Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Humans are selective social learners. In a cultural landscape with many potential models, learners must balance the cost associated with learning from successful models with learning from accessible ones. Using structured interviews, we investigate the model selection biases of Congolese BaYaka adolescent boys learning to hunt with spears (n p 24; mage p 15.79 years; range, 12– 20 years). Results from social relations models suggest that adolescents nominated accessible adult men (closely related kin and neighbors) as preferred spear hunting models. Direct cues for success were not strong predictors for adolescent nomination in the statistical models, despite learners justifying model selection according to teaching and spear hunting skill. Indirect cues including body mass index, age, and cross-domain prestige were weak predictors for adolescent nomination. We interpret these findings as suggesting that BaYaka spear hunting knowledge is widely shared in the community, with all adult men participating in spear hunting and therefore having the requisite experience to transmit this skill. This supports previous findings that in egalitarian societies with low rates of role specialization, prestige has limited importance for cross-domain learning.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Kitanishi [39] reports that group sizes for day-long hunting excursions (esondo) range from three to 13 participants (mean = 5.8). Among Congo Basin foragers including BaYaka, learning to hunt with spears starts around the age of 3 years, when children participate in target practice games, pretense play, and rat hunting with lightweight wooden spears [43,[45][46][47][48]. In situ learning starts in early adolescence, when boys accompany fathers and other adult men on spear hunts [22,39,49]. ...
... Our previous research demonstrated that while spear hunting is widely practised by BaYaka, they consider it to be an especially complex task [22]. We found that most spear hunting knowledge transmission reportedly occurred from fathers and other closely related male kin, primarily via teaching [22,46]. The present study builds on this work by investigating the types of teaching that contribute to BaYaka spear hunting knowledge acquisition. ...
... Following BaYaka views on maturity, all unmarried male adolescents and young adults (n = 24) inhabiting the larger two village neighbourhoods at the time of data collection participated in an interview (see [46] for full details). We assessed previous adolescent spear hunting experiences by asking them to list the number and species of animals they had successfully spear hunted in the past. ...
Article
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.
... As children grow, adults may ask them to perform increasingly complex tasks (e.g. from fetching items across camp to carrying messages kilometres away) as a means of engaging them in daily routines ( [81], also see [82]). A valued role for fathers in BaYaka culture is having children accompany them to the forest to learn during hunting and gathering trips [83,84]. With peers, children collaboratively learn subsistence knowledge and social norms essential to life in the forest and in society [85][86][87][88]. ...
Article
Investigating past and present human adaptation to the Congo Basin tropical forest can shed light on how climate and ecosystem variability have shaped human evolution. Here, we first review and synthesize genetic, palaeoclimatological, linguistic and historical data on the peopling of the Congo Basin. While forest fragmentation led to the increased genetic and geographical divergence of forest foragers, these groups maintained long-distance connectivity. The eventual expansion of Bantu speakers into the Congo Basin provided new opportunities for forging inter-group links, as evidenced by linguistic shifts and historical accounts. Building from our ethnographic work in the northern Republic of the Congo, we show how these inter-group links between forest forager communities as well as trade relationships with neighbouring farmers facilitate adaptation to ecoregions through knowledge exchange. While researchers tend to emphasize forager–farmer interactions that began in the Iron Age, we argue that foragers' cultivation of relational wealth with groups across the region played a major role in the initial occupation of the Congo Basin and, consequently, in cultural evolution among the ancestors of contemporary peoples. This article is part of the theme issue ‘Tropical forests in the deep human past’.
Article
Full-text available
Aspects of human life history and cognition, such as our long childhoods and extensive use of teaching, theoretically evolved to facilitate the acquisition of complex tasks. The present paper empirically examines the relationship between subsistence task difficulty and age of acquisition, rates of teaching, and rates of oblique transmission among Hadza and BaYaka foragers from Tanzania and the Republic of Congo. We further examine cross-cultural variation in how and from whom learning occurred. Learning patterns and community perceptions of task difficulty were assessed through interviews. We found no relationship between task difficulty, age of acquisition, and oblique transmission, and a weak but positive relationship between task difficulty and rates of teaching. While same-sex transmission was normative in both societies, tasks ranked as more difficult were more likely to be transmitted by men among the BaYaka, but not among the Hadza, potentially reflecting cross-cultural differences in the sexual division of subsistence and teaching labor. Further, the BaYaka were more likely to report learning via teaching, and less likely to report learning via observation, than the Hadza, possibly owing to differences in socialization practices.
Article
Full-text available
Objectives: The study goals were to (a) characterize the cultural model of fatherhood among the BaYaka, a community of egalitarian foragers in the Republic of the Congo; (b) test if BaYaka fathers' quality in relation to the cultural model predicts their children's energetic status; and (c) compare the variance in BaYaka children's energetic status to that of children of neighboring Bondongo fisher-farmers, among whom there is less cooperative caregiving, less resource sharing, and greater social inequality. Methods: We used informal interviews to establish the cultural model of fatherhood, which we used to build a peer ranking task to quantify father quality. Children's energetic status was assessed by measuring height, weight, and triceps skinfold thickness. We then tested for associations between father quality scores derived from the ranking task and children's energetic status using ordinary least squares regression. Equality of variance tests were used to compare BaYaka and Bondongo children's energetic statuses. Results: The BaYaka described fathers as responsible for acquiring resources and maintaining marital harmony, welcoming others to the community and sharing well with them, and teaching their children about the forest. Agreement on men's quality in these domains was high, but father quality did not significantly predict children's energetic status. BaYaka children had lower variance in energetic status overall compared to Bondongo children. Conclusions: We suggest that the core BaYaka values and practices that maintain egalitarian social relations and distribution of resources help buffer children's health and well-being from variation in their fathers' qualities in culturally valued domains.
Preprint
Full-text available
Human adaptation depends upon the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning will benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring individual hunters' of hunting skill gain and loss from approximately 23,000 hunting records generated by more than 1,800 individuals at 40 locations. The model provides an improved picture of ages of peak productivity as well as variation within and among ages. The data reveal an average age of peak productivity between 30 and 35 years of age, though high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more upon heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the co-evolution of human life history and cultural adaptation. It also demonstrates new statistical algorithms and models that expand the potential inferences drawn from detailed quantitative data collected in the field.
Article
Full-text available
Cultural evolution theory posits that a major factor in human ecological success is our high-fidelity and selective social learning, which permits the accumulation of adaptive knowledge and skills over successive generations. One way to acquire adaptive social information is by preferentially copying competent individuals within a valuable domain (success bias). However, competence within a domain is often difficult or impossible to directly assess. Almost 20 years ago, Henrich and Gil-White (H&GW) suggested that people use indirect cues of success (e.g., differential levels of attention paid to models by other social learners) as adaptive short-cuts to select models from whom to learn. They called this use of indirect markers of success prestige bias. In this review, we re-visit H&GW’s proposal, examining the evidence amassed since for the adaptiveness and use of prestige bias in humans. First, we briefly outline H&GW’s theory. Second, we analyse whether prestige is associated with competence within valuable domains, which is a crucial assumption underlying the adaptiveness of prestige bias. Third, we discuss prestige cues that people use to infer success (e.g., the amount of voluntary deference and attention received by models). Fourth, we examine the evidence for and against the use of prestige bias in human adults and children. Finally, we point out limitations in the current literature and present new avenues for research on prestige bias.
Article
Full-text available
The appearance of weaponry - technology designed to kill - is a critical but poorly established threshold in human evolution. It is an important behavioural marker representing evolutionary changes in ecology, cognition, language and social behaviours. While the earliest weapons are often considered to be hand-held and consequently short-ranged, the subsequent appearance of distance weapons is a crucial development. Projectiles are seen as an improvement over contact weapons, and are considered by some to have originated only with our own species in the Middle Stone Age and Upper Palaeolithic. Despite the importance of distance weapons in the emergence of full behavioral modernity, systematic experimentation using trained throwers to evaluate the ballistics of thrown spears during flight and at impact is lacking. This paper addresses this by presenting results from a trial of trained javelin athletes, providing new estimates for key performance parameters. Overlaps in distances and impact energies between hand-thrown spears and spearthrowers are evidenced, and skill emerges as a significant factor in successful use. The results show that distance hunting was likely within the repertoire of hunting strategies of Neanderthals, and the resulting behavioural flexibility closely mirrors that of our own species.
Article
Full-text available
For individuals, status is derived both from their personal attributes and the groups with whom they are affiliated. Depending on the performance of their groups, the status of individuals may benefit or suffer from identifying closely with the group. When the group excels, high-status members potentially receive much of the credit and increased status. Conversely, high-status members of underperforming groups potentially suffer disproportionate declines in their status relative to the low-status group members. We therefore predict an interaction between group performance and individual status on the willingness to associate with the group and its members. We test our prediction by examining social media ties among teammates in the National Basketball Association. Specifically, we investigate the “following” ties of teammates on Twitter at the end of the 2014–2015 season. Elections to All-Star games are used to measure the status of players, and team performance is measured by recent success in the postseason playoffs. The results show that compared to high-status players on successful teams, high-status players on underperforming teams are less likely to follow their teammates. This result aligns with research on status inconsistency, suggesting that individuals deemphasize their group affiliation when it jeopardizes their individual status. An additional contribution is the advancement of the probit Social Relations Model for the analysis of binary ties in social networks.
Article
Full-text available
The brms package implements Bayesian multilevel models in R using the probabilistic programming language Stan. A wide range of distributions and link functions are supported, allowing users to fit – among others – linear, robust linear, binomial, Poisson, survival, ordinal, zero-inflated, hurdle, and even non-linear models all in a multilevel context. Further modeling options include autocorrelation of the response variable, user defined covariance structures, censored data, as well as meta-analytic standard errors. Prior specifications are flexible and explicitly encourage users to apply prior distributions that actually reflect their beliefs. In addition, model fit can easily be assessed and compared with the Watanabe-Akaike information criterion and leave-one-out cross-validation.
Article
Full-text available
Precise estimation of age is essential in evolutionary anthropology, especially to infer population age structures and understand the evolution of human life history diversity. However, in small-scale societies, such as hunter-gatherer populations, time is often not referred to in calendar years, and accurate age estimation remains a challenge. We address this issue by proposing a Bayesian approach that accounts for age uncertainty inherent to fieldwork data. We developed a Gibbs sampling Markov chain Monte Carlo algorithm that produces posterior distributions of ages for each individual, based on a ranking order of individuals from youngest to oldest and age ranges for each individual. We first validate our method on 65 Agta foragers from the Philippines with known ages, and show that our method generates age estimations that are superior to previously published regression-based approaches. We then use data on 587 Agta collected during recent fieldwork to demonstrate how multiple partial age ranks coming from multiple camps of hunter-gatherers can be integrated. Finally, we exemplify how the distributions generated by our method can be used to estimate important demographic parameters in small-scale societies: here, age-specific fertility patterns. Our flexible Bayesian approach will be especially useful to improve cross-cultural life history datasets for small-scale societies for which reliable age records are difficult to acquire.
Article
Full-text available
Most of what we know about teaching comes from research among people living in large, politically and economically stratified societies with formal education systems and highly specialized roles with a global market economy. In this paper, we review and synthesize research on teaching among contemporary hunter-gatherer societies. The hunter-gatherer lifeway is the oldest humanity has known and is more representative of the circumstances under which teaching evolved and was utilized most often throughout human history. Research among contemporary hunter-gatherers also illustrates a complex pattern of teaching that is both consistent with and distinct from teaching in other small- and large-scale societies with different subsistence practices and cultural forms. In particular, we find that the cultural emphasis on individual autonomy and socio-political egalitarianism among hunter-gatherers differently shapes how teaching occurs. For example, teaching clearly exists among hunter-gatherers and appears in many forms, including institutionalized instruction in valued cultural and technical skills. However, teaching tends to be less common in hunter-gatherer societies because people live in small, intimate egalitarian, groups that support each other’s learning in a variety of ways without teaching. Furthermore, foundational cultural schemas of autonomy and egalitarianism impact the nature of teaching. For example, adults and older children limit their interventions, permitting autonomous learning, and, when they occur, teaching episodes are generally brief, subtle, indirect, and situated in a present activity (i.e. knowledge is not objectified or intended to be generalizable). We discuss the implications of this research in terms of discussions of the evolution of human cognition and the co-evolution of teaching and culture through the process of cultural niche construction.
Chapter
Full-text available
Social learning among hunter-gatherers has been widely discussed in the literature and authors often draw on ethnographic cases to support theoretical models. In this study we report on the cross-cultural occurrence of various modes and processes of social learning in distinct cultural domains from the ethnographic record. To our knowledge this is the first systematic, cross-cultural study of hunter-gatherer social learning. We rely on the sample of hunter-gatherers in the electronic Human Relations Area Files (eHRAF) to generate our source of ethnographic texts. We have coded and analyzed 982 ethnographic texts from 23 diverse societies. Oblique and vertical transmission appear at similar rates. Various forms of teaching are the most common processes of social learning and account for more than half of all coded texts. Vertical and oblique social learning are predominantly characterized by teaching, whereas horizontal social learning is primarily through collaborative learning. Approximations of age reveal a general developmental pattern in which social learning of miscellaneous skills characterizes infancy, subsistence skills dominate early and middle childhood, and the social learning of religious beliefs are most frequent during adolescence. Across development we identify a reduction in the importance of vertical transmission in favor of oblique transmission, for subsistence skills in particular. These results highlight the importance of teaching in the ethnographic record of hunter-gatherer social learning and provide a systematic, cross-cultural, framework for theoretical models to rely on.
Chapter
Full-text available
Based on generational differences and social relations, researchers have hypothesized that the transmission of cultural knowledge occurs through at least three different, not mutually exclusive, paths: (1) parents (vertical), (2) age peers (horizontal), and (3) elders (oblique). Here we contribute to this body of research by presenting three case studies showing evidence of a multistage model of cultural learning in which vertical transmission in childhood loses preeminence toward horizontal and oblique models as subjects’ age. The first case study documents and analyzes Baka children's daily activities (southeast Cameroon) in an attempt to understand (1) how time investments might affect the acquisition of knowledge and (2) the importance of scaffolding on knowledge acquisition. Building on this idea, the second case study explores the transmission of knowledge through the life cycle, documenting the accumulation of knowledge required for collecting wild honey among children and adults from a Jenu Kuruba tribal community in South India. The last case study uses data from the Tsimane’ (Bolivian Amazon) to analyze the correspondence between levels of adult knowledge and the knowledge of (a) the same-sex parent, (b) age peers, and (c) parental cohort. Results from this study suggest that – at adulthood – cultural knowledge is most likely a mix of information gathered from a variety of sources. Overall, the three case studies give evidence to support the multistage learning model for cultural transmission but also emphasize the importance of social learning during childhood, a period during which individuals acquire the baseline knowledge that allow the latter development of complex skills through scaffolding and the integration of information from multiple models.
Article
Full-text available
Previous research on food sharing in small-scale societies provides support for multiple evolutionary hypotheses, but evolutionary anthropologists have devoted relatively little attention to the broader relational context of inter-household transfers of food. The present research observes transfers of meat over a yearlong period among 25 households of indigenous Mayangna and Miskito horticulturalists in Nicaragua. To analyze these data, we extend the multilevel formulation of the social relations model to count data, namely the number of portions of meat exchanged between households. Along with other covariates, we examine the effect of an “association index,” which reflects the amount of time that households interact with one another. The association index exhibits a positive effect on sharing, and our overall results indicate that food sharing networks largely correspond to kin-based networks of social interaction, suggesting that food sharing is embedded in broader social relationships between households. We discuss possible extensions of our methodological approach, as appropriate for research on food sharing and social network analysis more broadly.
Article
Full-text available
In the ethnographic context, where answers to questions are unknown, consensus theory estimates the culturally appropriate or correct answers to the questions and individual differences in cultural knowledge. The cultural consensus model is a formal model of the process for asking and answering questions and is limited to categorical response data. An informal version of the model is available as a set of analytic procedures and obtains similar information with fewer assumptions. This article describes the assumptions, appropriate interview materials, and analytic procedures for carrying out a consensus analysis. Finally, issues that sometimes arise during the application of a consensus analysis are discussed.
Article
Full-text available
Much existing literature in anthropology suggests that teaching is rare in non-western societies, and that cultural transmission is mostly vertical (parent-to-offspring). However, applications of evolutionary theory to humans predict both teaching and non-vertical transmission of culturally learned skills, behaviors, and knowledge should be common cross- culturally. Here, we review this body of theory to derive predictions about when teaching and non-vertical transmission should be adaptive, and thus more likely to be observed empirically. Using three interviews conducted with rural Fijian populations, we find that: parents are more likely to teach than are other kin types, high-skill and highly-valued domains are more likely to be taught, and oblique transmission is associated with high-skill domains, which are learned later in life. Finally, we conclude that the apparent conflict between theory and empirical evidence is due to a mismatch of theoretical hypotheses and empirical claims across disciplines, and reconcile theory with the existing literature in light of our results.
Article
Full-text available
This article identifies the temporal sequence during which important cultural beliefs (food taboos) are transmitted to individuals in an oral society living in the Democratic Republic of Congo. Results are based on patterns of correlation in scaled measures of cultural similarity between same-household and same-clan members. In the first phase of the cultural life history (zero to ten years of age), individuals are innocent of food taboos. In Phase Two (11 to 20 years of age), when most taboos are acquired, parents dominate the enculturation of the young. Phase Three (over 20 years of age) consists of a less intense period of changing beliefs transmitted from individuals outside the family. This adult learning is usually ignored in socialization studies, but has a significant impact on cultural population dynamics. Since this sequence of early family-based, and later more broadly based, cultural influences reflects the temporal expansion of the social universe of individuals everywhere, this life history is probably representative of how cultural traits are generally acquired. Further, the timing of this ontogenetic process mirrors changes in the influence of family environment on cognitive ability in behavioral genetic studies. This parallel suggests that both cultural and psychological traits evolve similarly in response to age-related changes in the social environment. Finally, comparing studies based on statistical models of cultural similarity with those based on reported transmission pathways suggests that the latter, which indicate overwhelming parental influence, probably reflect normative response biases.
Article
Full-text available
Recent debates about memetics have revealed some widespread misunderstandings about Darwinian approaches to cultural evolution. Drawing from these debates, this paper disputes five common claims: (1) mental representations are rarely discrete, and therefore models that assume discrete, gene-like particles (i.e., replicators) are useless; (2) replicators are necessary for cumulative, adaptive evolution; (3) content-dependent psychological biases are the only important processes that affect the spread of cultural representations; (4) the “cultural fitness” of a mental representation can be inferred from its successful transmission; and (5) selective forces only matter if the sources of variation are random. We close by sketching the outlines of a unified evolutionary science of culture.
Article
Full-text available
We propose that the cognitive mechanisms that enable the transmission of cultural knowledge by communication between individuals constitute a system of 'natural pedagogy' in humans, and represent an evolutionary adaptation along the hominin lineage. We discuss three kinds of arguments that support this hypothesis. First, natural pedagogy is likely to be human-specific: while social learning and communication are both widespread in non-human animals, we know of no example of social learning by communication in any other species apart from humans. Second, natural pedagogy is universal: despite the huge variability in child-rearing practices, all human cultures rely on communication to transmit to novices a variety of different types of cultural knowledge, including information about artefact kinds, conventional behaviours, arbitrary referential symbols, cognitively opaque skills and know-how embedded in means-end actions. Third, the data available on early hominin technological culture are more compatible with the assumption that natural pedagogy was an independently selected adaptive cognitive system than considering it as a by-product of some other human-specific adaptation, such as language. By providing a qualitatively new type of social learning mechanism, natural pedagogy is not only the product but also one of the sources of the rich cultural heritage of our species.
Article
Full-text available
Unlike other animals, humans are heavily dependent on cumulative bodies of culturally learned information. Selective processes operating on this socially learned information can produce complex, functionally integrated, behavioural repertoires-cultural adaptations. To understand such non-genetic adaptations, evolutionary theorists propose that (i) natural selection has favoured the emergence of psychological biases for learning from those individuals most likely to possess adaptive information, and (ii) when these psychological learning biases operate in populations, over generations, they can generate cultural adaptations. Many laboratory experiments now provide evidence for these psychological biases. Here, we bridge from the laboratory to the field by examining if and how these biases emerge in a small-scale society. Data from three cultural domains-fishing, growing yams and using medicinal plants-show that Fijian villagers (ages 10 and up) are biased to learn from others perceived as more successful/knowledgeable, both within and across domains (prestige effects). We also find biases for sex and age, as well as proximity effects. These selective and centralized oblique transmission networks set up the conditions for adaptive cultural evolution.
Article
Full-text available
This thesis is about a forest hunter-gatherer people, the Mbendjele Yaka Pygmies of northern Congo-Brazzaville. The thesis is based on field research carried out between 1994 and 2001. I begin by examining certain key terms used in the thesis and by situating my research within the existing literature. Research methodologies are presented and the fieldwork experience described. I provide an overview of the historical, political and economic context of the research including an outline assessment of the main historical reconstructions of regional history. Conservationist and loggers' models of the forest are juxtaposed with Mbendjele ways of representing landscape and the forest environment. I discuss the significance of the forest in Mbendjele social experience and its role as the ideal environment for social life. I examine the way the Mbendjele classify animals and the cosmological significance of hunting and killing. This theme is continued with a presentation of ekila, a complex set of practices and beliefs that regulate the interactions of people with animals and express a complex relationship between human fertility and the correct handling of prey animals. I continue the analysis of Mbendjele collective representations with a presentation of the activity of massana. The link between children's play and adult rituals implicit in the use of this term is analysed. I then build on this understanding to present an analysis of aspects of two ritual associations, Ejengi and Ngoku, central to men's and women's power in society. The thesis is brought to a close by moving beyond the forest to examine Mbendjele relations with and conceptualisations of outsiders and property rights. New technological developments and financial incentives are increasingly transforming the Mbendjele forest into faunal and floral assets for distribution to international organizations.
Article
Full-text available
This paper advances an "information goods" theory that explains prestige processes as an emergent product of psychological adaptations that evolved to improve the quality of information acquired via cultural transmission. Natural selection favored social learners who could evaluate potential models and copy the most successful among them. In order to improve the fidelity and comprehensiveness of such ranked-biased copying, social learners further evolved dispositions to sycophantically ingratiate themselves with their chosen models, so as to gain close proximity to, and prolonged interaction with, these models. Once common, these dispositions created, at the group level, distributions of deference that new entrants may adaptively exploit to decide who to begin copying. This generated a preference for models who seem generally "popular." Building on social exchange theories, we argue that a wider range of phenomena associated with prestige processes can more plausibly be explained by this simple theory than by others, and we test its predictions with data from throughout the social sciences. In addition, we distinguish carefully between dominance (force or force threat) and prestige (freely conferred deference).
Article
Investigating past and present human adaptation to the Congo Basin tropical forest can shed light on how climate and ecosystem variability have shaped human evolution. Here, we first review and synthesize genetic, palaeoclimatological, linguistic and historical data on the peopling of the Congo Basin. While forest fragmentation led to the increased genetic and geographical divergence of forest foragers, these groups maintained long-distance connectivity. The eventual expansion of Bantu speakers into the Congo Basin provided new opportunities for forging inter-group links, as evidenced by linguistic shifts and historical accounts. Building from our ethnographic work in the northern Republic of the Congo, we show how these inter-group links between forest forager communities as well as trade relationships with neighbouring farmers facilitate adaptation to ecoregions through knowledge exchange. While researchers tend to emphasize forager–farmer interactions that began in the Iron Age, we argue that foragers' cultivation of relational wealth with groups across the region played a major role in the initial occupation of the Congo Basin and, consequently, in cultural evolution among the ancestors of contemporary peoples. This article is part of the theme issue ‘Tropical forests in the deep human past’.
Article
Teaching is cross-culturally widespread but few studies have considered children as teachers as well as learners. This is surprising, since forager children spend much of their time playing and foraging in child-only groups, and thus, have access to many potential child teachers. Using the Social Relations Model, we examined the prevalence of child-to-child teaching using focal follow data from 35 Hadza and 38 BaYaka 3- to 18-year-olds. We investigated the effect of age, sex and kinship on the teaching of subsistence skills. We found that child-to-child teaching was more frequent than adult-child teaching. Additionally, children taught more with age, teaching was more likely to occur within same-sex versus opposite-sex dyads, and close kin were more likely to teach than non-kin. The Hadza and BaYaka also showed distinct learning patterns; teaching was more likely to occur between sibling dyads among the Hadza than among the BaYaka, and a multistage learning model where younger children learn from peers, and older children from adults, was evident for the BaYaka, but not for the Hadza. We attribute these differences to subsistence and settlement patterns. These findings highlight the role of children in the intergenerational transmission of subsistence skills.
Article
The appearance of new projectile propulsion modes is viewed as an important element for understanding human behaviour during the Palaeolithic. Because the organic components of hunting weapons (the bow, spear‐thrower and arrow, and spear shaft) are only rarely preserved archaeologically, some effort has been invested in experiments to explore how the projecting modes could be identified through the analysis of stone points. The kinetic energy developed by each mode of propulsion has been considered a key variable in these experiments. However, the data used in these studies generally come from a few ballistic studies, with varied results. We present the results of a systematic study conducted with a ballistic pendulum and combined with a classic ballistic analysis. We quantified and compared the kinetic energy developed by the four standard modes of propulsion known for the Palaeolithic. The kinetic energy values that we attained, especially those measured for thrusting spears, clearly differ from what has been assumed up to now, and thus challenge current models on the evolution of hunting technology.
Book
Statistical Rethinking: A Bayesian Course with Examples in R and Stan builds readers’ knowledge of and confidence in statistical modeling. Reflecting the need for even minor programming in today’s model-based statistics, the book pushes readers to perform step-by-step calculations that are usually automated. This unique computational approach ensures that readers understand enough of the details to make reasonable choices and interpretations in their own modeling work. The text presents generalized linear multilevel models from a Bayesian perspective, relying on a simple logical interpretation of Bayesian probability and maximum entropy. It covers from the basics of regression to multilevel models. The author also discusses measurement error, missing data, and Gaussian process models for spatial and network autocorrelation. By using complete R code examples throughout, this book provides a practical foundation for performing statistical inference. Designed for both PhD students and seasoned professionals in the natural and social sciences, it prepares them for more advanced or specialized statistical modeling. Web Resource The book is accompanied by an R package (rethinking) that is available on the author’s website and GitHub. The two core functions (map and map2stan) of this package allow a variety of statistical models to be constructed from standard model formulas.
Article
Humans are thought to have evolved in small, egalitarian hunter-gatherer societies. Evolutionary theories of leadership, which draw heavily on studies of contemporary hunter-gatherer and other small-scale societies, have proposed numerous traits that putatively characterize leaders in domains of sociality, productivity, reproduction, dominance, and cognition. We investigated many such traits among the Chabu, an Ethiopian population of former hunter-gatherers who now subsist on hunting, gathering, horticulture, and cash crops. There were strong positive correlations among most traits across domains, which, in turn, were positively associated with elected leader status among both women and men. Measures of prestige and dominance were largely independent, and although both predicted leader status, prestige was more important. Biased social learning was a modest predictor of leader status but a stronger predictor of respect. Revised evolutionary theories of leadership must account for the importance of women leaders and the strong covariation of traits.
Chapter
Research indicates that children in small-scale cultures acquire many subsistence skills and knowledge relatively easily and quickly at an early age. However, the precise age and the developmental sequence of acquiring skills and knowledge are seldom described. Considerable debate also exists as to the importance of particular modes (e.g., vertical, horizontal, and oblique) and processes (e.g., role of teaching) of cultural transmission. This chapter examines some of these debates by focusing on how Chabu hunter-gatherer adolescents learn to spear hunt. Informal and structured interviews and systematic behavioral observations (focal follows) were utilized to try and understand when and how adolescent males learned to spear hunt. Data indicate that Chabu adolescents start learning to spear hunt in middle childhood (6–7 years of age) through play hunting (i.e., role-playing and collaborative learning) with their peers and listening to stories from their fathers. Adolescents learned the various skills and knowledge of spear hunting at different ages from multiple people, and they preferred to go on actual hunts with knowledgeable people and close friends. The data provide some support for model-based selective trust hypotheses. Oblique modes of cultural transmission were more common than vertical and horizontal forms of transmission during the acquistion of adolescent spear hunting and data from focal follows revealed that various forms of teaching were important to learning how to spear hunt.
Article
Since Margaret Mead's field studies in the South Pacific a century ago, there has been the tacit understanding that as culture varies, so too must the socialization of children to become competent culture users and bearers. More recently, the work of anthropologists has been mined to find broader patterns that may be common to childhood across a range of societies. One improbable commonality has been the tolerance, even encouragement, of toddler behavior that is patently risky, such as playing with or attempting to use a sharp-edged tool. This laissez faire approach to socialization follows from a reliance on children as "self-initiated learners." In this article, the ethnographic literature that shows why children are encouraged to learn without prompting or guidance and how that happens is reviewed.
Chapter
Innovation, as an element of behavioral plasticity, has been hypothesized to enhance the fitness and survivability of individuals, while overall increasing the diversity, and longevity of cultural traits overtime. This study examined innovations and their transmission amongst Aka forager adolescents of central Africa. Developmental studies and evolutionary models predict: older adolescents should be more innovative than children and adults; older adolescent males should be more likely to seek out innovations; innovations should spread by horizontal transmission and; adolescents should pay attention to prestigious (“successful”) peers. In-depth and structured interviews, informal observations, video taping, and systematic ranking and sorting techniques with 20 Aka adolescents of Central African Republic and 10 Aka adult individuals, with five identified as being “innovators,” were utilized to evaluate existing studies.
Article
Many animals, including humans, acquire information through social learning. Although such information can be acquired easily, its potential unreliability means it should not be used indiscriminately. Cultural ‘transmission biases’ may allow individuals to weigh their reliance on social information according to a model's characteristics. In one of the first studies to juxtapose two model-based biases, we investigated whether the age and knowledge state of a model affected the fidelity of children's copying. Eighty-five 5-year-old children watched a video demonstration of either an adult or child, who had professed either knowledge or ignorance regarding a tool-use task, extracting a reward from that task using both causally relevant and irrelevant actions. Relevant actions were imitated faithfully by children regardless of the model's characteristics, but children who observed an adult reproduced more irrelevant actions than those who observed a child. The professed knowledge state of the model showed a weaker effect on imitation of irrelevant actions. Overall, children favored the use of a ‘copy adults’ bias over a ‘copy task-knowledgeable individual’ bias, even though the latter could potentially have provided more reliable information. The use of such social learning strategies has significant implications for understanding the phenomenon of imitation of irrelevant actions (overimitation), instances of maladaptive information cascades, and cumulative culture.
Article
Reasoning about the evolution of our species' capacity for cumulative cultural learning has led culture–gene coevolutionary (CGC) theorists to predict that humans should possess several learning biases which robustly enhance the fitness of cultural learners. Meanwhile, developmental psychologists have begun using experimental procedures to probe the learning biases that young children actually possess — a methodology ripe for testing CGC. Here we report the first direct tests in children of CGC's prediction of prestige bias, a tendency to learn from individuals to whom others have preferentially attended, learned or deferred. Our first study showed that the odds of 3- and 4-year-old children learning from an adult model to whom bystanders had previously preferentially attended for 10 seconds (the prestigious model) were over twice those of their learning from a model whom bystanders ignored. Moreover, this effect appears domain-sensitive: in Study 2 when bystanders preferentially observed a prestigious model using artifacts, she was learned from more often on subsequent artifact-use tasks (odds almost five times greater) but not on food-preference tasks, while the reverse was true of a model who received preferential bystander attention while expressing food preferences.
Article
The Social Relations Model represents one method of studying two-person relationships. It attempts to separate the effects of persons and dyad. The Social Relations Model has three potential contributions to the study of dyads. First, it provides a purely methodological-statistical solution to the analysis of dyadic data. The Social Relations Model represents a new approach to the analysis of dyadic data structures. Second, the model can provide social psychology with better procedures to resolve the theoretical issues of the discipline. Third, the model is useful because it looks at social behavior as simultaneously operating at multiple levels. Very different principles operate at these different levels and only by simultaneously examining social behavior at different levels, the complexity and simplicity of social life can be fully appreciated.
Article
Egalitarian society is ''explained'' chiefly in terms of ecological or social factors that are self-organizing. However, egalitarian behavior is found in a wide variety of social and ecological settings, and the indications are that such societies are deliberately shaped by their members. This paper looks to egalitarian behavior as an instance of domination of leaders by their own followers, who are guided by an ethos that disapproves of hierarchical behavior in general and of bossiness in leaders in particular. A substantial cross-cultural survey reveals the specific mechanisms by which the political rank and file creates a reverse dominance hierarchy, an anomalous social arrangement which has important implications for cross-phylogenetic comparisons and for the theory of state formation.
Article
Numerous articles examine the relationship between men's hunting skill and other important biological and social traits. We analyzed more than 14,000 hunter days during 27 years of monitoring the Ache of Paraguay by using resampling methods to demonstrate that large sample sizes are generally required in order to distinguish individual men by hunting skill. A small published study on !Kung hunters shows that large-game hunters are even more difficult to distinguish by individual skill level. This is a serious problem because re-gressions using noisy hunting data as the independent variable systematically underestimate the association of hunting ability with other biosocial traits. The analysis suggests that some coresidents in many small-scale societies will be unable to accurately distinguish hunters by skill level, possibly favoring groupwide meat-sharing conventions and biased cultural transmission that emphasizes prestige rather than perceived hunting skill. Anthropologists have been interested in hunting for many reasons. First, the nutritional dependence on hunting rep-resents an important shift in ape feeding patterns possibly associated with other notable human behaviors such as food sharing, high levels of cooperation, the sexual division of labor, and important life-history shifts (e.g., Kaplan et al. 2000; Stanford and Bunn 2001). Because our hominin an-cestors were probably strongly dependent on meat for the past 2 million years and because faunal remains preserve well, much of the archeological record is dominated by discussions of hunting (and scavenging). Second, hunting still contributes significant nutrients to many small-scale societies in most regions of the world (e.g., Robinson and Bennett 2000). Third, success in hunting is often assumed to be associated with status and other social perks (Wiessner 1996), as well as suc-2009 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved.
Article
Accounting for age-dependent patterns of knowledge transmission is critical for understanding cultural evolution in age-structured populations. Cultural evolution theory predicts which social learning biases we expect people to use, but much less often when during a person's life cycle different social learning biases will be used. By measuring knowledge and skill variation among age cohorts, it is possible to infer how people socially acquire different types of knowledge at different ages. We use this strategy among the Jenu Kuruba, a tribal community in South India. We document the accumulation of local knowledge required for collecting wild honey among 71 children and 125 adults from five communities. Combining quantitative measurements of knowledge with measures of four honey-collecting skills and self-reported data on learning age, we infer patterns of social learning across the lifecycle. We find that (1) most knowledge related to honey collecting is acquired by the early 20s, and later social learning mainly functions to update information; (2) the eldest cohort has the highest average explicit knowledge, although the most knowledgeable or skilled individuals do not always belong to the most elderly cohort; (3) length of learning can be affected by age-dependent trade-offs of costs and benefits to learners; and (4) children tend to learn from parents, but individuals use other demonstrators later in life. These results have implications for current models of cultural evolution.
Article
From the individual-based records of hunting practice for 1,633 hr in total and from the hunters' visual acuity and grip strength observed among the Gidra Papuans in lowland Papua New Guinea, this paper aims to analyze the relationship between the hunting activity and aging. The sensorimotor functions determine the range of age in which the individuals act as active or productive hunters: determined to be from the late teen-age years to about 45 years among the present subjects. In this age range, hunting efficiency increases with age. In terms of weight of animals killed per hunting time, the efficiency of the elder married (aged about 35 to 45 years) was almost four times higher than that of the unmarried (16–17 to late 20s). This aging effect is judged to depend on behavioral abilities that increase in accordance with experience and cumulative knowledge. Simultaneously, the comparison of individual hunters' records in 1971–72 and in 1981 reveals that hunting efficiency is associated with the individualities of the hunters.
Article
The application of evolutionary theory to understanding the origins of our species' capacities for social learning has generated key insights into cultural evolution. By focusing on how our psychology has evolved to adaptively extract beliefs and practices by observing others, theorists have hypothesized how social learning can, over generations, give rise to culturally evolved adaptations. While much field research documents the subtle ways in which culturally transmitted beliefs and practices adapt people to their local environments, and much experimental work reveals the predicted patterns of social learning, little research connects real-world adaptive cultural traits to the patterns of transmission predicted by these theories. Addressing this gap, we show how food taboos for pregnant and lactating women in Fiji selectively target the most toxic marine species, effectively reducing a woman's chances of fish poisoning by 30 per cent during pregnancy and 60 per cent during breastfeeding. We further analyse how these taboos are transmitted, showing support for cultural evolutionary models that combine familial transmission with selective learning from locally prestigious individuals. In addition, we explore how particular aspects of human cognitive processes increase the frequency of some non-adaptive taboos. This case demonstrates how evolutionary theory can be deployed to explain both adaptive and non-adaptive behavioural patterns.
Article
In central Africa, a close relationship exists between the cultivators and the hunter-gatherers (Pygmies), who depend on agricultural foods exchanged for forest products or labor. In northeastern Congo, the Aka hunter-gatherers lead a dual mode of life in the forest and the village. They mainly depend on wild animal and plant food in the forest, whereas on agricultural food in the village. Their subsistence activities are influenced by the fluctuation in the availability of wild food resources that does not fall into a simple annual cycle, but fluctuates from year to year. The subsistence activities of the Aka are more complex than the other hunter-gatherers, and dependent on the ecology of the tropical rain forest and the local economy in northeastern Congo.
Article
An extensive survey was conducted in the Motaba River Area in northeastern Congo. It was based on interviews and line transect surveys. The following results were obtained: (1) Both chimpanzees and gorillas occur throughout this area. (2) The densities of both species decrease from the upper toward the lower streams, and also from inland forests to villages. (3) Overall densities are estimated at 0.3 chimpanzees per km2 and 0.2 gorillas per km2 . (4) Hunting of apes for meat occurs in every part of the area. Most resident people are willing to ear ape meat, and about half of them have a chance to eat it in a year. (5) Hunting pressures on apes are estimated at 0.020 chimpanzees and 0.010 gorillas per km2 per year. These results strongly suggest that the survival of both species is seriously threatened by local hunting. The threat is expected to increase with human population growth and with forthcoming forest exploitation in northeastern Congo.
Article
Humans are unique in their range of environments and in the nature and diversity of their behavioral adaptations. While a variety of local genetic adaptations exist within our species, it seems certain that the same basic genetic endowment produces arctic foraging, tropical horticulture, and desert pastoralism, a constellation that represents a greater range of subsistence behavior than the rest of the Primate Order combined. The behavioral adaptations that explain the immense success of our species are cultural in the sense that they are transmitted among individuals by social learning and have accumulated over generations. Understanding how and when such culturally evolved adaptations arise requires understanding of both the evolution of the psychological mechanisms that underlie human social learning and the evolutionary (population) dynamics of cultural systems.
Article
In two experiments, children aged 3, 4 and 5 years (N = 61) were given conflicting information about the names and functions of novel objects by two informants, one a familiar teacher, the other an unfamiliar teacher. On pre-test trials, all three age groups invested more trust in the familiar teacher. They preferred to ask for information and to endorse the information that she supplied. In a subsequent phase, children watched as the two teachers differed in the accuracy with which they named a set of familiar objects. Half the children saw the familiar teacher name the objects accurately and the unfamiliar teacher name them inaccurately. The remaining half saw the reverse arrangement. In post-test trials, the selective trust initially displayed by 3-year-olds was minimally affected by this intervening experience of differential accuracy. By contrast, the selective trust of 4- and 5-year-olds was affected. If the familiar teacher had been the more accurate, selective trust in her was intensified. If, on the other hand, the familiar teacher had been the less accurate, it was undermined, particularly among 5-year-olds. Thus, by 4 years of age, children trust familiar informants but moderate that trust depending on the informants' recent history of accuracy or inaccuracy.
Article
A genetical mathematical model is described which allows for interactions between relatives on one another's fitness. Making use of Wright's Coefficient of Relationship as the measure of the proportion of replica genes in a relative, a quantity is found which incorporates the maximizing property of Darwinian fitness. This quantity is named “inclusive fitness”. Species following the model should tend to evolve behaviour such that each organism appears to be attempting to maximize its inclusive fitness. This implies a limited restraint on selfish competitive behaviour and possibility of limited self-sacrifices.Special cases of the model are used to show (a) that selection in the social situations newly covered tends to be slower than classical selection, (b) how in populations of rather non-dispersive organisms the model may apply to genes affecting dispersion, and (c) how it may apply approximately to competition between relatives, for example, within sibships. Some artificialities of the model are discussed.
Article
Adult malnutrition is much more widespread than is commonly recognized. Described in this article is the use of body mass index (BMI = weight in kg/(height in metres)2) as a measure of adult nutritional status, both of individuals and of communities. Concurrent assessment of the nutritional status of children and adults permits conclusions to be drawn about whether there is generalized undernutrition in a community or whether other factors (e.g., childhood infections or feeding practices) are more important in childhood malnutrition. Included is a tabular presentation that permits rapid assessment of both thinness or underweight (BMI values < 16, 17 and 18.5) and overweight (BMI > 25, 30 and 40). Examples of the use of BMI in both clinical and public health practice are also given.
Article
This paper examines changes in hunting ability across the lifespan for the Ache of eastern Paraguay. Hunting ability is decomposed into two components-finding prey and probability of kill upon encounter- and analyzed for important prey species. Results support the argument that skill acquisition is an important aspect of the human foraging niche with hunting outcome variables reaching peaks surprisingly late in life, significantly after peaks in strength. The implications of this study are important for modeling the role of the human foraging niche in the co-evolution of various outstanding human life history characteristics such as large brains, long lifespans, and extended juvenile periods.