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Background Evolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial cues to assess traits of others. The use of facial and somatic cues by humans has been studied mainly in western industrialized countries, leaving unanswered whether results are valid across cultures. Methodology/Principal Findings Our objectives were to test (i) if previous finding about raters' ability to get accurate information about an individual by looking at his facial photograph held in low-income non western rural societies and (ii) whether women and men differ in this ability. To answer the questions we did a study during July-August 2007 among the Tsimane', a native Amazonian society of foragers-farmers in Bolivia. We asked 40 females and 40 males 16–25 years of age to rate four traits in 93 facial photographs of other Tsimane' males. The four traits were based on sexual selection theory, and included health, dominance, knowledge, and sociability. The rating scale for each trait ranged from one (least) to four (most). The average rating for each trait was calculated for each individual in the photograph and regressed against objective measures of the trait from the person in the photograph. We found that (i) female Tsimane' raters were able to assess facial cues related to health, dominance, and knowledge and (ii) male Tsimane' raters were able to assess facial cues related to dominance, knowledge, and sociability. Conclusions/Significance Our results support the existence of a human ability to identify objective traits from facial cues, as suggested by evolutionary theory.

Sibling configuration, including birth order, or the number, age, and sex of siblings is associated with parental resource allocation between children and is thus associated with a person's well-being. Little is known about the association between specific types of siblings and adult health outcomes. Here we test several hypotheses about sibling composition (number of older brothers, older sisters, younger sisters, younger brothers) and adult blood pressure in a foraging-farming society of native Amazonians in Bolivia (Tsimane'). We collected data in 2007 from 374 adults (16-60years of age) from 196 households in 13 villages. Household random-effects multiple regressions were run using systolic (SBP) or diastolic blood pressure (DBP) as outcomes; covariates included the four sibling categories and control variables (e.g., sex, age, education, body mass index [BMI]). Mean SBP and DBP were 114 (SD=14) and 66 (SD=11)mmHg. The prevalence of hypertension was 5.08%. Having an additional younger brother bore a small (3.3-5.9%) positive association with both SBP and DBP, with the effect weakening as people aged. Having an additional younger sister was associated with a small (3.8%) increase in SBP among women, with the magnitude shrinking as people aged. In a large family, the number of younger brothers may exert an impact on an individual's blood pressure.

Summary Although a growing body of research has documented important pathways by which the HPA axis mediates the interface between the psychosocial world and individual health, there is a paucity of data from nonwestern populations, particularly from those populations with distinct nutritional and infectious disease ecologies. The specific objectives of this study are: (1) to document variation in diurnal cortisol rhythms among the Tsimane’, a remote population in the Bolivian Amazon, (2) to explore this variation by age and by gender, and (3) to compare diurnal rhythms from this study to other population based studies of cortisol conducted in industrialized nations. Salivary cortisol samples were collected twice daily, immediately upon waking and before bed, for three consecutive days from 303 participants (age 1.6–82 years, 1564 samples) in conjunction with the Tsimane’ Amazonian Panel Study (TAPS). Cortisol rhythms showed strong age effects across the developmental span, with basal levels and slopes increasing into adulthood, although individuals older than 60 years demonstrated a precipitous flattening of the diurnal slope. Cortisol profiles were elevated in adult females compared to their age-matched male counterparts, and diurnal slopes, as well as mean cortisol concentrations among the Tsimane’ were the lowest reported in any population based study of HPA axis function. Although the within-population variation in cortisol profiles was consistent with the established correlates of time of day, age, and sex, the between-population comparisons revealed dramatically lower levels of HPA activity among the Tsimane’. This study provides a benchmark against which to reference cortisol levels from industrialized populations, and expands the range of documented variation in HPA axis function in a nonwestern context.

Growing evidence suggests that economic inequality in a community harms the health of a person. Using panel data from a small-scale, preindustrial rural society, we test whether individual wealth rank and village wealth inequality affects self-reported poor health in a foraging–farming native Amazonian society. A person's wealth rank was negatively but weakly associated with self-reported morbidity. Each step up/year in the village wealth hierarchy reduced total self-reported days ill by 0.4 percent. The Gini coefficient of village wealth inequality bore a positive association with self-reported poor health that was large in size, but not statistically significant. We found small village wealth inequality, and evidence that individual economic rank did not change. The modest effects may have to do with having used subjective rather than objective measures of health, having small village wealth inequality, and with the possibly true modest effect of a person's wealth rank on health in a small-scale, kin-based society. Finally, we also found that an increase in mean individual wealth by village was related to worse self-reported health. As the Tsimane’ integrate into the market economy, their possibilities of wealth accumulation rise, which may affect their well-being. Our work contributes to recent efforts in biocultural anthropology to link the study of social inequalities, human biology, and human-environment interactions.

The ubiquity and consequences of childhood growth stunting (

Despite the tremendous interest in understanding the effects of prenatal stress on fetal health and the programming of adult disease risk, the adaptive functions of hypothalamic–pituitary–adrenal (HPA) axis activity in healthy pregnancies and during lactation have been less widely considered. Existing research has addressed the influence of glucocorticoids on altered patterns of fetal growth and development in humans (Kuzawa and Sweet 2009; Seckl and Holmes 2007; Sloboda et al. 2005; 2009a, b) and the effects of prenatal stress in animal models, particularly with respect to offspring birth weight and stress reactivity (Drake et al. 2005; Neumann 2001; Seckl and Meaney 2004). With several important exceptions, the majority of this research has invoked the concept of “maternal stress” to encapsulate the premise that maternal activation of the HPA axis is associated with adverse birth outcomes, without the simultaneous acknowledgment that progressive elevation of the maternal HPA activity across the course of pregnancy is part of an anthropoid-typical pattern of neuroendocrine activity (Bowman et al. 2001; Smith et al. 1999). Even less is known about the HPA dynamics of pregnancy in non-Western populations with distinct infectious disease ecologies and marginal energetic status (Nyberg 2012). Given the human reproductive strategy of giving birth to secondarily altricial infants (Martin 2007), basal glucocorticoids may play a pivotal role in facilitating parturition and accelerating fetal tissue maturation in coordination with the timing of birth (Power and Schulkin 2006; Pike 2005; Smith et al. 2001). These constraints on the duration of gestation may be imposed, in part, by the metabolic demands of pregnancy (Ellison 2001, 2003; Martin 1996) and are further impacted by the obstetrical dilemma, imposed by the “tight fit” between fetal head circumference and the maternal pelvis that occurred as a result our hominin transition to obligate bipedalism (Rosenberg 2001; Rosenberg and Trevathan 1996). As a result, human birth is physiologically stressful, even by primate standards (Leigh 2004; Martin 1996; Rosenberg 2001; Rosenberg and Trevathan 1996).

Objective: Although psychosocial stress has also been implicated as a contributor to growth failure by imposing energetic constraints during development, the direct physiological pathways by which these life history trade-offs are imposed are not well understood. This study explores associations between diurnal cortisol rhythms and differential patterns of linear child growth among the Tsimane, a horticulturalist and foraging society in the Bolivian Amazon. Methods: Waking and bedtime salivary cortisol samples (n = 243) were collected from 53 Tsimane' children ages 1.6–6 over 3 days as part of a larger study of developmental trajectories in hypothalamic–pituitary–adrenal axis dynamics. Anthropometric measurements and survey data were collected in conjunction with the Tsimane' Amazonian panel study (TAPS). Results: Among children under the age of 6, diurnal rhythms in stunted versus nonstunted children vary dramatically: stunted children display elevated cortisol at both the AM (P = 0.03) and PM (P = 0.02) collection points. Multilevel regression analysis demonstrates an inverse relationship between cortisol and height-for-age z-score status (P = 0.00), which is mediated, in part, by infection (P = 0.00), and is strongest among male children (n.s.). Moreover, the poorest statural growth is exhibited among children with high cortisol living in more acculturated Tsimane' communities, a proxy for a more adverse developmental milieu. Conclusions: This study reports a small, but significant, life history cost of elevated diurnal cortisol rhythms on linear growth among Tsimane' children, and provides critical insight into the developmental origins of health differentials among an indigenous Amazonian population experiencing rapid lifestyle changes. Am. J. Hum. Biol., 2012. © 2012 Wiley Periodicals, Inc.

Growing evidence suggests that economic inequality in a community harms the health of a person. Using panel data from a small-scale, preindustrial rural society, we test whether individual wealth rank and village wealth inequality affects self-reported poor health in a foraging-farming native Amazonian society. A person's wealth rank was negatively but weakly associated with self-reported morbidity. Each step up/year in the village wealth hierarchy reduced total self-reported days ill by 0.4 percent. The Gini coefficient of village wealth inequality bore a positive association with self-reported poor health that was large in size, but not statistically significant. We found small village wealth inequality, and evidence that individual economic rank did not change. The modest effects may have to do with having used subjective rather than objective measures of health, having small village wealth inequality, and with the possibly true modest effect of a person's wealth rank on health in a small-scale, kin-based society. Finally, we also found that an increase in mean individual wealth by village was related to worse self-reported health. As the Tsimane' integrate into the market economy, their possibilities of wealth accumulation rise, which may affect their well-being. Our work contributes to recent efforts in biocultural anthropology to link the study of social inequalities, human biology, and human-environment interactions.

This paper examines three morphological indicators measuring obesity among a native Amazonian population of foragers-farmers in Bolivia (Tsimane') and estimates the associations between them and standard covariates of obesity (e.g., socioeconomic status [SES]). We collected annual data from 350 non-pregnant women and 385 men ≥20 years of age from all 311 households in 13 villages during five consecutive years (2002-2006). We used three indicators to measure obesity: body-mass index (BMI), waist circumference (WC), and body fat using bioelectrical impedance analysis (BF-BIA). We ran separate individual random-effect panel multiple regressions for women and men with wealth, acculturation, health, and household food availability as key covariates, and controlled for village and year fixed effects and village×year interaction effects. Although BMI increases by a statistically significant annual growth rate of 0.64% among women and 0.37% among men over the five years, the increase does not yield significant biological meanings. Neither do we find consistent and biologically meaningful covariates associated with adult obesity.

Among adults of industrial nations, growth stunting (-2 SD height Z score) is associated with worse indicators of adult well-being (e.g., income). Does adult stunting also inflict private costs in traditional societies? Adult stunting penalties or height premiums might only emerge when traditional societies modernize. Here we estimate the association between adult stunting and indicators of adult well-being using data from a panel study in progress among the Tsimane', a foraging-farming society of native Amazonians in Bolivia. Subjects included 248 women and 255 menor=age 22 measured annually during 5 consecutive years (2002-2006). Nine outcomes (wealth, monetary income, illness, access to credit, mirth, schooling, math skills, plant knowledge, forest clearance) were regressed separately against a stunting dummy variable and a wide range of control variables. We found no significant association between any of the indicators of own well-being and adult stunting. Additional analysis showed that stunting bore an association only with poorer mid-arm muscle area. Height premiums and stunting penalties, though evident and marked in modern societies, might not be common in all traditional societies.