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 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)

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)

A fundamental cognitive function found across a wide range of species and necessary for survival is the ability to navigate complex environments. It has been suggested that mobility may play an important role in the development of spatial skills. Despite evolutionary arguments offering logical explanations for why sex/gender differences in spatial abilities and mobility might exist, thus far there has been limited sampling from nonindustrialized and subsistence-based societies. This lack of sampling diversity has left many unanswered questions regarding the effects (...) that environmental variation and cultural norms may have in shaping mobility patterns during childhood and the development of spatial competencies that may be associated with it. Here we examine variation in mobility, performance on large-scale spatial skills, and performance on small-scale spatial skills among Twa forager/pastoralist children whose daily lives have been dramatically altered since settlement and the introduction of government-funded boarding schools. Unlike in previous findings among Twa adults, boys and girls show similar patterns of travel on all measures of mobility. We also find no significant differences in spatial task performance by gender for large- or small-scale spatial skills. Further, children performed as well as adults did on mental rotation, and they outperformed adults on the water-level task. We discuss how children’s early learning environments may influence the development of both large- and small-scale spatial skills. (shrink)