Evolution and Human Behavior最新文献

The role of warfare in human evolution is among the most contentious topics in the evolutionary sciences. The debate is especially heated because many assume that whether our evolutionary ancestors were peaceful or warlike has important implications for modern human nature. One side argues that warfare has a deep evolutionary history, possible dating to the last common ancestor of bonobos, chimpanzees, and humans, while the other views war as a recent innovation, primarily developing with the rise of sedentism and agriculture. I show that although both positions have some support warranting consideration, each sometimes ignores uncertainties about human evolution and simplifies the complex reality of hunter-gatherer worlds. Many characterizations about the evolution of war are partial truths. Bonobos and chimpanzees provide important insights relevant for understanding the origins of war, but using either species as a model for human evolution has important limitations. Hunter-gatherers often had war, but like humans everywhere, our ancestors likely had a range of relationships depending on the context, including cooperative intergroup affiliation. Taken together, the evidence strongly suggests that small-scale warfare is part of our evolutionary history predating agriculture and sedentism, but that cooperation across group boundaries is also part our evolutionary legacy.

Music is a product of both biological and cultural evolution. Cultural transmission is the engine of cultural evolution and may play a role in the establishment of musical universals. Here, we examined how transmission dynamics can shape melodic features in music. Specifically, we tested whether random melodic seeds, in their transformation, take on properties known to characterise music within or even across cultures. Using an iterated learning paradigm, we investigated the transmission of random melodic seeds through a chain of non-musician participants (N = 64). We found that melodies reproduced vocally between “generations” became more similar to known musical scales, exhibited a predominance of consonant intervals, and reduced the number of scale degrees used. Additionally, we observed the previously documented tendency for large intervals to be followed by a change in direction, as well as features common to both music and speech including phrase-final lengthening and the Zipfian distribution of signalling units. As participants' vocalisations converged towards greater memorability, they exhibited decreased entropy, and their contours became smoother and more consistent. Finally, certain short melodic patterns became prominent motifs within the incipient musical “traditions” simulated by the chains. These emerging features may reflect a process shaped by (i) cognitive bottlenecks such as learnability; (ii) statistical properties of the processes and structures involved in inter-generational vocal transmission; but also by (iii) idiosyncratic cultural artefacts specific to the lab samples employed. Overall, our results demonstrate that fundamental aspects of melodic structure emerge naturally through the process of cultural transmission, as simulated in the lab.

Despite numerous studies attempting to understand the influence of fertility and hormonal contraceptives on competitive outcomes, the association between these variables remain a contentious issue. Using a longitudinal, online diary study with over 5600 daily observations (N = 302 community and undergraduate student participants), we explored the effects of fertility probability and hormonal contraceptive use on a range of self-report competitive outcomes. Specifically, we sought to replicate existing findings by examining whether self-reported competitive motivation increases mid-cycle and how hormonal contraceptive use affects these patterns. We also sought to extend this literature by collecting a range of self-report measures of competitive behavior across the menstrual cycle. Using an evolutionary and data-driven framework, we combined six behaviors females use to compete for mates and status: gossip, social comparison, negative evaluations of others, appearance enhancement, giving advice and taking sexy self-portraits. Contrary to our predictions, fertility probability was not associated with fluctuations in self-reported competitive motivation or behavior. However, replicating existing literature, hormonal contraceptive users reported a general lack of interest in competition compared to non-users. This latter finding raises important questions about the long-term implications of hormonal contraceptive use and suggests a need for further research to investigate the psychosocial effects of hormonal contraceptives. Finally, as a near direct replication of an existing longitudinal study, the current research offers a unique contribution by considering the role of context in hormone mediated research. We question the idea that a failure to replicate reflects the quality of the theory or the research, but instead suggest that context should be considered when developing psychological theory.

Altruistic behavior can be modulated by many factors including hormonal levels, but their reported effects remain mixed. Understanding the proximate mechanisms of altruism such as these can help test predictions of ultimate, evolutionary explanations. We investigated the relationship of the endogenous salivary levels of testosterone and cortisol with Dictator Game (DG) offers as a proxy of altruism on a sample of general-population participants (N = 158, 84 F, 74 M). Bayesian data analysis and model comparison showed both testosterone and cortisol were negatively correlated with DG offers in women, while higher testosterone levels were associated with greater generosity in men. These results suggest that high testosterone may promote altruistic behavior in the service of status-seeking among men.

Males that behave violently to achieve social and reproductive objectives are a widespread phenomenon among mammals, as well as humans. Because this kind of behaviour can be socially very disruptive, its continued survival in human populations, in particular, remains a puzzle. We use historical data on the pedigrees of medieval Icelandic Vikings to test the hypothesis that males who killed had higher fitness than other males. Whereas most studies that examine the evolutionary benefits of behaviour focus on the numbers of offspring sired, in this paper we measure fitness more directly in terms of the number of grandchildren produced both directly and indirectly via collateral relatives, as well as determining the costs of pursuing alternative strategies in terms of experienced mortality rates. We show that, on average, killers gain a very significant fitness advantage despite the often high costs they pay and, more importantly, that they had a dramatic effect on the fitness of their male kin. We suggest that such behaviour represents a phenotypic, rather than genetic, response to opportunities provided by local circumstances.

Alloparental care—care provided to children who are not one's offspring—is ubiquitous across human populations. Empirical research reveals socioecological variation in who cares for children, but less attention has been paid to the type of care provided. To better understand the fitness outcomes of different forms of alloparental care, or allocare, we categorize such care into two broad forms based on economic cost structures: additive cost and declining marginal cost allocare. Additive cost allocare requires alloparents to pay equal costs for each child to whom care is provided, while declining marginal cost allocare entails reduced costs for additional children beyond the first. Given this general typology, we investigate how fitness is impacted by the type of allocare provided in socioecological conditions of scarcity or abundance. Results of an agent-based model indicate that allocare has fitness benefits in nearly all circumstances, but the impact of cost structures depends on resource availability. In contexts of abundance, the cost structure of allocare does not matter as individuals' reproductive success is instead constrained by fertility and mortality more than the availability of resources or time. In conditions of scarcity, however, the greatest increases in reproductive success are achieved when allocare has a declining marginal cost structure. This is due to an economy of scale permitting alloparents to scale up their care at discounted rates. Consequently, we expect allocare practices to exhibit these patterns cross-culturally: in contexts of scarcity allocare is anticipated to be focused on practices with declining marginal cost structures and to be much less variable than in contexts of abundance. We discuss several ethnographic examples that are consistent with the overall findings of our simulations, and we conclude with recommendations for future modeling and empirical work on allocare.

Parental influence over mate choice and marriage is a norm across many cultures and throughout human history; however, more attention has been given to preferences of the mating individuals than to the preferences of parents selecting a son- or daughter-in-law. Using data collected in Nepal, a culture with a tradition of arranged marriages, we compare the preferences of unmarried adults and parents of unmarried adults using a budget allocation task in which respondents allocated two budgets (high and low) to design their ideal spouse or in-law from a set of 14 traits. To compare overall similarities and differences in allocations across all 14 traits, we calculated the Mahalanobis Distance for each dyad type (father-son, father-daughter, mother-son, and mother-daughter) for high and low budgets separately. Parents and offspring disagreed more in high budget allocations than in low budget allocations, indicating that they may agree more on the minimally necessary traits in a spouse/in-law. Parents and offspring showed the largest divergence in allocations over same caste/ethnicity (preferred more by parents) and physical attractiveness (preferred more by offspring), in line with previous comparisons of parent and offspring preferences. Differences in the preferences of parents and offspring were at least as large as differences in preferences between men and women in this sample, indicating that parent-offspring disagreement is substantial and should be given more consideration in the literature on mate choice. Additional research is needed to investigate how parents and offspring negotiate their preferences in arranged marriage contexts.

As most organisms, humans and other apes compete for access to fitness-determining resources and competition is expected to increase with the competitor-to-resource ratio. We use 23 years of behavioural data on five wild groups from the two gorilla species which live in different socioecological environments, to test if female gorillas compete simultaneously for food, mates and/or protectors. Females were more aggressive to each other in medium-sized groups (∩ − shaped relationship) and when the groups contained more females but fewer males (lower sex ratio). Contrarily, female-female aggression was not influenced by the operational sex ratio and female mating activity. Hence, our results support the competition for food and protectors hypotheses but cast doubt on the competition for mates hypothesis. Yet, despite female western gorillas (Gorilla gorilla gorilla) experiencing higher monopolization potential of food and a lower abundance of food and males, they did not exhibit higher aggression rates than female mountain gorillas (Gorilla beringei beringei). Altogether, these results suggest that female competition for males outside the mating context is not unique to humans and might have common evolutionary origins in humans and other apes.

People vent, as when airing grievances about one mutual friend to another. Contrary to a Freudian account, such social venting does not alleviate anger. So, what function might it serve? That people bestow more and more likely support on relatively better-liked friends—support which is associated with greater health, happiness, and economic mobility—highlights a largely overlooked challenge in social groups: competing within the group for certain group members' affections and support. Social venting might be one effective tool for meeting this challenge. We test this—and also compare venting's efficacy with other forms of communication, including a well-studied tactic of partner competition (competitor derogation). In six experiments with U.S. CloudResearch participants (N = 1723), venting causes listeners (people vented to) to prefer venters over targets (people vented about) and to preferentially benefit better-liked venters over targets in a modified Dictator Game. By obscuring the venters' intent to aggress against the target, venting might communicate target-harming information in a way that buffers venters from being perceived unfavorably. Effective venting might thus manipulate listeners' attitudes and behavior in venters' favor.

Witchcraft beliefs are historically and geographically widespread, but little is known about the cultural inheritance processes that may explain their variation between populations. A core component of witchcraft belief is that certain people (‘witches’) are thought to harm others using supernatural means. Various traits, which we refer to as the ‘witchcraft phenotype’ accompany these beliefs. Some can be classified as ‘symbolic culture’, including ideas about the typical behaviour of witches and concepts such as familiars (witches' magical helpers), and demographic traits such as the age and sex of those likely to be accused. We conducted an exploratory study of the cultural evolution of 31 witchcraft traits to examine their inferred ancestry and associations with historic population movements. We coded a dataset from ethnographic accounts of Bantu and Bantoid-speaking societies in sub-Saharan Africa (N = 84) and analysed it using phylogenetic comparative methods (PCMs). Our results estimate that while some traits, such as an ordeal to test for witchcraft, have deep history, others, such as accusations of children, may have evolved more recently, or are limited to specific clusters of societies. Demographic and symbolic cultural traits do not typically co-evolve. Our findings suggest traits have different transmission patterns, and these may result from benefits they provide or from universal psychological mechanisms that produce their recurrent evolution.