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  • [2017-04-10]
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Humans are animals that specialize in thinking and knowing, and our extraordinary cognitive abilities have transformed every aspect of our lives. In contrast to our chimpanzee cousins and Stone Age ancestors, we are complex political, economic, scientific and artistic creatures, living in a vast range of habitats, many of which are our own creation. Research on the evolution of human cognition asks what types of thinking make us such peculiar animals, and how they have been generated by evolutionary processes. New research in this field looks deeper into the evolutionary history of human cognition, and adopts a more multi-disciplinary approach than earlier Evolutionary Psychology. It is informed by comparisons between humans and a range of primate and non-primate species, and integrates findings from anthropology, archaeology, economics, evolutionary biology, neuroscience, philosophy and psychology. Using these methods, recent research reveals profound commonalities, as well striking differences, between human and non-human minds, and suggests that the evolution of human cognition has been much more gradual and incremental than previously assumed. It accords crucial roles to cultural evolution, techno-social co-evolution and geneculture co-evolution. These have produced domain-general developmental processes with extraordinary powerpower that makes human cognition, and human lives, unique.
2012:08:20


Human cognitive abilities are extraordinary. Our large brains are significantly modified from those of our closest relatives, suggesting a history of intense natural selection. The conditions favoring the evolution of human cognitive adaptations, however, remain an enigma. Hypotheses based on traditional ecological demands, such as hunting or climatic variability, have not provided satisfying explanations. Recent models based on social problem solving linked with ecological conditions offer more convincing scenarios. But it has proven difficult to identify a set of selective pressures that would have been sufficiently unique to the hominin lineage. What was so special about the evolutionary environments of our ancestors that caused them, and them alone, to diverge in such astonishing ways from their close relatives and all other life forms?
2011:11:23


Although Darwin insisted that human intelligence could be fully explained by the theory of evolution, the codiscoverer of natural selection, Alfred Russel Wallace, claimed that abstract intelligence was of no use to ancestral humans and could only be explained by intelligent design.Wallaces apparent paradox can be dissolvedwith two hypotheses about human cognition.One is that intelligence is an adaptation to a knowledge-using, socially interdependent lifestyle, the cognitive niche. This embraces the ability to overcome the evolutionary fixed defenses of plants and animals by applications of reasoning, including weapons, traps, coordinated driving of game, and detoxification of plants. Such reasoning exploits intuitive theories about different aspects of the world, such as objects, forces, paths, places, states, substances, and other peoples beliefs and desires. The theory explains many zoologically unusual traits in Homo sapiens, including our complex toolkit, wide range of habitats and diets, extended childhoods and long lives, hypersociality, complex mating, division into cultures, and language (which multiplies the benefit of knowledge because know-how is useful not only for its practical benefits but as a trade good with others, enhancing the evolution of cooperation). The second hypothesis is that humans possess an ability of metaphorical abstraction, which allows them to coopt faculties that originally evolved for physical problem-solving and social coordination, apply them to abstract subject matter, and combine them productively. These abilities can help explain the emergence of abstract cognition without supernatural or exotic evolutionary forces and are in principle testable by analyses of statistical signs of selection in the human genome.
2010:07:06


In The Descent of Man, and Selection in Relation to Sex, published in 1871, Charles Darwin wrote: I fully . . . subscribe to the judgment of those writers who maintain that of all the differences between man and the lower animals the moral sense or conscience is by far the most important. I raise the question of whether morality is biologically or culturally determined. The question of whether the moral sense is biologically determined may refer either to the capacity for ethics (i.e., the proclivity to judge human actions as either right or wrong), or to the moral norms accepted by human beings for guiding their actions. I propose that the capacity for ethics is a necessary attribute of human nature, whereas moral codes are products of cultural evolution. Humans have a moral sense because their biological makeup determines the presence of three necessary conditions for ethical behavior: (i) the ability to anticipate the consequences of ones own actions; (ii) the ability to make value judgments; and (iii) the ability to choose between alternative courses of action. Ethical behavior came about in evolution not because it is adaptive in itself but as a necessary consequence of mans eminent intellectual abilities, which are an attribute directly promoted by natural selection. That is, morality evolved as an exaptation, not as an adaptation. Moral codes, however, are outcomes of cultural evolution, which accounts for the diversity of cultural norms among populations and for their evolution through time.
2010:07:06


This article identifies some of the most common concerns and attempts to elucidate evolutionary psychologys stance pertaining to them. These include issues of testability and falsifiability; the domain specificity versus domain generality of psychological mechanisms; the role of novel environments as they interact with evolved psychological circuits; the role of genes in the conceptual structure of evolutionary psychology; the roles of learning, socialization, and culture in evolutionary psychology; and the practical value of applied evolutionary psychology. The article concludes with a discussion of the limitations of current evolutionary psychology.
2010:02:16


With the decline of postmodernism (Lopez and Potter 2001:3-4) it has become evident to many social scientists that the varieties of neo-realist philosophy of science offered by Harr and Bhaskar in the 1970s provided the new promise of the possibility of naturalism in the social sciences. The science and humanist debate has thus been quietly reopened. In its traditional format the debate meant that the materialistic determinism of science threatened the humanist belief in freedom. But now there can be a shift away from renouncing science in order to affirm the latter (often disembodied). In its place we have a conception of science along realist lines that better serves the humanist affirmation of freedom.
2010:01:26


Although evolutionary psychology has been successful in explaining some species-typical and sexdifferentiated adaptations, a large question that has largely eluded the field is this: How can the field successfully explain personality and individual differences? This article highlights some promising theoretical directions for tackling this question. These include life-history theory, costly signaling theory, environmental variability in fitness optima, frequency-dependent selection, mutation load, and flexibly contingent shifts in strategy according to environmental conditions. Tackling the explanatory question also requires progress on three fronts: (a) reframing some personality traits as forms of strategic individual differences; (b) providing a nonarbitrary, evolutionary-based formulation of environments as distributions and salience profiles of adaptive problems; and (c) identifying which strategies thrive and which falter in these differing problem- defined environments.
2009:07:31


Modern humans have inherited the mating strategies that led to the success of their ancestors. These strategies include long-term mating, short-term mating, extra-pair mating, mate poaching, and mate guarding. This article presents empirical evidence supporting evolution-based hypotheses about the complexities of these mating strategies.
2008:07:24


In nonhuman animals, mate-choice copying has received much attention, with studies demonstrating that females tend to copy the choices of other females for specific males. Here we show, for both men and women, that pairing with an attractive partner increases the attractiveness of opposite-sex faces for long-term relationship decisions but not short-term decisions. Our study therefore shows social transmission of face preference in humans, which may have important consequences for the evolution of human traits. Our study also highlights the flexibility of human mate choice and suggests that, for humans, learning about nonphysical traits that are important to pair-bonding drives copying-like behavior.
2008:03:07


Because male height is associated with attractiveness, dominance, and reproductive success, taller men may be less jealous. And because female height has a curvilinear relationship with health and reproductive success (with average-height females having the advantages), female height may have a curvilinear relationship with jealousy. In Study 1, male height was found to be negatively correlated with self-reported global jealousy, whereas female height was curvilinearly related to jealousy, with average-height women reporting the lowest levels of jealousy. In Study 2, male height was found to be negatively correlated with jealousy in response to socially influential, physically dominant, and physically attractive rivals. Female height was negatively correlated with jealousy in response to physically attractive, physically dominant, and high-social-status rivals; in addition, quadratic effects revealed that approximately average-height women tend to be less jealous of physically attractive rivals but more jealous of rivals with masculine characteristics of physical dominance and social status
2008:03:07


Across human societies, people form long-term romantic bonds that can last a lifetime. Many theorists have proposed that the emotion love plays a causal role in maintaining these bonds, but no work to date has tested this hypothesis directly. In this study, we predicted that feeling love for a romantic partner would facilitate suppressing thoughts of attractive alternative mates. We used a relived emotion task to induce love or sexual desire for a romantic partner and asked participants to suppress thoughts of an attractive alternative. After suppression, participants in the love condition reported fewer thoughts of the attractive alternative and accurately recalled fewer attractiveness-related details about the alternative than those in the desire condition. Reports of love, but not sexual desire, predicted greater commitment to the current partner during the study. These results suggest that love serves a function distinct from desire and that love can operate as a commitment device.
2008:03:07


Relative social status strongly regulates human behavior, yet this factor has been largely ignored in research on risky decision making. Humans, like other animals, incur risks as they compete to defend or improve their standing in a social group. Among men, access to culturally important resources is a locus of intrasexual competition and a determinant of status. Thus, relative status should affect men's motivations for risk in relevant domains. Contrasting predictions about such effects were derived from dominance theory and risk-sensitive foraging theory. Experiments varied whether subjects thought they were being observed and evaluated by others of lower, equal or higher status, and whether decisions involved resources (status relevant) or medical treatments (status irrelevant). Across two experiments, men who thought others of equal status were viewing and evaluating their decisions were more likely to favor a high-risk/high-gain means of recouping a monetary loss over a no-risk/low-gain means with equal expected value. Supporting predictions from dominance theory, this motivation for risk taking appeared only in the equal status condition, only for men, and only for resource loss problems. Taken together, the results support the idea that motivational systems designed to negotiate a status-saturated social world regulate the cognitive processes that generate risky decision making in men.
2008:03:07


A distinctive feature of humans compared to other species is the high rate of cooperation with nonkin. One explanation is that humans are motivated by concerns for praise and blame. In this paper we experimentally investigate the impact of anticipated verbal feedback on altruistic behavior. We study pairwise interactions in which one subject, the divider, decides how to split a sum of money between herself and a recipient. Thereafter, the recipient can send an unrestricted anonymous message to the divider. The subjects' relationship is anonymous and one-shot to rule out any repeated interaction effects. Compared to a control treatment without feedback messages, donations increase substantially when recipients can communicate. With verbal feedback, the fraction of zero donations decreases from about 40% to about 20%, and there is a corresponding increase in the fraction of equal splits from about 30% to about 50%. Recipients who receive no money almost always express disapproval of the divider, sometimes strongly and in foul language. Following an equal split, almost all recipients praise the divider. The results suggest that anticipated verbal rewards and punishments play a role in promoting altruistic behavior among humans.
2008:03:07


Three studies tested the hypothesis derived from evolutionary psychological considerations of sex differences in the intentional object of romantic jealousy. In Studies 1 and 3, participants had to indicate in a forced choice whether their jealousy would be primarily directed towards the partner or the rival. In Study 2, participants rated separately the extent to which their jealousy would be primarily aimed at the partner and the rival. In Studies 1 and 2, the participants' answers referred to either a mate's actual emotional or sexual infidelity; in Study 3 they referred to suspected infidelity. As predicted, in each study, significantly more women than men reported that their jealousy would be primarily directed at the rival. Also, as predicted, these sex differences were especially pronounced when confronted with the adaptively primary infidelity type (i. e., male emotional and female sexual infidelity, respectively). Finally, Study 3 additionally showed that these sex differences are moderated by the participants' current relationship status and their own unfaithfulness. Limitations and implications of the findings are discussed.
2008:03:07


It has been shown that height is one of the morphological traits that influence a person's attractiveness. To date, few studies have addressed the relationship between different components of height and physical attractiveness. Here, we study how leg length influences attractiveness in men and women. Stimuli consisted of seven different pictures of a man and seven pictures of a woman in which the ratio between leg length and height was varied from the average phenotype by elongating and shortening the legs. One hundred men and 118 women were asked to assess the attractiveness of the silhouettes using a seven-point scale. We found that male and female pictures with shorter than average legs were perceived as less attractive by both sexes. Although longer legs appeared to be more attractive, this was true only for the slight (5%) leg length increase; excessively long legs decreased body attractiveness for both sexes. Because leg length conveys biological quality, we hypothesize that such preferences reflect the workings of evolved mate-selection mechanisms. Short and/or excessively long legs might indicate maladaptive biological conditions such as genetic diseases, health problems, or weak immune responses to adverse environmental factors acting during childhood and adolescence.
2008:03:07


Since natural selection produces genetically homogeneous populations with regard to adaptively important traits, the relatively high genetic variance associated with human personality is an enigma. In this article, we propose that humans adaptively control the activation of domain-specific mental mechanisms in accordance with personality. This process functions to reduce fitness differences among individuals with different genetic backgrounds associated with personality. Such control would facilitate the evolution of heritable personality traits. We conducted a twin study, showing that the level of general trust (trust of strangers) is controlled not only by environmental factors but also by personality factors, thus producing reactive heritability of general trust. This result supports our hypothesis.
2008:03:07


Social norms are a widely used concept for explaining human behavior, but there are few studies exploring how we cognitively utilize them. We incorporate here an evolutionary approach to studying social norms, predicting that if norms have been critical to biological fitness, then individuals should have adaptive mechanisms to conform to, and avoid violating, norms. A cognitive bias toward norms is one specific means by which individuals could achieve this. To test this, we assessed whether individuals have greater recall for normative information than for nonnormative information. Three experiments were performed in which participants read a text and were then tested on their recall of behavioral content. The data suggest that individuals have superior recall for normative social information and that performance is not related to rated importance. We discuss how such a cognitive bias may ontogenetically develop and identify possible hypotheses that distinguish between alternative explanatory accounts for social norms.
2008:03:07


Strategic pluralism suggests that women engage in short-term sexual relationships when the benefits to doing so outweigh the costs. We investigated attraction to indicators of good genes (namely, masculinity as demonstrated by point-light walkers) in women varying in menstrual cycle status and sociosexual orientation. When women are fertile, they have the ability to gain genetic benefits from a male partner and should also be attracted to high levels of masculinity in men as a signal of genetic benefits. Sociosexual orientation is an individual difference that indicates openness to short-term mating and, thus, should influence aspects of mating strategy. Women with an unrestricted sociosexual orientation, as compared to women with a restricted sociosexual orientation, are more likely to engage in short-term relationships and obtain fewer nongenetic resources from their mates. Thus, they should place heavy emphasis on male masculinity as a sign of genetic benefits available from their mates. In this study, women indicated the walker most attractive to them on a constructed continuum of male and female point-light walkers. In Study 1, fertile women, as compared to nonfertile women, showed a greater attraction to masculinity. In Study 2, women demonstrated a strong positive relationship between sociosexuality and attraction to masculinity.
2008:01:06


Conformity is a type of social learning that has received considerable attention among social psychologists and human evolutionary ecologists, but existing empirical research does not identify conformity cleanly. Conformity is more than just a tendency to follow the majority; it involves an exaggerated tendency to follow the majority. The exaggerated part of this definition ensures that conformists do not show just any bias toward the majority, but a bias sufficiently strong to increase the size of the majority through time. This definition of conformity is compelling because it is the only form of frequency-dependent social influence that produces behaviorally homogeneous social groups. We conducted an experiment to see if players were conformists by separating individual and social learners. Players chose between two technologies repeatedly. Payoffs were random, but one technology had a higher expected payoff. Individual learners knew their realized payoffs after each choice, while social learners only knew the distribution of choices among individual learners. A subset of social learners behaved according to a classic model of conformity. The remaining social learners did not respond to frequency information. They were neither conformists nor nonconformists, but mavericks. Given this heterogeneity in learning strategies, a tendency to conform increased earnings dramatically.
2008:01:06


Relatedness is a cornerstone of the evolution of social behavior. In the human lineage, the existence of cooperative kin networks was likely a critical stepping stone in the evolution of modern social complexity. Here we report the results of the first experimental manipulation of a putative cue of human kinship (facial self-resemblance) among ostensible players in a variant of the tragedy of the commons, the one-shot public goods game, in which group-level cooperationvia contributions made to the public good and the punishment of free ridersis supported at a personal cost. In accordance with theoretical predictions, contributions increased as a function of the kin density of the group. Moreover, the distribution of punishment was not contingent on kin density level. Our findings indicate that the presence of a subtle cue of genealogical relatedness facilitates group cooperation, supporting the hypothesis that the mechanisms fostering contemporary sociality took root in extended family networks.
2008:01:06


Cooperation between individuals is an important requisite for the maintenance of social relationships. The purpose of this study was to investigate cooperation in children in the school environment, where individuals could cooperate or not with their classmates in a public goods game. We investigated which of the following variables influenced cooperation in children: sex, group size, and information on the number of sessions. Group size was the only factor to significantly affect cooperation, with small-group children cooperating significantly more than those in large groups. Both sex and information had no effect on cooperation. We suggest that these results reflect the fact that, in small groups, individuals were more efficient in controlling and retaliating theirs peers than in large groups.
2008:01:06


Mealey, Daood, and Krage (1996) reported that faces associated with an episode of cheating were better recognized than faces associated with irrelevant behavior, which, in turn, were recognized better than faces associated with an episode of trustworthiness. This pattern of findings was interpreted in favor of the social contract theory, which postulates that humans are equipped with brain mechanisms specialized in detecting cheaters in social interactions. We explicate a number of problems with the original findings and in this article report a series of three experiments designed to replicate the original findings under conditions that take those problems into account. Consistent across all experiments, oldnew recognition for faces associated with a history of cheating was not better than recognition for faces associated with a history of trustworthiness. The present findings cast doubt as to the validity and interpretation of the findings reported by Mealey et al.
2008:01:06


Upper-body fat has negative effects and lower-body fat has positive effects on the supply of long-chain polyunsaturated fatty acids that are essential for neurodevelopment. Thus, waist-hip ratio (WHR), a useful proxy for the ratio of upper-body fat to lower-body fat, should predict cognitive ability in women and their offspring. Moreover, because teenage mothers and their children compete for these resources, their cognitive development should be compromised, but less so for mothers with lower WHRs. These predictions are supported by data from the Third National Health and Nutrition Examination Survey. Controlling for other correlates of cognitive ability, women with lower WHRs and their children have significantly higher cognitive test scores, and teenage mothers with lower WHRs and their children are protected from cognitive decrements associated with teen births. These findings support the idea that WHR reflects the availability of neurodevelopmental resources and thus offer a new explanation for men's preference for low WHR.
2008:01:06


Mate preferences are condition dependent (i.e., females in better biological condition might be more demanding with respect to fitness-relevant male traits). Such traits usually indicate male biological quality or ability to secure resources that could be invested in offspring. Here we study female preferences for male resources, commitment, attractiveness, good sense of humor, and sensuality (when seeking both long-term and short-term partners) in relation to women's morphological traits such as height, weight, waist and hip girth, body mass index (BMI), and waist-to-hip ratio (WHR). We show that preferences for resources and attractiveness do indeed depend on women's phenotype. Women with relatively lower WHR and BMI more strongly prefer resources in a potential long-term partner than those with higher WHR and BMI. However, when controlling for age, place of residence, and whether they have had children, it is WHR (but not BMI) that influences female preference for resources and attractiveness. Women with higher WHR (those who, according to many studies, are considered as less attractive) are more prone to prefer physical attractiveness in a potential long-term partner. Furthermore, despite commitment having received the highest score in a long-term context, the preference for this trait in a potential partner was not related to women's body morphology. We suggest evolutionary and proximate explanations for such condition-dependent preferences.
2008:01:06


Children pose a problem. The extended period of childhood dependency and short interbirth intervals mean that human mothers have to care for several dependent children simultaneously. Most evolutionary anthropologists now agree that this is too much of an energetic burden for mothers to manage alone and that they must enlist help from other relatives to share the costs of raising children. Which kin help is the subject of much debate. Here, we review the evidence for whether the presence of kin affects child survival rates, in order to infer whether mothers do receive help in raising offspring and who provides this help. These 45 studies come from a variety of (mostly) natural fertility populations, both historical and contemporary, across a wide geographical range. We find that in almost all studies, at least one relative (apart from the mother) does improve the survival rates of children but that relatives differ in whether they are consistently beneficial to children or not. Maternal grandmothers tend to improve child survival rates as do potential sibling helpers at the nest (though the latter observation is based on rather few studies). Paternal grandmothers show somewhat more variation in their effects on child survival. Fathers have surprisingly little effect on child survival, with only a third of studies showing any beneficial effects. Overall, this review suggests that whilst help from kin may be a universal feature of human child-rearing, who helps is dependent on ecological conditions.
2008:01:06


Findings from previous studies suggest that only men who are in good physical condition can afford to pursue high-risk activities and that men who engage in high-risk activities are considered particularly attractive by women. Here, we show that men's interest in high-sensation activities, a personality trait that is known to increase the likelihood of those individuals engaging in high-risk behaviors, is positively related to the strength of their preferences for femininity in women's faces (Studies 13) but is not related to the strength of their preferences for femininity in men's faces (Study 2). We discuss these findings as evidence for potentially adaptive condition-dependent mate preferences, whereby men who exhibit signals of high quality demonstrate particularly strong preferences for facial cues of reproductive and medical health in potential mates because they are more likely than lower-quality men to succeed in acquiring such partners.
2007:12:16


The logic of inclusive fitness suggests that people should be attentive to the mating relationships of their kinespecially their genetically closest kin. This logic further suggests that people will be especially attentive to close kin members' relationships when a greater indirect fitness benefit is at stake. Three studies tested implications of this analysis. The primary results were that (a) people maintain greater vigilance over (and attempt greater influence on) the romantic relationships of genetically closer kin; (b) this effect is largely mediated by feelings of emotional closeness and perceptions of physical similarity; (c) women are more vigilant than men over their kin members' relationships; (d) people are more vigilant over the relationships of female kin, as compared to male kin, but only under conditions with especially clear implications for indirect fitness; and (e) people are more vigilant over kin members' long-term committed relationships, as compared to their casual relationships. These results indicate that a subtle form of nepotism is manifest in people's concern with their kin members' romantic relationships.
2007:12:16


Handgrip strength (HGS) is a noninvasive measure of physical health that is negatively correlated with disability, morbidity, and mortality rates in adults. Highly heritable, HGS is indicative of blood testosterone levels and levels of fat-free body mass. In this study, we investigated whether HGS was related to measures of body morphology [shoulder-to-hip ratio (SHR), waist-to-hip ratio, and second-digit-to-fourth-digit ratio (2D:4D)], aggressive behavior, and sexual history in 82 male and 61 female college students. Results showed that HGS was correlated with SHRs, aggressive behavior, age at first sexual intercourse, and promiscuity in males but not in females. HGS appears to be an honest signal for genetic quality in males.
2007:12:16


One of the proposed functions of human smiling is to advertise cooperative dispositions and thereby increase the likelihood that a social partner would invest resources in a relationship. In particular, smiles involving an emotional component would be honest signals of altruistic dispositions because they are not easy to produce voluntarily. In this study, 60 people were covertly filmed while interacting with a friend in two conditions: control and sharing. Smiles were classified into Duchenne (spontaneous) and non-Duchenne smiles. Participants also completed a series of questionnaires, including the Altruism Scale and a self-report questionnaire of emotional state. Interestingly, Duchenne smiles were displayed at higher rates in the sharing situation as opposed to the control situation, whereas non-Duchenne smiles were unaffected by the type of interaction. Furthermore, Duchenne smiles in the sharing interaction were positively affected by a measure of altruism. Self-reported emotional states did not vary between conditions and were poorly related to smiling. This study shows that the Duchenne smile is relevant to situations that involve the sharing of material resources because it would reliably advertise altruistic intentions. The Duchenne smile could therefore be an important signal in the formation and maintenance of cooperative relationships.
2007:12:16


Humans possess pathogen-avoidance mechanisms that respond to the visual perception of morphological anomalies in others. We investigated whether obesity may trigger these mechanisms. Study 1 revealed that people who are chronically concerned about pathogen transmission have more negative attitudes toward obese people; this effect was especially pronounced following visual exposure to obese individuals. Study 2 revealed that obesity is implicitly associated with disease-connoting concepts; this effect was especially pronounced when the threat of pathogen transmission is highly salient. Evolved pathogen-detection mechanisms are hypersensitive, and they appear to play a role in the stigmatization of obese people.
2007:12:16


Much of the evolutionary literature on human mating is based on the assumption of extensive female choice during the history of our species. However, ethnographic evidence from foraging societies reveals that, in societies thought to be akin to those of our ancestors, female choice is constrained by the control that parents exercise over their daughters. Data from 190 hunting and gathering societies indicate that almost all reproduction takes place while the woman is married and that the institution of marriage is regulated by parents and close kin. Parents are able to influence the mating decisions of both sons and daughters, but stronger control is exercised with regard to daughters; male parents have more say in selecting in-laws than their female counterparts. In light of the fact that parental control is the typical pattern of mate choice among extant foragers, it is likely that this pattern was also prevalent throughout human evolution. Because daughters' preferences can be expected not to fully coincide with those of their parents, research to date may thus have simultaneously overestimated the contribution of female preferences to processes of sexual selection and underestimated the contribution of parental preferences to such processes.
2007:12:16


Individuals diagnosed with morbid jealousy have hypersensitive jealousy mechanisms that cause them to have irrational thoughts about their partner's fidelity and to exhibit extreme behaviors. Using a newly constructed database of 398 cases of morbid jealousy reported in the literature from 1940 to 2002, we tested four evolutionarily informed hypotheses about normally functioning jealousy mechanisms and applied them to this novel population of individuals diagnosed with morbid jealousy. We hypothesized that a greater percentage of men than women diagnosed with morbid jealousy would be focused on a partner's sexual infidelity and on indicators of a rival's status and resources and that a greater percentage of women than men diagnosed with morbid jealousy would be focused on a partner's emotional infidelity and on indicators of a rival's youth and physical attractiveness. All four hypotheses were supported. The results suggest continuity between normal jealousy and morbid jealousy and highlight the heuristic value of using archival databases to test evolutionarily informed hypotheses.
2007:12:16


Recent theoretical perspectives concerning the structure of variation in human mating have focused less on conceptualizations of alternate mating strategies and more on the evolution of a conditional strategy. Empirical evidence suggests that this conditional strategy may involve the simultaneous pursuit of long-term and short-term mating tactics. Despite these developments, empirical measurement has proceeded using the Sociosexual Orientation Inventory (SOI), which measures restricted and unrestricted mating orientations along a single bipolar continuum. To fully capture the pluralistic nature of human mating, we suggest that a multidimensional empirical measure is required. To test our hypothesis, we subjected an expanded version of the SOI, which included items measuring psychological orientation toward short-term mating and long-term mating, to principal components analysis. A three-factor structure representing short-term mating orientation, long-term mating orientation, and previous sexual behavior emerged. In subsequent analyses, we demonstrate that our newly developed long-term and short-term dimensions (a) are largely independent and (b) correlate differentially with other theoretically relevant variables.
2007:12:16


To see whether estrus was really lost during human evolution (as researchers often claim), we examined ovulatory cycle effects on tip earnings by professional lap dancers working in gentlemen's clubs. Eighteen dancers recorded their menstrual periods, work shifts, and tip earnings for 60 days on a study web site. A mixed-model analysis of 296 work shifts (representing about 5300 lap dances) showed an interaction between cycle phase and hormonal contraception use. Normally cycling participants earned about US$335 per 5-h shift during estrus, US$260 per shift during the luteal phase, and US$185 per shift during menstruation. By contrast, participants using contraceptive pills showed no estrous earnings peak. These results constitute the first direct economic evidence for the existence and importance of estrus in contemporary human females, in a real-world work setting. These results have clear implications for human evolution, sexuality, and economics.
2007:12:16


Examining the association between socioeconomic status and reproductive output in modern societies has led to conflicting results. In this study, we used a representative sample of contemporary Swedish men and women to analyze possible reasons for the contradictory results. We found that the relationship between socioeconomic statusdescribed here by income and highest educational level attainedand reproductive output is dependent on sex and the inclusion or exclusion of childless individuals. In men, there is a strong positive association between income/education and average offspring count if childless individuals are included in the analysis; this association is absent when such individuals are excluded. We attribute this reversal mainly to the higher proportion of childless individuals among men of lower socioeconomic background. Among other factors, female choice appears to be a major cause of this association because the proportion of men who never married increased with decreasing income category and educational level. In women, however, including and excluding childless individuals both yielded a negative association between income and average offspring count as well as a null or negative relationship between education and average offspring count.
2007:12:16


Although unrelated friends are genetically equivalent to strangers, several lines of reasoning suggest that close friendship may sometimes activate processes more relevant to kinship and that this may be especially true for women. We compared responses to strangers, friends, and kin in two studies designed to address distinct domains for which kinship is known to have functional significance: incest avoidance and nepotism. Study 1 examined emotional responses to imagined sexual contact with kin, friends, and strangers. Results revealed that women, compared to men, treated friends more like kin. Study 2 examined benevolent attributions to actual kin, friends, and strangers. Results revealed that women treated friends very much like kin, whereas men treated friends very much like strangers. The current findings support a domain-specific over a domain-general approach to understanding intimate relationships and raise a number of interesting questions about the modular structure of cognitive and affective processes involved in these relationships.
2007:12:16


The effects of cultural framing on behavior in experimental games were explored with a trust game and the Maasai concept of osotua. Maasai use the term osotua to refer to gift-giving relationships based on obligation, need, respect, and restraint. In the trust game, the first player is given money and an opportunity to give any portion of it to the second player. The amount given is then multiplied by the experimenter, and the second player has an opportunity to give any amount back to the first player. Fifty trust games were played by Maasai men at a field site in north central Kenya. Half of the games were played without deliberate framing, and half were framed with the statement, This is an osotua game. Compared to games with no deliberate framing, those played within the osotua rhetorical frame were associated with lower transfers by both players and with lower expected returns on the part of the first players. Osotua rhetorical framing is also associated with a negative correlation between amounts given by the first player and amounts returned by the second. These results have implications both for the experimental game method and for our understanding of the relationship between culture and behavior.
2007:12:16


The relationship between self-esteem and aggression has yielded mixed results and generated much recent debate in the social psychology literature. Based on an evolutionary-psychological theory of self-esteem, Kirkpatrick et al. [Kirkpatrick, L. A., Waugh, C. E., Valencia, A., Webster, G., 2002. The functional domain-specificity of self-esteem and the differential prediction of aggression. Journal of Personality and Social Psychology 825, 756767] showed that multiple, functionally distinct self-esteem mechanisms predict aggression differentially: e.g., self-perceived superiority is positively related, and social inclusion inversely related, to behavioral aggression. The present study extends this research by further differentiating two distinct forms of superiority, dominance and prestige [Henrich, J., Gil-White, F. J. 2001. The evolution of prestige: Freely conferred deference as a mechanism for enhancing the benefits of cultural transmission. Evolution and Human Behavior 22, 165196], in the prediction of aggression in men and women and testosterone levels (measured in saliva samples) in men. Dominance was positively related, but prestige was either unrelated or inversely related, to self-report aggression measures. Dominance was unrelated but prestige inversely related to testosterone levels in men, perhaps suggesting a method of testosterone inhibition in individuals attaining prestige-based superiority. In addition to contributing to the growing literature on the aggressionself-esteem link, the results provide validation for the prestigedominance distinction and support, but also suggest an important refinement to, a theory of self-esteem as a collection of functionally distinct adaptations.
2007:12:16


Men's vocal folds and vocal tracts are longer than those of women, resulting in lower fundamental frequency (F0) and closer spacing of formant frequencies (formant dispersion, Df) in men than in women. The evolutionary reasons for these sex differences are uncertain, but some evidence implicates male dominance competition. Previous manipulations of F0 and Df affected perceptions of dominance among men. However, because these acoustic dimensions were manipulated simultaneously, their relative contributions are unclear. In unscripted recordings of men speaking to a competitor, we manipulated F0 and Df independently and by similar perceptual amounts to examine effects on social and physical dominance ratings. Recordings lowered in either F0 or Df were perceived as being produced by more dominant men than were the respective raised recordings. Df had a greater effect than did F0, and both Df and F0 tended to affect physical dominance more than social dominance, although this difference was significant only for Df.
2007:12:16


Human cooperation in a large group of genetically unrelated people is an evolutionary puzzle. Despite its costly nature, cooperative behavior is commonly found in all human societiesa fact that has interested researchers from a wide range of disciplines, including biology, economics, and psychology, to name a few. Many behavioral experiments have demonstrated that cooperation within a group can be sustained when free riders are punished. We argue that punishment has both a direct effect and an indirect effect on promoting cooperation. The direct effect of punishment alters the consequences of cooperation and defection in such a way as to make a rational person prefer cooperation. The indirect effect of punishment promotes cooperation among conditional cooperators by providing the condition necessary for their cooperation (i.e., the expectation that other members will also cooperate). Here we present data from two one-shot n-person prisoner's dilemma games, demonstrating that the indirect effect of punishment complements the direct effect to increase cooperation in the game. Furthermore, we show that direct and indirect effects are robust across two forms of punishment technology: either when punishment is voluntarily provided by game players themselves or when it is exogenously provided by the experimenter.
2007:12:16


Ethnographers have documented the prevalence of extreme forms of female neglect and female infanticide in Tamilnadu, India, among two caste groups: Thevars (a warrior caste) and Gounders (a landowning caste). Using a cultural ecological perspective, three field studies were conducted with Thevar, Gounder, and Brahmin participants to examine caste-specific psychological antecedents to female infanticide. Studies 1 and 2 investigated son bias using resource allocation tasks. Using a culture-of-honor task, Study 3 examined the relationship between honor and son preference. In general, Gounders' son bias was related to a desire to have more sons for patrilineal transfer of ancestral land, whereas Thevars' son preference was related to honor concerns. Furthermore, the relevance of cultural ecological perspective to study female neglect is discussed.
2007:12:16


In a preliminary pilot study, 82 university students were administered an extensive battery of musical and phonological memory tasks; their scores were examined for an association with promoter repeats in the arginine vasopressin 1a receptor and serotonin transporter genes. We previously showed that these genes were associated with another music-related phenotype, creative dance. Highly significant Gene×Gene epistatic interactions were observed between promoter region polymorphisms and musical as well as phonological memory using family-based and population-based tests. Given the prominent role of vasopressin in social behavior, the preliminary association found in our study between musical memory and vasopressin could serve to support evolutionary accounts postulating a social adaptive role in music, such as motherinfant communication, sexual selection, group cohesion, and even early protolanguage.
2007:12:16


Evolutionary studies of human behavior have emphasized the importance of kin selection in explaining social institutions and fitness outcomes. Our relatives can nevertheless be competitors as well as sources of altruism. This is particularly likely when there is local competition over resources, where conflict can lead to strife among nondispersing relatives, reducing or even negating the effects of relatedness on promoting altruism. Here, I present demographic data on a land-limited human population, utilizing large within-population variation in land ownership to determine the interactions between local resource competition and the benefits of kin in enhancing child survival, a key component of fitness in this population. As predicted, wealth affects the extent of kin altruism, in that paternal relatives (specifically father's brothers) appear to buffer young children from mortality much more effectively in rich than in poor households. This interaction effect is interpreted as evidence that the extent of nepotism among humans depends critically on resource availability. Further unanticipated evidence that maternal kin play a role in buffering children from mortality in situations where paternal kin control few resources speaks to the important role that specific local circumstance plays in shaping kin contributions to child welfare.
2007:12:16


Red athletic uniforms may have a psychological effect on the behavior of the wearer and/or opponent in combat sport. The aim of this study was to investigate the distractor effect of red color during a computerized Stroop task. A group of medical students (27 men and 23 women) were asked to accurately name the red, blue or green color of a series of equiluminant color words that appeared on a dark computer screen. The participants were told that their performance would be ranked. Stroop interference (SI) was quantified as the prolongation in response times (RTs) when naming colorcolor word incongruent stimuli than when naming noncolor words. We found that men experienced more SI when naming the red color in relation to RTs when naming the other colors. Men also experienced shorter RT than women, but this effect was not specific to naming of the red color. When the luminosity of the colored stimuli was halved, the RT was prolonged to a similar extent in both men and women but the gender discrepancy in SI during red color naming was maintained. Furthermore, in men SI for red positively correlated with scores on the depression subscale of the SCL-90-R questionnaire. Our data suggest that seeing red distracts men through a psychological rather than perceptual mechanism. Such a mechanism would associate red with aggression or dominance and may have a long evolutionary history, as indicated by behavioral evidence from nonhuman primates and other species.
2007:12:16


Although theoretical considerations suggest that a considerable portion of human altruism is driven by concerns about reputation, few experimental studies have examined the psychological correlates of individual decisions in real-life situations. Here we demonstrate that more subjects were willing to give assistance to unfamiliar people in need if they could make their charity offers in the presence of their group mates than in a situation where the offers remained concealed from others. In return, those who were willing to participate in a particular charitable activity received significantly higher scores than others on scales measuring sympathy and trustworthiness. Finally, a multiple regression analysis revealed that while several personality and behavior traits (cooperative ability, Machiavellianism, sensitivity to norms, and sex) play a role in the development of prosocial behavior, the possibility of gaining reputation within the group remains a measurable determinant of charitable behavior.
2007:12:16


Evolution-inspired research assumes the existence of brain mechanisms that scan for information that might signal noncooperative behavior. In this study, we demonstrate an automatic attention bias for threatening social interactions involving untrustworthy partners. Using a dot probe classification task, we found that, compared to unknown cooperators, attention was oriented significantly more toward the faces of unknown players who decided not to cooperate during a Prisoner's Dilemma Game. The present results thus suggest that an automatic, preconscious focus of attention underlies our ability to identify noncooperative players in social exchange situations.
2007:12:16


In accordance with evolutionary models of social exchange, we suggest the possible existence of a limited predictive cheater detection module. This module enables humans, to a certain extent, to predict how willing another might be to cooperate or not. Using unknown target subjects who had played a one-shot prisoner's dilemma game earlier, we asked participants in two experiments to rate how cooperative these target subjects were. Pictures were taken of the target subjects at three different moments: a neutral-expression picture taken prior to the game, an event-related picture taken during the decision-making moment of a practice round, and an event-related picture taken during the decision-making moment of a proper round. We found that participants in the experiments could accurately discriminate noncooperative pictures from cooperative ones, but only in response to those taken during the proper round. In both neutral-expression pictures and practice-round pictures, identification rates did not exceed chance level. These findings leave room for the existence of a predictive cheater detection module that deduces someone's decision to cooperate from event-related facial expressions.
2007:12:16


This study investigated associations between men's facial attractiveness, perceived personality, attitudes towards children, and the quality of their child-directed (CD) speech. Sixty-three males were photographed and completed a brief questionnaire concerning their family background and attitudes towards children. They then performed a task in which they gave directions to (imaginary) adults and children. Analyses of the acoustic properties of speech produced under each condition were performed in order to determine the extent to which individual men changed their speech to accommodate a child listener (i.e., exhibited CD speech). The men's faces were rated by 59 female participants, who assessed perceived prosociality, masculinity, health, and short- and long-term attractiveness. Although women's ratings of attractiveness and prosociality were related to men's self-reported liking for children, they were negatively correlated to men's use of CD speech (i.e., less attractive men used more features of CD speech when addressing an imaginary child). These findings are discussed in the context of halo effects and strategic pluralism in male mating behaviors.
2007:12:16


This study investigated sexual imprinting in human females. Facial proportions of fathers were compared to the proportions of stimulus faces the participants found attractive. Women who rated their childhood relationships with their father highly showed a significantly stronger relationship between the proportions of their father's face and their chosen stimulus than other women, primarily concerning the central face area. Women who rated their fathers less highly did not show similarity between fathers' and stimulus' faces. This supports previous research using photographs of parents' and spouses' faces.
2007:12:16


The ultimatum game measures cooperative tendencies in humans under experimental conditions. One individual can split money between oneself and another, while the other has the option of accepting or rejecting the offer, with each player receiving the accepted split or nothing if the split is rejected. We studied the association of players' degree of symmetry [fluctuating asymmetry (FA)] with behavior in the ultimatum game. Symmetrical males were expected to be less cooperative and, thus, make lower offers (while being more likely to reject unfair offers). In a population of young adult Jamaicans, who are well-characterized for bodily symmetry, we found that symmetrical males made significantly lower offers than asymmetrical ones (p<.001), but found no effect on rejection rates (perhaps due to a very small sample size). No significant association of symmetry and game playing was found in women, but women with a higher body mass index made less generous offers (p<.05).
2007:12:16

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