Recalling experiences of scarcity reduces children's generosity relative to recalling abundance.

Does a sense of having less or more than what one needs affect one's generosity? The question of how resource access influences prosocial behavior has received much attention in studies with adults but has produced conflicting findings. To better understand this relationship, we tested whether resource access affects generosity in the developing mind. In our preregistered investigation, we used a narrative recall method to explore how temporary, experimentally evoked states of resource abundance or scarcity affect children's sharing. In this study, 6- to 8-year-old American children (N = 148) recalled an experience of scarcity or abundance and then chose how many prizes to share with another child. We found that children in the scarce condition rated themselves as sadder, viewed their resource access as more limited, and shared fewer tokens than children in the abundant condition. Our results indicate that recalling past experiences of resource access creates distinct behavioral consequences for children and suggest that a sense of "having less" may encourage a strategy of resource conservation relative to a sense of "having more," even at a young age.

Computational signatures of inequity aversion in children across seven societies.

[Correction Notice: An Erratum for this article was reported online in Journal of Experimental Psychology: General on Aug 10 2023 (see record 2023-96713-001). In the original article, there were affiliation errors for the first and 14th authors. The affiliations for Dorsa Amir are Department of Psychology, University of California, Berkeley; and Department of Psychology, Boston College. The affiliation for Katherine McAuliffe is Department of Psychology, Boston College. All versions of this article have been corrected.] Inequity aversion is an important factor in fairness behavior. Previous work suggests that children show more cross-cultural variation in their willingness to reject allocations that would give them more rewards than their partner-advantageous inequity-as opposed to allocations that would give them less than their partner-disadvantageous inequity. However, as past work has relied solely on children's decisions to accept or reject these offers, the algorithms underlying this pattern of variation remain unclear. Here, we explore the computational signatures of inequity aversion by applying a computational model of decision-making to data from children (N = 807) who played the Inequity Game across seven societies. Specifically, we used drift-diffusion models to formally distinguish evaluative processing (i.e., the computation of the subjective value of accepting or rejecting inequity) from alternative factors such as decision speed and response strategies. Our results suggest that variation in the development of inequity aversion across societies is best accounted for by variation in the drift rate-the direction and strength of the evaluative preference. Our findings underscore the utility of looking beyond decision data to better understand behavioral diversity. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Acoustic regularities in infant-directed speech and song across cultures.

When interacting with infants, humans often alter their speech and song in ways thought to support communication. Theories of human child-rearing, informed by data on vocal signalling across species, predict that such alterations should appear globally. Here, we show acoustic differences between infant-directed and adult-directed vocalizations across cultures. We collected 1,615 recordings of infant- and adult-directed speech and song produced by 410 people in 21 urban, rural and small-scale societies. Infant-directedness was reliably classified from acoustic features only, with acoustic profiles of infant-directedness differing across language and music but in consistent fashions. We then studied listener sensitivity to these acoustic features. We played the recordings to 51,065 people from 187 countries, recruited via an English-language website, who guessed whether each vocalization was infant-directed. Their intuitions were more accurate than chance, predictable in part by common sets of acoustic features and robust to the effects of linguistic relatedness between vocalizer and listener. These findings inform hypotheses of the psychological functions and evolution of human communication.

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. 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.

What is the expected human childhood? Insights from evolutionary anthropology.

In psychological research, there are often assumptions about the conditions that children expect to encounter during their development. These assumptions shape prevailing ideas about the experiences that children are capable of adjusting to, and whether their responses are viewed as impairments or adaptations. Specifically, the expected childhood is often depicted as nurturing and safe, and characterized by high levels of caregiver investment. Here, we synthesize evidence from history, anthropology, and primatology to challenge this view. We integrate the findings of systematic reviews, meta-analyses, and cross-cultural investigations on three forms of threat (infanticide, violent conflict, and predation) and three forms of deprivation (social, cognitive, and nutritional) that children have faced throughout human evolution. Our results show that mean levels of threat and deprivation were higher than is typical in industrialized societies, and that our species has experienced much variation in the levels of these adversities across space and time. These conditions likely favored a high degree of phenotypic plasticity, or the ability to tailor development to different conditions. This body of evidence has implications for recognizing developmental adaptations to adversity, for cultural variation in responses to adverse experiences, and for definitions of adversity and deprivation as deviation from the expected human childhood.

Trustworthiness is distinct from generosity in children.

Interpersonal trust is a key component of cooperation, helping support the complex social networks found across societies. Trust typically involves two parties, one who trusts by taking on risk through investment in a second party, who can be trustworthy and produce mutual benefits. To date, the developmental literature has focused primarily on the trustor, meaning we know little about the ontogeny of trustworthiness. Whereas trusting can be motivated by self-interest, one-shot trustworthiness is more squarely situated in the prosocial domain, involving a direct tradeoff between self-interest and others' interests. However, this raises the question of whether trustworthiness is distinct from generosity. In this preregistered study, we examine the origins of trustworthiness using an intuitive version of the Trust Game, in which a first party invests resources in a second party who can split the gains. We recruited N = 118 5-to-8 year-old American children (Mage = 6.94, n = 59 girls, 57% White, 88% of parents with bachelor's degree or higher), split between the Trustworthiness condition, where another party's investment is instrumental for obtaining greater resources, and the Generosity condition, where the other party is a passive recipient. We found that children in the Trustworthiness condition shared significantly more resources than those in the Generosity condition. Further, children in the Trustworthiness condition predicted that the first party expected them to share a greater number of resources. Overall, these results demonstrate that trustworthiness is distinct from generosity in childhood and suggest that children spontaneously grasp and engage in a key aspect of cooperation. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Children are more forgiving of accidental harms across development.

Forgiveness is a powerful feature of human social life, allowing for the restoration of positive cooperative relationships. Despite its importance, we know relatively little about how forgiveness develops during early life and the features that shape forgiveness decisions. Here, we investigated forgiveness behavior in children aged 5-10 years (N = 257) from the United States, varying transgressor intent and remorse in a behavioral task that pitted punishment against forgiveness. We found that baseline levels of forgiveness are high, suggesting that children assume the best of transgressors in the absence of information about intent and remorse. We also found age-related increases in sensitivity to intent but not remorse, such that older children are more likely to forgive accidental transgressions. Because forgiveness is an important tool in the human social toolkit, exploring the ways in which this ability develops across age can help us to better understand the early roots of human cooperation.

The world within: Children are sensitive to internal complexity cues.

When reasoning about the mechanisms of complex entities, it is important to consider their internal parts. Previous research has shown that young children view "insides" as critical to how objects function. However, whether children hold specific expectations regarding complex objects' insides remains an open question. Here, children (n = 378) and adults (n = 124) made internal and causal complexity judgments regarding real-world objects. In Study 1, 5- and 6-year-olds, but not 4-year-olds, succeeded at internal complexity judgments and matched complex artifacts with complex insides. All age groups succeeded at causal complexity judgments and identified complex artifacts as causally complex. Study 2 tested whether the internal complexity cues of number/area, diversity, and connections of internal parts conveyed complexity to children. The 5-year-olds were sensitive only to number/area of internal parts as a complexity cue, but the older children and adults were sensitive to all three cues plus number of parts when controlling for area (Study 3). Despite limited exposure to insides, even young school-age children hold detailed and abstract expectations concerning internal complexity.

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. We find striking cross-cultural differences in behavior: children in India, the United States, and Argentina are more risk-seeking and future-oriented, whereas Shuar children are more risk-averse and exhibit more heterogeneous time preferences, on average preferring more today choices. To explore 1 of the socioecological forces that may be shaping these preferences, in Study 2, we compared the behavior of more and less market-integrated Shuar children, finding that those in market-integrated regions are more future-oriented and risk-seeking. These findings indicate that cross-cultural differences in risk and time preferences can be traced into childhood and may be influenced by the local environment. More broadly, our results contribute to a growing understanding of plasticity and variation in the development of behavior. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Measuring subjective social status in children of diverse societies.

Subjective Social Status (SSS) is a robust predictor of psychological and physiological outcomes, frequently measured as self-reported placement on the MacArthur Scale of Subjective Social Status. Despite its importance, however, there are still open questions regarding how early into ontogeny SSS can be measured, and how well SSS measures can be extended to non-Western and small-scale populations. Here, we investigate the internal consistency of responses to the MacArthur ladder across four cultures by comparing responses to more explicit social comparison questions. We conduct these comparisons among children and adolescents, ages 4 to 18, in India, the United States, and Argentina, in addition to those in two indigenous communities of the Ecuadorean Amazon marked by differing degrees of market integration (total N = 363). We find that responses are consistent in all populations, except for the more remote forager-horticulturalist Ecuadorian community. We also find that, consistent with findings among American adolescents, SSS declines with age. We then assess the test-retest reliability of the MacArthur Scale across two time-points: a subset of Indian participants (N = 43) within one week, and a larger, second sample of Indian participants after one year (N = 665). We find that responses are highly correlated within one week (ρ = 0.47), and moderately correlated after one year (ρ = 0.32). These results suggest that responses to the MacArthur ladder are internally consistent and reliable among children across a range of diverse populations, though care must be taken in utilizing these measures among children of non-industrial, small-scale societies.

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. 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 and Trichuris 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 with T. 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.

The Perception of Spontaneous and Volitional Laughter Across 21 Societies.

Laughter is a nonverbal vocalization occurring in every known culture, ubiquitous across all forms of human social interaction. Here, we examined whether listeners around the world, irrespective of their own native language and culture, can distinguish between spontaneous laughter and volitional laughter-laugh types likely generated by different vocal-production systems. Using a set of 36 recorded laughs produced by female English speakers in tests involving 884 participants from 21 societies across six regions of the world, we asked listeners to determine whether each laugh was real or fake, and listeners differentiated between the two laugh types with an accuracy of 56% to 69%. Acoustic analysis revealed that sound features associated with arousal in vocal production predicted listeners' judgments fairly uniformly across societies. These results demonstrate high consistency across cultures in laughter judgments, underscoring the potential importance of nonverbal vocal communicative phenomena in human affiliation and cooperation.

The behavioral constellation of deprivation may be best understood as risk management.

Although the authors make a compelling case that early-life deprivation leads to present orientation, we believe that such behaviors may be better understood in terms of an underlying risk-management strategy, in which those who experience such deprivation are more risk-averse. The model we sketch accommodates the authors' present-orientation observations and further explains differences in risk preferences and social preferences.

Are empathy and concern psychologically distinct?

Researchers have long been interested in the relationship between feeling what you believe others feel-often described as empathy-and caring about the welfare of others-often described as compassion or concern. Many propose that empathy is a prerequisite for concern and is therefore the ultimate motivator of prosocial actions. To assess this hypothesis, the authors developed the Empathy Index, which consists of 2 novel scales, and explored their relationship to a measure of concern as well as to measures of cooperative and altruistic behavior. A series of factor analyses reveal that empathy and concern consistently load on different factors. Furthermore, they show that empathy and concern motivate different behaviors: concern for others is a uniquely positive predictor of prosocial action whereas empathy is either not predictive or negatively predictive of prosocial actions. Together these studies suggest that empathy and concern are psychologically distinct and empathy plays a more limited role in our moral lives than many believe. (PsycINFO Database Record

Cultural evolution need not imply group selection.

Richerson et al. make a compelling case for cultural evolution. In focusing on cultural group selection, however, they neglect important individual-level accounts of cultural evolution. While scientific discourse typically links cultural evolution to group selection and genetic evolution to individual selection, this association is due to historical accident only. We thus call for more consideration of individual-level cultural evolution.

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. RESULTS: We found that subjectively high ratings of environmental danger and low access to economic resources in adolescence were significantly associated with an earlier age of menarche in girls and earlier, more robust fertility in young adulthood. CONCLUSION: While energetics and somatic condition remain as possible sources of variation, the results of this study support the hypothesis that perceptions of adversity early in life and limited access to economic resources are associated with differences in reproductive effort and scheduling. How these factors may covary with energetics and somatic condition merits further investigation.

Conditioning- and time-dependent increases in context fear and generalization.

A prominent feature of fear memories and anxiety disorders is that they endure across extended periods of time. Here, we examine how the severity of the initial fear experience influences incubation, generalization, and sensitization of contextual fear memories across time. Adult rats were presented with either five, two, one, or zero shocks (1.2 mA, 2 sec) during contextual fear conditioning. Following a recent (1 d) or remote (28 d) retention interval all subjects were returned to the original training context to measure fear memory and/or to a novel context to measure the specificity of fear conditioning. Our results indicate rats that received two or five shocks show an "incubation"-like enhancement of fear between recent and remote retention intervals, while single-shocked animals show stable levels of context fear memory. Moreover, when fear was tested in a novel context, 1 and 2 shocked groups failed to freeze, whereas five shocked rats showed a time-dependent generalization of context memory. Stress enhancement of fear learning to a second round of conditioning was evident in all previously shocked animals. Based on these results, we conclude that the severity or number of foot shocks determines not only the level of fear memory, but also the time-dependent incubation of fear and its generalization across distinct contexts.

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. SUBJECTS AND METHODS: Anthropometric data were collected between 2005-2014 from 2164 Shuar (aged 2-19 years) living in two geographic regions differing in general degree of MI. High-resolution household economic, lifestyle and dietary data were collected from a sub-sample of 631 participants. Analyses were performed to investigate relationships between body size and year of data collection, region and specific aspects of household MI. RESULTS: Results from temporal and regional analyses suggest that MI has a significant and overall positive impact on Shuar body size and nutritional status. However, household-level results exhibit nuanced and heterogeneous specific effects of MI underlying these overarching relationships. CONCLUSION: This study provides novel insight into the complex socio-ecological pathways linking MI, physical growth and health among the Shuar and other indigenous Amazonian populations.

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. Regardless, little attention has been paid to nonindustrialized, foraging populations such as the Ache Amerindians of Paraguay. As testosterone levels had previously been shown to diminish with age in this population (Bribiescas and Hill [2010]: Am J Hum Biol 22: 216-220), we hypothesized that cortisol levels would behave similarly, flattening in rhythmicity over age. METHODS: We examined morning and evening salivary cortisol samples in Ache Amerindian men in association with age (n = 40, age range 20-64 years). RESULTS: Men in the first age class (<20-29 years) exhibited significantly different morning (AM) and evening (PM) values as did men in the second age class (30-39 years). However, men in the third and fourth age classes (40-49 years, and >50 years, respectively) did not exhibit a significant difference between AM and PM values. CONCLUSION: Ache Amerindian men exhibit a flattening of the diurnal rhythm across age classes. Our results were able to capture both within- and between-individual variations in cortisol levels, and reflected age-related contrasts in daily cortisol fluctuations. The flattening of the diurnal rhythm with age among the Ache may reflect a common and shared aspect of male senescence across ecological contexts and lifestyles. Am. J. Hum. Biol. 27:344-348, 2015. © 2014 Wiley Periodicals, Inc.