Lawrence S. Sugiyama

Cross-cultural evidence of cognitive adaptations for social exchange among the Shiwiar of Ecuadorian Amazonia

On the basis of evolutionary game theory, it was hypothesized that humans have an evolved cognitive specialization for reasoning about social exchange, including a subroutine for detecting cheaters. This hypothesis led to a specific prediction: Although humans are known to be poor at detecting potential violations of conditional rules in general, they should nevertheless detect them easily when the rule involves social exchange and looking for violations corresponds to looking for cheaters. This prediction was subsequently confirmed by numerous tests. Evolutionary analyses further predict that: (i) in humans, complex adaptations will be distributed in a species-typical fashion; and (ii) aspects of cognitive organization relevant to performing the evolved function of an adaptation should be more buffered against environmental and cultural variation than function-irrelevant aspects. Here we report experiments testing whether social exchange reasoning exhibits these properties of adaptations. Existing tests of conditional reasoning were adapted for nonliterate experimental subjects and were administered to Shiwiar hunter–horticulturalists of the Ecuadorian Amazon. As predicted, Shiwiar subjects were as highly proficient at cheater detection as subjects from developed nations. Indeed, the frequency of cheater-relevant choices among Shiwiar hunter-horticulturalists was indistinguishable from that of Harvard undergraduates. Also as predicted, cultural variation was confined to those aspects of reasoning that are irrelevant to social exchange algorithms functioning as an evolutionarily stable strategy. Finally, Shiwiar subjects displayed the same low performance on descriptive conditionals as subjects from developed nations. Taken together, these findings support the hypotheses that social exchange algorithms are species-typical and that their evolutionarily stable strategy (ESS)-relevant subroutines are developmentally buffered against cultural variation.

Is beauty in the context-sensitive adaptations of the beholder?: Shiwiar use of waist-to-hip ratio in assessments of female mate value

The proposition that universal standards of female beauty reflect adaptations for reproductive value assessment does not preclude cross-cultural variation that is contingent on local environmental variation. Cross-cultural tests of the hypothesis that men have adaptations generating preference for low female waist-to-hip ratios (WHR) have used stimuli that were not scaled to local conditions, and have confounded WHR with level of body fat. I present a reassessment of the WHR hypothesis, showing that when effects of WHR and body weight are less confounded, and local environmental context is taken into account, it appears that Shiwiar forager–horticulturist men of Ecuadorian Amazonia may use both WHR and body weight in assessments of female sexual attractiveness in a manner consistent with the prediction of a context-sensitive preference psychology.

Human preferences for sexually dimorphic faces may be evolutionarily novel

Significance It is a popular assumption that certain perceptions—for example, that highly feminine women are attractive, or that masculine men are aggressive—reflect evolutionary processes operating within ancestral human populations. However, observations of these perceptions have mostly come from modern, urban populations. This study presents data on cross-cultural perceptions of facial masculinity and femininity. In contrast to expectations, we find that in less developed environments, typical “Western” perceptions are attenuated or even reversed, suggesting that Western perceptions may be relatively novel. We speculate that novel environments, which expose individuals to large numbers of unfamiliar faces, may provide novel opportunities—and motives—to discern subtle relationships between facial appearance and other traits. A large literature proposes that preferences for exaggerated sex typicality in human faces (masculinity/femininity) reflect a long evolutionary history of sexual and social selection. This proposal implies that dimorphism was important to judgments of attractiveness and personality in ancestral environments. It is difficult to evaluate, however, because most available data come from large-scale, industrialized, urban populations. Here, we report the results for 12 populations with very diverse levels of economic development. Surprisingly, preferences for exaggerated sex-specific traits are only found in the novel, highly developed environments. Similarly, perceptions that masculine males look aggressive increase strongly with development and, specifically, urbanization. These data challenge the hypothesis that facial dimorphism was an important ancestral signal of heritable mate value. One possibility is that highly developed environments provide novel opportunities to discern relationships between facial traits and behavior by exposing individuals to large numbers of unfamiliar faces, revealing patterns too subtle to detect with smaller samples.

Life History, Immune Function, and Intestinal Helminths: Trade-Offs Among Immunoglobulin E, C-Reactive Protein, and Growth in an Amazonian Population

Objectives. Infection with helminths is associated with shifts in host immunity, including increased production of immunoglobulin E (IgE) and reduced inflammation. Given limited energy budgets, these shifts may involve changes in energy allocation toward competing demands. Here we test for potential trade‐offs between growth, IgE, and the inflammatory marker C‐reactive protein (CRP).

Analysis of variability of high sensitivity C-reactive protein in lowland Ecuador reveals no evidence of chronic low-grade inflammation.

C‐reactive protein (CRP) is a central component of innate immune defenses, and high sensitivity CRP has emerged as an important biomarker of chronic inflammation and cardiovascular disease risk. Prior analyses of CRP variability have reported stable between‐individual differences in CRP over time, but a limitation of current knowledge is that it is based on research conducted in post‐epidemiologic transition populations.

Evidence for a peak shift in a humoral response to helminths: age profiles of IgE in the Shuar of Ecuador, the Tsimane of Bolivia, and the U.S. NHANES.

Background The peak shift model predicts that the age-profile of a pathogens prevalence depends upon its transmission rate, peaking earlier in populations with higher transmission and declining as partial immunity is acquired. Helminth infections are associated with increased immunoglobulin E (IgE), which may convey partial immunity and influence the peak shift. Although studies have noted peak shifts in helminths, corresponding peak shifts in total IgE have not been investigated, nor has the age-patterning been carefully examined across populations. We test for differences in the age-patterning of IgE between two South American forager-horticulturalist populations and the United States: the Tsimane of Bolivia (n = 832), the Shuar of Ecuador (n = 289), and the U.S. NHANES (n = 8,336). We then examine the relationship between total IgE and helminth prevalences in the Tsimane. Methodology/Principal Findings Total IgE levels were assessed in serum and dried blood spots and age-patterns examined with non-linear regression models. Tsimane had the highest IgE (geometric mean  = 8,182 IU/ml), followed by Shuar (1,252 IU/ml), and NHANES (52 IU/ml). Consistent with predictions, higher population IgE was associated with steeper increases at early ages and earlier peaks: Tsimane IgE peaked at 7 years, Shuar at 10 years, and NHANES at 17 years. For Tsimane, the age-pattern was compared with fecal helminth prevalences. Overall, 57% had detectable eggs or larva, with hookworm (45.4%) and Ascaris lumbricoides (19.9%) the most prevalent. The peak in total IgE occurred around the peak in A. lumbricoides, which was associated with higher IgE in children <10, but with lower IgE in adolescents. Conclusions The age-patterning suggests a peak shift in total IgE similar to that seen in helminth infections, particularly A. lumbricoides. This age-patterning may have implications for understanding the effects of helminths on other health outcomes, such as allergy, growth, and response to childhood vaccination.

Social roles, prestige, and health risk

Selection pressure from health risk is hypothesized to have shaped adaptations motivating individuals to attempt to become valued by other individuals by generously and recurrently providing beneficial goods and/or services to them because this strategy encouraged beneficiaries to provide costly health care to their benefactors when the latter were sick or injured. Additionally, adaptations are hypothesized to have co-evolved that motivate individuals to attend to and value those who recurrently provide them with important benefits so they are willing in turn to provide costly care when a valued person is disabled or in dire need. Individuals in egalitarian foraging bands can provide a number of valuable benefits, such as defense, diplomacy, food, healing, information, technical skill, or trading savvy. We therefore expect that humans have evolved psychological mechanisms motivating the pursuit and cultivation of a difficult-to-replace social role based on the provisioning of a benefit that confers a fitness advantage on its recipients. We call this phenomenon social niche specialization. One such niche that has been well-documented is meat-sharing. Here we present cross-cultural evidence that individuals cultivate two other niches, information and tool production, that serve (among other things) to buffer health risk.

Growth and Market Integration in Amazonia: A Comparison of Growth Indicators Between Shuar, Shiwiar, and Nonindigenous School Children

We describe and compare the growth of three groups of juveniles, aged 0–18, who experience different degrees of market integration and acculturation in the Ecuadorian Amazon. These include 1,384 indigenous Shuar from the Upano Valley of Ecuador and surrounding areas, 570 nonindigenous colono (or colonist) children from the same area, and 42 Shiwiar from the interior of Ecuador. We use differences between these populations in National Health and Nutrition Examination Survey (NHANES) z‐scores to assess the effects of changing subsistence patterns on Shuar growth and nutrition. Although, for all three groups, mean height‐for‐age z‐scores were negative, Shuar z‐scores were significantly lower than either colono or Shiwiar z‐scores. Mean weight‐for‐age z‐scores were also negative for Shuar and colono juveniles, while mean BMI‐for‐age and weight‐for‐height z‐scores were greater than zero for all three groups. Using NHANES standards, 41% of male and 38% of female Shuar were classified as stunted, versus 16% of male and 20% of female colonos. Compared to Shuar, colonos were three times less likely to be stunted (OR = 0.33, P < 0.01) and Shiwiar were eight times less likely to be stunted (OR = 0.13, P = 0.01). These differences suggest that changes in diet have negatively affected Shuar growth and nutrition. Am. J. Hum. Biol, 2009.

Implications of market integration for cardiovascular and metabolic health among an indigenous Amazonian Ecuadorian population

Background: Market integration (MI), the suite of social and cultural changes that occur with economic development, has been associated with negative health outcomes such as cardiovascular disease; however, key questions remain about how this transition manifests at the local level. Aim: The present paper investigates the effects of MI on health among Shuar, an indigenous lowland Ecuadorian population, with the goal of better understanding the mechanisms responsible for this health transition. Subjects and methods: This study examines associations between measures of MI and several dimensions of cardiovascular and metabolic health (fasting glucose, lipids [LDL, HDL and total cholesterol; triglycerides] and blood pressure) among 348 adults. Results: Overall, Shuar males and females have relatively favourable cardiovascular and metabolic health. Shuar who live closer to town have higher total (p < 0.001) and HDL cholesterol (p < 0.001), while Shuar in more remote regions have higher diastolic blood pressure (p = 0.007). HDL cholesterol is positively associated with consumption of market foods (r = 0.140; p = 0.045) and ownership of consumer products (r = 0.184; p = 0.029). Conclusions: This study provides evidence that MI among Shuar is not a uniformly negative process but instead produces complex cardiovascular and metabolic health outcomes.

Physical growth of the shuar: Height, Weight, and BMI references for an indigenous amazonian population

Information concerning physical growth among small‐scale populations remains limited, yet such data are critical to local health efforts and to foster basic understandings of human life history and variation in childhood development. Using a large dataset and robust modeling methods, this study aims to describe growth from birth to adulthood among the indigenous Shuar of Amazonian Ecuador.