One cultural parent makes no culture

Evolved Open-Endedness in Cultural Evolution: A New Dimension in Open-Ended Evolution Research

The goal of Artificial Life research, as articulated by Chris Langton, is "to contribute to theoretical biology by locating life-as-we-know-it within the larger picture of life-as-it-could-be." The study and pursuit of open-ended evolution in artificial evolutionary systems exemplify this goal. However, open-ended evolution research is hampered by two fundamental issues: the struggle to replicate open-endedness in an artificial evolutionary system and our assumption that we only have one system (genetic evolution) from which to draw inspiration. We argue not only that cultural evolution should be seen as another real-world example of an open-ended evolutionary system but that the unique qualities seen in cultural evolution provide us with a new perspective from which we can assess the fundamental properties of, and ask new questions about, open-ended evolutionary systems, especially with regard to evolved open-endedness and transitions from bounded to unbounded evolution. Here we provide an overview of culture as an evolutionary system, highlight the interesting case of human cultural evolution as an open-ended evolutionary system, and contextualize cultural evolution by developing a new framework of (evolved) open-ended evolution. We go on to provide a set of new questions that can be asked once we consider cultural evolution within the framework of open-ended evolution and introduce new insights that we may be able to gain about evolved open-endedness as a result of asking these questions.

To copy or not to copy? That is the question! From chimpanzees to the foundation of human technological culture

A prerequisite for copying innovative behaviour faithfully is the capacity of observers' brains, regarded as 'hierarchically mechanistic minds', to overcome cognitive 'surprisal' (see 2.), by maximising the evidence for their internal models, through active inference. Unlike modern humans, chimpanzees and other great apes show considerable limitations in their ability, or 'Zone of Bounded Surprisal', to overcome cognitive surprisal induced by innovative or unorthodox behaviour that rarely, therefore, is copied precisely or accurately. Most can copy adequately what is within their phenotypically habitual behavioural repertoire, in which technology plays scant part. Widespread intra- and intergenerational social transmission of complex technological innovations is not a hall-mark of great-ape taxa. 3 Ma, precursors of the genus Homo made stone artefacts, and stone-flaking likely was habitual before 2 Ma. After that time, early Homo erectus has left traces of technological innovations, though faithful copying of these and their intra- and intergenerational social transmission were rare before 1 Ma. This likely owed to a cerebral infrastructure of interconnected neuronal systems more limited than ours. Brains were smaller in size than ours, and cerebral neuronal systems ceased to develop when early Homo erectus attained full adult maturity by the mid-teen years, whereas its development continues until our mid-twenties nowadays. Pleistocene Homo underwent remarkable evolutionary adaptation of neurobiological propensities, and cerebral aspects are discussed that, it is proposed here, plausibly, were fundamental for faithful copying, which underpinned social transmission of technologies, cumulative learning, and culture. Here, observers' responses to an innovation are more important for ensuring its transmission than is an innovator's production of it, because, by themselves, the minimal cognitive prerequisites that are needed for encoding and assimilating innovations are insufficient for practical outcomes to accumulate and spread intra- and intergenerationally.

What Makes Inventions Become Traditions?

Although anthropology was the first academic discipline to investigate cultural change, many other disciplines have made noteworthy contributions to understanding what influences the adoption of new behaviors. Drawing on a broad, interdisciplinary literature covering both humans and nonhumans, we examine ( a) which features of behavioral traits make them more transmissible, ( b) which individual characteristics of inventors promote copying of their inventions, ( c) which characteristics of individuals make them more prone to adopting new behaviors, ( d) which characteristics of dyadic relationships promote cultural transmission, ( e) which properties of groups (e.g., network structures) promote transmission of traits, and ( f) which characteristics of groups promote retention, rather than extinction, of cultural traits. One of anthropology's strengths is its readiness to adopt and improve theories and methods from other disciplines, integrating them into a more holistic approach; hence, we identify approaches that might be particularly useful to biological and cultural anthropologists, and knowledge gaps that should be filled.

Costly teaching contributes to the acquisition of spear hunting skill among BaYaka forager adolescents

Teaching likely evolved in humans to facilitate the faithful transmission of complex tasks. As the oldest evidenced hunting technology, spear hunting requires acquiring several complex physical and cognitive competencies. In this study, we used observational and interview data collected among BaYaka foragers (Republic of the Congo) to test the predictions that costlier teaching types would be observed at a greater frequency than less costly teaching in the domain of spear hunting and that teachers would calibrate their teaching to pupil skill level. To observe naturalistic teaching during spear hunting, we invited teacher-pupil groupings to spear hunt while wearing GoPro cameras. We analysed 68 h of footage totalling 519 teaching episodes. Most observed teaching events were costly. Direct instruction was the most frequently observed teaching type. Older pupils received less teaching and more opportunities to lead the spear hunt than their younger counterparts. Teachers did not appear to adjust their teaching to pupil experience, potentially because age was a more easily accessible heuristic for pupil skill than experience. Our study shows that costly teaching is frequently used to transmit complex tasks and that instruction may play a privileged role in the transmission of spear hunting knowledge.

Maintenance of prior behaviour can enhance cultural selection

Many cultural phenomena evolve through a Darwinian process whereby adaptive variants are selected and spread at the expense of competing variants. While cultural evolutionary theory emphasises the importance of social learning to this process, experimental studies indicate that people's dominant response is to maintain their prior behaviour. In addition, while payoff-biased learning is crucial to Darwinian cultural evolution, learner behaviour is not always guided by variant payoffs. Here, we use agent-based modelling to investigate the role of maintenance in Darwinian cultural evolution. We vary the degree to which learner behaviour is payoff-biased (i.e., based on critical evaluation of variant payoffs), and compare three uncritical (non-payoff-biased) strategies that are used alongside payoff-biased learning: copying others, innovating new variants, and maintaining prior variants. In line with previous research, we show that some level of payoff-biased learning is crucial for populations to converge on adaptive cultural variants. Importantly, when combined with payoff-biased learning, uncritical maintenance leads to stronger population-level adaptation than uncritical copying or innovation, highlighting the importance of maintenance to cultural selection. This advantage of maintenance as a default learning strategy may help explain why it is a common human behaviour.

Evaluating the relative contributions of copying and reconstruction processes in cultural transmission episodes

The ability to transmit information between individuals through social learning is a foundational component of cultural evolution. However, how this transmission occurs is still debated. On the one hand, the copying account draws parallels with biological mechanisms for genetic inheritance, arguing that learners copy what they observe and novel variations occur through random copying errors. On the other hand, the reconstruction account claims that, rather than directly copying behaviour, learners reconstruct the information that they believe to be most relevant on the basis of pragmatic inference, environmental and contextual cues. Distinguishing these two accounts empirically is difficult based on data from typical transmission chain studies because the predictions they generate frequently overlap. In this study we present a methodological approach that generates different predictions of these accounts by manipulating the task context between model and learner in a transmission episode. We then report an empirical proof-of-concept that applies this approach. The results show that, when a model introduces context-dependent embedded signals to their actions that are not intended to be transmitted, it is possible to empirically distinguish between competing predictions made by these two accounts. Our approach can therefore serve to understand the underlying cognitive mechanisms at play in cultural transmission and can make important contributions to the debate between preservative and reconstructive schools of thought.

Beyond social learning

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. This article is part of the theme issue 'Foundations of cultural evolution'.

Underappreciated features of cultural evolution

Cultural evolution theory has long been inspired by evolutionary biology. Conceptual analogies between biological and cultural evolution have led to the adoption of a range of formal theoretical approaches from population dynamics and genetics. However, this has resulted in a research programme with a strong focus on cultural transmission. Here, we contrast biological with cultural evolution, and highlight aspects of cultural evolution that have not received sufficient attention previously. We outline possible implications for evolutionary dynamics and argue that not taking them into account will limit our understanding of cultural systems. We propose 12 key questions for future research, among which are calls to improve our understanding of the combinatorial properties of cultural innovation, and the role of development and life history in cultural dynamics. Finally, we discuss how this vibrant research field can make progress by embracing its multidisciplinary nature. This article is part of the theme issue 'Foundations of cultural evolution'.

Cultural Evolution of Genetic Heritability

Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior-largely independent of each other. Here we reconcile these two fields under a dual inheritance framework, offering a more nuanced understanding of the interaction between genes and culture. Going beyond typical analyses of gene-environment interactions, we describe the cultural dynamics that shape these interactions by shaping the environment and population structure. A cultural evolutionary approach can explain, for example, how factors such as rates of innovation and diffusion, density of cultural sub-groups, and tolerance for behavioral diversity impact heritability estimates, thus yielding predictions for different social contexts. Moreover, when cumulative culture functionally overlaps with genes, genetic effects become masked, unmasked, or even reversed, and the causal effects of an identified gene become confounded with features of the cultural environment. The manner of confounding is specific to a particular society at a particular time, but a WEIRD (Western, educated, industrialized, rich, democratic) sampling problem obscures this boundedness. Cultural evolutionary dynamics are typically missing from models of gene-to-phenotype causality, hindering generalizability of genetic effects across societies and across time. We lay out a reconciled framework and use it to predict the ways in which heritability should differ between societies, between socioeconomic levels and other groupings within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetic approach cuts through the nature-nurture debate and helps resolve controversies in topics such as IQ.

The Method of Local Restriction: in search of potential great ape culture-dependent forms

Humans possess a perhaps unique type of culture among primates called cumulative culture. In this type of culture, behavioural forms cumulate changes over time, which increases their complexity and/or efficiency, eventually making these forms culture-dependent. As changes cumulate, culture-dependent forms become causally opaque, preventing the overall behavioural form from being acquired by individuals on their own; in other words, culture-dependent forms must be copied between individuals and across generations. Despite the importance of cumulative culture for understanding the evolutionary history of our species, how and when cumulative culture evolved is still debated. One of the challenges faced when addressing these questions is how to identify culture-dependent forms that result from cumulative cultural evolution. Here we propose a novel method to identify the most likely cases of culture-dependent forms. The 'Method of Local Restriction' is based on the premise that as culture-dependent forms are repeatedly transmitted via copying, these forms will unavoidably cumulate population-specific changes (due to copying error) and therefore must be expected to become locally restricted over time. When we applied this method to our closest living relatives, the great apes, we found that most known ape behavioural forms are not locally restricted (across domains and species) and thus are unlikely to be acquired via copying. Nevertheless, we found 25 locally restricted forms across species and domains, three of which appear to be locally unique (having been observed in a single population of a single species). Locally unique forms represent the best current candidates for culture-dependent forms in non-human great apes. Besides these rare exceptions, our results show that overall, ape cultures do not rely heavily on copying, as most ape behaviours appear across sites and/or species, rendering them unlikely to be culture-dependent forms resulting from cumulative cultural evolution. Yet, the locally restricted forms (and especially the three locally unique forms) identified by our method should be tested further for their potential reliance on copying social learning mechanisms (and in turn, for their potential culture-dependence). Future studies could use the Method of Local Restriction to investigate the existence of culture-dependent forms in other animal species and in the hominin archaeological record to estimate how widespread copying is in the animal kingdom and to postulate a timeline for the emergence of copying in our lineage.

Can You Trust Who You See? The Evolution of Socially Cued Anticipatory Plasticity

AbstractThe social environment can affect development and fitness. However, we do not know how selection acts on individuals that cue developmental pathways using features of the social environment. Socially cued anticipatory plasticity (SCAP) is a hypothetical strategy whereby juveniles use social cues to alter development to match their adult phenotype to the social environment that they expect to encounter. While intuitively appealing, the evolution of such plasticity is a puzzle, because the cue changes when individuals use it. Can socially cued plasticity evolve when such a feedback occurs? We use individual-based simulations to model evolution of SCAP in an environment that fluctuates between favoring each of two discrete phenotypes. We found that socially cued plasticity evolved, but only when strong selection acted on survival rather than on fecundity differences between adult phenotypes. In this case, the social cue reliably predicted which phenotype would be favored on maturation. Surprisingly, costs to plasticity increased the range of conditions under which it was adaptive. In the absence of costs, evolution led to a state where SCAP individuals could not effectively respond to environmental changes. Costs to plasticity lowered the proportion of the population that used SCAP, which in turn increased the reliability of the social cue and allowed individuals that used socially cued plasticity to switch between the favored phenotypes more consistently. Our results suggest that the evolution of adaptive plasticity in response to social cues may represent a larger class of problems in which evolution is hard to predict because of feedbacks among critical processes.

Organized to learn: the influence of social structure on social learning opportunities in a group

Social learning, which is a mechanism that allows an individual to acquire skills from other individuals, occurs in a social context. Therefore, factors that influence social context, like social structure, will impact social learning opportunities. This review explores how features of social structure affect social learning opportunities in primates, either through their relationship with social tolerance or through the number of social learning models. Features that are investigated in this review and that we hypothesize affect social learning opportunities are parental investment, dominance hierarchy, nepotism, social bonds, dispersal, group size, fission-fusion dynamics, and sex ratio. For most of these features we find evidence, but support varies. Of all primate species, only humans show all the requirements of an optimal social structure to promote social learning. Future research into social learning and culture should not overlook the social context in which it takes place.

Time to extinction of a cultural trait in an overlapping generation model

How long a newly emerging trait will stay in a population is a fundamental but rarely asked question in cultural evolution. To tackle this question, the distribution and mean of the time to extinction of a discrete cultural trait are derived for models with overlapping generations, in which trait transmission occurs from multiple role models to a single newborn and may fail with a certain probability. We explore two models. The first is a Moran-type model, which allows us to derive the exact analytical formula for the mean time to extinction of a trait in a finite population. The second is a branching process, which assumes an infinitely large population and allows us to derive approximate analytical formulae for the distribution and mean of the time to extinction in the first model under a large population size. We show that in the first model, the mean time to extinction apparently diverges (becomes so large that even numerical computation is impractical) under a certain parameter condition as the population size tends to infinity. Using the second model, we explain the underlying mechanism of the apparent divergence found in the first model and derive the mathematical condition for this divergence in terms of transmission efficiency and the number of role models per newborn. When this mathematical condition is satisfied in the second model, the probability of extinction is less than 1, and the mean extinction time does not exist. In addition, we find that in both models, the time to extinction of the trait becomes longer as the number of role models per individual increases and as cultural transmission becomes more efficient.

It happened to a friend of a friend: inaccurate source reporting in rumour diffusion

People often attribute rumours to an individual in a knowledgeable position two steps removed from them (a credible friend of a friend), such as 'my friend's father, who's a cop, told me about a serial killer in town'. Little is known about the influence of such attributions on rumour propagation, or how they are maintained when the rumour is transmitted. In four studies (N = 1824) participants exposed to a rumour and asked to transmit it overwhelmingly attributed it either to a credible friend of a friend, or to a generic friend (e.g. 'a friend told me about a serial killer in town'). In both cases, participants engaged in source shortening: e.g. when told by a friend that 'a friend told me …' they shared the rumour as coming from 'a friend' instead of 'a friend of friend'. Source shortening and reliance on credible sources boosted rumour propagation by increasing the rumours' perceived plausibility and participants' willingness to share them. Models show that, in linear transmission chains, the generic friend attribution dominates, but that allowing each individual to be exposed to the rumour from several sources enables the maintenance of the credible friend of a friend attribution.

Cultural adaptation is maximised when intelligent individuals rarely think for themselves

Humans are remarkable in their reliance on cultural inheritance, and the ecological success this has produced. Nonetheless, we lack a thorough understanding of how the cognitive underpinnings of cultural transmission affect cultural adaptation across diverse tasks. Here, we use an agent-based simulation to investigate how different learning mechanisms (both social and asocial) interact with task structure to affect cultural adaptation. Specifically, we compared learning through refinement, recombination or both, in tasks of different difficulty, with learners of different asocial intelligence. We find that for simple tasks all learning mechanisms are roughly equivalent. However, for hard tasks, performance was maximised when populations consisted of highly intelligent individuals who nonetheless rarely innovated and instead recombined existing information. Our results thus show that cumulative cultural adaptation relies on the combination of individual intelligence and 'blind' population-level processes, although the former may be rarely used. The counterintuitive requirement that individuals be highly intelligent, but rarely use this intelligence, may help resolve the debate over the role of individual intelligence in cultural adaptation.

Modelling persistence over generations in biological and cultural evolution based on differential paces of change

Paces of change are faster in cultural evolution than in biological evolution due to different levels of stability in information storage. This study develops mathematical models to investigate the consequences of differential mutation rates on the ability of groups of information units to survive over many generations. We examined the ability of groups composed of connected units to live on despite the occurrence of deleterious mutations that occur at probabilities ranging from 10^-1 to 10^-6. It appears that the degree of connection between units should be high enough for groups to persist across generations, but this alone did not ensure their survival; when groups of units were limited in size and subjected to high mutation rates, they did not survive for very long. By contrast, a significant proportion of groups were able to survive numerous generations if mutation rates were low and/or group size was large. The results revealed that the mean number of surviving generations was minimized for certain sizes of groups. When allowing information units to duplicate at each generation, simulation showed that a great number of groups avoided extinction even when mutating at the rate of cultural change if the initial group size was large and the duplication rate was high enough to counteract the consequences of environmental perturbations. The modelling described in this study sets out the conditions under which groups of units can survive along generations. It should serve as a basis for further investigations about the links between processes of biological and cultural changes.

Traces of culture: The feedback loop between behavior, brain, and disorder

Culture is part of an extensive series of feedback loops, which involve multiple organismic levels including social contexts, cognitive mediations, neural processes, and behavior. Recent studies in neuroscience show that culturally contingent social processes shape some neural pathways. Studying the influence of cultural context on neural processes may yield new insights into psychiatric disorders. New methodologies in the neurosciences offer innovative ways to assess the impact of culture on mental health and illness. However, implementing these methodologies raises important theoretical and ethical concerns, which must be resolved to address patient individuality and the complexity of cultural diversity. This article discusses cultural context as a major influence on (and consequence of) human neural plasticity and advocates a culture-brain-behavior (CBB) interaction model for conceptualizing the relationship between culture, brain, and psychiatric disorders. Recommendations are made for integrating neuroscientific techniques into transcultural psychiatric research by taking a systems approach to evaluating disorders.

Attachment, culture, and gene-culture co-evolution: expanding the evolutionary toolbox of attachment theory

I argue that attachment relationships, and particularly secure ones, are important contexts for social learning and cultural transmission. Bowlby originally treated the attachment-behavioral system as serving only one evolutionary function: protection, via physical proximity. Yet the time is ripe to consider learning, especially social learning, as an additional functional consequence of attachment. Updated accordingly, attachment theory has the potential to serve as a much-needed developmental anchor for models of cultural evolution and gene-culture co-evolution. To support my arguments, I review progress in evolutionary science since Bowlby's lifetime, highlighting the growing recognition of ecological flexibility and the cultural embeddedness of animal behavior. I also review research pointing to a facilitating role of secure attachment relationships for social learning from caregivers among humans. For illustrational purposes, I show how one important aspect of human culture - religion - is culturally transmitted within attachment relationships, and of how the generalization of attachment-related working models biases the cultural transmission of religion from parents to offspring. I end the paper with a call for empirical research to test the role of attachment in cultural transmission beyond religion.

The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history

In the last few million years, the hominin brain more than tripled in size. Comparisons across evolutionary lineages suggest that this expansion may be part of a broader trend toward larger, more complex brains in many taxa. Efforts to understand the evolutionary forces driving brain expansion have focused on climatic, ecological, and social factors. Here, building on existing research on learning, we analytically and computationally model the predictions of two closely related hypotheses: The Cultural Brain Hypothesis and the Cumulative Cultural Brain Hypothesis. The Cultural Brain Hypothesis posits that brains have been selected for their ability to store and manage information, acquired through asocial or social learning. The model of the Cultural Brain Hypothesis reveals relationships between brain size, group size, innovation, social learning, mating structures, and the length of the juvenile period that are supported by the existing empirical literature. From this model, we derive a set of predictions-the Cumulative Cultural Brain Hypothesis-for the conditions that favor an autocatalytic take-off characteristic of human evolution. This narrow evolutionary pathway, created by cumulative cultural evolution, may help explain the rapid expansion of human brains and other aspects of our species' life history and psychology.

On the absence of a correlation between population size and 'toolkit size' in ethnographic hunter-gatherers

In apparent contradiction to the theoretically predicted effect of population size on the quality/quantity of material culture, statistical analyses on ethnographic hunter-gatherers have shown an absence of correlation between population size and toolkit size. This has sparked a heated, if sometimes tangential, debate as to the usefulness of the theoretical models and as to what modes of cultural transmission humans are capable of and hunter-gatherers rely on. I review the directly relevant theoretical literature and argue that much of the confusion is caused by a mismatch between the theoretical variable and the empirical observable. I then confirm that a model incorporating the appropriate variable does predict a positive association between population size and toolkit size for random oblique, vertical, best-of-K, conformist, anticonformist, success bias and one-to-many cultural transmission, with the caveat that for all populations sampled, the population size has remained constant and toolkit size has reached the equilibrium for this population size. Finally, I suggest three theoretical scenarios, two of them involving variable population size, that would attenuate or eliminate this association and hence help to explain the empirical absence of correlation.This article is part of the theme issue 'Bridging cultural gaps: interdisciplinary studies in human cultural evolution'.

Cultural transmission in an ever-changing world: trial-and-error copying may be more robust than precise imitation

Cultural transmission facilitates the spread of behaviours within social groups and may lead to the establishment of stable traditions in both human and non-human animals. The fidelity of transmission is frequently emphasized as a core component of cultural evolution and as a prerequisite for cumulative culture. Fidelity is often considered a synonym of precise copying of observed behaviours. However, while precise copying guarantees reliable transmission in an ideal static world, it may be vulnerable to realistic variability in the actual environment. Here, we argue that fidelity may be more naturally achieved when the social learning mechanisms incorporate trial-and-error; and that the robustness of social transmission is thereby increased. We employed a simple model to demonstrate how culture that is produced through exact copying is fragile in an (even slightly) noisy world. When incorporating a certain degree of trial-and-error, however, cultures are more readily formed in a stochastic environment and are less vulnerable to rare ecological changes. We suggest that considering trial-and-error learning as a stabilizing component of social transmission may provide insights into cultural evolution in a realistic, variable, world.This article is part of the theme issue 'Bridging cultural gaps: interdisciplinary studies in human cultural evolution'.

Young children fail to generate an additive ratchet effect in an open-ended construction task

The ratchet effect-the gradual accumulation of changes within a cultural trait beyond a level that individuals can achieve on their own-arguably rests on two key cognitive abilities: high-fidelity social learning and innovation. Researchers have started to simulate the ratchet effect in the laboratory to identify its underlying social learning mechanisms, but studies on the developmental origins of the ratchet effect remain sparse. We used the transmission chain method and a tower construction task that had previously been used with adults to investigate whether "generations" of children between 4 and 6 years were able to make a technological product that individual children could not yet achieve. 21 children in a baseline and 80 children in transmission chains (each consisting of 10 successive children) were asked to build something as tall as possible from plasticine and sticks. Children in the chains were presented with the constructions of the two preceding generations (endstate demonstration). Results showed that tower heights did not increase across the chains nor were they different from the height of baseline towers, demonstrating a lack of improvement in tower height. However, we found evidence for cultural lineages, i.e., construction styles: towers within chains were more similar to each other than to towers from different chains. Possible explanations for the findings and directions for future research are suggested.

Cumulative cultural learning: Development and diversity

The complexity and variability of human culture is unmatched by any other species. Humans live in culturally constructed niches filled with artifacts, skills, beliefs, and practices that have been inherited, accumulated, and modified over generations. A causal account of the complexity of human culture must explain its distinguishing characteristics: It is cumulative and highly variable within and across populations. I propose that the psychological adaptations supporting cumulative cultural transmission are universal but are sufficiently flexible to support the acquisition of highly variable behavioral repertoires. This paper describes variation in the transmission practices (teaching) and acquisition strategies (imitation) that support cumulative cultural learning in childhood. Examining flexibility and variation in caregiver socialization and children's learning extends our understanding of evolution in living systems by providing insight into the psychological foundations of cumulative cultural transmission-the cornerstone of human cultural diversity.

Kin-based cultural transmission of tool use in wild chimpanzees

Current research on animal culture has focused strongly on cataloging the diversity of socially transmitted behaviors and on the social learning mechanisms that sustain their spread. Comparably less is known about the persistence of cultural behavior following innovation in groups of wild animals. We present observational data and a field experiment designed to address this question in a wild chimpanzee community, capitalizing on a novel tool behavior, moss-sponging, which appeared naturally in the community in 2011. We found that, 3 years later, moss-sponging was still present in the individuals that acquired the behavior shortly after its emergence and that it had spread further, to other community members. Our field experiment suggests that this secondary radiation and consolidation of moss-sponging is the result of transmission through matrilines, in contrast to the previously documented association-based spread among the initial cohort. We conclude that the spread of cultural behavior in wild chimpanzees follows a sequential structure of initial proximity-based horizontal transmission followed by kin-based vertical transmission.

Innovation in the collective brain

Innovation is often assumed to be the work of a talented few, whose products are passed on to the masses. Here, we argue that innovations are instead an emergent property of our species' cultural learning abilities, applied within our societies and social networks. Our societies and social networks act as collective brains. We outline how many human brains, which evolved primarily for the acquisition of culture, together beget a collective brain. Within these collective brains, the three main sources of innovation are serendipity, recombination and incremental improvement. We argue that rates of innovation are heavily influenced by (i) sociality, (ii) transmission fidelity, and (iii) cultural variance. We discuss some of the forces that affect these factors. These factors can also shape each other. For example, we provide preliminary evidence that transmission efficiency is affected by sociality--languages with more speakers are more efficient. We argue that collective brains can make each of their constituent cultural brains more innovative. This perspective sheds light on traits, such as IQ, that have been implicated in innovation. A collective brain perspective can help us understand otherwise puzzling findings in the IQ literature, including group differences, heritability differences and the dramatic increase in IQ test scores over time.

Population size vs. social connectedness - A gene-culture coevolutionary approach to cumulative cultural evolution

It has long been debated if population size is a crucial determinant of the level of culture. While empirical results are mixed, recent theoretical studies suggest that social connectedness between people may be a more important factor than the size of the entire population. These models, however, do not take into account evolutionary responses of learning strategies determining the mode of transmission and innovation and are hence not suitable for predicting the long-term implications of parameters of interest. In the present paper, to address this issue, we provide a gene-culture coevolution model, in which the microscopic learning process of each individual is explicitly described as a continuous-time stochastic process and time allocation to social and individual learning is allowed to evolve. We have found that social connectedness has a larger impact on the equilibrium level of culture than population size especially when connectedness is weak and population size is large. This result, combined with those of previous culture-only models, points to the importance of studying separate effects of population size and internal social structure to better understand spatiotemporal variation in the level of culture.

Teaching in hunter-gatherer infancy

A debate exists as to whether teaching is part of human nature and central to understanding culture or whether it is a recent invention of Western, Educated, Industrial, Rich, Democratic cultures. Some social-cultural anthropologists and cultural psychologists indicate teaching is rare in small-scale cultures while cognitive psychologists and evolutionary biologists indicate it is universal and key to understanding human culture. This study addresses the following questions: Does teaching of infants exist in hunter-gatherers? If teaching occurs in infancy, what skills or knowledge is transmitted by this process, how often does it occur and who is teaching? The study focuses on late infancy because cognitive psychologists indicate that one form of teaching, called natural pedagogy, emerges at this age. Videotapes of Aka hunter-gatherer infants were used to evaluate whether or not teaching exists among Aka hunter-gatherers of central Africa. The study finds evidence of multiple forms of teaching, including natural pedagogy, that are used to enhance learning of a variety of skills and knowledge.

Imitation is necessary for cumulative cultural evolution in an unfamiliar, opaque task

Imitation, the replication of observed behaviors, has been proposed as the crucial social learning mechanism for the generation of humanlike cultural complexity. To date, the single published experimental microsociety study that tested this hypothesis found no advantage for imitation. In contrast, the current paper reports data in support of the imitation hypothesis. Participants in "microsociety" groups built weight-bearing devices from reed and clay. Each group was assigned to one of four conditions: three social learning conditions and one asocial learning control condition. Groups able to observe other participants building their devices, in contrast to groups that saw only completed devices, show evidence of successive improvement. These results are consistent with the hypothesis that imitation is required for cumulative cultural evolution. This study adds crucial data for understanding why imitation is needed for cultural accumulation, a central defining feature of our species.

Cultural variant interaction in teaching and transmission

Focus on the way in which cultural variants affect other variants' probabilities of transmission in modeling and empirical work can enrich Kline's conceptualization of teaching. For example, the problem of communicating complex cumulative culture is an adaptive problem; teaching methods that manage transmission so that acquisition of some cultural variants increases the probability of acquiring others, provide a partial solution.

From cultural traditions to cumulative culture: parameterizing the differences between human and nonhuman culture

Diverse species exhibit cultural traditions, i.e. population-specific profiles of socially learned traits, from songbird dialects to primate tool-use behaviours. However, only humans appear to possess cumulative culture, in which cultural traits increase in complexity over successive generations. Theoretically, it is currently unclear what factors give rise to these phenomena, and consequently why cultural traditions are found in several species but cumulative culture in only one. Here, we address this by constructing and analysing cultural evolutionary models of both phenomena that replicate empirically attestable levels of cultural variation and complexity in chimpanzees and humans. In our model of cultural traditions (Model 1), we find that realistic cultural variation between populations can be maintained even when individuals in different populations invent the same traits and migration between populations is frequent, and under a range of levels of social learning accuracy. This lends support to claims that putative cultural traditions are indeed cultural (rather than genetic) in origin, and suggests that cultural traditions should be widespread in species capable of social learning. Our model of cumulative culture (Model 2) indicates that both the accuracy of social learning and the number of cultural demonstrators interact to determine the complexity of a trait that can be maintained in a population. Combining these models (Model 3) creates two qualitatively distinct regimes in which there are either a few, simple traits, or many, complex traits. We suggest that these regimes correspond to nonhuman and human cultures, respectively. The rarity of cumulative culture in nature may result from this interaction between social learning accuracy and number of demonstrators.

Cultural memory

Humans have a form of externalised memory. They are able to transmit information across generations in the form of learned cultural traditions and preserve this knowledge in artefacts. How this capability evolved from the simpler traditions of other animals is an active area of research.

Sociality influences cultural complexity

Archaeological and ethnohistorical evidence suggests a link between a population's size and structure, and the diversity or sophistication of its toolkits or technologies. Addressing these patterns, several evolutionary models predict that both the size and social interconnectedness of populations can contribute to the complexity of its cultural repertoire. Some models also predict that a sudden loss of sociality or of population will result in subsequent losses of useful skills/technologies. Here, we test these predictions with two experiments that permit learners to access either one or five models (teachers). Experiment 1 demonstrates that naive participants who could observe five models, integrate this information and generate increasingly effective skills (using an image editing tool) over 10 laboratory generations, whereas those with access to only one model show no improvement. Experiment 2, which began with a generation of trained experts, shows how learners with access to only one model lose skills (in knot-tying) more rapidly than those with access to five models. In the final generation of both experiments, all participants with access to five models demonstrate superior skills to those with access to only one model. These results support theoretical predictions linking sociality to cumulative cultural evolution.

Human cumulative culture: a comparative perspective

Many animals exhibit social learning and behavioural traditions, but human culture exhibits unparalleled complexity and diversity, and is unambiguously cumulative in character. These similarities and differences have spawned a debate over whether animal traditions and human culture are reliant on homologous or analogous psychological processes. Human cumulative culture combines high-fidelity transmission of cultural knowledge with beneficial modifications to generate a 'ratcheting' in technological complexity, leading to the development of traits far more complex than one individual could invent alone. Claims have been made for cumulative culture in several species of animals, including chimpanzees, orangutans and New Caledonian crows, but these remain contentious. Whilst initial work on the topic of cumulative culture was largely theoretical, employing mathematical methods developed by population biologists, in recent years researchers from a wide range of disciplines, including psychology, biology, economics, biological anthropology, linguistics and archaeology, have turned their attention to the experimental investigation of cumulative culture. We review this literature, highlighting advances made in understanding the underlying processes of cumulative culture and emphasising areas of agreement and disagreement amongst investigators in separate fields.

Is killer whale dialect evolution random?

The killer whale is among the few species in which cultural change accumulates over many generations, leading to cumulative cultural evolution. Killer whales have group-specific vocal repertoires which are thought to be learned rather than being genetically coded. It is supposed that divergence between vocal repertoires of sister groups increases gradually over time due to random learning mistakes and innovations. In this case, the similarity of calls across groups must be correlated with pod relatedness and, consequently, with each other. In this study we tested this prediction by comparing the patterns of call similarity between matrilines of resident killer whales from Eastern Kamchatka. We calculated the similarity of seven components from three call types across 14 matrilines. In contrast to the theoretical predictions, matrilines formed different clusters on the dendrograms made by different calls and even by different components of the same call. We suggest three possible explanations for this phenomenon. First, the lack of agreement between similarity patterns of different components may be the result of constraints in the call structure. Second, it is possible that call components change in time with different speed and/or in different directions. Third, horizontal cultural transmission of call features may occur between matrilines.

Social networks reveal cultural behaviour in tool-using [corrected] dolphins

Animal tool use is of inherent interest given its relationship to intelligence, innovation and cultural behaviour. Here we investigate whether Shark Bay bottlenose dolphins that use marine sponges as hunting tools (spongers) are culturally distinct from other dolphins in the population based on the criteria that sponging is both socially learned and distinguishes between groups. We use social network analysis to determine social preferences among 36 spongers and 69 non-spongers sampled over a 22-year period while controlling for location, sex and matrilineal relatedness. Homophily (the tendency to associate with similar others) based on tool-using status was evident in every analysis, although maternal kinship, sex and location also contributed to social preference. Female spongers were more cliquish and preferentially associated with other spongers over non-spongers. Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.