Human biology and the study of precarity: How the intersection of uncertainty and inequality is taking us to new extremes.

Inequality represents an extreme environment to which humans must respond. One phenomenon that contributes to this growing extreme is precarity or the intersection of uncertainty and some form of inequality. While precarity has an important intellectual history in the fields of sociology and sociocultural anthropology, it has not been well studied in the field of human biology. Rather human biologists have engaged with the study of closely related concepts such as uncertainty and resource insecurity. In this article, we propose that human biology take on the study of precarity as a novel way of investigating inequality. We first provide a brief intellectual history of precarity which is followed by a review of research on uncertainty and resource security in human biology which, while not exhaustive, illustrates some key gaps that precarity may aid us in addressing. We then review some of the pathways through which precarity comes to affect human biology and health and some of the evidence for why the unpredictable nature of precarity may make it a unique physiological stress. A case study based on research in Nuñoa, Peru provides an important example of how precarity can elucidate the influences of health in an extreme setting, albeit with insights that apply more broadly. We conclude that precarity holds important potential for the study of human biology, including helping us more effectively operationalize and study uncertainty, encouraging us to explore the predictability of resources and stressors, and reminding us to think about the intersectional nature of stressors.

Beyond Dimorphism: Body Size Variation Among Adult Orangutans Is Not Dichotomous by Sex.

Among extant great apes, orangutans are considered the most sexually dimorphic in body size. However, the expression of sexual dimorphism in orangutans is more complex than simply males being larger than females. At sexual maturity, some male orangutans develop cheek pads (flanges), while other males remain unflanged even after becoming reproductively capable. Sometimes flange development is delayed in otherwise sexually mature males for a few years. In other cases, flange development is delayed for many years or decades, with some males even spending their entire lifespan as unflanged adults. Thus, unflanged males of various chronological ages can be mistakenly identified as "subadults." Unflanged adult males are typically described as "female-sized," but this may simply reflect the fact that unflanged male body size has only ever been measured in peri-pubescent individuals. In this study, we measured the skeletons of 111 wild adult orangutans (Pongo spp.), including 20 unflanged males, 45 flanged males, and 46 females, resulting in the largest skeletal sample of unflanged males yet studied. We assessed long bone lengths (as a proxy for stature) for all 111 individuals and recorded weights-at-death, femoral head diameters, bi-iliac breadths, and long bone cross-sectional areas (CSA) (as proxies for mass) for 27 of these individuals, including seven flanged males, three adult confirmed-unflanged males, and three young adult likely-unflanged males. ANOVA and Kruskal-Wallis tests with Tukey and Dunn post-hoc pairwise comparisons, respectively, showed that body sizes for young adult unflanged males are similar to those of the adult females in the sample (all P ≥ 0.09 except bi-iliac breadth), whereas body sizes for adult unflanged males ranged between those of adult flanged males and adult females for several measurements (all P < 0.001). Thus, sexually mature male orangutans exhibit body sizes that range from the female end of the spectrum to the flanged male end of the spectrum. These results exemplify that the term "sexual dimorphism" fails to capture the full range of variation in adult orangutan body size. By including adult unflanged males in analyses of body size and other aspects of morphology, not as aberrations but as an expected part of orangutan variation, we may begin to shift the way that we think about features typically considered dichotomous according to biological sex.

Malnutrition, illness, poverty, and infant growth: A test of a syndemic hypothesis in Nuñoa, Peru.

The concept of syndemics provides an important framework for understanding the complex interactions of biological and social conditions. Its use in public health and epidemiological research has increased substantially in the past ten years. Many syndemic analyses rely on the use of a sum score and subsequently fail to demonstrate biological interaction, leading some scholars to question the utility of the syndemic approach. Here, we utilize data from 86 mother/infant pairs from the rural district of Nuñoa, Peru to test a potential syndemic relationship among infection, malnutrition and infant growth. Between 2014 and 2015, surveys were conducted to assess household wealth, sanitation, dietary diversity, and reported illness, while anthropometric measures of mothers and infants were conducted to assess nutritional status via height-for-age and weight-for-height z-scores. Ethnographic insight was used in the selection of key economic variables including the development of an agricultural wealth index. We then assessed whether this constellation of health outcomes met the criteria for a syndemic by performing a quantitative analysis in which we tested for (1) an association between economic marginalization and high-risk environments; (2) the concentration of malnutrition, poor growth, and infection; and (3) biological interaction among these health outcomes. We found that economic measures were associated with pathogenic and nutritional risk, and that these in turn were associated with infectious disease, nutritional status, and growth. However, we did not find evidence that the proposed syndemic met criteria (2) or (3). We conclude that, despite being both socially and biologically plausible, a syndemic of malnutrition, poor growth, and infection did not exist in this context. This analysis moves syndemic research forward by demonstrating that such hypotheses are falsifiable, thus presenting a process by which they may be tested and lending support to the use of syndemic theory as an effective analytic framework.

The health impacts of eviction: Evidence from the national longitudinal study of adolescent to adult health.

Eviction represents an urgent social and economic issue in the United States, with nearly two million evictions occurring annually in the U.S. Still, the population health impacts of evictions, as well as the pathways linking eviction to health, are not well documented or understood, particularly among young adults. Using nationally-representative, longitudinal data from the National Longitudinal Study of Adolescent to Adult Health (1994-2008) (n = 9029), the present study uses a combination of analytic methods-including prospective lagged dependent variable regression models, inverse probabilities of treatment weighting, longitudinal first difference models, causal mediation techniques-to comprehensively assess whether and how evictions relate to depressive risk and self-rated health across early adulthood, paying particular attention to the stress-related pathways linking eviction and health. Results provide robust evidence of positive longitudinal associations between eviction and depressive risk, in particular. In the prospective regression models, young adults who experienced recent eviction had more depressive symptoms and worse self-rated health than those who were not evicted, net a host of background characteristics. Using treatment weighting techniques, results showed that young adults who experienced eviction had more depressive symptoms than those who were not evicted (5.921 vs. 4.998 depressive symptoms, p = 0.003). Perceived social stress mediated nearly 18 percent of the associations between eviction and the depressive symptoms (p < 0.001). In the first difference models, young people who experienced eviction between survey waves experienced greater increases in depressive symptoms over time compared to those who were not evicted, net of changes in other indicators of socioeconomic status and residential instability. Taken together, our results suggest that the recent surges in evictions in the U.S. serve as a potent threat to population health during the emerging adult period, with especially devastating consequences for low-income individuals and communities of color.

Doing biocultural anthropology: Continuity and change.

Biocultural anthropology has long represented an important approach in the study of human biology. However, despite demonstrated utility, its somewhat amorphous identity leaves some scholars questioning just what it means to be biocultural. In this article, rather than providing proscriptive doctrine, we contribute to these conversations about the nature of biocultural anthropology by considering what biocultural research does. We begin with a consideration of some of the foundational themes of biocultural work including recognition of the dialectical nature of sociocultural and biological forces, interest in inequality, and incorporation of both evolutionary and political economic perspectives. To emphasize the consistency of biocultural work over time, we also trace these themes from originating work to their appearance in current research. We then identify some of the key actions of the biocultural approach, noting that biocultural work can execute any number though rarely all of these actions simultaneously. We then offer brief introductions to the articles that make up this special issue, highlighting the ways in which each piece undertakes key biocultural actions. Following these introductions, we provide a discussion of some of the types of biocultural work that are not present in this special issue, recognizing the breadth of biocultural research across multiple subfields of anthropology. Finally, we point to some potentially fruitful directions for future biocultural research. In the end, we conclude that while biocultural anthropology may not have a cohesive or set agenda, it does have a clear and recognizable form of content and methodology illuminated by its actions.

A biocultural examination of home food production and child growth in highland Peru.

OBJECTIVES: Chronic malnutrition remains a persistent global health issue. This mixed methods investigation in rural Peru examines the role of home food production (HFP) in reducing child malnutrition by testing the following hypotheses: (a) higher HFP will be associated with higher infant z-scores than those with less HFP and (b) infants with higher HFP will exhibit improved longitudinal growth outcomes across 6 months. METHODS: Ethnographic methods include semi-structured interviews and participant observation. A household survey and anthropometric data were collected twice, from 86 infants under of 24 months old. A HFP index (HFI) was generated based on reports of animals for meat consumption, eggs, milk, and agricultural products for home consumption. Kruskal-Wallis tests were used to examine patterns of HFI and infant anthropometrics. Multivariate regressions were used to examine the relationships between HFP and infant height for age (HAZ), weight for age (WAZ), and triceps skinfold for age (TSAZ) in both rounds and 6-month change between rounds (6MΔ). RESULTS: There were no relationships between HFI and infant z-scores in round one, however, HFI was significantly positively related to HAZ (B = 0.091, P < .039) in round two and with 6MΔ in HAZ (B = 0.09, P < .047). HFI did not predict WAZ or TSAZ in either round. CONCLUSIONS: HFP represents an important influence of infant growth in Nuñoa, likely through nutritional improvement due to increased availability of animal-sourced foods and through contribution to household economy and maternal empowerment.

An examination of breastmilk composition among high altitude Peruvian women.

OBJECTIVE: Relatively little is known about sources of variation in human breastmilk composition. Previous research posits that composition may be affected by the low oxygen environment found at high altitude (HA). Our objective is to compare the milk composition of a sample of HA Andeans to previously published data on HA Tibetans and low altitude (LA) Peruvians. METHODS: Mid-feed milk samples were collected from 22 women and tested for lipid, carbohydrate and protein content in addition to dietary surveys and anthropometric measures. We examined relationships between maternal and infant characteristics (maternal BMI, adiposity, age, skinfold thickness, infant age) and milk composition using multiple regression analyses. A Welch-Satterthause t-test was used to compare summary measures from Andean sample and Tibetan samples. RESULTS: Milk fat, sugar, and true protein content were correlated with different maternal and infant characteristics, with only waist to hip ratio negatively affecting fat and positively affecting sugar content in full models. Nuñoan and LA Peruvian milk exhibited significantly lower lactose levels (6.01 ± .89 g/100 mL and 6.38 ± 0.03 g/100 mL) than Tibetans (7.25 ± 0.35 g/100 mL). Fat content among Nuñoans was similar to that of Tibetans (4.5 ± 0.78 g/100 mL and 4.6 ± 1.51 g/100 mL, respectively), and higher than those of LA Peruvians. CONCLUSIONS: Both HA populations demonstrate relatively high fat content and both Peruvian samples exhibited relatively higher protein and lower lactose than Tibetan samples, suggesting that both population-based differences in feeding behavior and climatic differences may influence composition.

Genome-wide analysis of DNA methylation in relation to socioeconomic status during development and early adulthood.

OBJECTIVES: Socioeconomic status (SES) is a powerful determinant of health, but the underlying biological mechanisms are poorly understood. This study investigates whether levels of DNA methylation at CpG sites across the genome are associated with SES in a cohort of young adults in the Philippines. METHODS: DNA methylation was assayed with the Illumina HumanMethylation450 Bead Chip, in leukocytes from 489 participants in the Cebu Longitudinal Health and Nutrition Survey (mean age = 20.9 years). SES was measured in infancy/childhood and adulthood, and was based on composite measures of income, assets, and education. Genome-wide analysis of variable probes identified CpG sites significantly associated with SES after adjustment for multiple comparisons. Functional enrichment analysis was used to identify biological pathways associated with these sites. RESULTS: A total of 2,546 CpG sites, across 1,537 annotated genes, were differentially methylated in association with SES. In comparison with high SES, low SES was associated with increased methylation at 1,777 sites, and decreased methylation at 769 sites. Functional enrichment analysis identified over-representation of biological pathways related to immune function, skeletal development, and development of the nervous system. CONCLUSIONS: Socioeconomic status predicts DNA methylation at a large number of CpG sites across the genome. The scope of these associations is commensurate with the wide range of biological systems and health outcomes that are shaped by SES, and these findings suggest that DNA methylation may play an important role.

Secular trends in growth in the high-altitude district of Nuñoa, Peru 1964-2015.

OBJECTIVES: Nuñoa, Peru has been the site of anthropological research on human adaptability, growth, and health since the 1960s. Previous studies documented a nascent secular trend in growth between 1964 and 1984. However, no secular trend was evident when the population was re-examined in 1999, following an intervening period of sociopolitical upheaval. Subsequently, the region experienced considerable economic development reflected in secular increases in height. We seek to evaluate trends in growth and BMI among Nuñoan children over 50 years. MATERIALS AND METHODS: Anthropometric data for 929 children collected in 2015 are compared with anthropometric data for 394 children from 1964, 912 children from 1984, and 292 children from 1999. The data were converted to z-scores using the WHO 2007 growth standards. anova is used to evaluate rates of stunting, underweight, overweight, and obesity across the study periods. RESULTS: We observe small increases in stature and weight between the 1960s and 1980s, almost no change between the 1980s and 1990s and statistically significant reductions in stunting and increases in height between the 1990s and 2015. DISCUSSION: There were relatively small differences in stature and weight and a high incidence of stunting between 1964 and 1999 attributed to extremely poor economic and health conditions. A large secular increase in height (7-8 cm on average) and consequent reduction in rates of stunting between 1999 and 2015 occurred due to improved social and economic conditions. In addition to political stabilization, enhanced infrastructure, social aid programs, improved healthcare, and economic expansion contribute to these trends.

Validation of endotoxin-core antibodies in dried blood spots as a measure of environmental enteropathy and intestinal permeability.

OBJECTIVE: To validate a method for measuring endotoxin-core antibodies (EndoCAb) from dried blood spots (DBS)-drops of capillary whole blood collected and dried on filter paper-as an indicator of environmental enteropathy (EE) in infancy and early childhood. METHODS: A commercially available enzyme immunoassay kit was adapted for use with DBS, with optimized steps for sample elution. Technical validation included analysis of linearity/recovery, precision and reliability, lower limit of detection, and correspondence between matched plasma and DBS samples. Validation in a field-based setting was implemented with samples from Peruvian infants (n = 82; age = 2-33 months) collected at two time points six months apart. RESULTS: A high correspondence between plasma and DBS levels of EndoCAb was observed (R2 = 0.93, P < .001). The lower limit of detection was found to be 0.01 GMU/mL. Interassay coefficient of variation (CV) was 10.9% and 8.06% for low and high controls, respectively. Mean intra-assay CVs were 3.22% and 1.83%, respectively. In a sample of Peruvian infants, EndoCAb levels increased with age as expected (P < .001). Age explained nearly 34.6% of the variance in EndoCAb across the sample. CONCLUSION: These findings demonstrate the validity and feasibility of measuring EndoCAb in remote field settings using minimally invasive DBS sampling.

Economic activity and patterns of infant growth in a high altitude district of Peru.

OBJECTIVES: Changing economic activities bring significant cultural, epidemiological, and nutritional transitions. Infancy represents a critical period when rapid growth and metabolic programming occur, making infants particularly vulnerable to long-lasting biological changes due to such transitions. This paper examines the relationship between residence in distinct economic production zones (urban, herding, and dairy) and early growth in a highland district of Peru. METHODS: The length, weight, body mass index, and triceps skinfold of 93 infants (55 boys and 38 girls, aged 2 to 24 months) from 3 economic zones were measured at two time points 6 months apart. Z-scores were calculated based on the WHO Growth Reference for children under 5 years of age. Comparisons were made to the reference group and between economic zones to examine the impacts of different economic activities on infant growth. RESULTS: Female infants had significantly higher height-for-age z-scores (HAZ) than males (P < 0.05). Across zones, dairying infants had the highest HAZ scores and the lowest prevalence of stunting. There was a significant association between zone and HAZ at baseline. While these associations were attenuated in measurements, taken 6 months later, longitudinal growth monitoring revealed differential patterns of weight gain and adiposity deposition across the zones with herding infants showing consistent high adiposity and urban infants gaining both weight and adiposity between rounds. DISCUSSION: Changes in economic activity are bringing about nutritional and epidemiological transitions in the Nuñoa district. Economic activity is a key factor influencing early growth with distinct longitudinal growth patterns in each economic zone.