DHEAS and nutritional status among Sidama, Ngandu, and Aka children: Effects of cortisol and implications for adrenarche.

OBJECTIVE: Adrenarche, the biological event marked by rising production of dehydroepiandrosterone and its sulfate (DHEAS), may represent a sensitive period in child development, with important implications for adolescence and beyond. Nutritional status, particularly BMI and/or adiposity, has long been hypothesized as a factor in DHEAS production but findings are inconsistent, and few studies have examined this among non-industrialized societies. In addition, cortisol has not been included in these models. We here evaluate effects of height- (HAZ), weight- (WAZ), and BMI- (BMIZ) for-age on DHEAS concentrations among Sidama agropastoralist, Ngandu horticulturalist, and Aka hunter-gatherer children. METHODS: Heights and weights were collected from 206 children aged 2-18 years old. HAZ, WAZ, and BMIZ were calculated using CDC standards. DHEAS and cortisol assays were used to determine biomarker concentrations in hair. Generalized linear modeling was used to examine effects of nutritional status on DHEAS concentrations, as well as cortisol, controlling for age, sex, and population. RESULTS: Despite the prevalence of low HAZ and WAZ scores, the majority (77%) of children had BMI z-scores >-2.0 SD. Nutritional status has no significant effect on DHEAS concentrations, controlling for age, sex, and population. Cortisol, however, is a significant predictor of DHEAS concentrations. CONCLUSIONS: Our findings do not support a relationship between nutritional status and DHEAS. Instead, results suggest an important role for stress and ecology in DHEAS concentrations across childhood. Specifically, effects of environment via cortisol may be influential to patterning of DHEAS. Future work should investigate local ecological stressors and their relationship to adrenarche.

Applying minimally invasive biomarkers of chronic stress across complex ecological contexts.

Chronic stress is both theoretically and methodologically challenging to operationalize through biomarkers. Yet minimally invasive, field-friendly biomarkers of chronic stress are valuable in research linking biology and culture, seeking to understand differential patterns of human development across ecological contexts, and exploring the evolution of human sociality. For human biologists, a central question in measurement and interpretation of biomarkers is how stress-responsive physiological systems are regulated across diverse human ecologies. This article aims to describe a conditional toolkit for human biologists interested in the study of chronic stress, highlighting a mix of longstanding and novel biomarkers, with special focus on hair/fingernail cortisol, latent herpesvirus antibodies, allostatic load indices, and serial/ambulatory data collection approaches. Future trends in chronic stress biomarker research, including epigenetic approaches, are briefly considered. This overview considers: (1) challenges in separating a distinctly psychosocial dimension of chronic stress from adversity more broadly; (2) essential characteristics of human ecology that shape interpretation; (3) retrospective vs. longitudinal sampling; (4) the role of age, developmental effects, and local biologies; (5) different timescales of chronicity; and (6) the role of culture.

Life history and socioecology of infancy.

OBJECTIVES: Evolution of human maternal investment strategies is hypothesized to be tied to biological constraints and environmental cues. It is likely, however, that the socioecological context in which mothers' decisions are made is equally important. Yet, a lack of studies examining maternal investment from a cross-cultural, holistic approach has hindered our ability to investigate the evolution of maternal investment strategies. Here, we take a systems-level approach to study how human life history characteristics, environments, and socioecology influence maternal investment in their children. MATERIALS AND METHODS: We test how infant age and sex, maternal age, parity, and child loss, and the composition of a child's cooperative breeding network are associated with maternal investment across three small-scale (hunter-gatherer, horticultural, and agropastoral), sub-Saharan populations (N = 212). Naturalistic behavioral observations also enable us to illustrate the breadth and depth of the human cooperative breeding system. RESULTS: Results indicate that infant age, maternal age and parity, and an infant's cooperative childcare network are significantly associated with maternal investment, controlling for population. We also find that human allomaternal care is conducted by a range of caregivers, occupying different relational, sex, and age categories. Moreover, investment by allomothers is widely distributed. DISCUSSION: Our findings illustrate the social context in which children are reared in contemporary small-scale populations, and in which they were likely reared throughout our evolutionary history. The diversity of the caregiving network, coupled with life history characteristics, is predictive of maternal investment strategies, demonstrating the importance of cooperation in the evolution of human ontogeny.

DHEAS patterning across childhood in three sub-Saharan populations: Associations with age, sex, ethnicity, and cortisol.

OBJECTIVES: Hormones have many roles in human ontogeny, including the timing of life history 'switch points' across development. Limited hormonal data exist from non-Western children, leaving a significant gap in our understanding of the diversity of life history patterning. This cross-sectional study examines dehydroepiandrosterone sulfate (DHEAS) production in relation to age, sex, ethnicity, and cortisol concentrations, as well as average age of adrenarche, among Aka and Ngandu children of the Central African Republic and Sidama children of Ethiopia. METHODS: Hair was collected from 480 children (160 per population) aged 3-18 years old. These samples were analyzed for DHEAS and cortisol concentrations using ELISAs. A generalized additive model was used to examine DHEAS patterning in relation to age, sex, cortisol, and ethnicity. The derivative of DHEAS as a function of age was used to identify average age of adrenarche in each population. RESULTS: DHEAS patterning in these three populations is distinct from Euro-American patterns of production. In all three groups, the population-level age at adrenarche onset occurs slightly later than Euro-American averages, with both Central African populations experiencing a later onset than the Ethiopian population. CONCLUSIONS: DHEAS patterns and age at adrenarche vary across cultures, perhaps indicating adaptive life history responses in diverse eco-cultural environments. Delayed involution of the fetal zone and DHEAS patterning may offer both cognitive protection and immune defense in high-risk, nutritionally-poor environments. Additional research in the majority world is essential to improving our understanding of the diversity of hormonal development and timing of 'switch points' in life history trajectories.

Social networks, cooperative breeding, and the human milk microbiome.

OBJECTIVES: We present the first available data on the human milk microbiome (HMM) from small-scale societies (hunter-gatherers and horticulturalists in the Central African Republic [CAR]) and explore relationships among subsistence type and seasonality on HMM diversity and composition. Additionally, as humans are cooperative breeders and, throughout our evolutionary history and today, we rear offspring within social networks, we examine associations between the social environment and the HMM. Childrearing and breastfeeding exist in a biosocial nexus, which we hypothesize influences the HMM. METHODS: Milk samples from hunter-gatherer and horticultural mothers (n = 41) collected over two seasons, were analyzed for their microbial composition. A subsample of these women's infants (n = 33) also participated in detailed naturalistic behavioral observations which identified the breadth of infants' social and caregiving networks and the frequency of contact they had with caregivers. RESULTS: Analyses of milk produced by CAR women indicated that HMM diversity and community composition were related to the size of the mother-infant dyad's social network and frequency of care that infants receive. The abundance of some microbial taxa also varied significantly across populations and seasons. Alpha diversity, however, was not related to subsistence type or seasonality. CONCLUSION: While the origins of the HMM are not fully understood, our results provide evidence regarding possible feedback loops among the infant, the mother, and the mother's social network that might influence HMM composition.

Sibling effects on nutritional status: Intersections of cooperation and competition across development.

OBJECTIVES: Examination of sibling effects on nutritional status is complicated by siblings being both alloparents and resource competitors, as well as the extensive changes children undergo across development. To evaluate sibling nutritional effects with consideration of these opposing roles, we use an evolutionary framework rooted in human ontogeny and cooperative breeding. METHODS: Anthropometric data were collected from 113 Ngandu horticulturalist children (birth-<18 years old).We generated weight-for-age (WAZ), height-for-age (HAZ), and BMI-for-age (BMIZ) z-scores. Nutritional status across developmental risk periods (<2.5, 2.5-<5, 5-<10, and ≥10 years) was assessed using one-way ANOVAs. OLS regression was used to examine interactions between presence of siblings and risk periods. RESULTS: A considerable percentage of Ngandu children are suffering from stunting, underweight, or caloric deficiencies, but many fall within healthy ranges for WAZ (65%), HAZ (60%), and BMIZ (88%). Siblings have significant impacts on children's nutritional status, but their impacts vary by risk period. In general, older siblings (≥5 years old) have positive effects on their same-aged siblings, while younger siblings (<5) negatively affect those between 2.5 and <10 years old. CONCLUSIONS: Closely aged siblings do not always represent competitors. In this ecocultural context, those aged ≥5 years old appear to cooperate to improve their siblings' nutritional status. By evaluating the effects of siblings during specific risk periods, we offer a strategy to untangle the intersections of cooperation and competition. Our results add to the growing body of evidence showing benefits to allocare and further demonstrate that even children target their assistance toward vulnerable periods in development.

Cooperative breeding and Aka children's nutritional status: is flexibility key?

Research suggests that nonmaternal caregivers (allomothers) offer essential assistance through caregiving and provisioning, helping to support lengthy child development. Here, we examine the role of allomothers and the broader social and sharing network on Aka forager children's anthropometrics. We hypothesize that nonmaternal investors strategically target their assistance when it is most needed and when it will have the greatest effect. We evaluate children's nutritional status using WHO standards [weight-for-age (WAZ), height-for-age (HAZ), and weight-for-height (WHZ)] during four periods of child development [early infancy (birth to <9 months), mobility to weaning (9 to <36 months), early childhood (36 to <72 months), and middle childhood (72 to <120 months); N = 127]. We explore the effects of allomothers and the social network across these different risk periods and examine whether the broader social network buffers the loss of a primary allomother. ANOVA results suggest that girls may be experiencing some growth faltering, while boys start smaller and remain small across these stages. We used OLS multiple regression models to evaluate the effects of sex, camp composition, risk periods, and allomothers' presence on WAZ, HAZ, and WHZ. Grandmothers are the most influential allomother, with their effect most evident during the 9 to <36 month period. Camp size was also associated with greater WAZ, suggesting that children residing in small camps may be disadvantaged. Our findings also indicate that, under specific residence patterns, cooperative child rearing networks buffer the loss of a grandmother. Overall, our results suggest the importance of social networks to children's nutritional status and that individuals target investment to critical phases.

The Sidama Model of Human Development.

Human ontogeny has been shaped through evolution, resulting in markers of physical, cognitive, and social development that are widely shared and often used to demarcate the lifespan. Yet, development is demonstrably biocultural and strongly influenced by context. As a result, emic age categories can vary in duration and composition, constituted by both common physical markers as well as culturally meaningful indicators, with implications for our understanding of the evolution of human life history. Semi-structured group interviews (n = 24) among Sidama adults and children, as well as individual interviews with children (n = 30), were used to identify age categories across the lifespan and to specifically investigate acquisition of sociocultural skills and cognitive development. Ten major age categories were identified, covering birth through death. These largely map onto patterning of human universals, but specific cultural beliefs and behaviors were indicated as important markers of development. Adults and children are oriented toward the dynamic relationships between physical development and acquisition of skills tied to social and cultural success. Culture, ecology, and ontogeny are co-determinants of human development, and the interactions among them should be considered in studies examining human life history and its evolution.

Effects of Family Demographics and Household Economics on Sidama Children's Nutritional Status.

Weight- (WAZ), height- (HAZ), and BMI-for-age (BMIZ) are frequently used to assess malnutrition among children. These measures represent different categories of risk and are usually hypothesized to be affected by distinct factors, despite their inherent relatedness. Life history theory suggests weight should be sacrificed before height, indicating a demonstrable relationship among them. Here we evaluate impact of family composition and household economics on these measures of nutritional status and explore the role of WAZ as a factor in HAZ. Anthropometrics, family demographics, and measures of household economy were collected from Sidama agropastoralist children in a peri-urban village in southwestern Ethiopia (n = 157; 79 girls). Just over half of the sample (50.9%) had z-scores of - 2SD or below on at least one measure, indicating an elevated risk of morbidity/mortality; 30% were at or below - 2SD on two or more measures. We used hierarchical linear regression with random intercept analysis to model WAZ and HAZ. Siblings and crop sales significantly decrease WAZ while electricity, agriculture, and polygyny improve z-scores; however, an interaction between polygyny and siblings indicates negative effects of siblings in polygynous families and positive effects in nonpolygynous ones (adj. R2 = 66.5%). For HAZ, agriculture and electricity are positively associated with z-scores whereas siblings have a negative effect; the interaction term again indicates that effects of siblings vary in polygynous and nonpolygynous families (adj. R2 = 74.2%). A mediation model exploring the role of weight in height outcomes suggests not only that WAZ has direct effects on HAZ but also that effects of electricity and agriculture on HAZ are partially mediated by WAZ. Our findings indicate that WAZ and HAZ are primarily affected by shared variables, but effects of siblings vary by polygyny status. Long-term outcomes (HAZ) among Sidama children would likely benefit from interventions focused on stabilizing WAZ across family members.