Evolution and Human Behavior最新文献

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.

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.

The Reproductive Compensation (RC) hypothesis and the Differential Allocation (DA) hypothesis predict that parents who mate under constraint will either increase or decrease, respectively, their reproductive effort and investment in offspring. One possible type of mate choice constraint in humans is arranged marriage in which parents or others choose mates. To test the RC and DA hypotheses in humans, we examine whether there are differences in parental investment between women in arranged marriages and those in self-choice marriages using data from the Indonesian Family Life Survey (n = 8393). Marriage type does not significantly correlate with parental investment except for fertility outcomes where women in self-choice marriages had more live births, living children, and greater marital fertility than woman in arranged marriages. Our findings better support the DA hypothesis than the RC hypothesis. We conclude that, like many other species, free mate choice is associated with increased reproductive success in this sample of humans.