For a long time, human language has been assumed to be genetically determined and therefore the product of biological evolution. It is only within the last decade that researchers have begun to investigate more closely the domaingeneral cognitive mechanisms of cultural evolution as an alternative explanation for the origins of language. Most of this more recent work focuses on the role of imperfect cultural transmission and abstracts away from the mechanisms of communication. Specifically, models developed to study the cultural evolution of language—both theoretical and computational—often tacitly assume that linguistic signals fully specify the meaning they communicate. They imply that ignoring the fact that this is not the case in actual language use is a justified idealisation which can be made without significant consequences. In this thesis, I show that by making this idealisation, we miss out on the extensive explanatory potential of an empirically attested property of language: its pragmatic plasticity. The meaning that a signal comes to communicate in a specific context usually differs to a certain degree from its conventional meaning. This thesis (i) introduces a model of the cultural evolution of language that acknowledges and incorporates the fact that communication exhibits pragmatic plasticity and (ii) explores the explanatory potential of this fact with regard to language evolution. The thesis falls into two parts. In the first part, I develop the model conceptually. I begin by analysing the components of extant models of general cultural evolution and discuss how models of language change and linguistic evolution map onto them. Innovative use is identified as the motor of cultural evolution. I then conceptualise the cognitive mechanisms underlying innovative language use and argue that they originate in pre-linguistic forms of ostensive-inferential communication. In a next step, the identified mechanisms are employed to provide a unified account of the two main explananda of evolutionary linguistics, the emergence of symbolism and the emergence of grammar. Finally, I discuss the implications of the presented analysis for the so-called proto-language debate. In the second part of the thesis, I propose a computational implementation of the developed conceptual model. This computational implementation allows for the simulation of the cultural emergence and evolution of symbolic communication and provides a laboratory-like environment to study individual aspects of this process. I employ such computer simulations to explore the role that pragmatic plasticity plays in the development of the expressivity, signal economy and ambiguity of emerging and evolving symbolic communication systems. As its main contribution to the study of language evolution, this thesis shows that a model of linguistic cultural evolution that incorporates the notion of pragmatic plasticity has the potential to explain two crucial evolutionary puzzles, namely (i) how language can emerge from no language, and (ii) how language can come to exhibit the appearance of design for communication. The proposed usage-based model of language evolution bridges the evolutionary gap between no language and language by identifying ostensive-inferential communication as the continual aspect present in both stages, and by demonstrating that the cognitive mechanisms involved in ostensive-inferential communication are sufficient for the transition from one stage to the other.

The ability to learn multiple languages simultaneously is a fundamental human linguistic capacity. Yet there has been little attempt to explain this in evolutionary terms. Perhaps one reason for this lack of attention is the idea that monolingualism is the default, most basic state and so needs to be explained before considering bilingualism. When thinking about bilingualism in this light, a paradox appears: Intuitively, learning two languages is harder than learning one, yet bilingualism is prevalent in the world. Previous explanations for linguistic diversity involve appeals to adaptation for group resistance to freeriders. However, the first statement of the paradox is a property of individuals, while the second part is a property of populations. This thesis shows that the properties of cultural transmission mean that the link between individual learning and population-level phenomena can be complex. A simple Bayesian model shows that just because learning one language is easier than two, it doesn't mean that monolingualism will be the most prevalent property of populations. Although this appears to resolve the paradox, by building models of bilingual language evolution the complexity of the problem is revealed. A bilingual is typically defined as an individual with "native-like control of two languages" (Bloomfield, 1933, p. 56), but how do we define a native speaker? How do we measure proficiency? How do we define a language? How can we draw boundaries between languages that are changing over large timescales and spoken by populations with dynamic structures? This thesis argues that there is no psychological reality to the concept of discrete, monolithic, static `languages' - they are epiphenomena that emerge from the way individuals use low-level linguistic features. Furthermore, dynamic social structures are what drives levels of bilingualism. This leads to a concrete definition of bilingualism: The amount of linguistic optionality that is conditioned on social variables. However, integrating continuous variation and dynamic social structures into existing top-down models is difficult because many make monolingual assumptions. Subsequently, introducing bilingualism into these models makes them qualitatively more complicated. The assumptions that are valid for studying the general processes of cultural transmission may not be suitable for asking questions about bilingualism. I present a bottom-up model that is specifically designed to address the bilingual paradox. In this model, individuals have a general learning mechanism that conditions linguistic variation on semantic variables and social variables such as the identity of the speaker. If speaker identity is an important conditioning factor, then `bilingualism' emerges. The mechanism required to learn one language in this model can also learn multiple languages. This suggests that the bilingual paradox derives from focussing on the wrong kind of question. Rather than having to explain the ability to learn multiple languages simultaneously as an adaptation, we should be asking how and why humans developed a flexible language learning mechanism. This argument coincides with a move in the field of bilingualism away from asking `how are monolinguals and bilinguals different?' to `how does the distribution of variation affect the way children learn?'. In this case, while studies of language evolution look at how learning biases affect linguistic variation, studies of bilingualism look at how linguistic variation affects learning biases. I suggest that the two fields have a lot to offer each other.

First systematically discussed by Darwin (1871), theories of a musical precursor to language have seen a revival in recent years, with researchers such as Tecumseh Fitch, Stephen Brown, and Stephen Mithen invigorating the field. The view that language and music have an evolutionary relationship has been discussed in light of recent comparative, musicological, and biological findings. However, little empirical data have been presented to support such theories. This thesis aims to address this oversight, by presenting a novel experimental paradigm, which tests the prediction of a novel hypothesis for the evolution of language from a musical precursor. The aim of this thesis is to encourage discussion and provide a framework for the empirical investigation of music’s role in the evolution of language. As a first step to addressing this relative dearth of empirical research, a hypothesis is outlined which describes a stable system of signalling cognitive ability through the transmission of culturally-learned, complex, music-like sequences. This is not hypothesised to have been semantically meaningful, rather a system which supported the honest transmission of information about the abilities of potential allies. Such a learned sequential precursor (LSP) to language would require both increased cognitive capacity and an investment of time and energy in learning. These requirements ensured the honesty of signalling, and so perceivers of the LSP could use it as a reliable indicator of the cognitive ability of producers. This was a necessary stage in evolution, prior to protolanguage, in which individuals exhibited a complex learned, culturally-transmitted, music-like signalling system. Such a learned sequential precursor may have arisen through a pressure for the reliable indication of cognitive ability, brought about by environmental and social changes with the advent of Homo erectus. These social changes included a new urge to cooperate, and so this precursor is proposed to have emerged and developed through collaborative partner choice. Perceivers of the system used cues within the musical sequences in order to determine the quality of a producer as a collaborative partner. Empirical tests are presented, which support the hypothesised LSP. The first study tested the complexity aspect of the hypothesis, asking participants to rate complex and non-complex pieces of music according to how much they liked the piece, how familiar it sounded, how attractive and intelligent they found the person who created it, and how likely they were to choose to collaborate with this individual. It was found that complexity was preferred under all measures but one, that of familiarity. The second, main, study predicted that a correlation should be found between measures of cognitive ability that are relevant to musical learning (processing speed and intelligence) and measures of musical learning (ability to replicate and recall target pieces, and make creative pieces). This prediction was upheld, supporting the hypothesis that a learned sequential precursor could have acted as an honest signal of cognitive ability. No correlations were found between these abilities and a measure of physical quality, supporting the hypothesis that this system may have undergone social selection. The third study further tested the question of selection and choice, predicting that collaborative partner choice was key to the selection of this learned sequential precursor. Raters were asked to rate the sexual or collaborative ability of performers of pieces of music, based solely on their musical output. This study has yielded interesting tendencies, but no statistical support of the hypothesis that collaborative partner choice was more important than mate choice in this system. Taken together, these empirical studies support the hypothesis of a musical, learned sequential system of signalling cognitive ability. At the moment, the question of the selection of this precursor remains open, with hopes that further studies can address this question. The methodology used here draws together approaches from birdsong research, evolutionary psychology, and musicological research, in an attempt to prompt further interdisciplinary investigation into the role of music in the evolution of language.

This thesis concerns the evolution of language. A proliferation of theoretical models have been presented in recent years purporting to offer evolutionary accounts for various aspects of modern languages. These models rely heavily on abstract mechanistic models of the production and reception of language by modern humans, drawn from various approaches in linguistics which aim at such models. A very basic and ubiquitous assumption is that expressions have meaning in virtue of being associated with internal representations, and that therefore the evolution of language can be modelled on the basis of individuals trying to produce external manifestations of these internal “meanings”. I examine the role of this assumption in language evolution theorising, and review evidence from neuroscience and first language acquisition relevant to the validity of this assumption. The chaotic nature of the relationship between “meaning” and the brain undermines the supposition that the evolution of language was driven by spontaneous association between internal structures and external forms. I then turn to the philosophical basis of language evolution theorising, adopting a Wittgensteinian perspective on the cognitive interpretation of linguistic theories. I argue that the theoretical apparatus of such approaches is embedded in language games whose complicated rules relate to linguistic behaviour (and idealisations of that behaviour) but not to neural organisation. The reinterpretation of such descriptions of language as descriptions of the internal structures of language users is rejected as a grammatical confusion: if the rules for constructing linguistic theory descriptions do not mention neural structures, then theoretical descriptions of the linguistic abilities of an individual say nothing non-trivial about their internal brain structure. I do not deny that it would, in principle, be possible to reduce linguistic theories (reinterpreted as mechanistic descriptions) to neural structures, but claim that this possibility is guaranteed only by leaving the practice of re-describing physical brain descriptions entirely unconstrained. Thus the idea that we can reasonably infer the behaviour of humans and prehumans in more primitive communicative environments by manipulation of the models of linguistic theories is unfounded: we have no idea how such a manipulation would translate into statements about neural organisation, and so no idea how plausible such statements about earlier neural organisation (and the resultant behaviours) are. As such, cognitive interpretations of linguistic theories provide no better ground for statements about behaviour during earlier stages in the evolution of language than guessing. Rejecting internal-mechanism based accounts as unfounded leaves the evolution of language unexplained. In the latter parts of this thesis, I offer a more neutral approach which is sensitive to the limited possibilities available for making predictions about human (and pre-human) behaviour at earlier stages in the evolution of language. Rather than focusing on the individual and imputed internal language machinery, the account considers the communicative affordances available to individuals. The shifts in what individuals can learn to do in interaction with others, that result in turn from the learning of interactive practices by others, form the basis of this account. General trends in the development of communicative affordances are used to account for generalisations over attested semantic change, and to suggest how certain aspects of modern language use developed without simply assuming that it is “natural” for humans to (spontaneously) behave in these ways. The model is used in an account of the evolution and common structure of colour terms across different languages.

Human languages are not just tools for transmitting cultural ideas, they are themselves culturally transmitted. This single observation has major implications for our understanding of how and why languages around the world are structured the way they are, and also for how scientists should be studying them. Accounting for the origins of what turns out to be such a uniquely human ability is, and should be, a priority for anyone interested in what makes us different from every other lifeform on Earth. The way the scientific community thinks about language has seen considerable changes over the years. In particular, we have witnessed movements away from a purely descriptive science of language, towards a more explanatory framework that is willing to embrace the difficult questions of not just how individual languages are currently structured and used, but also how and why they got to be that way in the first place. Seeing languages as historical entities is, of course, nothing new in linguistics. Seeing languages as complex adaptive systems, undergoing processes of evolution at multiple levels of interaction however, is. Broadly speaking, this thesis explores some of the implications that this perspective on language has, and argues that in addition to furthering our understanding of the processes of biological evolution and the mechanisms of individual learning required specifically for language, we also need to be mindful of the less well-understood cultural processes that mediate between the two. Human communication systems are not just direct expressions of our genes. Neither are they independently acquired by learners anew at every generation. Instead, languages are transmitted culturally from one generation to another, creating an opportunity for a different kind of evolutionary channel to exist. It is a central aim of this thesis to explore some of the adaptive dynamics that such a cultural channel has, and investigate the extent to which certain structural and statistical properties of language can be directly explained as adaptations to the transmission process and the learning biases of speakers. In order to address this aim, this thesis takes an experimental approach. Building on a rich set of empirical results from various computational simulations and mathematical models, it presents a novel methodological framework for exploring one type of cultural transmission mechanism, iterated learning, in the laboratory using human participants. In these experiments, we observe the evolution of artificial languages as they are acquired and then transmitted to new learners. Although there is no communication involved in these studies, and participants are unaware that their learning efforts are being propagated to future learners, we find that many functional features of language emerge naturally from the different constraints imposed upon them during transmission. These constraints can take a variety of forms, both internal and external to the learner. Taken collectively, the data presented here suggest several points: (i) that iterated language learning experiments can provide us with new insights about the emergence and evolution of language; (ii) that language-like structure can emerge as a result of cultural transmission alone; and (iii) that whilst structure in these systems has the appearance of design, and is in some sense ‘created’ by intentional beings, its emergence is in fact wholly the result of non-intentional processes. Put simply, cultural evolution plays a vital role in language. This work extends our framework for understanding it, and offers a new method for investigating it.

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In this thesis, I use an experimental model to investigate the role of social pressures in stimulating language divergence. Research into the evolution of cooperation has emphasised the usefulness of ingroup markers for swiftly identifying outsiders, who pose a threat to cooperative networks. Mechanisms for avoiding cheats and freeriders, which tend to rely on reputation, or on (explicit and implicit) contracts between individuals, are considerably less effective against short-term visitors. Outsiders, moreover, may behave according to different social norms, which may adversely affect cooperative interactions with them. There are many sources of markers by which insiders and outsiders can be distinguished, but language is a particularly impressive one. If human beings exploit linguistic variation for this purpose, we might expect the exploitation to have an influence on the cultural evolution of language, and to be involved in language divergence, since it introduces a selective pressure, by which linguistic variants are selected on the basis of their social significance. However, there is also a neutral, mechanistic model of dialect formation that relies on unconscious accommodation between interlocutors, coupled with variation in the frequency of interaction, to account for divergence. In studies of real-world communities, these factors are difficult to tease apart. The model described in this thesis put real speakers in the artificial environment of a computer game. A game consisted of a series of rounds in which players were paired up with each other in a pseudo-random order. During a round, pairs of players exchanged typed messages in a highly restricted artificial "alien language". Each player began the game with a certain number of points, distributed between various resources, and the purpose of sending messages was to negotiate to exchange these resources. Any points given away were worth double to the receiver, so, by exchanging resources, players could accumulate points for their team. However, the pairings were anonymous: until the end of a round, players were not told who they had been paired with. This basic paradigm allowed the investigation of the major factors influencing language divergence, as well as the small-scale individual strategies that contribute to it. Two major factors were manipulated: frequency of interaction and competitiveness. In one condition, all players in a game were working together; in another condition, players were put into teams, such that giving away resources to teammates was advantageous, but giving them to opponents was not. This put a pressure on players to use variation in the alien language to mark identity. A combination of this pressure and a minimum level of interaction between teammates was found to be sufficient for the alien language to diverge into "dialects". Neither factor was sufficient on its own. The results of these experiments suggest that a pressure for the socially based selection of linguistic variants can lead to divergence in a very short time, given sufficient levels of interaction between members of a group.

Domain-specific languages can significantly speed up the development of software applications. However, it usually takes a few iterations of the language design before it achieves such power. At the same time, many domains tend to evolve quite often today, which implies that domain-specific languages have to evolve accordingly. Thus, being able to evolve a language in a painless manner is crucial. Unfortunately, current state-of-the-art research does not provide enough answers on how to efficiently evolve domain-specific languages. We present an approach to evolving a language in order to reduce the amount of code cloning it introduces. The approach specifically targets those languages whose design causes users to create many duplicated code segments. We target domain-specific languages as they tend to be more challenging to evolve due to their specifics, but the approach may be applicable to general purpose programming languages as well. The approach was tested on a real-world domain-specific language that is used in a financial domain. We proposed three improvements and current users helped us evaluate them. We found that the proposed improvements would reduce code cloning, which provides evidence that the approach can be used in a real-world environment. Furthermore, this work provides a solid basis for further research in the area of application of code cloning detection results. In particular, code cloning detection results and the ideas we presented show potential to be extended and used to facilitate domain analysis.

Programmers rely on programming idioms, design patterns, and workaround techniques to express fundamental design not directly supported by the language. Evolving languages often address frequently encountered problems by adding language and library support to subsequent releases. By using new features, programmers can express their intent more directly. As new concerns, such as parallelism or security, arise, early idioms and language facilities can become serious liabilities. Modern code sometimes bene fits from optimization techniques not feasible for code that uses less expressive constructs. Manual source code migration is expensive, time-consuming, and prone to errors. This dissertation discusses the introduction of new language features and libraries, exemplifi ed by open-methods and a non-blocking growable array library. We describe the relationship of open-methods to various alternative implementation techniques. The benefi ts of open-methods materialize in simpler code, better performance, and similar memory footprint when compared to using alternative implementation techniques. Based on these findings, we develop the notion of source code rejuvenation, the automated migration of legacy code. Source code rejuvenation leverages enhanced program language and library facilities by finding and replacing coding patterns that can be expressed through higher-level software abstractions. Raising the level of abstraction improves code quality by lowering software entropy. In conjunction with extensions to programming languages, source code rejuvenation o ers an evolutionary trajectory towards more reliable, more secure, and better performing code. We describe the tools that allow us efficient implementations of code rejuvenations. The Pivot source-to-source translation infrastructure and its traversal mechanism forms the core of our machinery. In order to free programmers from representation details, we use a light-weight pattern matching generator that turns a C like input language into pattern matching code. The generated code integrates seamlessly with the rest of the analysis framework. We utilize the framework to build analysis systems that find common workaround techniques for designated language extensions of C 0x (e.g., initializer lists). Moreover, we describe a novel system (TACE | template analysis and concept extraction) for the analysis of uninstantiated template code. Our tool automatically extracts requirements from the body of template functions. TACE helps programmers understand the requirements that their code de facto imposes on arguments and compare those de facto requirements to formal and informal specifications.

This thesis centres around a sensory theory of protolanguage emergence, or STP. The STP proposes that shared biases to make associations between sensory modalities provided the basis for the emergence of a shared protolinguistic lexicon. Crucially, this lexicon would have been grounded in our perceptual systems, and thus fundamentally non-arbitrary. The foundation of such a lexicon lies in shared cross-modal associations: biases shared among language users to map properties in one modality (e.g., visual size) onto another (e.g., vowel sounds). While there is broad evidence that we make associations between a variety of modalities (Spence, 2011), this thesis focuses specifically on associations involving linguistic sound, arguing that these associations would have been most important in language emergence. Early linguistic utterances, by virtue of their grounding in shared cross-modal associations, could be formed and understood with high mutual intelligibility. The first chapter of the thesis will outline this theory in detail, addressing the nature of the proposed protolanguage system, arguing for the utility of non-arbitrariness at the point of language emergence, and proposing evidence for the likely transition form a non-arbitrary protolanguage to the predominantly arbitrary language systems we observe today. The remainder of the thesis will focus on providing empirical evidence to support this theory in two ways: (i) presenting experimental data showing evidence of shared associations between linguistic sound and other modalities, and (ii) providing evidence that such associations are evident cross-linguistically, despite the predominantly arbitrary nature of modern languages. Chapter two will examine well-documented associations between vowel quality and physical size (e.g., /i/ is small, and /a/ is large; Sapir, 1929). This chapter presents a new experimental approach which fails to find robust associations between vowel quality and size absent the use of a forced choice paradigm. Chapter three turns to associations between linguistic sound and shape angularity, taking a critical perspective on the classic takete/maluma experiment (Kohler, 1929). New empirical evidence shows that the acquisition of visual word forms plays a highly influential role in mediating associations between linguistic sound and angularity, but that associations between linguistic sound and visual form also play a minor role in auditory tasks. Chapter four will examine a relatively unexplored modality: taste. A simple survey which asks participants to choose non-words to match representative tastes shows that certain linguistic sounds are preferred for certain food items. In a more detailed study, we use a more direct perceptual matching task with actual tastants and synthesises speech sounds, further showing that people make robust shared associations between linguistic sound and taste. Chapter five returns to the visual modality, considering previously unexmained associations between linguistic sound and motion, specifically the feature of speed. This study demonstrates that people do make robust associations between the two modalities, particularly for vowel quality. Chapter six will aim to take a different empirical approach, considering non-arbitrariness in natural language. Motivated by the experimental data from the previous chapters, we turn to corpus analyses to assess the presence of non-arbitrariness in natural language which concurs with behavioural data showing linguistic cross-modal associations. First, a corpus analysis of taste synonyms in English shows small but significant correlations between form and meaning. With the goal of addressing the universality of specific sound-meaning associations, we examine cross-linguistic corpora of taste and motion terms, showing that particular phonological features tend to connect to certain tastes and types of motion across genetically and geographically distinct languages. Lastly, the thesis will conclude by considering the STP in light of the empirical evidence presented, and suggesting possible future empirical directions to explore the theory more broadly.