Evolution and Human Behavior最新文献

Why do people blame, devalue or derogate the victims of misfortune? The literature suggests general factors like a belief in a just world or a desire to distance oneself from misfortune, but the empirical results are often unclear. Here we suggest another potential factor in victim-devaluation in particular. Attitudes to victims should be seen in the context of human cooperation, as victims can be a source of costs for others and, therefore, may constitute poor potential cooperation partners. If that is the case, devaluation should be associated with a reluctance to offer help to victims. As predicted, across six pre-registered studies, we found that participants' reluctance to donate their own money (their bonus for participation), or allocate other people's money to a victim predicted the devaluation of the victim's character. Both devaluation and willingness to help were influenced by manipulating the victim's apparent competence, and the victim's concern for other people's possible costs, two crucial dimensions of cooperative potential. These results are consistent with the overall hypothesis that people's intuitions about a victim's cooperation potential are relevant to victim-devaluation.

Social scientists have often claimed or implied that hazing selects out uncommitted newcomers in voluntary associations. Because groups that engage in hazing are generally secretive about their practices, there has never been a real-world, in situ test of this claim. Using an American social fraternity, we report the first real-world, longitudinal test of hazing's relationship with selective newcomer attrition. Our data are derived from six sets of fraternity inductees who experienced the fraternity's hazing induction process (N = 126). Our analyses suggest that experienced hazing severity is a predictor of attrition and that hazing severity differentially predicts the attrition of low-commitment newcomers. However, real-world fraternity inductions (and measurements thereof) are complex in ways that add important caveats to our findings. Our discussion focuses on the best means by which to confirm or disconfirm our results through future replications.

According to the Trivers-Willard hypothesis, mothers who give birth to sons when their general condition is good and daughters when their condition is bad have an advantage in fitness. The purpose of this study was to test this hypothesis in humans by examining sex differences in birth weight according to maternal age based on a comparison of the birth weights of twins. A total of 2138 Indian twins (668 opposite sex, 2940 same sex) from the 2015–2016 National Family Health Survey IV database were identified for analysis. In total, 3700 mothers were at low risk for having low-birth-weight babies in terms of maternal age (ages 20–34 years) and 576 mothers were at high risk in terms of maternal age (20 years younger or 35 years or older). The results of the analysis of covariance showed that: 1) the birth weight ratio of opposite-sex twins is small (female newborns are heavier) when the mothers are at a high risk age. 2) At a high risk age, female newborns in opposite-sex twins, who can receive sex-based discriminatory investments, are heavier at birth than female babies in same-sex twins. These results remained significant after controlling for variables potentially related to birth weight. This study provides potential evidence that in utero selection is retained by the mother as a countermeasure against threats in terms of fitness.

Studies investigating facial attractiveness in humans have frequently been limited to studying the effect of individual morphological factors in isolation from other facial shape components in the same population. In this study, we go beyond this approach by focusing on multiple components and populations while combining geometric morphometrics of 72 standardized frontal facial landmarks and a Bayesian statistical framework. We investigate preferences in both sexes for three structural components of other sex facial beauty that are traditionally considered indicators of biological quality: symmetry, sexual dimorphism, and distinctiveness (i.e., the opposite of averageness). Based on a large sample of faces (n = 1550) from 10 populations across the world (Brazil, Cameroon, Czechia, Colombia, India, Namibia, Romania, Turkey, UK, and Vietnam), we found that distinctiveness negatively affects the perception of attractiveness in both sexes and that this association is stable across all studied populations. We corroborated some previous results indicating both a positive effect of femininity on male assessment of female facial beauty and a null or weak effect of masculinity on female evaluation of male facial attractiveness. Facial symmetry had no effect on facial attractiveness. In concert with other recent studies, our results support the importance of facial prototypicality but cast doubt on the role of symmetry as one of the key constituents of attractiveness in the human face.

Parochial altruism (PA), or ingroup favoritism paired with outgroup hostility, is sometimes treated as a synonym for human intergroup relations. However, empirical data suggest that PA is highly variable—across individuals, across situations, and across groups. Here, we review theory and data on PA to explore the candidate sources for this variability. Along the way, we unpack assumptions (e.g., what constitutes a group?), identify precursors to PA behavior (e.g., context and internal states), and review evidence for the pairing of ingroup favoritism with outgroup hostility. We discuss phenomena with measurable impact on downstream behavior, including resource access and cultural institutions, but also flag how researcher expectations and methodological design impact reported variability in PA. We close by making recommendations for how researchers can reduce noise in the study of PA by checking assumptions and being deliberate in research design; this is key, as the PA literature is part of sensitive public discourse.

Recent experimental evidence has led to the idea that the neural mechanisms supporting spatial navigation have been flexibly adapted to organize concepts and memories through spatial codes. The “phylogenetic continuity hypothesis” (Buszáki & Moser, 2013) further proposes that the mechanisms supporting episodic and semantic memory would have respectively evolved from self-based (i.e. egocentric) and map-based (i.e. allocentric) spatial navigation mechanisms. Recent studies have observed traces of this phylogenetic continuity in human behavior, but the full original model has not yet been tested. Here, we evaluated the relationships between the four model components by using two sets of tasks in the spatial navigation and declarative memory domains based on complex materials and emphasizing the self vs. map-based processing (i.e. route vs. survey component for spatial navigation and episodic vs. semantic component for declarative memory). Consistent with the model predictions, the results of a multiple multivariate regression analysis revealed a specific across-domain relationship, such that route-based navigation performance specifically predicted episodic memory performance (self-based, egocentric components), while survey navigation performance specifically predicted the semantic memory one (map-based, allocentric components). The results of an additional regression analysis on the within-domain transformation process from self-based to map-based representations confirmed that route-based navigation specifically predicted survey navigation, while episodic memory specifically predicted semantic memory. Our results provide further behavioral evidence in support of the general hypothesis that the neural machinery evolved to map the physical world might have been recycled to organize memory and conceptual knowledge. Crucially, they also support the more specific hypothesis that the organizational principles involved in higher-level processing of information have inherited the fundamental distinction between different reference frames (egocentric vs. allocentric) for navigation in the physical world.

The degree to which culture and context contribute to variability in human behaviour is a critical scientific question. While most research in the human behavioural sciences is based on WEIRD samples, the last decade has seen a rise in research on traditionally under-represented populations, including small-scall societies, to demonstrate reproducibility of results. Considering this framework as a major objective, here we explore cross-cultural ubiquity in the production and perception of human baby cries, focusing on remote rural communities in the Democratic Republic of Congo, compared to analogous data from French and British samples. Through acoustic analysis of Congolese baby cries recorded in natural discomfort (bath) and pain (vaccine) contexts, combined with psychoacoustic experiments on Congolese adult listeners, we show that distress is reliably encoded in the acoustic cry signal, namely in nonlinear acoustic phenomena. Despite the absence of sexual dimorphism in cries, low-pitched cries are more often perceived as produced by boys than girls, and cries experimentally attributed to boys are perceived as expressing more distress than the same cries experimentally attributed to girls. Having obtained similar results in European samples, this study provides compelling evidence that these voice-based stereotypes are stable and robust, observed across extremely distinct human populations.

A common life history theory trade-off is that which males face between mating effort and parental effort. This trade-off is observed across species, among individuals within a species, and within individuals across their lifespan. Recent studies suggest the possibility of more rapid trade-offs or motivational shifts in response to transient aspects of the social environment. We were interested in whether exposure to mating-related stimuli would negatively impact men's evaluation of parental-related stimuli and vice-versa, and whether this response would differ between fathers and non-fathers. In two separate experiments, a total of 160 heterosexual or bisexual men rated how appealing they found 40 images of attractive infants and 40 images of attractive adult females. Half of all participants viewed infant images before viewing female images, and the other half viewed female images before infant images. In both experiments, fathers rated infant stimuli as more appealing than did non-fathers when infants were presented before females, but not when infants were presented after females. That is, priming fathers with female stimuli negatively impacted their ratings of infants. On the other hand, priming men with pictures of cute infants before viewing females did not impact ratings of female pictures, in either fathers or non-fathers. Nor did priming fathers with pictures of another highly rewarding stimulus - highly appealing foods - decrease their ratings of infants. The negative effect of female pictures on fathers' subsequent ratings of infant stimuli is consistent with the possibility that the female pictures activated motivational systems related to mating effort, which in turn inhibited motivational systems related to parental effort, rendering the infant stimuli less appealing. Our findings suggest that human fathers may be susceptible to transient shifts in life history strategy as a function of their immediate social environment.