Evolution and Human Behavior最新文献

In low fertility settings, religious people tend to have larger families than non-religious people. One way religious individuals may achieve larger relative family sizes is through support from their families. In this paper, we investigate the relationships between religiosity, kin contact, allomaternal investment from relatives, and fertility in two high income low fertility settings: the United Kingdom and the United States. Data for this pre-registered research come from an online survey of 609 women living in the US and 919 women living in the UK, recruited through Prolific, who answered questions about their religious practices, childbirth histories, social networks, and allomaternal networks. We find that, compared with less religious peers, more religious women: 1) have more geographically diffuse kin networks (particularly in the UK) but have social networks that are equally kin-dense; 2) receive more allomaternal support from kin beyond their partner, particularly help with household tasks, though the countries differ in the exhibited relationship between religiosity and partner support; and 3) have higher fertility in both countries. We do not find strong evidence for a mediating role of allomaternal support on the relationship between religiosity and fertility. Our study highlights important variation in the relationship between religion and fertility across two high income low fertility countries and raises new questions about the role that religion plays in allomaternal support networks in these settings.

Costly ritual behaviours have frequently been of interest to evolutionary researchers seeking to understand whether they have an adaptive benefit. Here we examine the costliness of initiation rituals across a large group of hunter-gather societies in Pama-Nyungan Australia and compare these with a range of possible adaptive benefits, including warfare, food sharing, demography, and mate competition. We find that in Australia, desert habitat was mostly strongly associated with these rites. Such rites may support the collective action, such as food sharing, necessary for survival in such a precarious environment.

Religious practices vary greatly worldwide. Lifelong celibacy is present in many world religions, but it remains unclear why the frequency of monks and nuns (male and female celibates) varies at different times and places. Here, we develop a two-sex inclusive fitness model of lifelong celibacy. We find that the sex that competes more over parental resources is favoured to have more celibates, that is more monks than nuns are expected when brother-brother competition is higher than sister-sister competition. Moreover, the extent to which brothers and sisters compete over the same parental resources influences these patterns: intermediate sibling competition leads to more extreme differences in the proportion of monks and nuns. The sex that disperses less is also favoured to have more celibates. We show how our model can explain variation in the frequency of monks and nuns in three populations that differ in post-marital residence, marriage systems and inheritance rules.

A reliable assortment of committed individuals is crucial for success in intergroup conflict due to the danger of shirking. Theory predicts that reliable communication of commitment is afforded by costly signals that track cooperative intent. Across four pre-registered studies (total N = 1440, general US population), we used the public goods game where groups competed for resources to investigate whether and how costly signals function to assort cooperators. We found that costly signals assorted more cooperative participants, creating groups that would win most of the between-group clashes. The same effects were not observed when participants were assigned to signal, implying that signaling tracks but does not create cooperative intent. However, contrary to costly signaling theory, we found that low cost signals were more effective in cooperator assortment compared to high cost signals and suggest that future studies need to focus on signaler perception of cost/benefit trade-off of signaling.

Considered a part of the behavioral immune system, disgust functions as a protective mechanism against potential pathogen threat. There is evidence that disgust sensitivity varies depending on immunological and hormonal changes, including those occurring during the menstrual cycle or pregnancy. Although some studies indicate that disgust is elevated in early pregnancy, no study has yet compared disgust sensitivity in pregnant and non-pregnant women. This study aimed to examine differences in disgust sensitivity in pregnant versus non-pregnant women, while investigating whether disgust sensitivity differs depending on the phase of the menstrual cycle in non-pregnant women. The sample included 172 women (aged 21–40) in the first trimester of pregnancy and 354 non-pregnant, naturally cycling women (aged 20–40), out of whom 218 (61.6%) were in the luteal phase. All women filled out the Disgust Scale-Revised and the Three Domains of Disgust Scale. Non-pregnant women also completed the Culpepper Disgust Image Set. We observed that pregnant women had significantly higher pathogen-related and sexual disgust sensitivity than their non-pregnant counterparts (in both the follicular and luteal cycle phases). In non-pregnant women, there was no difference in disgust sensitivity between women in the follicular and luteal phases. When comparing pregnant women, women in the follicular phase, and those in the luteal phase, pathogen-related disgust sensitivity was lowest in the follicular, then in the luteal phase, and the highest in early pregnancy, although the difference between women in the follicular and luteal phase was not significant. Our results provide further evidence for the hypothesis that disgust is elevated when there is a need for increased protection, such as in the critical period of organogenesis in the first trimester of pregnancy.

Two well-supported generalizations from aggression research are that: a) people are less likely to commit homicide against close kin compared to non-kin, and b) females are less likely to engage in direct aggression than are males. Aggression between siblings, however, is somewhat more complicated than one might surmise from those two generalizations. Data from 3 studies collected using undergraduate and Prolific samples (N = 1640) reveal classic sex differences in direct aggression between non-relatives, but not between sisters and brothers. Whereas only a small minority of females have hit a friend or an acquaintance, the majority of females, like the majority of males, have hit a sibling. Although reputational aggression is substantially less likely between siblings than between friends or acquaintances, mild forms of direct aggression (such as hitting) are quite frequent between siblings. Discussion considers several possible limitations of the findings reported here and considers results in light of Trivers' theory of parent-offspring conflict.

Young children sometimes help others at a cost to themselves, but little is known about the emotional mechanisms underlying this behaviour. Here, 5-year-old children (n = 96, 45 girls, mean age = 5.57 years, SD = 1.79 months, range = 5.19 years to 5.9 years, families recruited from a local database based in a medium-sized German city) were engaged in one task and then asked either to help (child-helps) or watch (child-watches) an adult complete another task. Children would lose (cost) or not lose (no-cost) the progress they had made on their own task if they engaged with the adult. Children were more likely to interrupt their own task in the helping condition and were overall faster to do so when helping was not costly. Children who chose to incur a cost to help showed more positive emotions after helping—as measured via changes in their postural elevation—compared to helping at no cost. This pattern was not found in the child-watches condition. This suggests that costly helping holds emotional rewards for children in ways that non-costly helping does not.

Research on close relationships often focuses on the dyad (e.g., dyads of romantic partners) and on how dyad members affect each other's welfare. But dyads exist embedded in broader, densely-interconnected social networks, and less research attention has been paid to the myriad ways in which people outside the dyad impact one's welfare through their interactions with, or even their attitudes about, the other member of the dyad. What drives our feelings toward such extra-dyadic individuals? Balance Theory, an influential formalist theory in social psychology, suggests that our feelings are driven by the need for affective balance, achieved by, for example, liking strangers who share our feelings toward our existing partners or by disliking strangers who do not. We propose an alternative theory, the Embedded Dyad Framework, which foregrounds the substantive effects that strangers can have on our welfare through their interactions with our dyadic partners. Across four experiments (N = 1589) with U.S.-residing participants we predict and find, consistent with the Embedded Dyad Framework, that we like strangers who share our hatred for our rivals and our love for our friends (consistent with Balance Theory); but we dislike strangers who share our love for our spouses (contradicting Balance Theory). Further supporting predictions from an Embedded Dyad Framework, (a) greater perceived exclusivity in welfare-enhancing dyadic relationships (e.g., friendships) drives our lesser liking of strangers who share our love for our partners, and (b) greater perceived welfare suppression by our antagonistic partners (e.g., rivals) drives our liking of strangers who share our hatred of our antagonists. This framework outpredicts cognitive consistency views by emphasizing the real threats and opportunities that dyadic relationships afford people when dyads are embedded in social networks.

Many primates produce copulation calls, but we have surprisingly little data on what human sex sounds like. I present 34 h of audio recordings from 2239 authentic sexual episodes shared online. These include partnered sex or masturbation, but each recording has only one main vocalizer (1950 female, 289 male). Both acoustic features and arousal ratings from an online perceptual experiment with 109 listeners recruited on Prolific follow an inverted-U curve, revealing the likely time of orgasm. Sexual vocalizations become longer, louder, more high-pitched, voiced, and unpredictable at orgasm in both men and women. Men are not less vocal overall in this sample, but women start moaning at an earlier stage; speech or even minimally verbalized exclamations are uncommon. While excessive vocalizing sounds inauthentic to listeners, vocal bursts at peak arousal are ubiquitous and less verbalized than in the build-up phase, suggesting limited volitional control. Human sexual vocalizations likely include both consciously controlled and spontaneous moans of pleasure, which are perhaps best understood as sounds of liking rather than signals specific to copulation.