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Abstract Background and objectivesThe optimal iron hypothesis (OIH) posits that risk for infection is lowest at a mild level of iron deficiency. The extent to which this protection results from arms race dynamics in the evolution of iron acquisition and sequestration mechanisms is unclear. We evaluated the OIH with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an emerging infectious agent. MethodologyWe tested 304 healthcare workers at baseline for iron deficiency (zinc protoporphyrin:heme), anemia (hemoglobin), and SARS-CoV-2 (salivary PCR), and followed them for ~3 months with biweekly SARS-CoV-2 tests. We fit logistic regression models based on Akaike Information Criterion. ResultsAdequate data were available for 199 participants. Iron replete (OR: 2.87, 95% CI: 0.85, 9.75) and anemia (OR: 2.48; 95% CI: 0.82, 7.85) were associated with higher risk for SARS-CoV-2 infection after control for covariates. Logistic regression and Cox proportional hazards models of the SARS-CoV-2 outcome were similar. Anemia (OR: 1.81; 95% CI: 0.88, 3.71) was associated with respiratory symptoms regardless of SARS-CoV-2 infection. Conclusions and implicationsThese findings provide partial support for the OIH: SARS-CoV-2 infection risk was elevated at the high end of the range of iron availability; however, the elevated risk among those with anemia was not, as expected, specific to severe iron deficiency. Narrowly, for COVID-19 epidemiology, these findings accord with evidence that SARS-CoV-2’s ability to establish infection is enhanced by access to iron. More broadly, these findings suggest that the OIH does not hinge on a long history of evolutionary arms race dynamics in access to host iron. 

Cooperative networks are essential features of human society. Evolutionary theory hypothesizes that networks are used differently by men and women, yet the bulk of evidence supporting this hypothesis is based on studies conducted in a limited range of contexts and on few domains of cooperation. In this paper, we compare individual-level cooperative networks from two communities in Southwest China that differ systematically in kinship norms and institutions—one matrilineal and one patrilineal—while sharing an ethnic identity. Specifically, we investigate whether network structures differ based on prevailing kinship norms and type of gendered cooperative activity, one woman-centred (preparation of community meals) and one man-centred (farm equipment lending). Our descriptive results show a mixture of ‘feminine’ and ‘masculine’ features in all four networks. The matrilineal meals network stands out in terms of high degree skew. Exponential random graph models reveal a stronger role for geographical proximity in patriliny and a limited role of affinal relatedness across all networks. Our results point to the need to consider domains of cooperative activity alongside gender and cultural context to fully understand variation in how women and men leverage social relationships toward different ends. This article is part of the theme issue ‘Cooperation among women: evolutionary and cross-cultural perspectives’. 

Abstract ObjectivesThe immune system of milk (ISOM) creates a mother–infant immune axis that plays an important role in protecting infants against infectious disease (ID). Tradeoffs in the immune system suggest the potential for both protection and harm, so we conceive of two dimensions via which the ISOM impacts infants: promotion of protective activity and control of activity directed at benign targets. High variability in ISOM activity across mother–infant dyads suggests investment the ISOM may have evolved to be sensitive to maternal and/or infant characteristics. We assessed predictors of appropriate and misdirected proinflammatory ISOM activity in an environment of high ID risk, testing predictions drawn from life history theory and other evolutionary perspectives. MethodsWe characterized milk in vitro interleukin‐6 (IL‐6) responses toSalmonella enterica(a target of protective immune activity;N = 96) andEscherichia coli(a benign target;N = 85) among mother–infant dyads in rural Kilimanjaro, Tanzania. We used ordered logistic regression and mixture models to evaluate maternal and infant characteristics as predictors of IL‐6 responses. ResultsIn all models, IL‐6 responses toS.entericaincreased with maternal age and decreased with gravidity. In mixture models, IL‐6 responses toE.colideclined with maternal age and increased with gravidity. No other considered variables were consistently associated with IL‐6 responses. ConclusionsThe ISOM's capacities for appropriate proinflammatory activity and control of misdirected proinflammatory activity increases with maternal age and decreases with gravidity. These findings are consistent with the hypothesis that the mother–infant immune axis has evolved to respond to maternal life history characteristics. 

Abstract Background Human populations native to high altitude exhibit numerous genetic adaptations to hypobaric hypoxia. Among Tibetan plateau peoples, these include increased vasodilation and uncoupling of erythropoiesis from hypoxia. Objective/Methods We tested the hypothesis that these high-altitude adaptations reduce risk for hypertension and diabetes-associated anemia among the Mosuo, a Tibetan-descended population in the mountains of Southwest China that is experiencing rapid economic change and increased chronic disease risk. Results Hypertension was substantially less common among Mosuo than low-altitude Han populations, and models fit to the Han predicted higher probability of hypertension than models fit to the Mosuo. Diabetes was positively associated with anemia among the Han, but not the Mosuo. Conclusion The Mosuo have lower risk for hypertension and diabetes-associated anemia than the Han, supporting the hypothesis that high-altitude adaptations affecting blood and circulation intersect with chronic disease processes to lower risk for these outcomes. As chronic diseases continue to grow as global health concerns, it is important to investigate how they may be affected by local genetic adaptations. 

Women experience higher morbidity than men, despite living longer. This is often attributed to biological differences between the sexes; however, the majority of societies in which these disparities are observed exhibit gender norms that favor men. We tested the hypothesis that female-biased gender norms ameliorate gender disparities in health by comparing gender differences in inflammation and hypertension among the matrilineal and patrilineal Mosuo of China. Widely reported gender disparities in health were reversed among matrilineal Mosuo compared with patrilineal Mosuo, due to substantial improvements in women’s health, with no concomitant detrimental effects on men. These findings offer evidence that gender norms limiting women’s autonomy and biasing inheritance toward men adversely affect the health of women, increasing women’s risk for chronic diseases with tremendous global health impact. 

The goal of assessing psychosocial stress as a process and outcome in naturalistic (i.e., field) settings is applicable across the social, biological, and health sciences. Meaningful measurement of biology-in-context is, however, far from simple or straightforward. In this brief methods review, we introduce theoretical framings, methodological conventions, and ethical concerns around field-collection of markers of psychosocial stress that have emerged from 50 years of research at the intersection of anthropology and human biology. Highlighting measures of psychosocial stress outcomes most often used in biocultural studies, we identify the circumstances under which varied measures are most appropriately applied and provide examples of the types of cutting-edge research questions these measures can address. We explain that field-based psychosocial stress measures embedded in different body systems are neither equivalent nor interchangeable, but this recognition strengthens the study of stress as always simultaneously cultural and biological, situated in local ecologies, social–political structures, and time. 

Abstract BackgroundMaternal anemia has adverse consequences for the mother‐infant dyad. To evaluate whether and how milk nutrient content may change in ways that could “buffer” infants against the conditions underlying maternal anemia, this study assessed associations between milk macronutrients and maternal iron‐deficiency anemia (IDA), non‐iron‐deficiency anemia (NIDA), and inflammation. MethodsA secondary analysis of cross‐sectional data and milk from northern Kenya was conducted (n = 204). The combination of hemoglobin and transferrin receptor defined IDA/NIDA. Elevated serum C‐reactive protein defined acute inflammation. The effects of IDA, NIDA, and inflammation on milk macronutrients were evaluated in regression models. ResultsIDA (β = 0.077,p =.022) and NIDA (β = 0.083,p =.100) predicted higher total protein (ln). IDA (β = −0.293,p =.002), NIDA (β = −0.313,p =.047), and inflammation (β = −0.269,p =.007) each predicted lower fat (ln); however, anemia accompanying inflammation predictedhigherfat (β = 0.655,p =.007 for IDA and β = 0.468,p =.092 for NIDA). NIDA predicted higher lactose (β = 1.020,p =.003). ConclusionsMilk macronutrient content both increases and decreases in the presence of maternal anemia and inflammation, suggesting a more complicated and dynamic change than simple impairment of nutrient delivery during maternal stress. Maternal fat delivery to milk may be impaired under anemia. Mothers may buffer infant nutrition against adverse conditions or poor maternal health by elevating milk protein (mothers with IDA/NIDA), lactose (mothers with NIDA), or fat (mothers with anemiaandinflammation). This study demonstrates the foundational importance of maternal micronutrient health and inflammation or infection for advancing the ecological understanding of human milk nutrient variation.