Courtney L. Meehan

The Effects of Residential Locality on Parental and Alloparental Investment among the Aka Foragers of the Central African Republic

In this paper I examine the intracultural variability of parental and alloparental caregiving among the Aka foragers of the Central African Republic. It has been suggested that maternal kin offer higher frequencies of allocare than paternal kin and that maternal investment in infants will decrease when alloparental assistance is provided. Behavioral observations were conducted on 15 eight- to twelve-monthold infants. The practice of brideservice and the flexibility of Aka residence patterns offered a means to test the effect of maternal residence on parental and alloparental investment. There was significant variation in the frequency of investment and who supplied care to infants depending on whether mothers resided with their kin or their husbands’ kin. However, in spite of the variation in allocare, when all categories of caregivers were examined collectively, infants received similar overall levels of care.

What’s normal? Oligosaccharide concentrations and profiles in milk produced by healthy women vary geographically

Background: Human milk is a complex fluid comprised of myriad substances, with one of the most abundant substances being a group of complex carbohydrates referred to as human milk oligosaccharides (HMOs). There has been some evidence that HMO profiles differ in populations, but few studies have rigorously explored this variability. Objectives: We tested the hypothesis that HMO profiles differ in diverse populations of healthy women. Next, we examined relations between HMO and maternal anthropometric and reproductive indexes and indirectly examined whether differences were likely related to genetic or environmental variations. Design: In this cross-sectional, observational study, milk was collected from a total of 410 healthy, breastfeeding women in 11 international cohorts and analyzed for HMOs by using high-performance liquid chromatography. Results: There was an effect of the cohort (P < 0.05) on concentrations of almost all HMOs. For instance, the mean 3-fucosyllactose concentration was >4 times higher in milk collected in Sweden than in milk collected in rural Gambia (mean ± SEM: 473 ± 55 compared with 103 ± 16 nmol/mL, respectively; P < 0.05), and disialyllacto-N-tetraose (DSLNT) concentrations ranged from 216 ± 14 nmol/mL (in Sweden) to 870 ± 68 nmol/mL (in rural Gambia) (P < 0.05). Maternal age, time postpartum, weight, and body mass index were all correlated with several HMOs, and multiple differences in HMOs [e.g., lacto-N-neotetrose and DSLNT] were shown between ethnically similar (and likely genetically similar) populations who were living in different locations, which suggests that the environment may play a role in regulating the synthesis of HMOs. Conclusions: The results of this study support our hypothesis that normal HMO concentrations and profiles vary geographically, even in healthy women. Targeted genomic analyses are required to determine whether these differences are due at least in part to genetic variation. A careful examination of sociocultural, behavioral, and environmental factors is needed to determine their roles in this regard. This study was registered at clinicaltrials.gov as NCT02670278.

Early supplementary feeding among central African foragers and farmers: A biocultural approach

The World Health Organization (WHO) recommends exclusive breastfeeding (EBF) for six months, yet this recommendation has proven difficult to implement. Here, we examine the nature of and influences on early supplementation (ES) in light of current evidence regarding evolved human caregiving patterns (cooperative breeding). We utilize a biocultural approach, which takes into consideration that infant feeding is influenced by an array of evolutionary, physiological, structural, ecological, and cultural factors. The research is cross-cultural, conducted among the Aka foragers and Ngandu farmers in the Central African Republic. We explore emic perspectives of ES as well as infant characteristics and socioecological factors that, when combined with evidence of human care patterns, offers a more holistic understanding of early infant feeding. We employ a mixed-methods approach, utilizing qualitative interview and quantitative focal-follow behavioral observation data, collected from 2009 to 2012. Results indicate that foragers introduce ES earlier than farmers; nevertheless, only a small proportion of Ngandu mothers EBF. Maternal and non-maternal caregiver ES patterns are predicted by different factors. Maternal ES is associated with infant age, while non-maternal ES is associated with maternal labor activities and the infants caregiving network. Non-maternal ES, but not maternal ES, reduces breastfeeding. Results suggest that neither subsistence ecology nor maternal labor patterns fully explain the timing of ES. However, cooperative caregiving, infant mortality risk, and cultural models of caregiving offer insights into why foragers commence ES so early. We discuss the implications of ES on weaning age, inter-birth intervals, and fertility. Throughout our evolutionary history and today, non-maternal caregivers were and are essential participants in childcare and provisioning, yet are rarely viewed as active participants in early infant feeding. Consideration of evolved caregiving patterns and the role of others in feeding practice will enhance public health outreach.

Allomaternal Investment and Relational Uncertainty among Ngandu Farmers of the Central African Republic

Several studies have suggested a matrilateral bias in allomaternal (non-maternal) infant and child caregiving. The bias has been associated with the allomother’s certainty of genetic relatedness, where allomothers with high certainty of genetic relatedness will invest more in children because of potential fitness benefits. Using quantitative behavioral observations collected on Ngandu 8- to 12-month-old infants from the Central African Republic, I examine who is caring for infants and test whether certainty of genetic relatedness may influence investment by allomothers. Results indicate a matrilateral bias in caregiving by extended kin members, but this does not affect the total level of care infants receive when fathers and siblings are included in the analysis. These results replicate a previous study done among an adjacent foraging population and emphasize the importance of examining children’s complete social environments when addressing caregiving and child development.

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

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.

What’s Normal? Immune Profiling of Human Milk from Healthy Women Living in Different Geographical and Socioeconomic Settings

Human milk provides a very wide range of nutrients and bioactive components, including immune factors, human milk oligosaccharides, and a commensal microbiota. These factors are essential for interconnected processes including immunity programming and the development of a normal infant gastrointestinal microbiome. Newborn immune protection mostly relies on maternal immune factors provided through milk. However, studies dealing with an in-depth profiling of the different immune compounds present in human milk and with the assessment of their natural variation in healthy women from different populations are scarce. In this context, the objective of this work was the detection and quantification of a wide array of immune compounds, including innate immunity factors (IL1β, IL6, IL12, INFγ, TNFα), acquired immunity factors (IL2, IL4, IL10, IL13, IL17), chemokines (IL8, Groα, MCP1, MIP1β), growth factors [IL5, IL7, epidermal growth factor (EGF), granulocyte colony-stimulating factor, granulocyte–macrophage colony-stimulating factor, TGFβ2], and immunoglobulins (IgA, IgG, IgM), in milk produced by healthy women of different ethnicities living in different geographic, dietary, socioeconomic, and environmental settings. Among the analyzed factors, IgA, IgG, IgM, EGF, TGFβ2, IL7, IL8, Groα, and MIP1β were detected in all or most of the samples collected in each population and, therefore, this specific set of compounds might be considered as the “core” soluble immune factors in milk produced by healthy women worldwide. This approach may help define which immune factors are (or are not) common in milk produced by women living in various conditions, and to identify host, lifestyle, and environmental factors that affect the immunological composition of this complex biological fluid. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02670278.

An Evolutionary, Biosocial Perspective on Variation in Human Milk Microbes and Oligosaccharides: An Example of Eco-Homeorhesis?

Researchers have long known that milk composition varies among and within mammalian taxa. The origins of this variation among phylogenies are thought to be due to evolutionary shifts driven by Darwinian selection to maximize fitness across often substantially different physical, biological, and social environments. Conversely, milk composition variation within a taxon (e.g., Homo sapiens ) is generally ascribed to more proximate factors such as dietary intake, time postpartum, acute and chronic maternal health, and (all-too-often, unfortunately) differences in sample collection, storage, and analysis. Here, we argue that at least a portion of this intraspecies variation in human milk composition—particularly as it relates to microbial and carbohydrate contents—may also be due to genomic variation driven over the millennia by historical environmental and biosocial selective pressures, particularly those related to pathogen exposure. We also outline a possible experimental approach, using combined population genetics and anthropological methodologies, to test the possibility that variation of “normal” milk composition is related to fitness within a specific context (an example of eco-homeorhesis).

Persistence of Infant Care Patterns Among Aka Foragers

Early research found commonalities across hunter-gatherer communities in regards to infant care. Infants were held frequently, spent most of the day and night in skin-to-skin contact, breastfed on demand, received intimate caregiving, and experienced low levels of distress. These shared infant care practices are assumed to have deep evolutionary roots and together serve as a defining characteristic of hunter-gatherer life. Yet, the degree to which hunter-gatherers are experiencing social, economic, and environmental change may have created conditions that alter these defining characteristics. In this chapter we explore infant care among the Aka foragers in the Central African Republic. We utilize naturalistic behavioral observations collected over almost 20 years to examine whether care patterns have persisted or changed over the course of a generational timespan. The Aka discussed in this chapter remain a mobile foraging population, but they have also experienced change at multiple levels. Whether or how these changes influence infant care has not yet been examined. Results indicate that Aka infant care patterns have persisted. Although some significant changes were noted, not all caregiving showed a decline, some increased and some changes were only limited to one age category. Additionally, the vast majority of caregiving practices remained constant across the periods. Cross-cultural data presented also support this finding. Aka infant care patterns are comparable to other hunter-gatherer populations and the frequency of care and interactions match or exceed most farming and Euro-American patterns. We argue that Aka infant care patterns have persisted because they are vertically transmitted and highly-conserved. Moreover, Aka infant care is indicative of a much larger cultural pattern of trust, intimacy and sharing, not immediately affected by outside influences.

Social networks, cooperative breeding, and the human milk microbiome

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.

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

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.