Variation in diurnal cortisol patterns among the Indigenous Shuar of Amazonian Ecuador.

Objectives: The hypothalamic-pituitary-adrenal (HPA) axis and its primary end product, the glucocorticoid cortisol, are major components of the evolved human stress response. However, most studies have examined these systems among populations in high-income settings, which differ from the high pathogen and limited resource contexts in which the HPA axis functioned for most of human evolution.

Methods: We investigated variability in diurnal salivary cortisol patterns among 298 Indigenous Shuar from Amazonian Ecuador (147 males, 151 females; age 2-86 years), focusing on the effects of age, biological sex, and body mass index (BMI) in shaping differences in diurnal cortisol production.

Hierarchies in the energy budget: Thyroid hormones and the evolution of human life history patterns.

The evolution of human life history characteristics required dramatic shifts in energy allocation mechanisms compared with our primate ancestors. Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), are sensitive to energy balance, and are significant determinants for both tissue-specific and whole-body metabolic rate. Thus, thyroid hormones are in part responsible for setting the body's overall energy budget and likely played an important role in the evolution of human life history patterns.

The impact of thawing duration on leptin and adiponectin levels in frozen human milk samples.

Background: Measurements of hormone concentrations in human milk from understudied populations across the world is of growing scientific interest. Due to limited access to suitable laboratory facilities at many research sites, human milk samples are often shipped frozen to distant laboratories for analysis. Shipping and handling exposes samples to the risk of thawing and degradation as the results of delays, mishandling, or other unforeseen circumstances.

C-reactive protein in adult Samoans: Population variation and physiological correlates.

Objectives: C-reactive protein (CRP) has been associated with adiposity and cardiometabolic disease risk in many populations but remains remarkably understudied in Pacific Islander populations. Here, we provide the first examination of correlates of CRP in adult Samoans (n = 108, ages 35-55 years) to test the hypotheses that CRP exhibits sex-dependent associations with measures of BMI, adiposity, and cardiometabolic disease risks.

Methods: We analyzed associations between measures of adiposity (total fat mass, visceral fat mass, percent total body fat), body mass index (BMI), cardiometabolic risks, behaviors, demographics, and CRP.

Replicability of leptin associations with testosterone, estradiol, follicle-stimulating hormone, and luteinizing hormone in healthy Ache men of Paraguay: A multiple daily assessment.

Objective: Associations between leptin and male reproductive hormone levels have been reported in men. However, few of these investigations have focused on associations in healthy men without obesity or overweight or nonindustrial societies.

Methods: We test hypotheses that leptin is associated with testosterone, estradiol, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) within healthy Ache men, an indigenous nonindustrialized South American community using archived data.

Low prevalence of anemia among Shuar communities of Amazonian Ecuador.

Objective: Anemia is an important global health challenge. We investigate anemia prevalence among Indigenous Shuar of Ecuador to expand our understanding of population-level variation, and to test hypotheses about how anemia variation is related to age, sex, and market integration.

Methods: Hemoglobin levels were measured in a total sample of 1650 Shuar participants (ages 6 months to 86 years) from 46 communities between 2008 and 2017 to compare anemia prevalence across regions characterized by different levels of market integration.

Oxidative stress as a hidden cost of attractiveness in postmenopausal women.

Perceived facial attractiveness, a putative marker of high biological fitness, is costly to maintain throughout a lifetime and may cause higher oxidative stress (OS). We investigated the association between the facial features of 97 postmenopausal women and their levels of OS biomarkers 8-hydroxy-2'-deoxyguanosine (8-OHdG), superoxide dismutase (Cu-Zn SOD), and thiobarbituric acid reactive substances (TBARS). In study 1, 966 judges rated the composites (facial averages) of women with higher OS as more attractive, healthier, younger, and less symmetric.

Accelerated senescence as a cost of reproduction: Testing associations between oxidative stress and reproductive effort in rural and urban women.

Objectives: Oxidative stress is hypothesized to contribute to age-related somatic deterioration. Both reproductive and ecological context may necessitate tradeoffs that influence this outcome. We examined whether measures of lifetime reproductive effort were related to levels of oxidative stress biomarkers in peri- and post-menopausal women and whether associations were moderated by rural or urban residence.

The developmental origins of risk and time preferences across diverse societies.

Risk and time preferences have often been viewed as reflecting inherent traits such as impatience and self-control. Here, we offer an alternative perspective, arguing that they are flexible and environmentally informed. In Study 1, we investigated risk and time preferences among children in the United States, India, and Argentina, as well as forager-horticulturalist Shuar children in Amazonian Ecuador.

Soil-transmitted helminth infection and intestinal inflammation among the Shuar of Amazonian Ecuador.

Objectives: Little research exists documenting levels of intestinal inflammation among indigenous populations where exposure to macroparasites, like soil-transmitted helminths (STHs), is common. Reduced STH exposure is hypothesized to contribute to increased prevalence of elevated intestinal inflammation in wealthy nations, likely due to coevolutionary histories between STHs and human immune systems that favored anti-inflammatory pathways. Here, we document levels of intestinal inflammation and test associations with STH infection among the Shuar of Ecuador, an indigenous population undergoing socioeconomic/lifestyle changes that influence their hygienic environment.

High energy requirements and water throughput of adult Shuar forager-horticulturalists of Amazonian Ecuador.

Objectives: We measured total energy expenditure (TEE; kcal/d) and water throughput (L/d) among Shuar forager-horticulturalists from Amazonian Ecuador to compare their daily energy and water demands to adults in other small-scale and industrialized populations.

Methods: TEE and water throughput were measured using the doubly labeled water method among 15 Shuar adults (eight women, seven men; age range 18-60 years) living in a relatively remote village. We used multiple regression to assess the effects of anthropometric variables (body size, fat free mass, age, and sex) on TEE and water throughput.

A comparison of testosterone and cortisol levels between gay fathers and non-fathers: A preliminary investigation.

Humans are unique among great apes and most other mammals, in that our wide range of offspring investment behaviors includes significant paternal care and provisioning of children. Moreover, hormones play an important role in modulating male paternal investment. Despite a growing body of research on the hormonal associations with paternal care in humans, fathers who self-identify as gay have not received the same level of research attention.

The cost of reproduction in women: Reproductive effort and oxidative stress in premenopausal and postmenopausal American women.

Objectives: Life history theory predicts a trade-off between female investment in reproduction and somatic maintenance, which can result in accelerated senescence. Oxidative stress has been shown to be a causal physiological mechanism for accelerated aging and a possible contributor to this trade-off. We aimed to test the hypothesis for the existence of significant associations between measures of reproductive effort and the level of oxidative stress biomarkers in premenopausal and postmenopausal American women.

Human reproduction and health: an evolutionary perspective.

According to life history theory, increased investment in reproductive function (physiology and behaviour) at different times throughout the life course affects the risk of many diseases and, ultimately, longevity. Although genetic factors contribute to interindividual and interpopulation variation in reproductive traits, the dominant source of variability is phenotypic plasticity during development and adult life. Reproductive traits in both sexes evolved sensitivity to ecological conditions, as reflected in contemporary associations of hormone concentrations with geographical setting, nutritional status, and physical activity level.

A Longitudinal Assessment of Associations between Adolescent Environment, Adversity Perception, and Economic Status on Fertility and Age of Menarche.

Purpose: Perceptions of environmental adversity and access to economic resources in adolescence can theoretically affect the timing of life history transitions and investment in reproductive effort. Here we present evidence of correlations between variables associated with subjective extrinsic mortality, economic status, and reproductive effort in a nationally representative American population of young adults.

Methods: We used a longitudinal database that sampled American participants (N ≥ 1,579) at four points during early adolescence and early adulthood to test whether perceptions of environmental adversity and early economic status were associated with reproductive effort.

Heterogeneous effects of market integration on sub-adult body size and nutritional status among the Shuar of Amazonian Ecuador.

Background: Market integration (MI)-increasing production for and consumption from a market-based economy-is drastically altering traditional ways of life and environmental conditions among indigenous Amazonian peoples. The effects of MI on the biology and health of Amazonian children and adolescents, however, remain unclear.

Aim: This study examines the impact of MI on sub-adult body size and nutritional status at the population, regional and household levels among the Shuar of Amazonian Ecuador.

Septic systems, but not sanitary sewer lines, are associated with elevated estradiol in male frog metamorphs from suburban ponds.

Suburban neighborhoods are a dominant type of human land use. Many housing regions globally rely on septic systems, rather than sanitary sewers, for wastewater management. There is evidence that septic systems may contaminate waterbodies more than sewer lines.

Evidence for the Cost of Reproduction in Humans: High Lifetime Reproductive Effort Is Associated with Greater Oxidative Stress in Post-Menopausal Women.

Life history theory predicts trade-offs between reproductive effort and maternal survivorship in energy-restricted environments. However, empirical evidence for the positive association between maternal mortality and reproductive effort from energetically challenged human populations are mixed and physiological mechanisms that may underlie this association are poorly understood. We hypothesized that increases in aerobic metabolism during repeated periods of pregnancy and lactation result in increased oxidative stress that may contribute to somatic deterioration, vulnerability to illness, and accelerated aging.

Redtail and red colobus monkeys show intersite urinary cortisol concentration variation in Kibale National Park, Uganda.

Non-invasive measurement of urinary cortisol is a proven method of evaluating the impact of environmental stressors on wild primates. Variation in cortisol concentrations can reflect physiological stress, and prolonged elevation of circulating cortisol can significantly affect individual and population-level health. In a previous study, we found that urinary cortisol concentrations in grey-cheeked mangabeys (Lophocebus albigena) were higher at a highly disturbed site (Mainaro) in Kibale National Park, Uganda compared with a minimally disturbed site (Ngogo) in the same habitat.

Diurnal variation in salivary cortisol across age classes in Ache Amerindian males of Paraguay.

Objectives: Cortisol levels exhibit a diurnal rhythm in healthy men, with peaks in the morning and troughs in the evening. Throughout age, however, this rhythm tends to flatten. This diurnal flattening has been demonstrated in a majority of industrialized populations, although the results have not been unanimous.

Oxytocin and Epstein-Barr virus: Stress biomarkers in the postpartum period among first-time mothers from São Paulo, Brazil.

Objectives: The purpose of the study was to examine the relationship between self-reported stress levels among new mothers in São Paulo, Brazil and two biomarkers of stressful experience, oxytocin (OT) and Epstein-Barr Virus antibody level (EBV-ab), with planned pregnancy hypothesized as a moderator of biological response to stressful conditions.

Methods: Sixty-three first-time mothers between the ages of 15 and 45 were recruited from neighborhoods in São Paulo, Brazil. Quantitative and qualitative data were collected longitudinally, bi-weekly between two and 12 weeks postpartum.

Relationships between biomarkers of inflammation, ovarian steroids, and age at menarche in a rural Polish sample.

Objectives: To test the hypothesis that life history trade-offs between maintenance and reproductive effort would be evident through inverse associations between levels of a biomarker of inflammation [C-reactive protein (CRP)], and ovarian hormones. Associations between CRP and age at menarche were also explored.

Methods: Urinary CRP, salivary progesterone, and estradiol were measured over one menstrual cycle from rural Polish women (n = 25), representing a natural fertility sample.

An evolutionary and life history perspective on human male reproductive senescence.

Unlike menopause, male reproductive senescence does not involve an acute drop in fertility. Men do, however, manifest distinct changes in somatic and gonadal function with age. Moreover, population variation in male reproductive senescence reveals phenotypic plasticity resulting from environmental, lifestyle, and genetic factors.

Is group size related to longevity in mammals?

Life-history theory predicts that reduced extrinsic risk of mortality should increase species longevity over evolutionary time. Increasing group size should reduce an individual's risk of predation, and consequently reduce its extrinsic risk of mortality. Therefore, we should expect a relationship between group size and maximum longevity across species, while controlling for well-known correlates of longevity.

Leptin associations with age, weight, and sex among chimpanzees (Pan troglodytes).

Background: Leptin is a hormone secreted primarily by adipocytes, a lipostatic signal to the hypothalamus, and is often correlated with adiposity. Associations between leptin, age, and development are unknown in human's closest evolutionary relative, the common chimpanzee (Pan troglodytes).

Methods: Serum leptin was assessed cross sectionally in association with age, weight, and sex in healthy captive chimpanzee males (n = 47) and females (n = 49) to test hypotheses related to predicted differences in leptin levels with body mass, development, and sexual dimorphism.