In some small-scale societies, a sexual division of labor is common. For subadult hunter-gatherers, the onset of this division dates to middle childhood and the start of puberty; however, there is apparently no physiological explanation for this timing. The present study uses an experimental approach to evaluate possible energetic differences by sex in gathering-related activities. The energetic cost of gathering-related activities was measured in a sample of 42 subjects of both sexes aged between 8 and 14 years. Body mass and (...) other anthropometric variables were also recorded. Our results show that the energetic differences in the simulated gathering activities depend only on body mass. Both sexes expend a similar amount of energy during locomotion activities related to gathering. Discarding the energetic factor, the sexual division of tasks may be explained as an adaptation to acquire the skills needed to undertake the complex activities required during adulthood as early as possible. Carrying out gathering activities during childhood and adolescence could be favored by the growth and development cycles of Homo sapiens. Moreover, if most of the energetic costs of gathering activities depend on body mass, the delayed growth in humans relative to other primates allows subadults to practice these tasks for longer periods, and to become better at performing them. In fact, this strategy could enable them to acquire adults’ complex skills at a low energetic cost that can be easily subsidized by other members of the group. (shrink)

The evolution of modern human life history has involved substantial changes in the overall length of the subadult period, the introduction of a novel early childhood stage, and many changes in the initiation, termination, and character of the other stages. The fossil record is explored for evidence of this evolutionary process, with a special emphasis on middle childhood, which many argue is equivalent to the juvenile stage of African apes. Although the “juvenile” and “middle childhood” stages appear to be the (...) same from a broad comparative perspective, in that they begin with the eruption of the first molar and the achievement of the majority of adult brain size and end with sexual maturity, the detailed differences in the expression of these two stages, and how they relate to the preceding and following stages, suggest that a distinction should be maintained between them to avoid blurring subtle, but important, differences. (shrink)

We investigate whether age profiles of ethnobiological knowledge development are consistent with predictions derived from life history theory about the timing of productivity and reproduction. Life history models predict complementary knowledge profiles developing across the lifespan for women and men as they experience changes in embodied capital and the needs of dependent offspring. We evaluate these predictions using an ethnobiological knowledge assessment tool developed for an off-grid pastoralist population known as Choyeros, from Baja California Sur, Mexico. Our results indicate that (...) while individuals acquire knowledge of most dangerous items and edible resources by early adulthood, knowledge of plants and animals relevant to the age and sex divided labor domains and ecologies (e.g., women’s house gardens, men’s herding activities in the wilderness) continues to develop into middle adulthood but to different degrees and at different rates for men and women. As the demands of offspring on parents accumulate with age, reproductive-aged adults continue to develop their knowledge to meet their children’s needs. After controlling for vision, our analysis indicates that many post-reproductive adults show the greatest ethnobiological knowledge. These findings extend our understanding of the evolved human life history by illustrating how changes in embodied capital and the needs of dependent offspring predict the development of men’s and women’s ethnobiological knowledge across the lifespan. (shrink)

Patterns of human kinship commonly involve preferential treatment of relatives based on lineal descent (lineages) rather than degree of genetic relatedness (kindreds), presenting a challenge for inclusive fitness theory. Here, we examine effects of lineage and kindred characteristics on reproductive success (RS) and number of grandchildren for 130 men and 124 women in a horticultural community on Dominica. Kindreds had little effect on fitness independently of lineage characteristics. Fitness increased with the number of lineal relatives residing in the community but (...) decreased beyond an apparently optimal lineage size, suggesting resource enhancement and competition among kin. Female-biased patrilineage sex ratio was positively associated with men’s fitness, while male-biased matrilineage sex ratio was positively associated with women’s fitness. Number of brothers in the community was negatively associated with men’s, but not women’s, fitness. Parents and number of sisters had no effect on either male or female reproduction; however, women with younger sisters had higher RS, suggesting benefits of kin support for childcare. In sum, imposed norms for lineage social organization may enhance lineal ancestors’ inclusive fitness at a cost to individual inclusive fitness. (shrink)

Parental investment decisions guide parental actions regarding children’s productive work and are shaped by ecological context. Urban ecology enhances long-term payoffs to investment in human capital, increasing opportunity costs for work performed by children, and decreased workload should result. Using an embodied capital framework, self-reported data on urban and rural Indo-Fijian children’s work activities are compared. Results show higher workloads for older children, rural children, and girls. High scholastic achievement is associated with lower workloads for girls, but not boys. This (...) pattern is interpreted as daughter-biased investment in the context of urbanization. (shrink)

Health research has shown that overweight and obesity in children and adults are becoming significant public health problems in the developing world. Evidence suggests that this phenomenon is more marked in urban than rural areas and may be associated with modernization. However, the underlying reasons for this nutrition transition remain unclear. Dietary shifts, often in conjunction with income and time constraints in urban environments, may entail a greater reliance on more convenient sugar and fat-dense food. Also, the necessity of labor-intensive (...) agricultural work to meet rural subsistence needs is supplanted in urban environments by sedentary work. This paper extends the application of human behavioral ecology theory into the realm of international development and policy by applying Kaplan’s embodied capital theory to explore differences in food habits and nutritional status of Indo-Fijian children within the context of urbanization. Urban high-embodied-capital women demonstrate higher rates of wage-earning employment than urban low-embodied-capital or rural women. Findings indicate that urban high-embodied-capital households spend significantly more on food purchases, purchase a greater proportion of processed foods, and have children with higher body mass indexes (BMI) than do urban low-embodied-capital or rural households. This suggests that urban high-embodied-capital mothers, who tend to be employed, may be making trade-offs between income and food choices. (shrink)

Parental investment strategies are contingent on parental capacities and ecology. Parental embodied capital may be important in aspiration construction and investments in children’s human capital, which is especially important in urban environments where skills are directly tied to wage income. For Indo-Fijians, rural ecology strongly limits opportunities. Here this limitation is conceptualized as extrinsic risk and immune to reduction through enhanced parental investment. Urban migration is interpreted as a risk reduction strategy, given an expanded urban opportunity structure (lower extrinsic risk). (...) Qualitative and quantitative data from 678 Indo-Fijian children suggest that, contingent on parental capacities, parents migrate in response to their perceptions of decreased opportunities that manifest as high levels of extrinsic risk in rural environments. Parental investment in quality and quantity corresponds to parental perceptions of extrinsic risk, which in turn correspond to migration status, indicating that parental strategies do respond to perceived limits on investment payoffs. (shrink)

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. (shrink)

This paper is a cross-cultural examination of the development of hunting skills and the implications for the debate on the role of learning in the evolution of human life history patterns. While life history theory has proven to be a powerful tool for understanding the evolution of the human life course, other schools, such as cultural transmission and social learning theory, also provide theoretical insights. These disparate theories are reviewed, and alternative and exclusive predictions are identified. This study of cross-cultural (...) regularities in how children learn hunting skills, based on the ethnographic literature on traditional hunters, complements existing empirical work and highlights future areas for investigation. (shrink)

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. (shrink)

Learning to use, make, and modify tools is key to our species’ success. Researchers have hypothesized that play with objects may have a foundational role in the ontogeny of tool use and, over evolutionary timescales, in cumulative technological innovation. Yet, there are few systematic studies investigating children’s interactions with objects outside the post-industrialized West. Here, we survey the ethnohistorical record to uncover cross-cultural trends regarding hunter-gatherer children’s use of objects during play and instrumental activities. Our dataset, consisting of 434 observations (...) of children’s toys and tools from 54 hunter-gatherer societies, reveals several salient trends: Most objects in our dataset are used in play. Children readily manufacture their own toys, such as dolls and shelters. Most of the objects that children interact with are constructed from multiple materials. Most of the objects in our dataset are full-sized or miniature versions of adult tools, reflecting learning for adult roles. Children also engage with objects related to child culture, primarily during play. Taken together, our findings show that hunter-gatherer children grow up playing, making, and learning with objects. (shrink)

Hunting and gathering is, evolutionarily, the defining subsistence strategy of our species. Studying how children learn foraging skills can, therefore, provide us with key data to test theories about the evolution of human life history, cognition, and social behavior. Modern foragers, with their vast cultural and environmental diversity, have mostly been studied individually. However, cross-cultural studies allow us to extrapolate forager-wide trends in how, when, and from whom hunter-gatherer children learn their subsistence skills. We perform a meta-ethnography, which allows us (...) to systematically extract, summarize, and compare both quantitative and qualitative literature. We found 58 publications focusing on learning subsistence skills. Learning begins early in infancy, when parents take children on foraging expeditions and give them toy versions of tools. In early and middle childhood, children transition into the multi-age playgroup, where they learn skills through play, observation, and participation. By the end of middle childhood, most children are proficient food collectors. However, it is not until adolescence that adults (not necessarily parents) begin directly teaching children complex skills such as hunting and complex tool manufacture. Adolescents seek to learn innovations from adults, but they themselves do not innovate. These findings support predictive models that find social learning should occur before individual learning. Furthermore, these results show that teaching does indeed exist in hunter-gatherer societies. And, finally, though children are competent foragers by late childhood, learning to extract more complex resources, such as hunting large game, takes a lifetime. (shrink)

Work-themed play may allow children to learn complex skills, and ethno-typical and gender-typical behaviors. Thus, play may have made important contributions to the evolution of childhood through the development of embodied capital. Using data from Aka foragers and Ngandu farmer children from the Central African Republic, we ask whether children perform ethno- and gender-typical play and work activities, and whether play prepares children for complex work. Focal follows of 50 Aka and 48 Ngandu children were conducted with the aim of (...) recording children’s participation in 12 categories of work and work-themed play. Using these data, we test a set of hypotheses regarding how age, gender, ethnicity, and task complexity influence children’s activities. As hypothesized, we find performance of work-themed play is negatively correlated with age. Contrary to our hypothesis, children do not play more than they work at complex tasks, but they work more than they play at simple ones. Gender and ethnicity are associated with play and work at culturally salient activities, despite availability of other-gender and other-ethnicity social partners. Our findings show that ethnic and gender biases are apparent in the play and work behavior of Aka and Ngandu children. Moreover, our results show that play helps both forager and farmer children learn complex skills, consistent with play having an adaptive learning function. (shrink)

Notable in cross-cultural comparisons is the variable span of time between when children become economically self-sufficient and when they initiate their own reproductive careers. That variation is of interest because it shapes the age range of children reliant on others for support and the age range of children available to help out, which in turn affects the competing demands on parents to support multiple dependents of different ages. The age at positive net production is used as a proxy to estimate (...) the close of juvenile economic dependence among a group of Maya subsistence agriculturalists. Maya children produce more than they consume by their early to mid teens but remain in their natal households for a number of years before leaving home and beginning families of their own. The Maya results contrast markedly with those from several groups of hunter-gatherers and horticulturalists for whom we have similar data. Even in the Maya case, where children are self-sufficient at a relatively young age, parents are unable to support their children without help from others. The production surplus of older children appears to help underwrite the cost of large Maya families and subsidize their parents’ continued reproduction. (shrink)

Attention has been given to cross-cultural differences in adolescent growth, but far less is known about developmental variability during juvenility (ages 3–10). Previous research among the Pumé, a group of South American foragers, found that girls achieve a greater proportion of their adult stature during juvenility compared with normative growth expectations. To explain rapid juvenile growth, in this paper we consider girls’ activity levels and energy expended in subsistence effort. Results show that Pumé girls spend far less time in subsistence (...) tasks in proportion to their body size compared with adults, and they have lower physical activity levels compared with many juveniles cross-culturally. Low activity levels help to explain where the extra energy comes from to support rapid growth in a challenging environment. We suggest that activity levels are important to account for the variation of resource and labor transfers in mediating energy availability. (shrink)

Research in nonindustrial small-scale societies challenges the common perception that human childhood is universally characterized by a long period of intensive adult investment and dedicated instruction. Using return rate and time allocation data for the Savanna Pumé, a group of South American hunter-gatherers, age patterns in how children learn to become productive foragers and from whom they learn are observed across the transition from childhood to adolescence. Results show that Savanna Pumé children care for their siblings, are important economic contributors, (...) learn by doing rather than by instruction, and spend their time principally in the company of other children. This developmental experience contrasts with that of children in postindustrial societies, who are dependent on adults, often well past maturity; learn in formal settings; and spend much of their time in the company of adults. These differences raise questions about whether normative behaviors observed in postindustrial societies are representative of human children. This comparison also identifies the potential mismatch between hunter-gatherer and postindustrial societies in the extent to which children may be well adapted to learn from and teach each other. In particular, spending time in autonomous work and play groups develops the cooperation and coordination skills that are foundational to human subsistence and growing up to be socially and productively adept adults and parents. (shrink)

Notable in cross-cultural comparisons is the variable span of time between when children become economically self-sufficient and when they initiate their own reproductive careers. That variation is of interest because it shapes the age range of children reliant on others for support and the age range of children available to help out, which in turn affects the competing demands on parents to support multiple dependents of different ages. The age at positive net production is used as a proxy to estimate (...) the close of juvenile economic dependence among a group of Maya subsistence agriculturalists. Maya children produce more than they consume by their early to mid teens but remain in their natal households for a number of years before leaving home and beginning families of their own. The Maya results contrast markedly with those from several groups of hunter-gatherers and horticulturalists for whom we have similar data. Even in the Maya case, where children are self-sufficient at a relatively young age, parents are unable to support their children without help from others. The production surplus of older children appears to help underwrite the cost of large Maya families and subsidize their parents’ continued reproduction. (shrink)

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 we reconcile theory with the existing literature in light of our results. (shrink)

Humans have a much longer juvenile period (weaning to first reproduction, 14 or more years) than their closest relatives (chimpanzees, 8 years). Three explanations are prominent in the literature. (a) Humans need the extra time to learn their complex subsistence techniques. (b) Among mammals, since length of the juvenile period bears a constant relationship to adult lifespan, the human juvenile period is just as expected. We therefore only need to explain the elongated adult lifespan, which can be explained by the (...) opportunity for older individuals to increase their fitness by providing for grandchildren. (c) The recent model by Kaplan and colleagues suggests that longevity and investment in "embodied capital" will coevolve, and that the need to learn subsistence technology contributed to selection for our extended lifespan.We report experiments designed to test the first explanation: human subsistence technology takes many years to learn, and spending more time learning it gives reproductive benefits that outweight lost time. Taking away some of this time should lead to deficits in efficiency. We paid Hadza foragers to participate in tests of important subsistence skills. We compared efficiency of males and females at digging tubers. They differ greatly in time spent practicing digging but show no difference in efficiency. Children who lost "bush experience" by spending years in boarding school performed no worse at digging tubers or target archery than those who had spent their entire lives in the bush. Climbing baobab trees, an important and dangerous skill, showed no change with age among those who attempted it. We could show no effects of practice time.These findings do not support what we label "the practice theory," but we discuss ways in which the theory could be defended; for example, some as-yet-untested skill may be greatly impaired by loss of a few years of the juvenile period. Our data also show that it is not safe to assume that increases in skill with age are entirely due to learning or practice; they may instead be due to increases in size and strength. (shrink)

We hypothesize that juvenile baboons are less efficient foragers than adult baboons owing to their small size, lower level of knowledge and skill, and/or lesser ability to maintain access to resources. We predict that as resources are more difficult to extract, juvenile baboons will demonstrate lower efficiency than adults will because of their lower levels of experience. In addition, we hypothesize that juvenile baboons will be more likely to allocate foraging time to easier-to-extract resources owing to their greater efficiency in (...) acquiring those resources.We use feeding efficiency and time allocation data collected on a wild, free-ranging, non-provisioned population of chacma baboons (Papio hamadryas ursinus) in the Moremi Wildlife Reserve, Okavango Delta, Botswana to test these hypotheses. The major findings of this study are:1. Juvenile baboons are significantly less efficient foragers than adult baboons primarily for difficult-to-extract resources.We propose that this age-dependent variation in efficiency is due to differences in memory and other cognitive functions related to locating food resources, as is indicated by the greater amount of time juvenile baboons spend searching for food. There is no evidence that smaller body size or competitive disruption influences the differences in return rates found between adult and juvenile baboons in this study.2. An individual baboon’s feeding efficiency for a given resource can be used to predict the duration of its foraging bouts for that resource.These results contribute both to our understanding of the ontogeny of behavioral development in nonhuman primates, especially regarding foraging ability, and to current debate within the field of human behavioral ecology regarding the evolution of the juvenile period in primates and humans. (shrink)

Considerable research on helpers-at-the-nest demonstrates the positive effects of firstborn daughters on a mother’s reproductive success and the survival of her children compared with women who have firstborn sons. This research is largely restricted to agricultural settings. In the present study we ask: “Does ‘daughter first’ improve mothers’ reproductive success in a hunting and gathering context?” Through an analysis of 84 postreproductive women in this population we find that the sex of the first- or second-born child has no effect on (...) a mother’s fertility or the survival of her offspring. We conclude that specific environmental and economic factors underlay the helpers-at-the-nest phenomenon. (shrink)

This paper lays the groundwork for a theory of time allocation across the life course, based on the idea that strength and skill vary as a function of age, and that return rates for different activities vary as a function of the combination of strength and skills involved in performing those tasks. We apply the model to traditional human subsistence patterns. The model predicts that young children engage most heavily in low-strength/low-skill activities, middle-aged adults in high-strength/high-skill activities, and older adults (...) in low-strength/high-skill activities. Tests among Machiguenga and Piro forager-horticulturalists of southeastern Peru show that males and females focus on low-strength/low-skill tasks early in life (domestic tasks and several forms of fishing), switch to higher-strength/higher-skill activities in their twenties and thirties (hunting, fishing, and gardening for males; fishing and gardening for females), and shift focus to high-skill activities late in life (manufacture/repair, food processing). (shrink)

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. 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. (shrink)

Children’s play is widely believed by educators and social scientists to have a training function that contributes to psychosocial development as well as the acquisition of skills related to adult competency in task performance. In this paper we examine these assumptions from the perspective of life-history theory using behavioral observation and household economic data collected among children in a community in the Okavango Delta of Botswana where people engage in mixed subsistence regimes of dry farming, foraging, and herding. We hypothesize (...) that if play contributes to adult competency then time allocation to play will decrease as children approach adult levels of competence. This hypothesis generates the following predictions: (1) time allocated to play activities that develop specific productive skills should decline in relation to the proportion of adult competency achieved; (2) children will spend more time in forms of play that are related to skill development in tasks specific to the subsistence ecology in which that child participates or expects to participate; and (3) children will spend more time in forms of play that are related to skill development in tasks clearly related to the gender-specific productive role in the subsistence ecology in which that child participates or expects to participate. We contrast these expectations with the alternative hypothesis that if play is not preparatory for adult competence then time allocated to each play activity should diminish at the same rate. This latter hypothesis generates the following two predictions: (1) time allocation to play should be unaffected by subsistence regime and (2) patterns of time allocation to play should track patterns of growth and energy balance. Results from multiple regression analysis support earlier research in this community showing that trade-offs between immediate productivity and future returns were a primary determinant of children’s activity patterns. Children whose labor was in greater demand spent significantly less time playing. In addition, controlling for age and gender, children spent significantly more time in play activities related to tasks specific to their household subsistence economy. These results are consistent with the assertion that play is an important factor in the development of adult competency and highlight the important contributions of an evolutionary ecological perspective in understanding children’s developmental trajectories. (shrink)