To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women’s fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species—including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.
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The goal of assessing psychosocial stress as a process and outcome in naturalistic (i.e., field) settings is applicable across the social, biological, and health sciences. Meaningful measurement of biology-in-context is, however, far from simple or straightforward. In this brief methods review, we introduce theoretical framings, methodological conventions, and ethical concerns around field-collection of markers of psychosocial stress that have emerged from 50 years of research at the intersection of anthropology and human biology. Highlighting measures of psychosocial stress outcomes most often used in biocultural studies, we identify the circumstances under which varied measures are most appropriately applied and provide examples of the types of cutting-edge research questions these measures can address. We explain that field-based psychosocial stress measures embedded in different body systems are neither equivalent nor interchangeable, but this recognition strengthens the study of stress as always simultaneously cultural and biological, situated in local ecologies, social–political structures, and time.
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Abstract Objectives This study investigates bone density across the life course among Bolivian Tsimane and Ecuadorian Shuar of Amazonia. Both groups are rural, high‐fertility forager‐horticulturalists, with high lifetime physical activity levels. We test whether Tsimane and Shuar bone density patterns are different from each other, and if both groups are characterized by lower osteoporosis risk compared to U.S. references.
Methods Anthropometric and calcaneal bone density data, obtained via quantitative ultrasonometry (QUS), were collected from 678 Tsimane and 235 Shuar (13–92 years old). Population and sex differences in QUS values (estimated bone mineral density, speed of sound, broadband ultrasound attenuation) by age group were assessed using Mann–Whitney
U tests. Age‐related change and age at peak QUS value were determined using polynomial regressions. One‐way analyses of covariance assessed population‐level differences in QUS values by age group adjusting for body mass index. Participants aged 50+ years at elevated osteoporosis risk were identified using aT score < −1.8; binomial tests assessed risk compared to U.S. references.Results Shuar males and females <50 years old have QUS values 3–36% higher than Tsimane, with differences evident in adolescence. Among Tsimane and Shuar, 49 and 23% of participants aged 50+ years old, respectively, are at high risk for osteoporosis, compared to 34% of Americans; Shuar osteoporosis risk is comparable to Americans, while Tsimane risk is elevated.
Conclusions Disparate patterns in QUS values are documented for Tsimane and Shuar, with pronounced differences early in life. Potential explanations for differences include gene–environment interactions and/or degree of market integration, which influences diet, activity profiles, pathogen exposures, and other lifestyle covariates. As Tsimane osteoporosis risk is greater than in the United States, findings point to alternative risk factors for low bone density that are not readily discernible in industrialized populations.
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Abstract 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.
Results Shuar anemia rates among children under 15 years (12.2%), adult women (10.5%), and adult men (5.3%) were less than half of those previously documented in other neo‐tropical Indigenous populations. Anemia prevalence did not vary between more traditional and market integrated communities (
OR = 0.47,p = .52). However, anemia was negatively associated with body mass index (OR = 0.47,p = .002).Conclusions Compared to other South American Indigenous populations, anemia prevalence is relatively low among Shuar of Ecuador and invariant with market integration. Understanding this pattern can provide valuable insights into anemia prevention among at‐risk populations.
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Soil‐transmitted helminth infection and intestinal inflammation among the Shuar of Amazonian Ecuadormore » « less
Abstract 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. We predict that fecal calprotectin (FC; a measure of intestinal inflammation) will be lower in STH infected individuals and that FC will be negatively associated with infection intensity.
Methods Stool samples to analyze FC levels and STH infection were collected from 69 Shuar participants (ages 5–75 years). Children (<15 years) and adults (15+ years) were analyzed separately to understand the role of exposure in immune system development and the intestinal inflammatory response.
Results Two species of STH were present:
Ascaris lumbricoides andTrichuris trichiura . The relationships between infection and intestinal inflammation were age‐ and species‐specific. While no significant relationships were found among adults, children who were singly infected withT. trichiura had lower FC levels than uninfected children. Infection intensity was not significantly associated with FC in children or adults.Conclusions These preliminary results provide limited support for our hypotheses, documenting tentative age‐ and species‐specific associations between FC and infection status. Findings may point to the importance of species‐specific STH exposure during immune system development.
