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.

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.

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.

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.

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.