Evolution and Human Behavior最新文献

Why do people categorize others by race? Building on recent work integrating affordance management with a life history perspective, we propose that one reason perceivers categorize others by race is because race is a cue to the environments/ecologies in which groups live. In the U.S., because Black and White individuals differentially live in environments that vary in ecological harshness/unpredictability, race may be used as a cue of a person's home ecology. In three experiments (undergraduate and online U.S. samples; N = 1260) with the memory confusion paradigm (“who-said-what”), when American perceivers are presented with information on both a person's race (i.e., Black/White) and the ecologies in which they live (i.e., harsh/hopeful), racial categorization decreases, and ecology categorization emerges (Studies 1–3). Hence, in the minds of perceivers, the ecologies that others come from “replaces” others' race. However, counter to expectations, instructing perceivers to form social impressions of others on traits linked to ecological harshness (i.e., “planfulness”) led to ecology categorization disappearing (Study 3). We discuss implications of our findings for race perception and for social perception at large.

Social bonds can be a way for individuals to gain access to crucial resources and services that cannot be taken by force and are therefore subject to leverage. Bonds between the sexes can provide access to services that are specific to the other sex. Females exert leverage over males in terms of mating access, males have leverage over females in terms of the service protection, and both sexes exert leverage over the other sex in terms of tolerance and agonistic support. While mating access can be coerced in some circumstances, most services cannot be forced. Here, we use theoretical considerations to explore when sources of leverage over the opposite sex lead to between-sex bonds. Focussing on primates living in multi-male multi-female groups, we predict that leverage over the other sex will be higher, when 1) the receiver benefits on average more than the provider, 2) receivers cannot share the resource, and 3) the resource is rare and valuable. If these conditions are fulfilled, and given the mutual nature of a social bond, we expect bonds to be found, 4) when long-term targeting of the same partner yields benefits. We argue that a female's main source of leverage is mating access, whereas males mainly exert leverage over females in terms of protection of females and offspring. The combination of female mate choice with male protection and care for young is expected to promote between-sex bonds; reduced female cohesion and/or secondary female dispersal are expected to further increase the strength of between-sex bonds. The investment in shared offspring results in interdependency between male and female strategies, but the different services provided by females and males indicate that affiliative exchanges associated with bonds between the sexes will be typically asymmetric and vary over time. Thus, bonds between the sexes are expected to form in a limited number of circumstances where both sexes have leverage over the other sex in terms of their respective sex-specific services. While a systematic test of this proposal is hampered by the dearth of data on species lacking social bonds between the sexes, the data currently available are consistent with our hypothesis.

People worldwide invest substantial resources in improving their physical attractiveness. We employed a qualitative approach to investigate the ‘what’, ‘how intensely’, and ‘why’ behind this phenomenon. We conducted semi-structured in-depth interviews with 96 members of four distinct societies, including the Cook Islands, Guatemala, Pakistan, and Poland. The thematic analysis, guided by the four Tinbergen's questions, provided valuable insight on the beauty-enhancing practices across the studied societies. Commonly shared practices included maintaining hygiene, using make-up, cosmetics, accessories, perfumes, exercising, and caring for clothing and hair. Additionally, interviewees from different countries placed particular importance on some distinctive characteristics, such as flowers in the Cook Islands, fashionable clothing in Guatemala, beards and golden jewelry in Pakistan, and body shape in Poland. Conforming with evolutionary theories, all interviewees unanimously agreed that women devote more time than men to the pursuit of beauty, albeit with variations across the four societies. Furthermore, aligning with basic principles of mate choice, the present research delineated fundamental motives driving appearance enhancement, that is, inter-sexual and intra-sexual competition. We also shed more light on other motives, seldomly investigated in the past, including, for instance, religious reasoning. By juxtaposing perspectives from culturally and geographically diverse societies, we offer a nuanced understanding of the multifaceted nature of self-enhancement practices.

Interest in dealbreakers has blossomed over the last decade, but we do not know how dealbreakers are used in mate choice. Here, we propose that some dealbreaker traits may act as disqualifiers, traits that we use to recognize others as potential mates. Alternatively, other dealbreaker traits may act like mate preferences and influence how attractive we find a potential mate relative to other potential mates. We use agent-based modeling and two samples of real-life couples, n = 1044, and n = 518, collected through Qualtrics' panel service, to test between these two possibilities. We find evidence that many of the traits colloquially considered to be dealbreakers, such as smoking status, height, and religion, are not used by the mind as disqualifiers, rather they act like preferences and are integrated into overall assessments of mate value. However, we find evidence that a person's sex is incorporated into mate choice like a disqualifier. Overall, considering and testing the evolved function of dealbreakers in the long-term mating process illuminates new directions for future research.

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.