactions can account for the emergence of linguistic compositionality.

In this paper we present a computational model for the emergence of a fixed word order in the language of a society of babbling agents. In contrast to the majority of research modeling the emergence of syntactic principles, in which a very strong governing role is set aside for the semantic aspect of communication, this paper touches on the possibility that one of the most basic grammatical principles, i.e. fixed word order, can develop without direct reference to concepts of shared meaning. With its rigid data-driven approach, the system described in this paper introduces a hitherto unexplored baseline perspective to the research efforts modeling the emergence of grammatical properties in language.

In this paper, we present an agent-based simulation model for the evolution of language. This is based on a previous model proposed by the authors and inspired by Nowak's simplest mathematical model. We extend our previous work with the introduction of a significant characteristic: a world where the languages live and evolve, and which influences interactions among individuals. The main goal of this research is to present a model which shows how the presence of a topological structure influences the communication among individuals and contributes to the emergence of clusters of different languages.

The Recent Out-of-Africa human evolutionary model seems to be generally accepted. This impression is very prevalent outside palaeoanthropological circles (including studies of language evolution), but proves to be unwarranted. This paper offers a short review of the main challenges facing ROA and concludes that alternative models based on the concept of metapopulation must be also considered. The implications of such a model for language evolution and diversity are briefly reviewed.

Most studies of vocalizations with chimpanzees and Bonobos focus on the interpretation of the vocal behaviour of both captive and free-ranging groups to relate sounds produced to their semantic contexts. Spectrographic analyses reveal the acoustic structure of the vocalizations but rarely raise the question of the specific articulatory capacities of Bonobos in relation to the acoustics. This point is essential if one wants to understand the articulatory control that Bonobos have on their vocalizations. It is also important when the vocalizations of Bonobos and the sound produced by modern humans are compared.

The systematic and universal communicative behaviour that drives human beings to give honest information to conspecifics during long-lasting conversational episodes still represents a Darwinian paradox. Attempts to solve it by comparing conversation with a mere reciprocal cooperative information exchange is at odds with the reality of spontaneous language use. The Costly Signalling Theory has recently attracted attention as a tentative explanation of the evolutionary stability of language. Unfortunately, it makes the wrong prediction that only elite individuals would talk. I show that as far as social bonding is assortative in our species, generalised signalling through language becomes a viable strategy to attract allies.

Is the range of languages we observe today explainable in terms of which languages can be learned easily and which cannot? If so, the key to understanding language is to understand innate learning biases, and the process of biological evolution through which they have evolved. Using mathematical and computer modelling, we show how a very small bias towards regularity can be accentuated by the process of cultural transmission in which language is passed from generation to generation, resulting in languages that are overwhelmingly regular. Cultural evolution therefore plays as big a role as prior bias in determining the form of emergent languages, showing that language can only be explained in terms of the interaction of biological evolution, individual development, and cultural transmission.

Isolating-Monocategorial-Associational (IMA) Language is language with the following three properties: (a) morphologically isolating, without word-internal morphological structure; (b) syntactically monocategorial, without distinct syntactic categories; and (c) semantically associational, without distinct construction-specific semantic rules, compositional semantics relying instead on the association operator, which says that the meaning of a composite expression is associated with the meanings of its constituents in an underspecified fashion. IMA Language is present in the following five domains: (a) phylogeny: at some stage in evolution, early language was IMA Language; (b) ontogeny: at some stage in acquisition, early child language is IMA Language; (c) semiotics: some artificial languages are IMA Language; (d) typology: some languages are closer than others to IMA Language; and (e) cognition: IMA Language is a feature of general human cognition. This paper presents arguments pertaining to the first of these domains, namely phylogeny, citing evidence from the linguistic behaviour of captive apes which points towards the conclusion that early human language was IMA Language.

Compositionality and regularity are universals in human languages; in most languages, complex expressions are determined by their structures and their components' meanings. Based on a multi-agent computational model, the coevolution of compositionality and one type of regularity, word order, is traced during the emergence of compositional language out of holistic signals. The model modifies some questionable aspects in the Iterated Learning Model and Fluid Construction Grammar by considering the conventionalization in horizontal transmission and the gradual formation of syntactic categories which mirror the semantic categories. The model also implements a bottom-up syntactic developmental process, i.e., the global orders for regulating multiple arguments are gradually formed from simple local orders between two categories.

Although Hauser, Chomsky and Fitch (HCF/FHC) and Pinker and Jackendoff (PJ/JP) differ in the epistemic questions they ask concerning, respectively, the nature of language (what language is), and the evolution of language (what language evolved for), it will be argued that both questions are part of the same methodological framework. This framework resembles the classical manner in which scientific knowledge is to be obtained while newer epistemological methods are suggested that can complement the study of the characteristics of language and evolutionary transitions that led to language.

I describe and assess the Minimalist Program (MP) as an approach to the evolution of language. The MP is less about evolution than explanation, but if its attempt to vindicate a certain idea of 'design perfection' was successful, a deeper level of explanation would be achieved than historical narrative and functional explanation affords, and the evolution problem would be solved along the way. Arguably, a minimalist methodology is also a necessary component in any explanatory approach to language evolution, no matter its theoretical orientation. While these are clear virtues, I question the MP's central explanatory claim, that language can be understood as an optimal solution to the problem of satisfying interface conditions imposed by pre-linguistic cognitive systems.

Ambiguity is a defining property of natural language distinguishing it from artificial languages. It would seem to be dysfunctional, and therefore its ubiquity in language poses an evolutionary puzzle. This paper discusses the implications of a typical iterated learning model on the conditions under which syntactic ambiguity emerges and stabilises in language. It contrasts the purely nativist stance that language imperfections such as syntactic ambiguity are artifacts arising from internal constraints of the genetically determined language faculty with the view that they are frozen accidents persisting because they are easily learnt.

Before the evolution of languages as public conventional communication systems, pre-humans had somewhat complex private mental schemes for representing the external world. What is known about human and some animal vision suggests that proposition-like cognitive structures existed for the mental representation of perceived scenes before the advent of complex language. The structures traditionally adopted by formal Logic can be modified to conform to known constraints on the visual representation of scenes. While this modification slightly reduces the expressive power of representations (in that the meanings of some complex sentences cannot naturally be represented), it provides a unified, ontologically parsimonious, primitive notation for cognitive representations, suitable for later recruitment by complex syntactic language. The most basic semantic elements later mapped onto sentences are all present in the prelinguistic mental representation, which reflects the workings of the visual attention system.

Gärdenfors (2000) argues that natural denotations of natural language predicates are convex regions in a conceptual space. Using techniques from evolutionary game theory, the paper shows that this convexity criterion is a consequence of the evolutionary dynamics of language use.

ChickenHawk is a social-dilemma game in which the only way to win is to play "Hawk" against "Chicken." The purpose of the game is to distinguish between uncoordinated and coordinated self-sacrifice. In a test of four signaling conditions with players who belong to a culturally homogeneous population, a "cheap talk" condition led to efficient coordination, whereas signaling opportunities engaging social reputation and allowing eye-contact without speech yielded poorly coordinated altruistic behavior. The implications are: (1) without language, mere willingness to cooperate on a social dilemma is insufficient for coordinating intentions, and (2) given a sufficiently cohesive social group, language can coordinate inequitable, altruistic sacrifices of modest but real material incentives, even where fully anonymous defection is an option.

The precise timing of the emergence of language in human prehistory cannot be resolved. But the available evidence is sufficient to constrain it to some degree. This is a review and synthesis of the available evidence, leading to the conclusion that the time when speech became important for our ancestors can be constrained to be not less than 500,000 years ago, thus excluding several popular theories involving a late transition to speech.

The possibilities for a stepwise evolution of grammar are evaluated through an analysis of which components of modern human grammar are removable, and in what order, while still leaving a functional communication system. It is found that recursivity is a prime candidate for being a late evolutionary addition, with flexibility and hierarchical rules coming next. Furthermore, it is argued that recursivity need not be the unitary infinite-loop concept of formal grammars, but can evolve in several smaller steps.

Many scholars assume a connection between the evolution of language and that of distinctively human group-level morality. Unfortunately, such thinkers frequently downplay a central implication of modern Darwinian theory, which precludes the possibility of innate psychological mechanisms evolving to benefit the group at the expense of the individual. Group level moral regulation is indeed central to sexual, social and political life in all known hunter-gatherer communities. The production of speech acts would be impossible without such regulation. The challenge, therefore, is to explain on a Darwinian basis how life could have become subject to the rule of law. Only then will we have an appropriate social framework in which to contextualize our models of how language may have evolved.

The debate over the evolution of an innate language capacity seems to divide into two principle camps. The neo-Darwinian approach generally argues that human psychological modules, including the language faculty, must have arisen gradually and incrementally having been honed by natural selection. Thus Pinker, when theorizing about language evolution, sees "no reason to doubt that the principle explanation is the same as for any other complex instinct or organ, Darwin's theory of natural selection" (Pinker, 1994, 333). However, as Knight et al. (2000) have pointed out, little attention has been paid by the neo-Darwinian approach to address the causes of the emergence of novelty. The saltationist approach gleans much of its evidence from the archaeological and paleontological record, which is interpreted as unsupportive of the neo-Darwinian paradigm. Jackendoff (1999) accuses those who do not accept that language arose gradually through natural selection as having been "forced to devalue evolutionary argumentation". Jackendoff's concern seems to stem from the view that there is only one way that evolution can proceed, through gradual change driven by natural selection. My concern is for the neglect of the vast amount of evidence supporting the theory that modern humans did not emerged in a gradual, step-wise fashion, so there is no reason to believe that cognition and language evolved in this manner. Here I argue that hominins evolved through major evolutionary leaps, which may have numbered only two or three significant mutation "events". Neoteny (the retention of infant or juvenile growth rates) appears to have been a major force in the evolution of our primate ancestors and this process can explain the sudden emergence of many of the traits that define what it means to be human. Further evidence from the fossil and archaeological record supports a "sudden" emergence of human cognition and language.

No abstract received.

A major feature that sets language apart from other communication systems is the use of categorylabels—words. In addition to providing a means of communication, there is growing evidence that category labels play a role in the formation and shaping of concepts. If verbal labels help humans acquire or use category information, one can ask whether it is easier to learn labeled categories compared to unlabeled ones. Normal English-speaking adults participated in a category-learning task in which categories were labeled or unlabeled. The presence of labels facilitated the learning of unfamiliar categories and resulted in more robust category representations. The advantage for acquiring named categories was observed even though the category labels did not convey any additional information and all participants had equivalent experience categorizing the stimuli. This work provides empirical support for the idea of labels as conceptual anchor points (Clark, 1997).

In this paper we will describe the results of an experiment in which an effective communication system arises among a collection of initially non-communicating agents through a self-organization process based on an evolutionary process. Evolved agents communicate by producing and detecting five different signals that affect both their motor and signaling behavior. These signals identify features of the environment and of the agents/agents and agents/environmental relations that are crucial for solving the given problem. The obtained results also indicate that individual and social/communicative behaviors are tightly co-adapted.

The majority of extant languages have one of three basic word orders: SVO, SOV or VSO. Various hypotheses have been put forward to explain aspects of this bias, including the existence of a universal grammar, learnability imposed by non-linguistic-specific cognitive constraints, and the descent of the extant languages from a common ancestral proto-language. Here, we adopt a multi-agent model for language emergence that simulates the coevolution of a lexicon and syntax from a holistic signaling system. The syntax evolves through a process of categorization; local syntactic rules are constructed that assign a relative order (e.g., S before V) to the elements of the two categories to which each rule applies. We demonstrate that local syntax encoding the relative position of S and O are the most stable, allowing the coexistence of the global word order pairs SOV/SVO and VOS/OVS. The structure of the semantic space that the language encodes further constrains the global syntax that is stable.

Selective pressures for the evolutionary emergence of human language tend to be interpreted as social in nature, i.e., for better social communication and coordination. Using a simple neural network model of language acquisition we demonstrate that even using language for oneself, i.e., as private or inner speech, improves an individual's categorization of the world and, therefore, makes the individual's behavior more adaptive. We conclude that language may have first emerged due to the advantages it confers on individual cognition, and not only for its social advantages.

In this paper, we present a model of language acquisition which can be used to explain how children learn a grammar by interacting with their surroundings. We build upon the model proposed by Komarova et al in the context of evolution of grammars. We test our model for two situations: One, in which an individual is trying to learn a grammar in an environment where everybody uses the same grammar, and the other in which different groups in the population use different grammars.

No abstract received.

A recent proposal (Hauser, Chomsky & Fitch, 2002) suggests that the crucial defining property of human language is recursion. In this paper, following a critical analysis of what is meant by the term, I examine three reasons why the recursion-only hypothesis cannot be correct: (i) recursion is neither unique to language in humans, nor unique to our species, (ii) human language consists of many properties which are unique to it, and independent of recursion, and (iii) recursion may not even be necessary to human communication. Consequently, if recursion is not the key defining property of human language, it should not be granted special status in an evolutionary account of the system.

Within a semiogenetic theory of the emergence and evolution of the language sign, I claim that a structural-notional analysis of submorphemic data provided by certain reconstructed PIE roots and their reflexes, projected as far back as theories of the evolution of speech will permit by a principle of articulatory invariance, points to the existence of an unconscious neurophysiologically grounded strategy for 'naming' parts of the body. Specifically, it is claimed that the occlusive sounds produced by open-close movements of the mouth, which have been shown experimentally to be synchronized with open-close movements of the hand(s), may have functioned as 'core invariants'. Morphogenetically transformed into conventionalized language signs, these could have served to 'name' not only the mouth movements and articulators involved, but also the hand movements with which they appear to be coordinated, as well as the hand itself.

No abstract received.

The majority of studies on animal communication provide evidence that gestural signaling plays an important role in the communication of nonhuman primates and resembles that of pre-linguistic and just-linguistic human infants in some important ways. However, ape gestures also differ from the gestures of human infants in some important ways as well, and these differences might provide crucial clues for answering the question of how human language –at least in its cognitive and social-cognitive aspects- evolved from the gestural communication of our ape-like ancestors. The present manuscript summarizes and compares recent studies on the gestural signaling of the great apes (Gorilla gorilla, Pan paniscus, Pan troglodytes, Pongo pygmaeus) to enable a comparison with gestures in children. We focused on the three following aspects: 1) nature of gestures, 2) intentional use of gestures, 3) and learning of gestures. Our results show, that apes have multifaceted gestural repertoires and use their gestures intentionally. Although some group-specific gestures seem to be acquired via a social learning process, the majority of gestures are learned via individual learning. Importantly, all of the intentional produced gestures share two important characteristics that make them crucially different from human deictic and symbolic gestures: 1) they are almost invariably used in dyadic contexts and 2) they are used exclusively for imperative purposes. Implications for these differences are discussed.

This paper argues that the evolution of human language is a prerequisite to the evolution of human morality. Human moral systems are not possible without fully complex language. Though protolanguage can extend moral systems, the design features of human language greatly extend human moral ability. Specifically, this paper focuses on how recursion, linguistic creativity, naming ability, displacement, and compositionality extend moral systems. The argument descriptively defines altruism as self-sacrificial behavior for others and morality as how a group classifies right and wrong behavior. No comment is made on how altruism squares with the replicatory selfishness of genes, or on the controversy of group selection. However, along with Dawkins (Dawkins, 1976), the author concurs that humans can use linguistically based concepts to help constrain genetic selfishness and promote degrees of altruism and morality. Though drawing on previous research, the ideas presented here are novel to the extent that they demonstrate how the design features of language support and extend human altruism and morality.

Vocal learning is a key component of the human language faculty, and is a behaviour we share with only a few other species in nature. Perhaps the most studied example of this phenomenon is bird song which displays a number of striking parallels with human language, particularly in its development. In this paper we present a simple computational model of bird song development and then use this in a model of evolution to investigate some of the ecological conditions under which vocal behaviour can become more or less reliant on cultural transmission.

We present a framework and first set of simulations for evolving a language for communicating about space. The framework comprises two components: (1) An established mobile robot platform, RatSLAM, which has a "brain" architecture based on rodent hippocampus with the ability to integrate visual and odometric cues to create internal maps of its environment. (2) A language learning system based on a neural network architecture that has been designed and implemented with the ability to evolve generalizable languages which can be learned by naive learners. A study using visual scenes and internal maps streamed from the simulated world of the robots to evolve languages is presented. This study investigated the structure of the evolved languages showing that with these inputs, expressive languages can effectively categorize the world. Ongoing studies are extending these investigations to evolve languages that use the full power of the robots representations in populations of agents.

Many theories of language evolution assume a selection pressure for the communication of propositional content. However, if the content of such utterances is of value then information sharing is altruistic, in that it provides a benefit to others at possible expense to oneself. Close consideration of cross-disciplinary evidence suggests that speaking is in fact selfish, in that the speaker receives a direct payoff when successful communication takes place. This is congruent with the orthodox view of animal communication, and it is suggested that future research be conducted within this context.

Much of the current debate about the development of modern language from protolanguage focuses on whether the process was primarily synthetic or analytic. I investigate attested mechanisms of language change and emphasise the uncertainty inherent in the inferential nature of communication. Both synthesis and analysis are involved in the complexification of language, but the most significant pressure is the need for meanings to be reconstructible from context.

Synthetic and holistic theories of protolanguage are typically seen as being in opposition. In this paper I 1) evaluate a recent critique of holistic protolanguage 2) sketch how the differences between these two theories can be reconciled, 3) consider a more fundamental problem with the concept of protolanguage.

The paper discusses methodological issues for developing computer simulations, analytic models, or experiments in artificial language evolution. It examines a few examples, evaluation criteria, and conclusions that can be drawn from such efforts.

Simultaneous acquisition of multiple languages to a native level of fluency is common in many areas of the world. This ability must be represented in any cognitive mechanisms used for language. Potential explanations of the evolution of language must also account for the bilingual case. Surprisingly, this fact has not been widely considered in the literature on language origins and evolution. We consider any array of potential accounts for this phenomenon, including arguments by selectionists on the basis for language variation. We find scant evidence for specific selection of the multilingual ability prior to language origins. Thus it seems more parsimonious that bilingualism "came for free" along with whatever mechanisms did evolve. Sequential learning mechanisms may be able to accomplish multilingual acquisition without specific adaptations. In support of this perspective, we present a simple recurrent network model that is capable of learning two idealized grammars simultaneously. These results are compared with recent studies of bilingual processing using eyetracking and fMRJ showing vast overlap in the areas in the brain used in processing two different languages.

This paper describes evolutionary dynamics in language and presents a genetic framework of language akin to those of Croft (2000) and Mufwene (2001), where language is a complex system that inhabits, interacts with and evolves in communities of human speakers. The novelty of the present framework resides in the separation between form (phonology and syntax) and meaning (semantics), which are described as two different selection systems, connected by symbolic association and by probabilistic encoding of information.

We propose to address a series of questions related to the evolution of languages by statistical analysis of written text. We develop a "statistical signature" of a language, analogous to the genetic signature proposed by Karlin in biology, and we show its stability within languages and its discriminative power between languages. Using this representation, we address the question of its trajectory during language evolution. We first reconstruct a phylogenetic tree of IE languages using this property, in this way showing that it also contains enough information to act as a "tracking" tag for a language during its evolution. One advantage of this kind of phylogenetic trees is that they do not depend on any semantic assessment or on any choice of words. We use the "statistical signature" to analyze a time-series of documents from four romance languages, following their transition from latin. The languages are italian, french, spanish and portuguese, and the time points correspond to all centuries from III bC to XX AD.

An evolutionary perspective on signaling games is adopted to explain some semantic universals concerning truth-conditional connectives; property denoting expressions, and generalized quantifiers. The question to be addressed is: of the many meanings of a particular type that can be expressed, why are only some of them expressed in natural languages by 'simple' expressions?

This paper investigates the effect overextensions of words may have on the emergence of compositional structures in language. The study is done using a recently developed computer model that integrates the iterated learning model with the language game model. Experiments show that overextensions due to an incremental acquisition of meanings on the one hand attracts languages into compositional structures, but on the other hand introduces ambiguities that may act as an antagonising pressure.

Grammaticalisation is relevant for language evolution in two ways. First, it is possible to model grammaticalisation processes by evolutionary simulations (iterated learning). This paper provides two such models of a central step in the grammaticalisation process: the recruitment of lexical and functional words for a new functional role. These models help in better understanding the processes involved. Second, it is possible to reason backwards to earlier stages of human language. The paper argues that all that is necessary for the genesis of natural languages is the conventionality of the form-meaning association and the possibility of introducing new lexical words. Once there is a communication system of this kind, all the additional complexities of human languages follow.

We present the rationale and ongoing research of an interdisciplinary international project aiming at developing a novel theory of semiotic development, on the basis of broad developmental, cross-species and cross-cultural research. We focus on five social-cognitive domains: (i) perception and categorization, (ii) iconcity and pictures, (iii) space and metaphor, (iv) imitation and mimesis and (v) intersubjectivity and conventions, each of which is briefly described. Our main hypothesis is that what distinguishes human beings from other animals is an advanced capacity to engage in sign use, which on its part allowed for the evolution of language.

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Author Index.