Pursuing Darwin's curious parallel: Prospects for a science of cultural evolution

Machine culture

The ability of humans to create and disseminate culture is often credited as the single most important factor of our success as a species. In this Perspective, we explore the notion of 'machine culture', culture mediated or generated by machines. We argue that intelligent machines simultaneously transform the cultural evolutionary processes of variation, transmission and selection. Recommender algorithms are altering social learning dynamics. Chatbots are forming a new mode of cultural transmission, serving as cultural models. Furthermore, intelligent machines are evolving as contributors in generating cultural traits-from game strategies and visual art to scientific results. We provide a conceptual framework for studying the present and anticipated future impact of machines on cultural evolution, and present a research agenda for the study of machine culture.

Adversarial Dynamics in Centralized Versus Decentralized Intelligent Systems

Artificial intelligence (AI) is often used to predict human behavior, thus potentially posing limitations to individuals' and collectives' freedom to act. AI's most controversial and contested applications range from targeted advertisements to crime prevention, including the suppression of civil disorder. Scholars and civil society watchdogs are discussing the oppressive dangers of AI being used by centralized institutions, like governments or private corporations. Some suggest that AI gives asymmetrical power to governments, compared to their citizens. On the other hand, civil protests often rely on distributed networks of activists without centralized leadership or planning. Civil protests create an adversarial tension between centralized and decentralized intelligence, opening the question of how distributed human networks can collectively adapt and outperform a hostile centralized AI trying to anticipate and control their activities. This paper leverages multi-agent reinforcement learning to simulate dynamics within a human-machine hybrid society. We ask how decentralized intelligent agents can collectively adapt when competing with a centralized predictive algorithm, wherein prediction involves suppressing coordination. In particular, we investigate an adversarial game between a collective of individual learners and a central predictive algorithm, each trained through deep Q-learning. We compare different predictive architectures and showcase conditions in which the adversarial nature of this dynamic pushes each intelligence to increase its behavioral complexity to outperform its counterpart. We further show that a shared predictive algorithm drives decentralized agents to align their behavior. This work sheds light on the totalitarian danger posed by AI and provides evidence that decentrally organized humans can overcome its risks by developing increasingly complex coordination strategies.

Cultural evolution with uncertain provision of learning resources

An essential feature of human progress is the use of different modes of learning so agents acquire the appropriate behaviour to survive in a changing environment. Learning may result from agents who discover new knowledge on their own (individual learning), or imitate the behaviour of others (social learning). Social learning is less costly than discovery, but imitation might yield no benefit. Early theoretical models of a population consisting of purely individual and purely social learners found that both types are present in an evolutionary equilibrium. However, the presence of social learners did not provide any improvement to the average population fitness. Subsequent research showed that the presence of social learners could improve the average population fitness, provided that the pure characterisation of the agents' learning is relaxed. We return to the pure conceptualisation of agents to challenge an assumption in the early work: agents were guaranteed enough resources to perform their desired learning. We show that, if the resources an agent receives are uncertain, this turns social learning into a source of fitness improvement at the population level. Perhaps counter-intuitively, uncertain provision of resources prompts an increase in the proportion of the population that pursues the costlier individual learning activity in equilibrium.

The experimental evolution of human culture: flexibility, fidelity and environmental instability

The past 2 Myr have seen both unprecedented environmental instability and the evolution of the human capacity for complex culture. This, along with the observation that cultural evolution occurs faster than genetic evolution, has led to the suggestion that culture is an adaptation to an unstable environment. We test this hypothesis by examining the ability of human social learning to respond to environmental changes. We do this by inserting human participants (n = 4800) into evolutionary simulations with a changing environment while varying the social information available to individuals across five conditions. We find that human social learning shows some signs of adaptation to environmental instability, including critical social learning, the adoption of up-and-coming traits and, unexpectedly, contrariness. However, these are insufficient to avoid significant fitness declines when the environment changes, and many individuals are highly conformist, which exacerbates the fitness effects of environmental change. We conclude that human social learning reflects a compromise between the competing needs for flexibility to accommodate environmental change and fidelity to accurately transmit valuable cultural information.

Expanding the measurement of culture with a sample of two billion humans

Culture has played a pivotal role in human evolution. Yet, the ability of social scientists to study culture is limited by the currently available measurement instruments. Scholars of culture must regularly choose between scalable but sparse survey-based methods or restricted but rich ethnographic methods. Here, we demonstrate that massive online social networks can advance the study of human culture by providing quantitative, scalable and high-resolution measurement of behaviourally revealed cultural values and preferences. We employ data across nearly 60 000 topic dimensions drawn from two billion Facebook users across 225 countries and territories. We first validate that cultural distances calculated from this measurement instrument correspond to traditional survey-based and objective measures of cross-national cultural differences. We then demonstrate that this expanded measure enables rich insight into the cultural landscape globally at previously impossible resolution. We analyse the importance of national borders in shaping culture and compare subnational divisiveness with gender divisiveness across countries. Our measure enables detailed investigation into the geopolitical stability of countries, social cleavages within small- and large-scale human groups, the integration of migrant populations and the disaffection of certain population groups from the political process, among myriad other potential future applications.

Major Evolutionary Transitions and the Roles of Facilitation and Information in Ecosystem Transformations

A small number of extraordinary “Major Evolutionary Transitions” (METs) have attracted attention among biologists. They comprise novel forms of individuality and information, and are defined in relation to organismal complexity, irrespective of broader ecosystem-level effects. This divorce between evolutionary and ecological consequences qualifies unicellular eukaryotes, for example, as a MET although they alone failed to significantly alter ecosystems. Additionally, this definition excludes revolutionary innovations not fitting into either MET type (e.g., photosynthesis). We recombine evolution with ecology to explore how and why entire ecosystems were newly created or radically altered – as Major System Transitions (MSTs). In doing so, we highlight important morphological adaptations that spread through populations because of their immediate, direct-fitness advantages for individuals. These are Major Competitive Transitions, or MCTs. We argue that often multiple METs and MCTs must be present to produce MSTs. For example, sexually-reproducing, multicellular eukaryotes (METs) with anisogamy and exoskeletons (MCTs) significantly altered ecosystems during the Cambrian. Therefore, we introduce the concepts of Facilitating Evolutionary Transitions (FETs) and Catalysts as key events or agents that are insufficient themselves to set a MST into motion, but are essential parts of synergies that do. We further elucidate the role of information in MSTs as transitions across five levels: (I) Encoded; (II) Epigenomic; (III) Learned; (IV) Inscribed; and (V) Dark Information. The latter is ‘authored’ by abiotic entities rather than biological organisms. Level IV has arguably allowed humans to produce a MST, and V perhaps makes us a FET for a future transition that melds biotic and abiotic life into one entity. Understanding the interactive processes involved in past major transitions will illuminate both current events and the surprising possibilities that abiotically-created information may produce.

Personality predicts innovation and social learning in children: Implications for cultural evolution

Innovation and social learning are the pillars of cultural evolution, allowing cultural behaviours to cumulatively advance over generations. Yet, little is known about individual differences in the use of social and asocial information. We examined whether personality influenced 7-11-year-old children's (N = 282) propensity to elect to observe others first or independently generate solutions to novel problems. Conscientiousness was associated with electing for no demonstrations, while agreeableness was associated with opting for demonstrations. For children receiving demonstrations, openness to experience consistently predicted deviation from observed methods. Children who opted for no demonstrations were also more likely than those opting for demonstrations to exhibit tool manufacture on an innovation challenge and displayed higher creativity, as measured by an alternate uses task. These results highlight how new cultural traditions emerge, establish and advance by identifying which individuals generate new cultural variants in populations and which are influential in the diffusion of these variants, and help reduce the apparent tension within the 'ratchet' of cumulative culture.

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'.

Population turnover facilitates cultural selection for efficiency in birds

Culture, defined as socially transmitted information and behaviors that are shared in groups and persist over time, is increasingly accepted to occur across a wide range of taxa and behavioral domains.¹ While persistent, cultural traits are not necessarily static, and their distribution can change in frequency and type in response to selective pressures, analogous to that of genetic alleles. This has led to the treatment of culture as an evolutionary process, with cultural evolutionary theory arguing that culture exhibits the three fundamental components of Darwinian evolution: variation, competition, and inheritance.^2-5 Selection for more efficient behaviors over alternatives is a crucial component of cumulative cultural evolution,⁶ yet our understanding of how and when such cultural selection occurs in non-human animals is limited. We performed a cultural diffusion experiment using 18 captive populations of wild-caught great tits (Parus major) to ask whether more efficient foraging traditions are selected for, and whether this process is affected by a fundamental demographic process-population turnover. Our results showed that gradual replacement of individuals with naive immigrants greatly increased the probability that a more efficient behavior invaded a population's cultural repertoire and outcompeted an established inefficient behavior. Fine-scale, automated behavioral tracking revealed that turnover did not increase innovation rates, but instead acted on adoption rates, as immigrants disproportionately sampled novel, efficient behaviors relative to available social information. These results provide strong evidence for cultural selection for efficiency in animals, and highlight the mechanism that links population turnover to this process.

Cultural selection and biased transformation: two dynamics of cultural evolution

Here, I discuss two broad versions of human cultural evolution which currently exist in the literature and which emphasize different underlying dynamics. One, which originates in population-genetic-style modelling, emphasizes how cultural selection causes some cultural variants to be favoured and gradually increase in frequency over others. The other, which draws more from cognitive science, holds that cultural change is driven by the biased transformation of cultural variants by individuals in non-random and consistent directions. Despite claims that cultural evolution is characterized by one or the other of these dynamics, these are neither mutually exclusive nor a dichotomy. Different domains of human culture are likely to be more or less strongly weighted towards cultural selection or biased transformation. Identifying cultural dynamics in real-world cultural data is challenging given that they can generate the same population-level patterns, such as directional change or cross-cultural stability, and the same cognitive and emotional mechanisms may underlie both cultural selection and biased transformation. Nevertheless, fine-grained historical analysis and laboratory experiments, combined with formal models to generate quantitative predictions, offer the best way of distinguishing them. This article is part of the theme issue 'Foundations of cultural evolution'.

Comparative bioacoustics: a roadmap for quantifying and comparing animal sounds across diverse taxa

Animals produce a wide array of sounds with highly variable acoustic structures. It is possible to understand the causes and consequences of this variation across taxa with phylogenetic comparative analyses. Acoustic and evolutionary analyses are rapidly increasing in sophistication such that choosing appropriate acoustic and evolutionary approaches is increasingly difficult. However, the correct choice of analysis can have profound effects on output and evolutionary inferences. Here, we identify and address some of the challenges for this growing field by providing a roadmap for quantifying and comparing sound in a phylogenetic context for researchers with a broad range of scientific backgrounds. Sound, as a continuous, multidimensional trait can be particularly challenging to measure because it can be hard to identify variables that can be compared across taxa and it is also no small feat to process and analyse the resulting high-dimensional acoustic data using approaches that are appropriate for subsequent evolutionary analysis. Additionally, terminological inconsistencies and the role of learning in the development of acoustic traits need to be considered. Phylogenetic comparative analyses also have their own sets of caveats to consider. We provide a set of recommendations for delimiting acoustic signals into discrete, comparable acoustic units. We also present a three-stage workflow for extracting relevant acoustic data, including options for multivariate analyses and dimensionality reduction that is compatible with phylogenetic comparative analysis. We then summarize available phylogenetic comparative approaches and how they have been used in comparative bioacoustics, and address the limitations of comparative analyses with behavioural data. Lastly, we recommend how to apply these methods to acoustic data across a range of study systems. In this way, we provide an integrated framework to aid in quantitative analysis of cross-taxa variation in animal sounds for comparative phylogenetic analysis. In addition, we advocate the standardization of acoustic terminology across disciplines and taxa, adoption of automated methods for acoustic feature extraction, and establishment of strong data archival practices for acoustic recordings and data analyses. Combining such practices with our proposed workflow will greatly advance the reproducibility, biological interpretation, and longevity of comparative bioacoustic studies.

Empowering Urban Governance through Urban Science: Multi-Scale Dynamics of Urban Systems Worldwide

Cities are facing many sustainability issues in the context of the current global interdependency characterized by an economic uncertainty coupled to climate changes, which challenge their local policies aiming to better conciliate reasonable growth with livable urban environment. The urban dynamic models developed by the so-called “urban science” can provide a useful foundation for more sustainable urban policies. It implies that their proposals have been validated by correct observations of the diversity of situations in the world. However, international comparisons of the evolution of cities often produce unclear results because national territorial frameworks are not always in strict correspondence with the dynamics of urban systems. We propose to provide various compositions of systems of cities in order to better take into account the dynamic networking of cities that go beyond regional and national territorial boundaries. Different models conceived for explaining city size and urban growth distributions enable the establishing of a correspondence between urban trajectories when observed at the level of cities and systems of cities. We test the validity and representativeness of several dynamic models of complex urban systems and their variations across regions of the world, at the macroscopic scale of systems of cities. The originality of the approach resides in the way it considers spatial interaction and evolutionary path dependence as major features in the general behavior of urban entities. The models studied include diverse and complementary processes, such as economic exchanges, diffusion of innovations, and physical network flows. Complex systems dynamics is in principle unpredictable, but contextualizing it regarding demographic, income, and resource components may help in minimizing the forecasting errors. We use, among others, a new unique source correlating population and built-up footprint at world scale: the Global Human Settlement built-up areas (GHS-BU). Following the methodology and results already obtained in the European GeoDiverCity project, including USA, Europe, and BRICS countries, we complete them with this new dataset at world scale and different models. This research helps in further empirical testing of the hypotheses of the evolutionary theory of urban systems and partially revising them. We also suggest research directions towards the coupling of these models into a multi-scale model of urban growth.

How to Translate a Verbal Theory Into a Formal Model

Abstract. Turning verbal theories into formal models is an essential business of a mature science. Here I elaborate on taxonomies of models, provide ten lessons for translating a verbal theory into a formal model, and discuss the specific challenges involved in collaborations between modelers and non-modelers. It’s a start.

Open-ended cumulative cultural evolution of Hollywood film crews

Are there large-scale trends in art history that surpass individual creativity or relatively short artistic movements? Many theories describe art history as a process similar to a change of fashions, while others suggest that art can be progressive - getting better, in some sense, over time. We approach this question anew with the theory of cumulative cultural evolution, which describes cultural accomplishments in terms of innovations that are maintained across generations and accumulated to support ever greater creative potential. In this paper, we empirically test the possibility for cumulative evolution in the techniques used to make an artistic product. Specifically, we measure the size and structure of the production crews in American films in 1910-2010 based on a dataset of 1000 popular films across the century. We find that film crews become exponentially more complex, with a growing set of core jobs, and more innovative in creating new jobs in filmmaking. Our study shows that art history can be cumulative, showing the progressive maintenance of innovative techniques, and thus providing an alternative to the widespread view of art history as a mere fluctuation of trends and fashions.

Editors' Review and Introduction: The Cultural Evolution of Cognition

This topic addresses a question of key interest to cognitive science, namely which factors may have triggered, constrained, or shaped the course of cognitive evolution. It highlights the relevance of culture as a driving force in this process, with a special focus on social learning and language, conceptual tools, and material culture. In so doing, the topic combines two goals: to provide an overview of current empirical and theoretical work leading this field, tailored for a wider cognitive science audience, and to investigate the potential for integrating multiple perspectives across several timescales and levels of analysis, from the microlevel of individual behavior to the macrolevel of cultural change and language diversification. One key purpose is to assess the extent to which the different research approaches can cross-fertilize each other, thereby also contributing to the advancement of cognitive science more broadly.

Wissen für den Wandel – Wissenstheoretische Grundlagen einer nachhaltigen Bioökonomiepolitik

Eine Strategie zur Umsetzung einer nachhaltigen Bioökonomie muss neben disziplinären und technischen Zielvorstellungen auch den gesellschaftlichen Wandel einplanen und vorbereiten. Eine zukunftsfähige politische Strategie muss also neben dem techno-ökonomischen Wissen ebenso solches Wissen fördern, welches es Produzenten und Konsumenten ermöglicht, nicht-nachhaltige Verfahren und Verhaltensweisen nicht nur zu reduzieren, sondern radikal zu verändern. Dazu gehören neben den technologischen Fertigkeiten auch ein interdisziplinäres Verständnis systemischer Zusammenhänge, demokratisch legitimierte Zielvorstellungen sowie die notwendigen Fähigkeiten, um diese Ziele partizipativ umzusetzen. Nur durch die Anerkennung und gezielte Förderung dieses als dediziert bezeichneten Wissens können nachhaltige Veränderungen erwachsen. Der Beitrag ergänzt das evolutionsökonomische Konzept des wissensbasierten Wandels durch Ansätze aus den Nachhaltigkeitswissenschaften. Konkret werden die besonderen Eigenschaften dieses dedizierten Wissens diskutiert, wodurch nicht zuletzt eine Grundlage für neue Ansätze in der Bioökonomiepolitik geschaffen wird.

The Development of Cumulative Cultural Learning

Human culture is unique among animals in its complexity, variability, and cumulative quality. This article describes the development and diversity of cumulative cultural learning. Children inhabit cultural ecologies that consist of group-specific knowledge, practices, and technologies that are inherited and modified over generations. The learning processes that enable cultural acquisition and transmission are universal but are sufficiently flexible to accommodate the highly diverse cultural repertoires of human populations. Children learn culture in several complementary ways, including through exploration, observation, participation, imitation, and instruction. These methods of learning vary in frequency and kind within and between populations due to variation in socialization values and practices associated with specific educational institutions, skill sets, and knowledge systems. The processes by which children acquire and transmit the cumulative culture of their communities provide unique insight into the evolution and ontogeny of human cognition and culture.

What is cumulative cultural evolution?

In recent years, the phenomenon of cumulative cultural evolution (CCE) has become the focus of major research interest in biology, psychology and anthropology. Some researchers argue that CCE is unique to humans and underlies our extraordinary evolutionary success as a species. Others claim to have found CCE in non-human species. Yet others remain sceptical that CCE is even important for explaining human behavioural diversity and complexity. These debates are hampered by multiple and often ambiguous definitions of CCE. Here, we review how researchers define, use and test CCE. We identify a core set of criteria for CCE which are both necessary and sufficient, and may be found in non-human species. We also identify a set of extended criteria that are observed in human CCE but not, to date, in other species. Different socio-cognitive mechanisms may underlie these different criteria. We reinterpret previous theoretical models and observational and experimental studies of both human and non-human species in light of these more fine-grained criteria. Finally, we discuss key issues surrounding information, fitness and cognition. We recommend that researchers are more explicit about what components of CCE they are testing and claiming to demonstrate.

Cultural flies: Conformist social learning in fruitflies predicts long-lasting mate-choice traditions

Despite theoretical justification for the evolution of animal culture, empirical evidence for it beyond mammals and birds remains scant, and we still know little about the process of cultural inheritance. In this study, we propose a mechanism-driven definition of animal culture and test it in the fruitfly. We found that fruitflies have five cognitive capacities that enable them to transmit mating preferences culturally across generations, potentially fostering persistent traditions (the main marker of culture) in mating preference. A transmission chain experiment validates a model of the emergence of local traditions, indicating that such social transmission may lead initially neutral traits to become adaptive, hence strongly selecting for copying and conformity. Although this situation was suggested decades ago, it previously had little empirical support.

Large-scale quantitative profiling of the Old English verse tradition

The corpus of Old English verse is an indispensable source for scholars of the Indo-European tradition, early Germanic culture and English literary history. Although it has been the focus of sustained literary scholarship for over two centuries, Old English poetry has not been subjected to corpus-wide computational profiling, in part because of the sparseness and extreme fragmentation of the surviving material. Here we report a detailed quantitative analysis of the whole corpus that considers a broad range of features reflective of sound, metre and diction. This integrated examination of fine-grained features enabled us to identify salient stylistic patterns, despite the inherent limitations of the corpus. In particular, we provide quantitative evidence consistent with the unitary authorship of Beowulf and the Cynewulfian authorship of Andreas, shedding light on two longstanding questions in Old English philology. Our results demonstrate the usefulness of high-dimensional stylometric profiling for fragmentary literary traditions and lay the foundation for future studies of the cultural evolution of English literature.

Migration, acculturation, and the maintenance of between-group cultural variation

How do migration and acculturation (i.e. psychological or behavioral change resulting from migration) affect within- and between-group cultural variation? Here I address this question by drawing analogies between genetic and cultural evolution. Population genetic models show that migration rapidly breaks down between-group genetic structure. In cultural evolution, however, migrants or their descendants can acculturate to local behaviors via social learning processes such as conformity, potentially preventing migration from eliminating between-group cultural variation. An analysis of the empirical literature on migration suggests that acculturation is common, with second and subsequent migrant generations shifting, sometimes substantially, towards the cultural values of the adopted society. Yet there is little understanding of the individual-level dynamics that underlie these population-level shifts. To explore this formally, I present models quantifying the effect of migration and acculturation on between-group cultural variation, for both neutral and costly cooperative traits. In the models, between-group cultural variation, measured using F statistics, is eliminated by migration and maintained by conformist acculturation. The extent of acculturation is determined by the strength of conformist bias and the number of demonstrators from whom individuals learn. Acculturation is countered by assortation, the tendency for individuals to preferentially interact with culturally-similar others. Unlike neutral traits, cooperative traits can additionally be maintained by payoff-biased social learning, but only in the presence of strong sanctioning mechanisms (e.g. institutions). Overall, the models show that surprisingly little conformist acculturation is required to maintain realistic amounts of between-group cultural diversity. While these models provide insight into the potential dynamics of acculturation and migration in cultural evolution, they also highlight the need for more empirical research into the individual-level learning biases that underlie migrant acculturation.

Compression in cultural evolution: Homogeneity and structure in the emergence and evolution of a large-scale online collaborative art project

Cultural evolutionary theory provides a framework for explaining change in population-level distributions. A consistent finding in the literature is that multiple transmission episodes shape a distribution of cultural traits to become more compressible, i.e., a set of derived traits are more compressed than their ancestral forms. Importantly, this amplification of compressible patterns can become manifest in two ways, either via the homogenisation of variation or through the organisation of variation into structured and specialised patterns. Using a novel, large-scale dataset from Reddit Place, an online collaborative art project, we investigate the emergence and evolution of compressible patterns on a 1000x1000 pixel canvas. Here, all Reddit users could select a coloured pixel, place it on the canvas, and then wait for a fixed period before placing another pixel. By analysing all 16.5 million pixel placements by over 1 million individuals, we found that compression follows a quadratic trajectory through time. From a non-structured state, where individual artworks exist relatively independently from one another, Place gradually transitions to a structured state where pixel placements form specialised, interdependent patterns.

Four misunderstandings about cultural attraction

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 (Box ). This naturalistic quality distinguishes CAT from other evolutionary approaches to culture.

Parasites and politics: why cross-cultural studies must control for relatedness, proximity and covariation

A growing number of studies seek to identify predictors of broad-scale patterns in human cultural diversity, but three sources of non-independence in human cultural variables can bias the results of cross-cultural studies. First, related cultures tend to have many traits in common, regardless of whether those traits are functionally linked. Second, societies in geographical proximity will share many aspects of culture, environment and demography. Third, many cultural traits covary, leading to spurious relationships between traits. Here, we demonstrate tractable methods for dealing with all three sources of bias. We use cross-cultural analyses of proposed associations between human cultural traits and parasite load to illustrate the potential problems of failing to correct for these three forms of statistical non-independence. Associations between parasite stress and sociosexuality, authoritarianism, democracy and language diversity are weak or absent once relatedness and proximity are taken into account, and parasite load has no more power to explain variation in traditionalism, religiosity and collectivism than other measures of biodiversity, climate or population size do. Without correction for statistical non-independence and covariation in cross-cultural analyses, we risk misinterpreting associations between culture and environment.

Cultural evolutionary theory: How culture evolves and why it matters

Human cultural traits-behaviors, ideas, and technologies that can be learned from other individuals-can exhibit complex patterns of transmission and evolution, and researchers have developed theoretical models, both verbal and mathematical, to facilitate our understanding of these patterns. Many of the first quantitative models of cultural evolution were modified from existing concepts in theoretical population genetics because cultural evolution has many parallels with, as well as clear differences from, genetic evolution. Furthermore, cultural and genetic evolution can interact with one another and influence both transmission and selection. This interaction requires theoretical treatments of gene-culture coevolution and dual inheritance, in addition to purely cultural evolution. In addition, cultural evolutionary theory is a natural component of studies in demography, human ecology, and many other disciplines. Here, we review the core concepts in cultural evolutionary theory as they pertain to the extension of biology through culture, focusing on cultural evolutionary applications in population genetics, ecology, and demography. For each of these disciplines, we review the theoretical literature and highlight relevant empirical studies. We also discuss the societal implications of the study of cultural evolution and of the interactions of humans with one another and with their environment.

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.

Culture extends the scope of evolutionary biology in the great apes

Discoveries about the cultures and cultural capacities of the great apes have played a leading role in the recognition emerging in recent decades that cultural inheritance can be a significant factor in the lives not only of humans but also of nonhuman animals. This prominence derives in part from these primates being those with whom we share the most recent common ancestry, thus offering clues to the origins of our own thoroughgoing reliance on cumulative cultural achievements. In addition, the intense research focus on these species has spawned an unprecedented diversity of complementary methodological approaches, the results of which suggest that cultural phenomena pervade the lives of these apes, with potentially major implications for their broader evolutionary biology. Here I review what this extremely broad array of observational and experimental methodologies has taught us about the cultural lives of chimpanzees, gorillas, and orangutans and consider the ways in which this knowledge extends our wider understanding of primate biology and the processes of adaptation and evolution that shape it. I address these issues first by evaluating the extent to which the results of cultural inheritance echo a suite of core principles that underlie organic Darwinian evolution but also extend them in new ways and then by assessing the principal causal interactions between the primary, genetically based organic processes of evolution and the secondary system of cultural inheritance that is based on social learning from others.

Synchronized practice helps bearded capuchin monkeys learn to extend attention while learning a tradition

Culture extends biology in that the setting of development shapes the traditions that individuals learn, and over time, traditions evolve as occasional variations are learned by others. In humans, interactions with others impact the development of cognitive processes, such as sustained attention, that shape how individuals learn as well as what they learn. Thus, learning itself is impacted by culture. Here, we explore how social partners might shape the development of psychological processes impacting learning a tradition. We studied bearded capuchin monkeys learning a traditional tool-using skill, cracking nuts using stone hammers. Young monkeys practice components of cracking nuts with stones for years before achieving proficiency. We examined the time course of young monkeys' activity with nuts before, during, and following others' cracking nuts. Results demonstrate that the onset of others' cracking nuts immediately prompts young monkeys to start handling and percussing nuts, and they continue these activities while others are cracking. When others stop cracking nuts, young monkeys sustain the uncommon actions of percussing and striking nuts for shorter periods than the more common actions of handling nuts. We conclude that nut-cracking by adults can promote the development of sustained attention for the critical but less common actions that young monkeys must practice to learn this traditional skill. This work suggests that in nonhuman species, as in humans, socially specified settings of development impact learning processes as well as learning outcomes. Nonhumans, like humans, may be culturally variable learners.