Who teaches children to forage? Exploring the primacy of child-to-child teaching among Hadza and BaYaka Hunter-Gatherers of Tanzania and Congo

Women's subsistence networks scaffold cultural transmission among BaYaka foragers in the Congo Basin

In hunter-gatherer societies, women's subsistence activities are crucial for food provisioning and children's social learning but are understudied relative to men's activities. To understand the structure of women's foraging networks, we present 230 days of focal-follow data in a BaYaka community. To analyze these data, we develop a stochastic blockmodel for repeat observations with uneven sampling. We find that women's subsistence networks are characterized by cooperation between kin, gender homophily, and mixed age-group composition. During early childhood, individuals preferentially coforage with adult kin, but those in middle childhood and adolescence are likely to coforage with nonkin peers, providing opportunities for horizontal learning. By quantifying the probability of coforaging ties across age classes and relatedness levels, our findings provide insights into the scope for social learning during women's subsistence activities in a real-world foraging population and provide ground-truth values for key parameters used in formal models of cumulative culture.

Development of teaching in ni-Vanuatu children

Teaching is an important mechanism of social learning. In industrialized societies, 3-year-olds tend to teach through demonstrations and short commands, while 5-year-olds use more verbal communication and abstract explanations. However, it remains unclear whether this generalizes to other cultures. This study presents results from a peer teaching game with 55 Melanesian children (4.7-11.4 years, 24 female) conducted in Vanuatu in 2019. Up to age 8, most participants taught through a participatory approach, emphasizing learning-by-doing, demonstrations, and short commands (57.1% of children aged 4-6 and 57.9% of children aged 7-8). Contrary to Western findings, abstract verbal communication only became common in children aged 9-11 (63.6%), suggesting that the ontogeny of teaching is shaped by the socio-cultural environment.

Simulating peers: Can puppets simulate peer interactions in studies on children's socio-cognitive development?

Interactions with peers are fundamental to socio-cognitive development, but assessing peer interactions in standardized experiments is challenging. Therefore, researchers commonly utilize puppetry to simulate peers. This Registered Report investigated urban German children's (AgeRange  = 3.5-4.5 years; N = 144; 76♀) mind ascriptions and social cognition to test whether they treat puppets like peers, adults, or neither. Children attributed less mind properties to puppets than peers or adults. However, children's social cognition (i.e., normativity, prosociality, and theory of mind) varied little across partners. Puppetry relies on children's ability for pretense, but can provide valid insights into socio-cognitive development. Implications for using puppets as stand-ins for peers in developmental research are discussed.

The cultural evolution of teaching

Teaching is an important process of cultural transmission. Some have argued that human teaching is a cognitive instinct - a form of 'natural cognition' centred on mindreading, shaped by genetic evolution for the education of juveniles, and with a normative developmental trajectory driven by the unfolding of a genetically inherited predisposition to teach. Here, we argue instead that human teaching is a culturally evolved trait that exhibits characteristics of a cognitive gadget. Children learn to teach by participating in teaching interactions with socialising agents, which shape their own teaching practices. This process hijacks psychological mechanisms involved in prosociality and a range of domain-general cognitive abilities, such as reinforcement learning and executive function, but not a suite of cognitive adaptations specifically for teaching. Four lines of evidence converge on this hypothesis. The first, based on psychological experiments in industrialised societies, indicates that domain-general cognitive processes are important for teaching. The second and third lines, based on naturalistic and experimental research in small-scale societies, indicate marked cross-cultural variation in mature teaching practice and in the ontogeny of teaching among children. The fourth line indicates that teaching has been subject to cumulative cultural evolution, i.e. the gradual accumulation of functional changes across generations.

Human major transitions from the perspective of distributed adaptations

Distributed adaptations are cases in which adaptation is dependent on the population as a whole: the adaptation is conferred by a structural or compositional aspect of the population; the adaptively relevant information cannot be reduced to information possessed by a single individual. Possible examples of human-distributed adaptations are song lines, traditions, trail systems, game drive lanes and systems of water collection and irrigation. Here we discuss the possible role of distributed adaptations in human cultural macro-evolution. Several kinds of human-distributed adaptations are presented, and their evolutionary implications are highlighted. In particular, we discuss the implications of population size, density and bottlenecks on the distributed adaptations that a population may possess and how they in turn would affect the population's resilience to ecological change. We discuss the implications that distributed adaptations may have for human collective action and the possibility that they played a role in colonization of new areas and niches, in seasonal migration, and in setting constraints for minimal inter-population connectivity. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Children over-imitate adults and peers more than puppets

Researchers commonly use puppets in development science. Amongst other things, puppets are employed to reduce social hierarchies between child participants and adult experimenters akin to peer interactions. However, it remains controversial whether children treat puppets like real-world social partners in these settings. This study investigated children's imitation of causally irrelevant actions (i.e., over-imitation) performed by puppet, adult, or child models. Seventy-two German children (Age_Range  = 4.6-6.5 years; 36 girls) from urban, socioeconomically diverse backgrounds observed a model retrieving stickers from reward containers. The model performed causally irrelevant actions either in contact with the reward container or not. Children were more likely to over-imitate adults' and peers' actions as compared to puppets' actions. Across models, they copied contact actions more than no-contact actions. While children imitate causally irrelevant actions from puppet models to some extent, their social learning from puppets does not necessarily match their social learning from real-world social agents, such as children or adults. RESEARCH HIGHLIGHTS: We examined children's over-imitation from adult, child, and puppet models to validate puppetry as an approach to simulate non-hierarchical interactions. Children imitated adults and child models at slightly higher rates than puppets. This effect was present regardless of whether the irrelevant actions involved physical contact to the reward container or not. In our study children's social learning from puppets does not match their social learning from human models.

Development of embodied capital: Diet composition, foraging skills, and botanical knowledge of forager children in the Congo Basin

The embodied capital theory states that the extended juvenile period has enabled human foragers to acquire the complex foraging skills and knowledge needed to obtain food. Yet we lack detailed data on how forager children develop these skills and knowledge. Here, we examine the seasonal diet composition, foraging behavior, and botanical knowledge of Mbendjele BaYaka forager children in the Republic of the Congo. Our data, acquired through long-term observations involving full-day focal follows, show a high level of seasonal fluctuation in diet and foraging activities of BaYaka children, in response to the seasonal availability of their food sources. BaYaka children foraged more than half of the time independent from adults, predominantly collecting and eating fruits, tubers, and seeds. For these most-consumed food types, we found an early onset of specialization of foraging skills in children, similar to the gendered division in foraging in adults. Specifically, children were more likely to eat fruit and seed species when there were more boys and men in the group, and girls were more likely than boys to collect tuber species. In a botanical knowledge test, children were more accurate at identifying plant food species with increasing age, and they used fruits and trunks for species identification, more so than using leaves and barks. These results show how the foraging activities of BaYaka children may facilitate the acquisition of foraging skills and botanical knowledge and provide insights into the development of embodied capital. Additionally, BaYaka children consumed agricultural foods more than forest foods, probably reflecting BaYaka’s transition into a horticultural lifestyle. This change in diet composition may have significant consequences for the cognitive development of BaYaka children.

Psychometric validation of the sibling inventory of behavior in three- to six-year-old Chinese children

With increasing attention on sibling relationship studies in China, one problem that has been neglected is the limited validation of instruments used to assess these relationships. The present study evaluated the psychometric properties of the Sibling Inventory of Behavior to measure Chinese children's sibling relationships using a stratified random sample of 590 parents of three- to six-year-olds in three economic regions. The confirmatory factor analysis obtained an adequate fit, suggesting that the Chinese version of the instrument had a six-factor structure (i.e., Companionship, Empathy, Teaching, Rivalry, Aggression, and Avoidance). It demonstrated satisfactory internal consistency as well as test-retest reliability. Results of discriminant, convergent, and criterion-related validity test also fulfilled psychometric requirements. Furthermore, the residual measurement invariance across regions was discovered. Given the importance, emergence, and tendency of sibling studies in China, having a reliable and valid instrument with robust psychometric properties is essential and impactful.

Girls in early childhood increase food returns of nursing women during subsistence activities of the BaYaka in the Republic of Congo

Nursing mothers face an energetic trade-off between infant care and work. Under pooled energy budgets, this trade-off can be reduced by assistance in food acquisition and infant care tasks from non-maternal carers. Across cultures, children also often provide infant care. Yet the question of who helps nursing mothers during foraging has been understudied, especially the role of children. Using focal follow data from 140 subsistence expeditions by BaYaka women in the Republic of Congo, we investigated how potential support from carers increased mothers' foraging productivity. We found that the number of girls in early childhood (ages 4–7 years) in subsistence groups increased food returns of nursing women with infants (kcal collected per minute). This effect was stronger than that of other adult women, and older girls in middle childhood (ages 8–13 years) and adolescence (ages 14–19 years). Child helpers were not necessarily genetically related to nursing women. Our results suggest that it is young girls who provide infant care while nursing mothers are acquiring food—by holding, monitoring and playing with infants—and, thus, that they also contribute to the energy pool of the community during women's subsistence activities. Our study highlights the critical role of children as carers from early childhood.

Let’s Play at Digging

Extractive foraging tasks, such as digging, are broadly practiced among hunter-gatherer populations in different ecological conditions. Despite tuber-gathering tasks being widely practiced by children and adolescents, little research has focused on the physical traits associated with digging ability. Here, we assess how age and energetic expenditure affect the performance of this extractive task. Using an experimental approach, the energetic cost of digging to extract simulated tubers is evaluated in a sample of 40 urban children and adolescents of both sexes to measure the intensity of the physical effort and the influence of several anatomical variables. Digging is a moderately vigorous activity for inexperienced girls and boys from 8 to 14 years old, and it requires significant physical effort depending on strength and body size. However, extracting subterranean resources is a task that may be performed effectively without previous training. Sex-specific and age-specific differences in the net energy expenditure of digging were detected, even though both sexes exhibited similar proficiency levels when performing the task. Our results highlight that both boys and girls spend considerable energy while digging, with differences largely driven by body size and age. Other factors beyond ability and experience, such as strength and body size, may influence the proficiency of juveniles in performing certain physically intensive foraging tasks, such as gathering tubers.

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

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

Social ties in the Congo Basin: insights into tropical forest adaptation from BaYaka and their neighbours

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'.

Growing up in the Betsileo landscape: Children’s wild edible plants knowledge in Madagascar

Understanding local knowledge about wild edible plants (WEP) is essential for assessing plant services, reducing the risks of knowledge extinction, recognizing the rights of local communities, and improving biodiversity conservation efforts. However, the knowledge of specific groups such as women or children tends to be under-represented in local ecological knowledge (LEK) research. In this study, we explore how knowledge of WEP is distributed across gender and life stages (adults/children) among Betsileo people in the southern highlands of Madagascar. Using data from free listings with 42 adults and 40 children, gender-balanced, we show that knowledge on WEP differs widely across gender and life stage. In addition, we find that children have extended knowledge of WEP while reporting different species than adults. Women’s knowledge specializes in herbaceous species (versus other plant life forms), while men’s knowledge specializes in endemic species (versus native or introduced). Finally, we find that introduced species are more frequently cited by children, while adults cite more endemic species. We discuss the LEK differentiation mechanisms and the implications of acquiring life stage’s knowledge in the highland landscapes of Madagascar. Given our findings, we highlight the importance of considering groups with under-represented knowledge repositories, such as children and women, into future research.

Young children spontaneously invent three different types of associative tool use behaviour

Associative Tool Use (ATU) describes the use of two or more tools in combination, with the literature further differentiating between Tool set use, Tool composite use, Sequential tool use and Secondary tool use. Research investigating the cognitive processes underlying ATU has shown that some primate and bird species spontaneously invent Tool set and Sequential tool use. Yet studies with humans are sparse. Whether children are also able to spontaneously invent ATU behaviours and at what age this ability emerges is poorly understood. We addressed this gap in the literature with two experiments involving preschoolers (E1, N = 66, 3 years 6 months to 4 years 9 months; E2, N = 119, 3 years 0 months to 6 years 10 months) who were administered novel tasks measuring Tool set, Metatool and Sequential tool use. Participants needed to solve the tasks individually, without the opportunity for social learning (except for enhancement effects). Children from 3 years of age spontaneously invented all of the types of investigated ATU behaviours. Success rates were low, suggesting that individual invention of ATU in novel tasks is still challenging for preschoolers. We discuss how future studies can use and expand our tasks to deepen our understanding of tool use and problem-solving in humans and non-human animals.

The origins of human cumulative culture: from the foraging niche to collective intelligence

Various studies have investigated cognitive mechanisms underlying culture in humans and other great apes. However, the adaptive reasons for the evolution of uniquely sophisticated cumulative culture in our species remain unclear. We propose that the cultural capabilities of humans are the evolutionary result of a stepwise transition from the ape-like lifestyle of earlier hominins to the foraging niche still observed in extant hunter-gatherers. Recent ethnographic, archaeological and genetic studies have provided compelling evidence that the components of the foraging niche (social egalitarianism, sexual and social division of labour, extensive co-residence and cooperation with unrelated individuals, multilocality, fluid sociality and high between-camp mobility) engendered a unique multilevel social structure where the cognitive mechanisms underlying cultural evolution (high-fidelity transmission, innovation, teaching, recombination, ratcheting) evolved as adaptations. Therefore, multilevel sociality underlies a 'social ratchet' or irreversible task specialization splitting the burden of cultural knowledge across individuals, which may explain why human collective intelligence is uniquely able to produce sophisticated cumulative culture. The foraging niche perspective may explain why a complex gene-culture dual inheritance system evolved uniquely in humans and interprets the cultural, morphological and genetic origins of Homo sapiens as a process of recombination of innovations appearing in differentiated but interconnected populations. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.

A cognitive-evolutionary model for the evolution of teaching

Mechanisms for social learning have rightly been the focus of much work in cultural evolution. But mechanisms for teaching-mechanisms that determine what information is available for learners to learn in the first place-are equally important to cultural evolution, especially in the case of humans. Here, we propose a simple model of teaching in the context of skill transmission. Our model derives the evolutionary cost and benefit of teaching by explicitly representing cognitive aspects of skill transmission as a dual-inheritance process. We then show that teaching cannot evolve when its direct cost is too high. We also show that there is an "explain-exploit" trade-off inherent to teaching: when payoffs from sharing information are not constant, there can be an indirect cost to teaching. This gives rise to an opportunity cost that goes beyond any direct cost that it may also entail. Finally, we show that evolution limits the strength of teaching provided that the direct cost of teaching is an increasing function of teaching effort. We then discuss how these factors might explain why teaching mechanisms are self-limiting, suggesting that such mechanisms may nevertheless play an important role in the evolution of cumulative culture in humans.

Revisiting an extant framework: Concerns about culture and task generalization

The target article elaborates upon an extant theoretical framework, “Imitation and Innovation: The Dual Engines of Cultural Learning.” We raise three major concerns: (1) There is limited discussion of cross-cultural universality and variation; (2) overgeneralization of overimitation and omission of other social learning types; and (3) selective imitation in infants and toddlers is not discussed.

Children's Evolved Learning Abilities and Their Implications for Education

In this article, I examine children's evolved learning mechanisms that make humans the most educable of animals. These include (1) skeletal perceptual and cognitive mechanisms that get fleshed out over the course of development, mainly through play; (2) a high level of plasticity that is greatest early in life but that persists into adulthood; (3) remarkable social-learning capabilities; and (4) dispositions toward exploration and play. I next examine some evolutionary mismatches-conflicts between psychological mechanisms evolved in ancient environments and their utility in modern ones-specifically with respect to modern educational systems. I then suggest some ways educators can take advantage of children's evolved learning abilities to minimize the effects of evolutionary mismatches, including (1) following developmentally appropriate practices (which are also evolutionarily appropriate practices), (2) increasing opportunities for physical activities, (3) increasing opportunities to learn through play, and (4) taking advantage of stress-adapted children's "hidden talents." I argue that evolutionary theory informs teachers and parents about how children evolved to learn and can result in more-enlightened teaching methods that will result in a more enjoyable and successful learning experiences for children.

How small-scale societies achieve large-scale cooperation

For most of our species' history, humans have lived in relatively small subsistence communities, often called small-scale societies. While these groups lack centralized institutions, they can and often do maintain large-scale cooperation. Here, we explore several mechanisms promoting cooperation in small-scale societies, including (a) the development of social norms that encourage prosocial behavior, (b) reciprocal exchange relationships, (c) reputation that facilitates high-cost cooperation, (d) relational wealth, and (e) risk buffering institutions. We illustrate these with ethnographic and psychological evidence from contemporary small-scale societies. We argue that these mechanisms for cooperation helped past and present small-scale communities adapt to diverse ecological and social niches.

DieTryin: An R package for data collection, automated data entry, and post-processing of network-structured economic games, social networks, and other roster-based dyadic data

Researchers studying social networks and inter-personal sentiments in bounded or small-scale communities face a trade-off between the use of roster-based and free-recall/name-generator-based survey tools. Roster-based methods scale poorly with sample size, and can more easily lead to respondent fatigue; however, they generally yield higher quality data that are less susceptible to recall bias and that require less post-processing. Name-generator-based methods, in contrast, scale well with sample size and are less likely to lead to respondent fatigue. However, they may be more sensitive to recall bias, and they entail a large amount of highly error-prone post-processing after data collection in order to link elicited names to unique identifiers. Here, we introduce an R package, DieTryin, that allows for roster-based dyadic data to be collected and entered as rapidly as name-generator-based data; DieTryin can be used to run network-structured economic games, as well as collect and process standard social network data and round-robin Likert-scale peer ratings. DieTryin automates photograph standardization, survey tool compilation, and data entry. We present a complete methodological workflow using DieTryin to teach end-users its full functionality.

Foragers and Their Tools: Risk, Technology and Complexity

The subsistence technology of forager communities has varied greatly over space and time. This paper (i) reviews briefly the main causal factors the literature identifies as responsible for this variation; (ii) analyzes in some detail the most prominent idea in the literature on spatial variation:Complex technology is an adaptive response to elevated risks of subsistence failure; (iii) it argues that the alleged empirical support for this hypothesis depends on dubious proxies of risk; (iv) it argues that it fails to explain the subsistence technologies of desert foragers, who generally live with simple technologies in high-risk environments; (v) it offers an alternative analysis, based on the reduced opportunity costs of complex technologies in highly seasonal environments, on the high value of typical forager targets in those environments and their relatively predictable location in space and time; and (v) the paper concludes with a conjecture about the role of environmental variation in toolkit change over deep time.

Gender differences in BaYaka forager sleep-wake patterns in forest and village contexts

Sleep studies in small-scale subsistence societies have broadened our understanding of cross-cultural sleep patterns, revealing the flexibility of human sleep. We examined sleep biology among BaYaka foragers from the Republic of Congo who move between environmentally similar but socio-ecologically distinct locations to access seasonal resources. We analyzed the sleep-wake patterns of 51 individuals as they resided in a village location (n = 39) and a forest camp (n = 23) (362 nights total). Overall, BaYaka exhibited high sleep fragmentation (50.5) and short total sleep time (5.94 h), suggestive of segmented sleep patterns. Sleep duration did not differ between locations, although poorer sleep quality was exhibited in the village. Linear mixed effect models demonstrated that women's sleep differed significantly from men's in the forest, with longer total sleep time (β ± SE =  - 0.22 ± 0.09, confidence interval (CI) = [- 0.4, - 0.03]), and higher sleep quality (efficiency; β ± SE =  - 0.24 ± 0.09, CI = [- 0.42, - 0.05]). These findings may be due to gender-specific social and economic activities. Circadian rhythms were consistent between locations, with women exhibiting stronger circadian stability. We highlight the importance of considering intra-cultural variation in sleep-wake patterns when taking sleep research into the field.

Cultural Components of Sex Differences in Color Preference

Preferences for pink and blue were tested in children aged 4-11 years in three small-scale societies: Shipibo villages in the Peruvian Amazon, kastom villages in the highlands of Tanna Island, Vanuatu, and BaYaka foragers in the northern Republic of Congo; and compared to children from an Australian global city (total N = 232). No sex differences were found in preference for pink in any of the three societies not influenced by global culture (ds - 0.31-0.23), in contrast to a female preference for pink in the global city (d = 1.24). Results suggest that the pairing of female and pink is a cultural phenomenon and is not driven by an essential preference for pink in girls.

Harm Avoidance and Mobility During Middle Childhood and Adolescence among Hadza Foragers

Cross-cultural sex differences in mobility and harm avoidance have been widely reported, often emphasizing fitness benefits of long-distance travel for males and high costs for females. Data emerging from adults in small-scale societies, however, are challenging the assumption that female mobility is restricted during reproduction. Such findings warrant further exploration of the ontogeny of mobility. Here, using a combination of machine-learning, mixed-effects linear regression, and GIS mapping, we analyze range size, daily distance traveled, and harm avoidance among Hadza foragers during middle childhood and adolescence. Distance traveled increased with age and, while male adolescents had the longest daily ranges, average daily distance traveled by each sex was similar. We found few age- or sex-related patterns in harm-avoidant responses and a high degree of individual variation. When queried on the same issues, children and their parents were often in alignment as to expectations pertaining to harm avoidance, and siblings tended to behave in similar ways. To the extent that sex differences in mobility did emerge, they were associated with ecological differences in physical threats associated with sex-specific foraging behaviors. Further, we found no strong association between harm avoidance and mobility. Young Hadza foragers of both sexes are highly mobile, regardless of how harm avoidant they are. Taken together, our findings indicate that the causal arrows between harm avoidance and mobility must be evaluated in ecologically specific frameworks where cultural expectations of juvenile mobility can be contextualized.

Ecological and Developmental Perspectives on Social Learning : Introduction to the Special Issue

In this special issue of Human Nature we explore the possible adaptive links between teaching and learning during childhood, and we aim to expand the dialogue on the ways in which the social sciences, and in particular current anthropological research, may better inform our shifting understanding of how these processes vary in different social and ecological environments. Despite the cross-disciplinary trend toward incorporating more behavioral and cognitive data outside of postindustrial state societies, much of the published cross-cultural data is presented as stand-alone population-level studies, making it challenging to extrapolate trends or incorporate both ecological and developmental perspectives. Here, contributors explore how human life history, ecological experience, cumulative culture, and ethnolinguistics impact social learning and child development in foraging and transitioning societies around the world. Using historical ethnographic data and qualitative and quantitative data from studies with contemporary populations, authors interrogate the array of factors that likely interact with cognitive development and learning. They provide contributions that explore the unique environmental, social, and cultural conditions that characterize such populations, offering key insights into processes of social learning, adaptive learning responses, and culture change. This series of articles demonstrates that children are taught culturally and environmentally salient skills in myriad ways, ranging from institutionalized instruction to brief, nuanced, and indirect instruction. Our hope is that this collection stimulates more research on the evolutionary and developmental implications associated with teaching and learning among humans.

I Want to Participate—Communities of Practice in Foraging and Gardening Projects as a Contribution to Social and Cultural Sustainability in Early Childhood Education

Learning and development in early childhood is highly dependent on social interaction and exploration through continuous encounters with the real world. Foraging and gardening are outdoor pedagogical practices that have relevance to education for sustainability. Previous work suggests that engagement in such activities can be characterized by the concept “community of practice” (CoP). In this paper, we explore how characteristics of the CoP can be recognized in foraging and gardening projects performed in the Arctic region of Norway, and we discuss how these activities can contribute to social and cultural aspects of sustainability. Data collection included focus group interviews with kindergarten staff (teachers and assistants) and videos taken of foraging and gardening activities with the children. Our data indicate that the hallmarks of CoP, domain, community, and practice, are strongly recognized in these projects through increased interest, social interaction, and agency for learning. This mutual engagement and participation in the CoPs for foraging and gardening connect both staff and children to local food heritage and culture for a sustainable future.

The Life History of Learning Subsistence Skills among Hadza and BaYaka Foragers from Tanzania and the Republic of Congo

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.

Veiled agency? Children, innovation and the archaeological record

Children and subadults were obviously part of ancient human communities, and almost certainly, in important ways their activities were distinctive; they did not routinely act like scaled down adults. Yet their presence was quite cryptic, but not entirely hidden. Their lives and acts did leave traces, although these tend to be be fragile, ambiguous and fast-fading. In addition to pursuing the methodological issues posed by the detection of subadult lives, this special issue raises important questions about the role of children, and their willingness to experiment and play, on innovation. It is true that ethnographically known forager children are almost certainly more autonomous, experimental and adventurous than WEIRD children, and this was probably true of the young foragers of the early Holocene and late Pleistocene too. Their greater willingness to experiment probably fuelled a supply of variation, and perhaps occasionally adaptation as well, especially finding new uses for existing materials. Much more certainly, innovations tend to be noted, taken up and spread by adolescents. They were vectors of change, even if perhaps only rarely initiators of change.

Sharing and caring: Testosterone, fathering, and generosity among BaYaka foragers of the Congo Basin

Humans are rare among mammals in exhibiting paternal care and the capacity for broad hyper-cooperation, which were likely critical to the evolutionary emergence of human life history. In humans and other species, testosterone is often a mediator of life history trade-offs between mating/competition and parenting. There is also evidence that lower testosterone men may often engage in greater prosocial behavior compared to higher testosterone men. Given the evolutionary importance of paternal care and heightened cooperation to human life history, human fathers' testosterone may be linked to these two behavioral domains, but they have not been studied together. We conducted research among highly egalitarian Congolese BaYaka foragers and compared them with their more hierarchical Bondongo fisher-farmer neighbors. Testing whether BaYaka men's testosterone was linked to locally-valued fathering roles, we found that fathers who were seen as better community sharers had lower testosterone than less generous men. BaYaka fathers who were better providers also tended to have lower testosterone. In both BaYaka and Bondongo communities, men in marriages with greater conflict had higher testosterone. The current findings from BaYaka fathers point to testosterone as a psychobiological correlate of cooperative behavior under ecological conditions with evolutionarily-relevant features in which mutual aid and sharing of resources help ensure survival and community health.

The optimal timing of teaching and learning across the life course

The evolutionary biologist W. D. Hamilton (Hamilton 1966 J. Theor. Biol.12, 12-45. (doi:10.1016/0022-5193(66)90184-6)) famously showed that the force of natural selection declines with age, and reaches zero by the age of reproductive cessation. However, in social species, the transfer of fitness-enhancing resources by postreproductive adults increases the value of survival to late ages. While most research has focused on intergenerational food transfers in social animals, here we consider the potential fitness benefits of information transfer, and investigate the ecological contexts where pedagogy is likely to occur. Although the evolution of teaching is an important topic in behavioural biology and in studies of human cultural evolution, few formal models of teaching exist. Here, we present a modelling framework for predicting the timing of both information transfer and learning across the life course, and find that under a broad range of conditions, optimal patterns of information transfer in a skills-intensive ecology often involve postreproductive aged teachers. We explore several implications among human subsistence populations, evaluating the cost of hunting pedagogy and the relationship between activity skill complexity and the timing of pedagogy for several subsistence activities. Long lifespan and extended juvenility that characterize the human life history likely evolved in the context of a skills-intensive ecological niche with multi-stage pedagogy and multigenerational cooperation. This article is part of the theme issue 'Life history and learning: how childhood, caregiving and old age shape cognition and culture in humans and other animals'.

Culture and early social-cognitive development

From a developmental systems perspective, this chapter focuses on the question whether culture matters for children's early social-cognitive development. Based on a review of the current cross-cultural literature, we evaluate the current state of research on cross-cultural similarities and differences in major developmental milestones of early social cognition, namely (i) the development of self-awareness and an understanding of self and others as intentional agents, (ii) advanced forms of social learning and (iii) prosocial cognition and behavior. Overall, the current cross-cultural research suggests universality without uniformity: the common suite of social-cognitive skills emerges reliably and, at the same time, there are culture-specific accentuations of social-cognitive development across domains that mostly are in line with cultural values, beliefs and practices. By following different agendas when providing and structuring physical and social settings for their children, caregivers coherently organize infants' nascent intuitions, sentiments, and inclinations into increasingly coherent patterns of attention, appraisal, experience and behavior that are in line with cultural ideals and beliefs. By doing so, culturally informed social interaction sets the stage for culture-specific modulations of social cognition already in the first years of life.

Learner-driven innovation in the stone tool technology of early Homo sapiens

Current perspectives of stone tool technology tend to emphasize homogeneity in tool forms and core reduction strategies across time and space. This homogeneity is understood to represent shared cultural traditions that are passed down through the generations. This represents a top-down perspective on how and why stone tools are manufactured that largely restricts technological agency to experts, adults and teachers. However, just as bottom-up processes driven by children and youth influence technological innovation today, they are likely to have played a role in the past. This paper considers evidence from the archaeological record of early Homo sapiens' lithic technology in Africa that may attest to our long history of bottom-up social learning processes and learner-driven innovation. This evidence includes the role of emulative social learning in generating assemblages with diverse reduction strategies, a high degree of technological fragmentation across southern Africa during some time periods, and technological convergence through the Pleistocene. Counter to some perspectives on the uniqueness of our species, our ability to learn independently, to 'break the rules' and to play, as opposed to conforming to top-down influences, may also account for our technological success.

Effects of a mixed-subsistence diet on the growth of Hadza children

INTRODUCTION

We investigated the preliminary effects of dietary changes on the anthropometric measurements of child and adolescent Hadza foragers.

METHODS

We conducted a cross-sectional study comparing height and weight of participants (aged 0-17 years) at two time points, 2005 (n = 195) and 2017 (n = 52), from two locations: semi-nomadic "bush camps" and sedentary "village camps". World Health Organization (WHO) calculators were used to generate standardized z-scores for weight-for-height (WHZ), weight-for-age (WAZ), height-for-age (HAZ), and BMI-for-age (BMIFAZ). Cross tabulations were constructed for each measurement variable as a function of z-score categories and the variables year, location, and sex.

RESULTS

Residency in a village, and associated mixed-subsistence diet, was associated with favorable growth, including greater WAZ (P < .001), HAZ (P < .001), and BMIFAZ (P = .004), but not WHZ (P = .717). Regardless of residency location, participants showed an improved WAZ (P = .021) and HAZ (P < .001) in the 2017 study year. We found no sex differences.

DISCUSSION AND CONCLUSION

These preliminary findings suggest that a mixed-subsistence diet may confer advantages over an exclusive wild food diet, a trend also reported among other transitioning foragers.

Where innovations flourish: an ethnographic and archaeological overview of hunter-gatherer learning contexts

Research in developmental psychology suggests that children are poor tool innovators. However, such research often overlooks the ways in which children's social and physical environments may lead to cross-cultural variation in their opportunities and proclivity to innovate. In this paper, we examine contemporary hunter-gatherer child and adolescent contributions to tool innovation. We posit that the cultural and subsistence context of many hunter-gatherer societies fosters behavioural flexibility, including innovative capabilities. Using the ethnographic and developmental literature, we suggest that socialisation practices emphasised in hunter-gatherer societies, including learning through autonomous exploration, adult and peer teaching, play and innovation seeking may bolster children's ability to innovate. We also discuss whether similar socialisation practices can be interpreted from the archaeological record. We end by pointing to areas of future study for understanding the role of children and adolescents in the development of tool innovations across cultures in the past and present.