This list of my academic papers is organised by method. Here is my Google Scholar page.
Synthetic philosophy
Analysing and linking findings from multiple fields, to achieve deeper understanding of complex phenomena.
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The rapid growth of cultural evolutionary science, its expansion into numerous fields, its use of diverse methods, and several conceptual problems have outpaced corollary developments in theory and philosophy of science. This has led to concern, exemplified in results from a recent survey conducted with members of the Cultural Evolution Society, that the field lacks ‘knowledge synthesis’, is poorly supported by ‘theory’, has an ambiguous relation to biological evolution and uses key terms (e.g. ‘culture’, ‘social learning’, ‘cumulative culture’) in ways that hamper operationalization in models, experiments and field studies. Although numerous review papers in the field represent and categorize its empirical findings, the field's theoretical challenges receive less critical attention even though challenges of a theoretical or conceptual nature underlie most of the problems identified by Cultural Evolution Society members. Guided by the heterogeneous ‘grand challenges’ emergent in this survey, this paper restates those challenges and adopts an organizational style requisite to discussion of them. The paper's goal is to contribute to increasing conceptual clarity and theoretical discernment around the most pressing challenges facing the field of cultural evolutionary science. It will be of most interest to cultural evolutionary scientists, theoreticians, philosophers of science and interdisciplinary researchers.
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Non-human great apes inform one another in ways that can seem very humanlike. Especially in the gestural domain, their behavior exhibits many similarities with human interaction, meeting widely used empirical criteria for intentionality. At the same time, there remain some manifest differences, most obviously the enormous range and scope of human expression. How to account for these similarities and differences in a unified way remains a major challenge. Here we make a key distinction between the expression of intentions (Ladyginian) and the expression of specifically informative intentions (Gricean), and we situate this distinction within a ‘special case of’ framework for classifying different modes of attention manipulation. We hence describe how the attested tendencies of great ape interaction—for instance, to be dyadic rather than triadic, to be about the here-and-now rather than ‘displaced’, and to have a high degree of perceptual resemblance between form and meaning—are products of its Ladyginian but not Gricean character. We also reinterpret video footage of great ape gesture as Ladyginian but not Gricean, and we distinguish several varieties of meaning that are continuous with one another. We conclude that the evolutionary origins of linguistic meaning lie in gradual changes in not communication systems as such, but rather in social cognition, and specifically in what modes of attention manipulation are enabled by a species’ cognitive phenotype: first Ladyginian and in turn Gricean. The second of these shifts rendered humans, and only humans, ‘language ready’.
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PDF (including 18 commentaries and our response, ‘Being ostensive’)
Human expression is open-ended, versatile, and diverse, ranging from ordinary language use to painting, from exaggerated displays of affection to micro-movements that aid coordination. Here we present and defend the claim that this expressive diversity is united by an interrelated suite of cognitive capacities, the evolved functions of which are the expression and recognition of informative intentions. We describe how evolutionary dynamics normally leash communication to narrow domains of statistical mutual benefit, and how expression is unleashed in humans. The relevant cognitive capacities are cognitive adaptations to living in a partner choice social ecology; and they are, correspondingly, part of the ordinarily developing human cognitive phenotype, emerging early and reliably in ontogeny. In other words, we identify distinctive features of our species' social ecology to explain how and why humans, and only humans, evolved the cognitive capacities that, in turn, lead to massive diversity and open-endedness in means and modes of expression. Language use is but one of these modes of expression, albeit one of manifestly high importance. We make cross-species comparisons, describe how the relevant cognitive capacities can evolve in a gradual manner, and survey how unleashed expression facilitates not only language use, but also novel behaviour in many other domains too, focusing on the examples of joint action, teaching, punishment, and art, all of which are ubiquitous in human societies but relatively rare in other species. Much of this diversity derives from graded aspects of human expression, which can be used to satisfy informative intentions in creative and new ways. We aim to help reorient cognitive pragmatics, as a phenomenon that is not a supplement to linguistic communication and on the periphery of language science, but rather the foundation of the many of the most distinctive features of human behaviour, society, and culture.
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The last 30 years has seen the emergence of a self-styled ‘evolutionary’ paradigm within psychology (henceforth, EP). EP is often presented and critiqued as a distinctive, contentious paradigm, to be contrasted with other accounts of human psychology. However, little attention has been paid to the sense in which those other accounts are not also evolutionary. We outline the core commitments of canonical EP. These are, from least distinctive to most: mechanism, interactionism, functionalism, adaptationism, and functional specialization. We argue that the minimal requirement for an approach to psychology to qualify as evolutionary in an important sense is functionalism. This is because the notion of functional design in organismal structures presupposes a history of evolution by natural selection. On this criterion, we argue, most, perhaps all of psychology qualifies as evolutionary, either implicitly or explicitly. We review several approaches that are typically contrasted with EP, showing that these are all evolutionary too by our criteria. We suggest that the EP/non-EP dichotomy be retired. However, though all psychology is evolutionary, psychologists do not always need to foreground evolution in their research, just as is true for biologists. At the same time, more space for evolution does not mean any less space for environment, context, culture, meaning or agency.
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..the notion of open society is an attempt to answer the question of how we can most effectively live together in large and modern environments… Here I present an updated model of the panhuman cognitive phenotype (“human nature”) based on the findings of modern evolutionary, cognitive, and anthropological sciences; and I summarize what I believe these findings imply for how to think about collective governance… I shall describe the human mind as a primarily social mind, far more finely tuned to the challenges of living together than we understood even two decades ago; and I shall conclude that we should embrace far more overtly open approaches to governance. Standard liberal demands made in the name of open society do not go far enough.
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According to several interlinked and influential lines of argument, human minds have been shaped by natural selection so as to include biological adaptations with the evolved, naturally selected function to facilitate the transmission of cultural knowledge. This ‘cultural minds’ hypothesis has proved highly influential, and if it is correct it is a major step forward in understanding how and why humans have survived and prospered in a hugely diverse range of ecologies. It can be contrasted with a ‘social minds’ hypothesis, according to which cultural transmission occurs as an outcome, but not the biologically evolved function, of social cognition the domain of which is relatively small-group interaction. Here, I critique the cultural minds hypothesis and I argue that the data favour the social minds perspective. Cultural phenomena can clearly emerge and persist over time without cognitive adaptations for cultural transmission. Overtly intentional communication plays an especially pivotal role.
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A short paper arguing that there is a substantial divide between the cognitive sciences and the social sciences. Addressing this divide is a key problem that should receive greater research attention.
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Non-cognitive gadgets are fancy tools shaped to meet specific, local needs. Cecilia Heyes defines cognitive gadgets as dedicated psychological mechanisms (e.g. cooking and sporting expertise) created through social interactions and culturally, not genetically, inherited by humans. She has boldly proposed that many human cognitive mechanisms (including imitation, numeracy, literacy, language and mindreading) are gadgets. If true, these claims would have far-reaching implications for our scientific understanding of human social cognition. Here we assess Heyes’s cognitive gadget approach as it applies to mindreading. We do not think that the evidence supports Heyes’s thought-provoking thesis that human children are taught to read minds the way they are taught to read words. We highlight a potential circularity lurking behind this analogy, and we explain why we are unpersuaded by Heyes’s anti-mentalistic proposal for handling data inconsistent with the gadget view, which others take to be evidence for mindreading in human infancy. We conclude that while human minds may well be filled with gadgets, mindreading is unlikely to be one of them.
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Art theory has consistently emphasised the importance of situational, cultural, institu- tional and historical factors in viewers’ experience of fine art. However, the link between this heavily context-dependent interpretation and the workings of the mind is often left unexamined. Drawing on relevance theory—a prominent, cogent and productive body of work in cognitive pragmatics—we here argue that fine art achieves its effects by prompting the use of cognitive processes that are more commonly employed in the interpretation of words and other stimuli presented in a communicative context. We describe in particular how institutional factors effectively co-opt these processes for new ends, allowing viewers to achieve cognitive effects that they otherwise would not, and so provide cognitivist backing for an Institutional Theory of Art, such as that put forward by Arthur Danto. More generally, we situate and describe the Western fine art tradition as a phenomenon that is a consequence of both the cognitive processes involved in communication, and of cultural norms, practices and institutions.
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Cultural attraction theory (CAT) is a research agenda the purpose of which is to develop causal explanations of cultural phenomena. CAT is also an evolutionary approach to culture, in the sense that it treats culture as a population of items of different types, with the frequency of tokens of those types changing over time. Now more than 20 years old, CAT has made many positive contributions, theoretical and empirical, to the naturalization of the social sciences. In consequence of this growing impact, CAT has, in recent years, been the subject of critical discussion. Here, we review and respond to these critiques. In so doing, we also provide a clear and concise introduction to CAT. We give clear characterizations of CAT's key theoretical notions, and we outline how these notions are derived from consideration of the natural character of cultural phenomena. This naturalistic quality distinguishes CAT from other evolutionary approaches to culture.
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Pragmatics has historically played a relatively peripheral role in language evolution research. This is a profound mistake. Here I describe how a pragmatic perspective can inform language evolution in the most fundamental way: by making clear what the natural objects of study are, and hence what the aims of the field should be.
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What is meaning? While traditionally the domain of philosophy and linguistics, this question, and others related to it, is critical for cognitive and comparative approaches to communication. This short essay provides a concise and accessible description of how the term meaning can and should be used, how it relates to ‘intentional communication’, and what would constitute good evidence of meaning in animal communication, in the sense that is relevant for comparisons with human language.
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Comparisons with the cognition and communication of other species have long informed discussions of the origins and evolution of human communication and language. This research has often focused on similarities and differences with the linguistic code, but more recently there has been an increased focus on the social-cognitive foundations of linguistic communication. However, exactly what these comparisons tell us is not clear because the theoretical concepts used in the animal communication literature are different from those used in the corresponding literature on human communication, specifically those used in linguistic pragmatics. In this article, I bridge the gap between these two areas and in doing so specify exactly what great ape communication tells us about the origins of human communication and language. I conclude that great ape communication probably does not share the same social-cognitive foundations as linguistic communication but that it probably does involve the use of metacognitive abilities that, once they evolved to a more sophisticated degree, were exapted for use in what is an evolutionarily novel form of communication: human ostensive communication. This in turn laid the foundations for the emergence of linguistic communication. More generally, I highlight the often-neglected importance of pragmatics for the study of language origins.
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Darwin-inspired population thinking suggests approaching culture as a population of items of different types, whose relative frequencies may change over time. Three nested subtypes of populational models can be distinguished: evolutionary, selectional and replicative. Substantial progress has been made in the study of cultural evolution by modelling it within the selectional frame. This progress has involved idealizing away from phenomena that may be critical to an adequate understanding of culture and cultural evolution, particularly the constructive aspect of the mechanisms of cultural transmission. Taking these aspects into account, we describe cultural evolution in terms of cultural attraction, which is populational and evolutionary, but only selectional under certain circumstances. As such, in order to model cultural evolution, we must not simply adjust existing replicative or selectional models but we should rather generalize them, so that, just as replicator-based selection is one form that Darwinian selection can take, selection itself is one of several different forms that attraction can take. We present an elementary formalization of the idea of cultural attraction.
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Niche construction refers to the activities of organisms that bring about changes in their environments, many of which are evolutionarily and ecologically consequential. Advocates of niche construction theory (NCT) believe that standard evolutionary theory fails to recognize the full importance of niche construction, and consequently propose a novel view of evolution, in which niche construction and its legacy over time (ecological inheritance) are described as evolutionary processes, equivalent in importance to natural selection. Here, we subject NCT to critical evaluation, in the form of a collaboration between one prominent advocate of NCT, and a team of skeptics. We discuss whether niche construction is an evolutionary process, whether NCT obscures or clarifies how natural selection leads to organismal adaptation, and whether niche construction and natural selection are of equivalent explanatory importance. We also consider whether the literature that promotes NCT overstates the significance of niche construction, whether it is internally coherent, and whether it accurately portrays standard evolutionary theory. Our disagreements reflect a wider dispute within evolutionary theory over whether the neo-Darwinian synthesis is in need of reformulation, as well as different usages of some key terms (e.g., evolutionary process).
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The study of pragmatics is typically concerned with ostensive communication (especially through language), in which we not only provide evidence for our intended speaker meaning, but also make manifest our intention to do so. This is not, however, the only way in which humans communicate. We also communicate in many non-ostensive ways, and these expressions often interplay with and complement ostensive communication. For example, fear, embarrassment, surprise and other emotions are often expressed with linguistic expressions, which they complement through changes in prosodic cues, facial and bodily muscular configuration, pupil dilatation and skin colouration, among others. However, some basic but important questions about non-ostensive communication, in particular those concerned with evolutionary stability, are unaddressed. Our objective is to address, albeit tentatively, this issue, focusing our discussion on one particular class of non-ostensive communication: emotional expressions. We argue that existing solutions to the problem of stability of emotional communication are problematic and we suggest introducing a new class of mechanisms—mechanisms of emotional vigilance—that, we think, more adequately accounts for the stability of emotional communication.
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“..consideration of language highlights the need for discussion about the nature of communication to develop an account that is sufficiently general to describe a communication system that is heavily context-dependent. Our overall objectives are thus to present a unified, consilient account of communication, and to discuss the implications…”
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To properly understand behavior, we must obtain both ultimate and proximate explanations. Put briefly, ultimate explanations are concerned with why a behavior exists, and proximate explanations are concerned with how it works. These two types of explanation are complementary and the distinction is critical to evolutionary explanation. We are concerned that they have become conflated in some areas of the evolutionary literature on human behavior. This article brings attention to these issues. We focus on three specific areas: the evolution of cooperation, transmitted culture, and epigenetics. We do this to avoid confusion and wasted effort—dangers that are particularly acute in interdisciplinary research. Throughout this article, we suggest ways in which misunderstanding may be avoided in the future.
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Communication is a fundamentally interactive phenomenon. Evolutionary biology recognises this fact in its definition of communication, in which signals are those actions that cause reactions, and where both action and reaction are designed for that reason. Where only one or the other is designed then the behaviours are classed as either cues or coercion. Since mutually dependent behaviours are unlikely to emerge simultaneously, the symmetry inherent in these definitions gives rise to a prediction that communication will only emerge if cues or coercive behaviours do so first. They will then be co-opted for communication. A range of case studies, from animal signalling, evolutionary robotics, comparative psychology, and evolutionary linguistics are used to test this prediction. The first three are found to be supportive. However in the Embodied Communication Game, a recent experimental approach to the emergence of communication between adult humans, communication emerges even when cues or coerced behaviours are not possible. This suggests that humans are exceptional in this regard. It is argued that the reason for this is the degree to which we are able and compelled to read and interpret the behaviour of others in intentional terms.
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Communication is ubiquitous in biology, and agreement on terms essential for scientific progress. Yet there is no agreed definition of biological communication. Definitions couched in terms of adaptation are often used, but there is significant variability in exactly which criteria are invoked. An alternative is to define communication in terms of information transfer. This article reviews the merits of these approaches, and argues that the former is to be preferred, so long as we demand that both the signal and the response be adaptive, rather than just one or the other, as is common. Specific concerns with the definition are addressed, and it is then explained why an account of communication predicated on information transfer is necessarily derivative upon such an approach. Other alternatives and some variants of the adaptationist definition are also briefly discussed.
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Recent years have witnessed an increased interest in the evolution of the human capacity for language. Such a project is necessarily interdisciplinary. However, that interdisciplinarity brings with it a risk: terms with a technical meaning in their own field are used wrongly or too loosely by those from other backgrounds. Unfortunately, this risk has been realized in the case of language evolution, where many of the terms of social evolution theory (reciprocal altruism, honest signaling, etc.) are incorrectly used in a way that suggests that certain key fundamentals have been misunderstood. In particular the distinction between proximate and ultimate explanations is often lost, with the result that several claims made by those interested in language evolution are epistemically incoherent. However, the correct application of social evolution theory provides simple, clear explanations of why language most likely evolved and how the signals used in language—words—remain cheap yet arbitrary.
Experimental & other empirical studies
Cognitive psychology, Cognitive development, Language evolution, Bacterial communication
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People often deny having meant what the audience understood. Such denials occur in both interpersonal and institutional contexts, such as in political discourse, the interpretation of laws and the perception of lies. In practice, denials have a wide range of possible effects on the audience, such as conversational repair, reinterpretation of the original utterance, moral judgements about the speaker, and rejection of the denial. When are these different reactions triggered? What factors make denials credible? There are surprisingly few experimental studies directly targeting such questions. Here, we present two pre-registered experiments focusing on (i) the speaker’s incentives to mislead their audience, and (ii) the impact of speaker denials on audiences’ moral and epistemic assessments of what has been said. We find that the extent to which speakers are judged responsible for the audience’s interpretations is modulated by their (the speakers’) incentives to mislead, but not by denials themselves. We also find that people are more willing than we expected to revise their interpretation of the speaker’s utterance when they learn that the ascribed meaning is false, regardless of whether the speaker is known to have had incentives to deceive their audience. In general, these findings are consistent with the idea that communicators are held responsible for the cognitive effects they trigger in their audience; rather than being responsible for, more narrowly, only the effects of what was “literally” said. In light of our findings, we present a new, cognitive analysis of how audiences react to denials, drawing in particular on the Relevance Theory approach to communication. We distinguish in particular: (a) the spontaneous and intuitive re-interpretation of the original utterance in light of a denial; (b) the attribution of responsibility to the speaker for the cognitive effects of what is communicated; and (c) the reflective attribution of a particular intention to the speaker, which include argumentative considerations, higher-order deniability, and reputational concerns. Existing experimental work, including our own, aims mostly at (a) and (b), and does not adequately control for (c). Deeper understanding of what can be credibly denied will be hindered unless and until this methodological problem is resolved.
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Image-making is a nearly universal human behavior, yet the visual strategies and conventions to represent things in pictures vary greatly over time and space. In particular, pictorial styles can differ in their degree of figurativeness, varying from intersubjectively recognizable representations of things to very stylized and abstract forms. Are there any patterns to this variability, and what might its ecological causes be? Experimental studies have shown that demography and the structure of interaction of cultural groups can play a key role: the greater the degree of contact with other groups, the more recognizable and less abstract are the representations. Here we test this hypothesis on a real-world dataset for the first time. We constructed a balanced database of Indigenous Australian rock art motifs from both isolated and contact Aboriginal groups (those often in contact with other groups). We then ran a survey asking participants to judge the recognizability of the motifs and to provide interpretations. Results show that motifs from contact Aboriginal groups were more likely to be judged as inter-subjectively recognizable and also elicited more convergent descriptions than motifs from isolated groups. This is consistent with the idea that intergroup contact is likely to be an important factor in the cultural evolution of pictorial representation. We discuss the implications of these findings for the archaeology and anthropology of art, and the parallels with language evolution.
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Are communicators perceived as committed to what they actually say (what is explicit), or to what they mean (including what is implicit)? Some research claims that explicit communication leads to a higher attribution of commitment and more accountability than implicit communication. Here we present theoretical arguments and experimental data to the contrary. We present three studies exploring whether the saying–meaning distinction affects commitment attribution in promises, and, crucially, whether commitment attribution is further modulated by the degree to which the hearer will actually rely on the promise. Our results support the conclusion that people perceive communicators to be committed to ‘what is meant’, and not simply to ‘what is said’. Our findings add to the experimental literature showing that the saying–meaning distinction is not as pivotal to social relations as often assumed, and that its role in commitment attribution might be overestimated. The attribution of commitment is strongly dependent on the (mutually known) relevance of ‘what is meant’.
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Data from a range of different experimental paradigms—in particular (but not only) the dot perspective task—have been interpreted as evidence that humans automatically track the perspective of other individuals. Results from other studies, however, have cast doubt on this interpretation, and some researchers have suggested that phenomena that seem like perspective-taking might instead be the products of simpler behavioural rules. The issue remains unsettled in significant part because different schools of thought, with different theoretical perspectives, implement the experimental tasks in subtly different ways, making direct comparisons difficult. Here, we explore the possibility that subtle differences in experimental method explain otherwise irreconcilable findings in the literature. Across five experiments we show that the classic result in the dot perspective task is not automatic (it is not purely stimulus-driven), but nor is it exclusively the product of simple behavioural rules that do not involve mentalising. Instead, participants do compute the perspectives of other individuals rapidly, unconsciously, and involuntarily, but only when attentional systems prompt them to do so (just as, for instance, the visual system puts external objects into focus only as and when required). This finding prompts us to clearly distinguish spontaneity from automaticity. Spontaneous perspective-taking may be a computationally efficient means of navigating the social world.
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Pictorial representation is a key human behaviour. Cultures around the world have made images to convey information about living kinds, objects and ideas for at least 75,000 years, in forms as diverse as cave paintings, religious icons and emojis. However, styles of pictorial representation vary greatly between cultures and historical periods. In particular, they can differ in figurativeness, i.e. varying from detailed depictions of subjects to stylised abstract forms. Here we show that pictorial styles can be shaped by intergroup contact. We use data from experimental microsocieties to show that drawings produced by groups in contact tended to become more figurative and transparent to outsiders, whereas in isolated groups drawings tended to become abstract and opaque. These results indicate that intergroup contact is likely to be an important factor in the cultural evolution of pictorial representation, because the need to communicate with outsiders ensures that some figurativeness is retained over time. We discuss the implications of this finding for understanding the history and anthropology of art, and the parallels with sociolinguistics and language evolution.
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Two complementary approaches to a naturalistic theory of culture are, on the one hand, mainstream cultural evolution research, and, on the other, work done under the banners of cultural attraction and the epidemiology of representations. There is much agreement between these two schools of thought, including in particular a commitment to population thinking. Both schools also acknowledge that the propagation of culture is not simply a matter of replication, but rather one of reconstruction. However, the two schools of thought differ on the relative importance of this point. The cultural attraction school believes it to be fundamental to genuinely causal explanations of culture. In contrast, most mainstream cultural evolution thinking abstracts away from it. In this paper I make flesh a simple thought experiment (first proposed by Dan Sperber) that directly contrasts the effects that replication and reconstruction have on cultural items. Results demonstrate, in a simple and graphic way, that (i) normal cultural propagation is not replicative, but reconstructive, and (ii) that these two different modes of propagation afford two qualitatively different explanations of stability. If propagation is replicative, as it is in biology, then stability arises from the fidelity of that replication, and hence an explanation of stability comes from an explanation of how and why this high-fidelity is achieved. If, on the other hand, propagation is reconstructive (as it is in culture), then stability arises from the fact that a subclass of cultural types are easily re-producible, while others are not, and hence an explanation of stability comes from a description of what types are easily re-producible, and an explanation of why they are. I discuss two implications of this result for research at the intersection of evolution, cognition, and culture.
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Because communication can be abused by senders, it is not inherently stable. One way of stabilizing communication is for senders to commit to their messages. If a sender is committed to a message, she is willing to incur a cost (direct or reputational) if the message is found to be unreliable. This cost provides a reason for receivers to accept messages to which senders are committed. We suggest that expressions of confidence can be used as commitment signals: messages expressed more confidently commit their senders more. On this basis, we make three predictions: that confidently expressed messages are more persuasive (H1’, already well established), that senders whose messages were accepted due to the senders' confidence but were then found to be unreliable should incur costs (H2’), and that if a message is accepted for reasons other than confidence, when it is found to be unreliable the sender should incur lower reputational costs than if the message had been accepted on the basis of the sender's confidence (H3’). A review of the literature revealed broadly supportive but still ambiguous evidence for H2’ and no tests of H3’. In experiments 1, 2, and 3 (testing H2’) participants received the same advice from two senders, one being confident and the other unconfident. Participants were more likely to follow the advice of the confident sender, but once the advice was revealed to have been misguided, participants adjust- ed their trust so that they trusted the initially unconfident sender more than the confident sender. In experiments 3 and 4 (testing H3’) participants chose between either two senders differing in confidence or two senders differing in competence. Participants followed the advice of the confident sender and of the competent sender. When it was revealed that the advice was misguided, the confident sender suffered from a larger drop in trust than the competent sender. These results are relevant for communicative theories of overconfidence.
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Recursive mindreading is the ability to embed mental representations inside other mental representations e.g. to hold beliefs about beliefs about beliefs. An advanced ability to entertain recursively embedded mental states is consistent with evolutionary perspectives that emphasise the importance of sociality and social cognition in human evolution: high levels of recursive mindreading are argued to be involved in several distinctive human behaviours and institutions, such as communication, religion, and story-telling. However, despite a wealth of research on first-level mindreading under the term Theory of Mind, the human ability for recursive mindreading is relatively understudied, and existing research on the topic has significant methodological flaws. Here we show experimentally that human recursive mindreading abilities are far more advanced than has previously been shown. Specifically, we show that humans are able to mindread to at least seven levels of embedding, both explicitly, through linguistic description, and implicitly, through observing social interactions. However, our data suggest that mindreading may be easier when stimuli are presented implicitly rather than explicitly. We argue that advanced mindreading abilities are to be expected in an extremely social species such as our own, where the ability to reason about others' mental states is an essential, ubiquitous and adaptive component of everyday life.
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Quorum sensing (QS) is a cell–cell communication system that controls gene expression in many bacterial species, mediated by diffusible signal molecules. Although the intracellular regulatory mechanisms of QS are often well-understood, the functional roles of QS remain controversial. In particular, the use of multiple signals by many bacterial species poses a serious challenge to current functional theories. Here, we address this challenge by showing that bacteria can use multiple QS signals to infer both their social (density) and physical (mass-transfer) environment. Analytical and evolutionary simulation models show that the detection of, and response to, complex social/physical contrasts requires multiple signals with distinct half-lives and combinatorial (nonadditive) responses to signal concentrations. We test these predictions using the opportunistic pathogen Pseudomonas aeruginosa and demonstrate significant differences in signal decay between its two primary signal molecules, as well as diverse combinatorial responses to dual-signal inputs. QS is associated with the control of secreted factors, and we show that secretome genes are preferentially controlled by synergistic “AND-gate” responses to multiple signal inputs, ensuring the effective expression of secreted factors in high-density and low mass-transfer environments. Our results support a new functional hypothesis for the use of multiple signals and, more generally, show that bacteria are capable of combinatorial communication.
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Combinatorial communication, in which two signals are used together to achieve an effect that is different to the sum of the effects of the component parts, is apparently rare in nature: it is ubiquitous in human language, appears to exist in a simple form in some non-human primates, but has not been demonstrated in other species. This observed distribution has led to the pair of related suggestions, that (i) these differences in the complexity of observed communication systems reflect cognitive differences between species; and (ii) that the combinations we see in non-human primates may be evolutionary pre-cursors of human language. Here we replicate the landmark experiments on combinatorial communication in non- human primates, but in an entirely different species, unrelated to humans, and with no higher cognition: the bacterium Pseudomonas aeruginosa. Using the same general methods as the primate studies, we find the same general pattern of results: the effect of the combined signal differs from the composite effect of the two individual signals. This suggests that advanced cognitive abilities and large brains do not necessarily explain why some species have combinatorial communication systems and others do not. We thus argue that it is premature to conclude that the systems observed in non-human primates are evolutionarily related to language. Our results illustrate the value of an extremely broad approach to comparative research.
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Human cooperative communication involves both an informative intention that the recipient understands the content of the signal and also a (Gricean) communicative intention that the recipient recognizes that the speaker has an informative intention. The degree to which children understand this 2-layered nature of communication is the subject of some debate. One phenomenon that would seem to constitute clear evidence of such understanding is hidden authorship, in which informative acts are produced but with the communicative intent behind them intentionally hidden. In this study, 3- and 5-year-old children were told that an adult was seeking a toy but wanted to find it on her own. Children of both ages often did something to make the toy easier for the adult to see while at the same time concealing their actions in some way. This suggests that by the age of 3, children are able to separate the multiple layers of intentionality involved in human cooperative communication.
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New referents are typically introduced into adult discourse with lexical nouns. This makes new referents maximally clear for listeners, and helps the listeners direct their attention appropriately. A different trend is observed in child language, where new referents may be realised with demonstratives or pronouns, or they may be omitted altogether. This has led some to claim that children are pragmatically immature and not sensitive to the perspective of their interlocutors. In this paper, we analyse a videotaped corpus of naturalistic spontaneous speech of four children acquiring Inuktitut (2;0--3;6) to examine the different ways in which they realise new referents. Our results show that in their realisation of new referents children are sensitive to the presence or absence of joint attention. Specifically, they tend to omit arguments when joint attention is present, and they use lexical forms when it is absent. Their use of demonstratives reflects similar sensitivity: they tend to use demonstrative clitics when joint attention is present but independent demonstrative forms when it is absent. The use of omitted forms in child language is thus not explained by any pragmatic deficiency; indeed, it shows that children adjust their messages for the interlocutor, strictly following the Gricean Maxim of Quantity.
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A unique hallmark of human language is that it uses signals that are both learnt and symbolic. The emergence of such signals was therefore a defining event in human cognitive evolution, yet very little is known about how such a process occurs. Previous work provides some insights on how meaning can become attached to form, but a more foundational issue is presently unaddressed. How does a signal signal its own signalhood? That is, how do humans even know that communicative behaviour is indeed communicative in nature? We introduce an experimental game that has been designed to tackle this problem. We find that it is commonly resolved with a bootstrapping process, and that this process influences the final form of the communication system. Furthermore, sufficient common ground is observed to be integral to the recognition of signalhood, and the emergence of dialogue is observed to be the key step in the development of a system that can be employed to achieve shared goals.
Mathematical & computational models
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Typical examples of cultural phenomena all exhibit a degree of similarity across time and space at the level of the population. As such, a fundamental question for any science of culture is, what ensures this stability in the first place? Here we focus on the evolutionary and stabilising role of ‘convergent transformation’, in which one item causes the production of another item whose form tends to deviate from the original in a directed, non-random way. We present a series of stochastic models of cultural evolution investigating its effects. The results show that cultural stability can emerge and be maintained by virtue of convergent transformation alone, in the absence of any form of copying or selection process. We show how high- fidelity copying and convergent transformation need not be opposing forces, and can jointly contribute to cultural stability. We finally analyse how non-random transformation and high-fidelity copying can have different evolutionary signatures at population level, and hence how their distinct effects can be distinguished in empirical records. Collectively, these results supplement existing approaches to cultural evolution based on the Darwinian analogy, while also providing formal support for other frameworks – such as Cultural Attraction Theory – that entail its further loosening.
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How communication systems emerge is a topic of relevance to several academic disciplines. Numerous existing models, both mathematical and computational, study this emergence. However, with few exceptions, these models all build some form of communication into their initial specification. Consequently, what these models study is how communication systems transition from one form to another, and not how communication itself emerges in the first place. Here we present a new computational model of the emergence of communication which, unlike previous models, does not pre-specify the existence of communication. We conduct two experiments using this model, in order to derive general statements about how communication systems emerge. The two main routes to communication that we identify correspond with findings from the empirical literature on the evolution of animal signals. We use this finding to explain when and why we should expect communication to emerge in nature. We also compare our model to experimental research on the origins of human communication systems, and hence show that humans are an important exception to the general trends we observe. We argue that this is because humans, and probably only humans, are able to ‘signal signalhood’, i.e. to express communicative intentions.
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In a combinatorial communication system, some signals consist of the combinations of other signals. Such systems are more efficient than equivalent, non-combinatorial systems, yet despite this they are rare in nature. Why? Previous explanations have focused on the adaptive limits of combinatorial communication, or on its purported cognitive difficulties, but neither of these explains the full distribution of combinatorial communication in the natural world. Here, we present a nonlinear dynamical model of the emergence of combinatorial communication that, unlike previous models, considers how initially non-communicative behaviour evolves to take on a communicative function. We derive three basic principles about the emergence of combinatorial communication. We hence show that the interdependence of signals and responses places significant constraints on the historical pathways by which combinatorial signals might emerge, to the extent that anything other than the most simple form of combinatorial communication is extremely unlikely. We also argue that these constraints can be bypassed if individuals have the socio-cognitive capacity to engage in ostensive communication. Humans, but probably no other species, have this ability. This may explain why language, which is massively combinatorial, is such an extreme exception to nature’s general trend for non-combinatorial communication.
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Communication involves a pair of behaviours—a signal and a response—that are functionally interdependent. Consequently, the emergence of communication involves a chicken-and-egg problem: if signals and responses are dependent on one another, then how does such a relationship emerge in the first place? The empirical literature suggests two solutions to this problem: ritualization and sensory manipulation; and instances of ritualization appear to be more common. However, it is not clear from a theoretical perspective why this should be the case, nor if there are any other routes to communication. Here, we develop an analytical model to examine how communication can emerge. We show that: (i) a state of non-interaction is evolutionarily stable, and so communication will not necessarily emerge even when it is in both parties’ interest; (ii) the conditions for sensory manipulation are more stringent than for ritualization, and hence ritualization is likely to be more common; and (iii) communication can arise by a third route, when the intention to communicate can itself be communicated, but this may be limited to humans. More generally, our results demonstrate the utility of a functional approach to communication.
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With human language, the same utterance can have different meanings in different contexts. Nevertheless, listeners almost invariably converge upon the correct intended meaning. The classic Gricean explanation of how this is achieved posits the existence of four maxims of conversation, which speakers are assumed to follow. Armed with this knowledge, listeners are able to interpret utterances in a contextually sensible way. This account enjoys wide acceptance, but it has not gone unchallenged. Specifically, Relevance Theory offers an explicitly cognitive account of utterance interpretation that presents a radical challenge to the neo-Gricean paradigm. Evolutionary considerations are one way in which we can choose between competing theories. A simple game-theoretic model of the evolution of communication is presented, and it is used to derive a number of basic qualities that will be satisfied by all evolved communication systems. These qualities are observed to precisely predict the foundational principles of Relevance Theory. The model thus provides biological support for that enterprise in general, and for the plausibility of the cognitive mechanisms that it describes in particular.
Literature reviews
Evolution of communication, language & culture
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Detailed comparative studies have revealed many surface similarities between linguistic communication and the communication of nonhumans. How should we interpret these discoveries in linguistic and cognitive perspective? We review the literature with a specific focus on analogy (similar features and function but not shared ancestry) and homology (shared ancestry). We conclude that combinatorial features of animal communication are analogous but not homologous to natural language. Homologies are found instead in cognitive capacities of attention manipulation, which are enriched in humans, making possible many distinctive forms of communication, including language use. We therefore present a new, graded taxonomy of means of attention manipulation, including a new class we call Ladyginian, which is related to but slightly broader than the more familiar class of Gricean interaction. Only in the latter do actors have the goal of revealing specifically informative intentions. Great ape interaction may be best characterized as Ladyginian but not Gricean.
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Cultural evolution requires the social transmission of information. For this reason, scholars have emphasized social learning when explaining how and why culture evolves. Yet cultural evolution results from many mechanisms operating in concert. Here, we argue that the emphasis on social learning has distracted scholars from appreciating both the full range of mechanisms contributing to cultural evolution and how interactions among those mechanisms and other factors affect the output of cultural evolution. We examine understudied mechanisms and other factors and call for a more inclusive programme of investigation that probes multiple levels of the organization, spanning the neural, cognitive-behavioural and populational levels. To guide our discussion, we focus on factors involved in three core topics of cultural evolution: the emergence of culture, the emergence of cumulative cultural evolution and the design of cultural traits. Studying mechanisms across levels can add explanatory power while revealing gaps and misconceptions in our knowledge.
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Several recent theories postulate communicative functions for cognitive mechanisms previously thought to have individualistic functions—in particular, reasoning and metacognition. These theories join older theories suggesting that many of our behaviors have communicative functions, for instance to communicate emotions or to influence how people perceive us. Using the framework of the evolution of communication, we offer a series of questions to test these hypotheses. The first question is whether the mechanism enables effective communication. The second question takes into account the different strategic incentives between agents who send signals and those who receive them, asking whether receivers can discriminate beneficial from harmful signals. However, serving a function well is not sufficient evidence that a mechanism evolved to this end in particular. Accordingly, the third question bears on whether the mechanism serves other purported functions well and the fourth on whether some of its features can be explained as specifically serving a communicative function. An overview of the literature suggests that these questions have been experimentally addressed for some cognitive mechanisms (reasoning in particular) but not others. This framework thus opens up avenues for further research that will enable researchers to better test hypotheses regarding the communicative functions of cognitive mechanisms.
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Human language is an incredibly powerful communication system reliant on complex cognitive processes. Tracing the evolutionary origins of this remarkable ability is the focus of considerable interdisciplinary research effort. Within this field, comparative research offers important insights into when and how the building blocks for language may have evolved in our evolutionary past. Understanding the aspects of communication and associated cognitive processes that are shared between chimpanzees and humans, and those that are uniquely human, can help us to identify the key changes that must have occurred in the human lineage since the divergence of the two species. Various approaches have been used to assess the similarities and differences between human and chimpanzee communication, from studying their natural communicative abilities to trying to teach them to master a human communication system. This chapter examines several different aspects of communication and language from this comparative perspective. It focuses in particular on structural, neurological, and cognitive factors. The chapter emphasizes the importance of the last of these, and the need for more comparative research on the cognitive foundations of human communication.
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The historical origins of natural language cannot be observed directly. We can, however, study systems that support language and we can also develop models that explore the plausibility of different hypotheses about how language emerged. More recently, evolutionary linguists have begun to conduct language evolution experiments in the laboratory, where the emergence of new languages used by human participants can be observed directly. This enables researchers to study both the cognitive capacities necessary for language and the ways in which languages themselves emerge. One theme that runs through this work is how individual-level behaviours result in population-level linguistic phenomena. A central challenge for the future will be to explore how different forms of information transmission affect this process.
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A naïve observer would be forgiven for assuming that the field of language evolution would, in terms of its scope and methodologies, look much like the field of evolutionary psychology, but with a particular emphasis on language. However, this is not the case. This editorial out- lines some reasons why such a research agenda has not so far been pursued in any large-scale or systematic way, and briefly discusses one foundational aspect of that agenda, the question of evolutionary function. This background provides context for an introduction of the articles that appear in this special issue on the evolution of language.