Human biologists often use observational data to explore the intricate relationships between cultural, environmental, and biological factors. However, drawing meaningful causal conclusions from these data can be challenging. This talk presents a structured roadmap for causal inference that integrates human biology into the broader movement toward responsible and rigorous research practices. The roadmap provides a clear framework to navigate the complexities of observational data, improving both the accuracy and transparency of findings.

The roadmap consists of five key steps: (1) using ethnographic experience, extant literature, and expert knowledge to specify the research question, causal model, and parameter of scientific interest; (2) assessing causal inference assumptions to determine what statistical parameter can be estimated using observed data; (3) committing to a statistical model that aligns with the specified causal model and parameter of interest; (4) estimating the parameter using appropriate methods; and (5) interpreting the results, considering how well causal assumptions are met and grounding the findings in substantive theory.

Causal directed acyclic graphs (DAGs) play a critical role in this process by clarifying relationships between variables and ensuring thoughtful confounder selection. We will demonstrate this approach using the example of estimating the effect of housing damage from a childhood typhoon on inflammation in young adulthood in Cebu, Philippines. This case study highlights how the roadmap helps define causal relationships, make appropriate statistical choices, and interpret results in alignment with responsible research practices.

Despite a strong understanding of proximate causes of cardiometabolic disease (CMD), less is known about how cumulative lifetime stress enhances risk of CMD. To understand how stress throughout the life course may have downstream effects on morbidity, we examine the association between childhood (≤16 years) and adult (>16 years) stress and CMD outcomes in adults (M: n=2345, F: n=2714, avg. age=63.38±13.10years). Demographic, sociocultural, and biomarker data were obtained from the Health and Aging in Africa: Longitudinal Studies in South Africa dataset, a nationally representative multiyear survey. Multivariate logistic regression analyses, adjusted for age, sex, marital status, education, and wealth index, were performed to determine the cross-sectional associations between metabolic biomarkers and CMD outcomes with childhood and adult stress across three longitudinal cohorts. In Cohort 1, adult stress was significantly associated with the incidence of stroke (p=0.012). In Cohort 2, adult stress was significantly associated with fasting glucose levels (p=0.043), stroke (p=0.017), high blood pressure (p=0.010), and high cholesterol (p=0.006), all indicators of CMD risk; stroke (p=0.016), high blood pressure (p=0.046), and high cholesterol (p=0.001) were associated with childhood stress. In Cohort 3, triglyceride levels were significantly associated with childhood (p=0.002) and adult (p=0.021) stress and high blood pressure was associated with childhood stress (p=0.045). Our results indicate that childhood and adult stress are significantly associated with increased CMD risk in older adults, positing the need for in-depth investigations into the potential causal relationships between lifetime stress and later-life health. Views expressed are not official US Army, DoD, or government policy.

Sexual orientation and gender identity change efforts (SOGICE), commonly referred to as conversion therapy, continue to occur across the United States despite their well-documented harm. This study explores the association between SOGICE exposure and cardiovascular disease risk in sexual and gender minority (SGM) young adults assigned male at birth (AMAB). Data were collected from the RADAR observational cohort in Chicago, Illinois. The sample consisted of 372 SGM AMAB individuals aged 21 to 38 years (M = 28.44; SD = 3.06). Primary outcomes were diastolic and systolic blood pressure (DBP, SBP), systemic inflammation (SI), and self-reported hypertension or high blood pressure (HHBP). Regression analyses adjusted for sociodemographic and behavioral health covariates. Among participants, 7.52% reported SOGICE exposure. Exposed individuals exhibited significantly higher levels of SI (β = 1.52; SE = 0.50), DBP (β = 5.42; SE = 2.44), SBP (β = 5.63; SE = 2.74), and greater odds of HHBP (OR = 3.13; 95% CI, 2.04-4.22). These associations remained significant after controlling for covariates. Our findings suggest that exposure to SOGICE may be a potential risk factor for cardiovascular disease among SGM young adults. Moreover, we observe a dose-response with duration of SOGICE exposure and increased cardiovascular disease risk. To our knowledge, this is the first study to investigate the association between SOGICE exposure and cardiovascular health among SGM young adults assigned male at birth. Our results highlight the need for healthcare providers and policymakers to consider the harmful effects of SOGICE on physical health in their efforts to support SGM populations.

Allostatic load (AL) refers to the cumulative burden of chronic stress on physiological systems and has been linked to long-term health outcomes. Understanding the developmental stability of AL during adolescence and its association with adult cardiometabolic health may provide insights into how early-life stressors become physiologically embedded to influence later life outcomes. Using longitudinal data from the Great Smoky Mountains Study, we examined the developmental trajectories of AL in a sample of youth ages 9-16 (n=646) repeatedly measured for biomarkers representing immune, neuroendocrine, cardiovascular, and metabolic systems. Further, we explored the association between adolescent AL and adult cardiometabolic health at age 30. An AL score was calculated at each adolescent age using log-transformed and scaled values for cortisol, DHEA-s, cortisol:DHEA-s ratio, C-Reactive Protein, Epstein-Barr Virus and body mass index (BMI). Adult cardiometabolic health was measured using a composite score of blood pressure, BMI, and waist-to-hip ratio. We used linear mixed effects models to evaluate the AL trajectories across adolescence and linear regression models to test the relationship between adolescent AL and adult outcomes. Allostatic load remained stable throughout adolescence: individuals with high AL at study entry maintained elevated AL throughout adolescence and vice versa (β=0.466; SE=0.038; p<0.001). Additionally, childhood AL was associated with adult cardiometabolic health (β=0.479; SE=0.023; p<0.001), with higher AL predicting worse cardiometabolic outcomes at age 30. These results suggest that early-life stress and dysregulation may set individuals on distinct health trajectories through adolescence and into adulthood, highlighting the importance of early intervention to mitigate long-term health risks.

The Developmental Origins of Health and Disease (DOHaD) framework posits that early life environments exert a robust and lasting influence on human health. To date, most research focuses on populations where early life and adult environments are highly correlated, hampering our ability to parse early life effects from those of the current environment. Here, we examine early life effects on later life health among the Orang Asli, the Indigenous peoples of Malaysia, many of whom have recently undergone major lifestyle changes such that the Orang Asli live in an extreme range of environments, from remote villages with subsistence-based lifestyles to market-integrated urban communities. Notably, some individuals have adult environments matched to their youth while others dramatic mismatch, allowing us to test the hypothesis that early life environments would independently predict cardiometabolic health measures after adjusting for contemporary lifestyle factors. Using retrospective interview data, we developed two principal component (PC) scores to assess the urbanicity of early life environments and tested associations with body size and cardiometabolic health. Higher PC1 scores (i.e., higher urbanicity in household possessions, diet, and housing) are associated with taller height (total, hip, and knee) and higher body fat in adulthood. Higher PC2 scores (i.e., parents spent less time foraging and growing crops) were associated with taller hip and knee heights, higher cholesterol, higher diastolic blood pressure, and greater central adiposity in adulthood. Importantly, these results exist independent of current environments, indicating persistent early life effects on adult health, supporting the general premise of the DOHaD model.

Sleep disparities, often linked to stressful physical and social environments, are associated with a higher risk of hypertension in high-income countries. However, research on the relationship between sleep, stress, and hypertension remains limited in low- and middle-income countries, where nearly two-thirds of global hypertension cases occur. We investigated whether sleep quantity and quality are associated with increased stress and higher blood pressure among farmers in Madagascar. Sleep quantity was measured using actual sleep time and sleep quality was measured using the fragmentation score. We also measured daytime sleepiness using the Epworth Sleepiness Scale (ESS), as a functional consequence of insufficient sleep. Stress was measured via the Perceived Stress Scale (PSS). Based on 452 nights of actigraphy data from 33 adults, the mean actual sleep time was 7.2 hours, mean fragmentation score was 31, and the majority experienced excessive daytime sleepiness. As predicted, a higher stress score on the PSS was associated with shorter actual sleep time, after adjusting for age and gender. Contrary to expectations, actual sleep time and fragmentation score were not significantly associated with blood pressure. Notably, increased blood pressure was associated with increased sleepiness based on the ESS score, consistent with insufficient sleep leading to high blood pressure. Overall, our findings support several expected relationships between stress, sleep, and hypertension in rural Madagascar, suggesting that addressing stress and improving sleep quality could help reduce the high prevalence of hypertension in this population.

Metrics of market engagement, specifically household construction and durable goods ownership, often predict declining cardiometabolic health as populations undergo market integration (MI). However, the mechanisms behind these associations remain unclear. One possible explanation is that these measures reflect changing patterns of social connectedness, a known predictor of health. We tested two hypotheses: 1) social networks change during MI and 2) the Social Support and Reactivity Hypothesis (SSRH), which posits that social connections buffer cardiovascular reactivity during stress. We investigated associations among social networks, MI, and systolic blood pressure in 1,297 participants across three rural villages in northeast Madagascar. In tests of the first hypothesis, we found that individuals with similar housing and goods ownership were more likely to be connected. However, in a linear model, MI metrics were not significantly associated with degree centrality, or the number of social ties reported (p > 0.05). Supporting SSRH, higher degree centrality was associated with lower blood pressure in a linear network autocorrelation model adjusted for age, sex, and body mass index (p < 0.01). Unlike findings from other settings, housing construction was not significantly associated with blood pressure in this model (p > 0.05), and greater durable goods ownership was significantly negatively associated with blood pressure (p < 0.01). Further analyses revealed that social connectedness may better explain blood pressure variation than MI assessments alone. These findings support the hypothesis that social networks change during MI and provide evidence for SSRH, highlighting the health benefits of social connectedness in agricultural contexts.

Understanding coping mechanisms and physiological responses to severe drought is essential for designing effective interventions against extreme climatic events among marginalized populations. The Greater Horn of Africa faced its worst drought in 40 years from October 2020 to 2023. This study draws on qualitative, survey, and fingernail cortisol concentration [FCC] data from the Daasanach Human Biology Project (2019-2024) to evaluate the impact of severe drought on coping strategies and chronic stress. We estimated random-effects panel regression models using 965 observations from 513 adult Daasanach semi-nomadic pastoralists in northern Kenya. Consumption of any fish, a previously unwanted food, rose from 34% in 2019 to 63.6% in 2024. Among a subsample from 2022-2023 with FCC data, each additional day of fish consumption was correlated with higher FCC (β=0.047; 95% CI:0.0004–0.095; P=0.048). Furthermore, FCC increased during the peak of the drought in 2022 from a geometric mean of 9.3pg/mg to 15.5pg/mg at the end of the drought in 2023, an increase of 0.4 SD (β=0.40; 95% CI: 0.29–0.53; P<0.001). Drawing on six focus group discussions conducted in 2024, the stigma against fishing and its consumption in 2019 changed during the drought as communities began to view catching, eating, and selling fish more favorably and as a viable livelihood. These findings highlight a significant change in livelihoods and consumption patterns in response to drought. While fishing served as a coping mechanism, it was associated with increased chronic stress demonstrating the unintended biological consequences of this behavior.

Adoption and fosterage are sometimes considered paradoxical from an evolutionary perspective because parents invest substantial resources into other people’s children. However, the prevalence of these practices over space and time suggest that the costs of adoption and fosterage may be compensated by a variety of benefits to adoptive/ foster (AF) families. We investigate whether demographic predictors of adoption and fosterage are consistent with plausible benefits to AF parents drawn from evolutionary theory. These include indirect benefits accruing via care of kin, remedying demographic deficits in the receiving household (e.g., lacking a child of a desired gender), and securing educational capital that benefits the household economy. Results indicate that roughly 15% of households with children include one or more children without a biological parent in the household. This is despite limited evidence of a formal or legal adoption. Loss of a biological parent due to unstable reproductive unions, migration, or parental death predicts AF, as does acquisition of formal education. Counter to expectations of AF children residing in low-fertility households, AF children tend to reside in larger, more demographically complex households. Overall, results shed light on a variety of motivations for adoption and fosterage that point to short-term costs, but also long-term benefits, for families who care for others’ children.

Pregnancy demands the performance of a delicate balancing act by the maternal immune system, which must maintain tolerance of the developing semi-allogeneic fetus while simultaneously sustaining adequate immune defenses to protect mother and baby from the threat of external pathogens. While prior research has explored the link between social support and immune function in population-based cohorts, few studies have addressed this relationship specifically during pregnancy. Here we follow a longitudinal cohort of 107 women belonging to the Mothers’ Cultural Experiences (MCE) study, an ongoing investigation of the impact that environmental, sociocultural, and political stressors may have on infant development and maternal psychology and biological function during pregnancy and the postpartum period. Maternal plasma pro-inflammatory cytokines were quantified using enzyme-linked immunosorbent assay (ELISA), while participants were simultaneously assessed using validated measures of mental health, social support, and social relationship quality, at multiple timepoints. In brief, familial social support and relationship quality with partner, maternal grandmother, and paternal grandmother predicted lower scores on measures of participant depression, anxiety, stress, loneliness, and perceived discrimination, and were additionally associated with elevated levels of pro-inflammatory cytokine interleukin-8 (IL-8). Our data reveal expected positive associations between psychological health and social support and relationship quality, while variation in immunological markers may reflect patterns of healthy physiological adaptation during pregnancy. Ongoing analyses of this cohort continue to work toward elucidating the precise interactions occurring between social support, psychological health, and immune function in pregnancy.

Background: Fewer pregnancies and shorter breastfeeding duration typify women in post-industrial society today, in contrast to norms throughout our species’ collective past. We must understand the consequences of these life-history changes to evaluate the fitness landscape of post-menopausal longevity. Here, we hypothesize that history of pregnancy and breastfeeding will be positively associated with neurocognitive health in post-menopausal women.

Methods: Data derive from the Women’s Health Initiative Memory Study (WHIMS), a cohort of 7,479 post-menopausal women age ≥65. Women completed reproductive history interviews at mean age 65, and then underwent annual global cognitive assessment for up to 13 years and memory testing for up to 8 years. We employed linear mixed-effects models controlling for several covariates.

Results: For our primary hypotheses, each additional month pregnant was associated with higher scores of global cognitive function (p<0.01). Each additional month of breastfeeding corresponded to higher scores of global cognitive function (p=0.003), verbal memory (p=0.008), and visual memory (p=0.013). Similar results were observed for our secondary hypotheses: gravid women showed superior cognitive function compared to nulligravida. Ever-breastfeeding was associated with superior cognitive function. Higher breastfeeding-to-pregnancy ratio was positively associated with superior cognitive function.

Conclusion: We posit that there is an evolutionary mismatch for female reproductive life-history between pre-modern past and contemporary post-industrial populations, contributing to evolutionarily novel susceptibility to cognitive decline. Therefore, to elucidate the fitness consequences of post-menopausal longevity, it may be appropriate to consider a context of post-menopausal women who were more cognitively competent than what is typical in post-industrial populations.

Older adults in the US often relocate to accommodate dynamic life priorities and physical care needs. An increasingly popular residential care model combines housing with a “continuum” of care distributed across three levels (Independent Living, Assisted Living, and Skilled Nursing), through which residents may move as need arises. The aims of this study were to identify associations between environmental factors and the residential experiences amongst 121 older adults living in two continuum-care communities in southern California. Quantitative data were collected with surveys, including questionnaires assessing residential normalcy, attachment to place (APAS), and quality of life (WHOQOL-BREF), and qualitative data were collected with semi-structured interviews and field observations. Data were analyzed for associations between environmental factors and residential experiences. Residence in Skilled Nursing reduced the odds of feeling at home (OR=0.33, 95% CI=0.10 – 1.01), as did shorter length of residence (OR=1.03, 95% CI=1.01 – 1.06). In linear regressions, higher levels of care were associated with feeling less normal in one’s residence (p<0.001) and with lower quality of life (p<0.01). Attachment to one’s residence was associated with the length of time residing in that space (p<0.05). Qualitative data suggest reduced privacy and limited personal belongings at higher levels of care may have affected residential experiences. In conclusion, level of care and length of residence appear to be important factors in the residential experiences of feeling at home and quality of life amongst older adults in continuum-care communities.