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.

Postpartum Maternal Mood Among Hadza Foragers of Tanzania: A Mixed Methods Approach.

Infant and maternal mortality rates are among the highest in the world in low and middle-income countries where postpartum depression impacts at least one in five women. Currently, there is a dearth of data on maternal mood and infant health outcomes in small-scale non-industrial populations from such countries, particularly during the postnatal period. Here, we present the first investigation of postpartum maternal mood among a foraging population, the Hadza of Tanzania. We administered the Edinburgh Postnatal Depression Scale (EPDS) to twenty-three women, all with infants under the age of 12 months. Semi-structured interviews on happiness and unhappiness during the post-partum period served as a validity cross-check for the EPDS. The combined results of the EPDS surveys and the interview responses suggest that a high proportion of Hadza women experience significant mood disturbances following birth and that postpartum unhappiness is associated with self-reports of pain, anxiety, and disturbed sleep patterns. These findings suggest that many of the mothers in our sample are experiencing post-partum unhappiness at levels similar to or higher than those reported for low to middle income countries in general, including Tanzania. These data are critical for improving our understanding of the etiologies of postpartum mood disturbances cross-culturally.

Physical activity and time budgets of Hadza forager children: Implications for self-provisioning and the ontogeny of the sexual division of labor.

OBJECTIVES: To determine the effects of age and sex on physical activity and time budgets of Hadza children and juveniles, 5-14 years old, including both in-camp and out-of-camp activities. METHODS: Behavioral data were derived from ~15 000 hourly in-camp scan observations of 76 individuals and 13 out-of-camp focal follows on nine individuals. The data were used to estimate energy expended and percentage of time engaged in a variety of routine activities, including food collection, childcare, making and repairing tools, and household maintenance. RESULTS: Our results suggest that (1) older children spend more time in economic activities; (2) females spend more time engaged in work-related and economic activities in camp, whereas males spend more time engaged in economic activities out of camp; and (3) foraging by both sexes tends to net caloric gains despite being energetically costly. CONCLUSIONS: These results show that, among the Hadza, a sexual division of labor begins to emerge in middle childhood and is well in place by adolescence. Furthermore, foraging tends to provide net caloric gains, suggesting that children are capable of reducing at least some of the energetic burden they place upon their parents or alloparents. The findings are relevant to our understanding of the ways in which young foragers allocate their time, the development of sex-specific behavior patterns, and the capacity of children's work efforts to offset the cost of their own care in a cooperative breeding environment.

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.

Changes in Juvenile Foraging Behavior among the Hadza of Tanzania during Early Transition to a Mixed-Subsistence Economy.

The Hadza foragers of Tanzania are currently experiencing a nutritional shift that includes the intensification of domesticated cultigens in the diet. Despite these changes, no study, to date, has examined the possible effects of this transition on the food collection behavior of young foragers. Here we present a cross-sectional study on foraging behavior taken from two time points, 2005 and 2017. We compare the number of days foraged and the type and amount of food collected for young foragers, aged 5-14 years, in age- and season-matched samples. Compared with 2005, in 2017 fewer subadults left camp to forage, and overall, they targeted a smaller variety of wild foods, with the noticeable absence of wild honey, figs, and tubers. In addition, participants in 2017 were significantly more likely to have attended school. Despite the increased presence of domesticated plant foods in the diet and increased attendance at school, some young foragers continue to be highly productive in collecting wild, undomesticated foods. Despite the preliminary nature of our results, our findings suggest that the range of wild foods targeted by subadults is decreasing as the amount of domesticated cultigens in the diet increases. These data underscore the importance of studying diet composition and foraging decisions across temporal, nutritional, and ecological landscapes.