Evolution of cultural traits occurs at similar relative rates in different world regions

A fundamental issue in understanding human diversity is whether or not there are regular patterns and processes involved in cultural change. Theoretical and mathematical models of cultural evolution have been developed and are increasingly being used and assessed in empirical analyses. Here, we test the hypothesis that the rates of change of features of human socio-cultural organization are governed by general rules. One prediction of this hypothesis is that different cultural traits will tend to evolve at similar relative rates in different world regions, despite the unique historical backgrounds of groups inhabiting these regions. We used phylogenetic comparative methods and systematic cross-cultural data to assess how different socio-cultural traits changed in (i) island southeast Asia and the Pacific, and (ii) sub-Saharan Africa. The relative rates of change in these two regions are significantly correlated. Furthermore, cultural traits that are more directly related to external environmental conditions evolve more slowly than traits related to social structures. This is consistent with the idea that a form of purifying selection is acting with greater strength on these more environmentally linked traits. These results suggest that despite contingent historical events and the role of humans as active agents in the historical process, culture does indeed evolve in ways that can be predicted from general principles     

Mode and tempo in the evolution of socio-political organization: reconciling 'Darwinian' and 'Spencerian' evolutionary approaches in anthropology

Traditional investigations of the evolution of human social and political institutions trace their ancestry back to nineteenth century social scientists such as Herbert Spencer, and have concentrated on the increase in socio-political complexity over time. More recent studies of cultural evolution have been explicitly informed by Darwinian evolutionary theory and focus on the transmission of cultural traits between individuals. These two approaches to investigating cultural change are often seen as incompatible. However, we argue that many of the defining features and assumptions of 'Spencerian' cultural evolutionary theory represent testable hypotheses that can and should be tackled within a broader 'Darwinian' framework. In this paper we apply phylogenetic comparative techniques to data from Austronesian-speaking societies of Island South-East Asia and the Pacific to test hypotheses about the mode and tempo of human socio-political evolution. We find support for three ideas often associated with Spencerian cultural evolutionary theory: (i) political organization has evolved through a regular sequence of forms, (ii) increases in hierarchical political complexity have been more common than decreases, and (iii) political organization has co-evolved with the wider presence of hereditary social stratification.     

Macro-evolutionary studies of cultural diversity: a review of empirical studies of cultural transmission and cultural adaptation

A growing body of theoretical and empirical research has examined cultural transmission and adaptive cultural behaviour at the individual, within-group level. However, relatively few studies have tried to examine proximate transmission or test ultimate adaptive hypotheses about behavioural or cultural diversity at a between-societies macro-level. In both the history of anthropology and in present-day work, a common approach to examining adaptive behaviour at the macro-level has been through correlating various cultural traits with features of ecology. We discuss some difficulties with simple ecological associations, and then review cultural phylogenetic studies that have attempted to go beyond correlations to understand the underlying cultural evolutionary processes. We conclude with an example of a phylogenetically controlled approach to understanding proximate transmission pathways in Austronesian cultural diversity.     

Mutual benefit cooperation and ethnic cultural diversity

We show that mutual benefit cooperation can favor the evolution of a preference to interact with individuals that are similar to themselves with respect to one or several arbitrary cultural tags. One necessary requisite to obtain this result is an asymmetry between partners in such a way that one of them (actor) proposes the cooperation and elects the partner, whereas the other (receiver) never rejects the offer because cooperation always reports benefits. The advantage of individuals possessing allele for preferential assortment is due to receiving more offers of mutually beneficial cooperation when there is linkage disequilibrium between the assortment locus and the cultural tags. An especially favorable scenario for the evolution of such preference is a subdivided metapopulation. In this case, the homogeneity within populations and the divergence between populations is favored, facilitating the existence of ethnic groups.     

Hominid cultural transmission and the evolution of language

This paper presents the hypothesis that linguistic capacity evolved through the action of natural selection as an instrument which increased the efficiency of the cultural transmission system of early hominids. We suggest that during the early stages of hominization, hominid social learning, based on indirect social learning mechanisms and true imitation, came to constitute cumulative cultural transmission based on true imitation and the approval or disapproval of the learned behaviour of offspring. A key factor for this transformation was the development of a conceptual capacity for categorizing learned behaviour in value terms - positive or negative, good or bad. We believe that some hominids developed this capacity for categorizing behaviour, and such an ability allowed them to approve or disapprove of their offsprings- learned behaviour. With such an ability, hominids were favoured, as they could transmit to their offspring all their behavioural experience about what can and cannot be done. This capacity triggered a cultural transmission system similar to the human one, though pre-linguistic. We suggest that the adaptive advantage provided by this new system of social learning generated a selection pressure in favour of the development of a linguistic capacity allowing children to better understand the new kind of evaluative information received from parents.     

Evolutionary Change and Epistemology

This paper is concerned with the debate in evolutionary epistemology about the nature of the evolutionary process at work in the development of science: whether it is Darwinian or Lamarckian. It is claimed that if we are to make progress through the many arguments that have grown up around this issue, we must return to an examination of the concepts of change and evolution, and examine the basic kinds of mechanism capable of bringing evolution about. This examination results in two kinds of processes being identified, dubbed direct and indirect, and these are claimed to exhaust all possibilities. These ideas are then applied to a selection of the debates within evolutionary epistemology. It is shown that while arguments about the pattern and rate of evolutionary change are necessarily inconclusive, those concerning the origin of novel variations and the mode of inheritance can be resolved by means of the distinctions made here. It is claimed that the process of selection in the evolution of science can also be clarified. The conclusion is that the main process producing the evolution of science is a direct or Lamarckian one although, if realism is correct, an indirect or Darwinian process plays a vital role.     

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.     

Interactions of genetic and cultural evolution: Models and examples

This paper proposes models and examples of five principal modes of interaction between genes and culture in human evolution. Because genes and culture ultimately interact in the minds of individuals, the models are focused on individual level processes of constrained microevolution. The central hypotheses are (1) that cultural evolution as well as genetic evolution commonly proceeds by the differential transmission of alternative instructions among individuals, (2) that genetic and cultural processes directly interact through mutual influence on each other's differentials of transmission in a population, (3) that the cultural process is often self-selecting by its own criteria, and (4) that these criteria generally operate to enhance rather than oppose human adaptation. Evolutionary change at higher levels, which is particularly important in sociocultural evolution, is interpreted as restructuring the nature and extent of the variability available at the individual level. To clarify the conceptual differences of the models and hopefully to stimulate related analyses in other areas, I discuss selected examples of each of these interactions. I conclude with some remarks on the relative importance of the models to human ecology and evolution.     

Evolutionary accounts of human behavioural diversity

Human beings persist in an extraordinary range of ecological settings, in the process exhibiting enormous behavioural diversity, both within and between populations. People vary in their social, mating and parental behaviour and have diverse and elaborate beliefs, traditions, norms and institutions. The aim of this theme issue is to ask whether, and how, evolutionary theory can help us to understand this diversity. In this introductory article, we provide a background to the debate surrounding how best to understand behavioural diversity using evolutionary models of human behaviour. In particular, we examine how diversity has been viewed by the main subdisciplines within the human evolutionary behavioural sciences, focusing in particular on the human behavioural ecology, evolutionary psychology and cultural evolution approaches. In addition to differences in focus and methodology, these subdisciplines have traditionally varied in the emphasis placed on human universals, ecological factors and socially learned behaviour, and on how they have addressed the issue of genetic variation. We reaffirm that evolutionary theory provides an essential framework for understanding behavioural diversity within and between human populations, but argue that greater integration between the subfields is critical to developing a satisfactory understanding of diversity.     

Individuals and the evolution of biological and cultural systems

Recently, it has been suggested that anthropologists could more effectively build scientific theories of cultural evolution by reference to biology rather than social science. In this way, the evolution of cultures might be more usefully viewed as an anolog to the evolution of species. In systematic biology, however, the nature of species continues to be the subject of a long-standing duality of thought. This duality is analogous to the longstanding conflict in anthropology over the nature of culture. We argue, by analogy to Michael Ghiselin’s work on species, that a culture is an individual, not a class, and that cultures, like other individual entities, evolve. This view is highly concordant with concepts of culture formulated in earlier decades of this century. It has also been the philosophical orientation of American archaeology for approximately the last 25 years. We conclude that both biology and anthropology have an equal potential of contributing to a general evolutionary theory.     

Modelling the evolution and diversity of cumulative culture

Previous work on mathematical models of cultural evolution has mainly focused on the diffusion of simple cultural elements. However, a characteristic feature of human cultural evolution is the seemingly limitless appearance of new and increasingly complex cultural elements. Here, we develop a general modelling framework to study such cumulative processes, in which we assume that the appearance and disappearance of cultural elements are stochastic events that depend on the current state of culture. Five scenarios are explored: evolution of independent cultural elements, stepwise modification of elements, differentiation or combination of elements and systems of cultural elements. As one application of our framework, we study the evolution of cultural diversity (in time as well as between groups).     

Review. The multiple roles of cultural transmission experiments in understanding human cultural evolution

In this paper, we explore how experimental studies of cultural transmission in adult humans can address general questions regarding the 'who, what, when and how' of human cultural transmission, and consequently inform a theory of human cultural evolution. Three methods are discussed. The transmission chain method, in which information is passed along linear chains of participants, has been used to identify content biases in cultural transmission. These concern the kind of information that is transmitted. Several such candidate content biases have now emerged from the experimental literature. The replacement method, in which participants in groups are gradually replaced or moved across groups, has been used to study phenomena such as cumulative cultural evolution, cultural group selection and cultural innovation. The closed-group method, in which participants learn in groups with no replacement, has been used to explore issues such as who people choose to learn from and when they learn culturally as opposed to individually. A number of the studies reviewed here have received relatively little attention within their own disciplines, but we suggest that these, and future experimental studies of cultural transmission that build on them, can play an important role in a broader science of cultural evolution.     

The cultural evolution of fertility decline

Cultural evolutionists have long been interested in the problem of why fertility declines as populations develop. By outlining plausible mechanistic links between individual decision-making, information flow in populations and competition between groups, models of cultural evolution offer a novel and powerful approach for integrating multiple levels of explanation of fertility transitions. However, only a modest number of models have been published. Their assumptions often differ from those in other evolutionary approaches to social behaviour, but their empirical predictions are often similar. Here I offer the first overview of cultural evolutionary research on demographic transition, critically compare it with approaches taken by other evolutionary researchers, identify gaps and overlaps, and highlight parallel debates in demography. I suggest that researchers divide their labour between three distinct phases of fertility decline—the origin, spread and maintenance of low fertility—each of which may be driven by different causal processes, at different scales, requiring different theoretical and empirical tools. A comparative, multi-level and mechanistic framework is essential for elucidating both the evolved aspects of our psychology that govern reproductive decision-making, and the social, ecological and cultural contingencies that precipitate and sustain fertility decline.     

Bicultural oscillation as a long-term adaptation to cultural frontiers: Cases and questions

Comparison of two nomadic peoples, one pastoral, the other food-collecting, reveals that rapid bicultural oscillation of both is an adaptation to their multizoned environments. One may speak of their being flexible in the face of temporally variable environmental hazards and opportunities. For each people, the more nomadic of their two cultures is associated with norms of propriety, the more sedentary one entails what Freilich calls smart norms. It is argued that this complementation gives both cultures continuing appeal, thereby facilitating rapid change. A major difference between decisionmaking mechanisms in the two cases underscores that we treat a system type in a very abstract sense. Other, possibly similar cases are noted from ethnographic literature. A formal theory is put forward concerning the tendency of people under certain conditions to develop oscillating biculturalism. Such rapidly oscillating systems are proposed to have a biological analogue in versatile acclimatizers.     

The evolution of the diversity of cultures

The abundant evidence that Homo sapiens evolved in Africa within the past 200,000 years, and dispersed across the world only within the past 100,000 years, provides us with a strong framework in which to consider the evolution of human diversity. While there is evidence that the human capacity for culture has a deeper history, going beyond the origin of the hominin clade, the tendency for humans to form cultures as part of being distinct communities and populations changed markedly with the evolution of H. sapiens. In this paper, we investigate 'cultures' as opposed to 'culture', and the question of how and why, compared to biological diversity, human communities and populations are so culturally diverse. We consider the way in which the diversity of human cultures has developed since 100,000 years ago, and how its rate was subject to environmental factors. We argue that the causes of this diversity lie in the distribution of resources and the way in which human communities reproduce over several generations, leading to fissioning of kin groups. We discuss the consequences of boundary formation through culture in their broader ecological and evolutionary contexts.     

A two level mutation-selection model of cultural evolution and diversity

Cultural evolution is a complex process that can happen at several levels. At the level of individuals in a population, each human bears a set of cultural traits that he or she can transmit to its offspring (vertical transmission) or to other members of his or her society (horizontal transmission). The relative frequency of a cultural trait in a population or society can thus increase or decrease with the relative reproductive success of its bearers (individual’s level) or the relative success of transmission (called the idea’s level). This article presents a mathematical model on the interplay between these two levels. The first aim of this article is to explore when cultural evolution is driven by the idea’s level, when it is driven by the individual’s level and when it is driven by both. These three possibilities are explored in relation to (a) the amount of interchange of cultural traits between individuals, (b) the selective pressure acting on individuals, (c) the rate of production of new cultural traits, (d) the individual’s capacity to remember cultural traits and to the population size. The aim is to explore the conditions in which cultural evolution does not lead to a better adaptation of individuals to the environment. This is to contrast the spread of fitness-enhancing ideas, which make individual bearers better adapted to the environment, to the spread of “selfish” ideas, which spread well simply because they are easy to remember but do not help their individual bearers (and may even hurt them). At the same time this article explores in which conditions the adaptation of individuals is maximal. The second aim is to explore how these factors affect cultural diversity, or the amount of different cultural traits in a population. This study suggests that a larger interchange of cultural traits between populations could lead to cultural evolution not improving the adaptation of individuals to their environment and to a decrease of cultural diversity.     

Higher frequency of social learning in China than in the West shows cultural variation in the dynamics of cultural evolution

Cultural evolutionary models have identified a range of conditions under which social learning (copying others) is predicted to be adaptive relative to asocial learning (learning on one''s own), particularly in humans where socially learned information can accumulate over successive generations. However, cultural evolution and behavioural economics experiments have consistently shown apparently maladaptive under-utilization of social information in Western populations. Here we provide experimental evidence of cultural variation in people''s use of social learning, potentially explaining this mismatch. People in mainland China showed significantly more social learning than British people in an artefact-design task designed to assess the adaptiveness of social information use. People in Hong Kong, and Chinese immigrants in the UK, resembled British people in their social information use, suggesting a recent shift in these groups from social to asocial learning due to exposure to Western culture. Finally, Chinese mainland participants responded less than other participants to increased environmental change within the task. Our results suggest that learning strategies in humans are culturally variable and not genetically fixed, necessitating the study of the ‘social learning of social learning strategies'' whereby the dynamics of cultural evolution are responsive to social processes, such as migration, education and globalization.     

Social Learning and the Maintenance of Cultural Variation: An Evolutionary Model and Data from East Africa

Human societies maintain between-group variation despite mixing of people and ideas. In order for variation to remain, migrants or their children must preferentially adopt local norms, customs, and beliefs. Yet the details of how cultural variation is maintained, despite mixing, remain unknown. This article addresses this problem by using a simple model of the evolution of cultural learning to interpret the results of a study of cultural variation in a small region of East Africa. I argue that the manner in which migrants of two diverse regions adapt to local beliefs and behavior depends on the costs and accuracy of learning in each domain. Observational studies are never definitive tests of any hypothesis, but these results suggest that conclusions about the significance of cultural learning for understanding individual attitudes and behavior depend strongly upon the domain of investigation.