Do descriptive social norms drive peer punishment? Conditional punishment strategies and their impact on cooperation

Peer punishment is widely considered a key mechanism supporting cooperation in human groups. Although much research shows that human behavior is shaped by the prevailing social norms, little is known about how punishment decisions are impacted by the social context. We present a set of large-scale incentivized experiments in which participants (999 American participants recruited via Amazon Mechanical Turk) could punish their partner conditional on either the level of cooperation or the level of punishment displayed by others who previously interacted in the same setting. While many participants punish independently of levels of cooperation or punishment, a substantial portion punishes free riding more severely when cooperation is more common (‘norm enforcement’), or when free riding is more severely punished by others (‘conformist punishment’). With a dynamic model we demonstrate that conditional punishment strategies can substantially promote cooperation. In particular, conformist punishment helps cooperation to gain a foothold in a population, and norm enforcement helps to maintain cooperation at high levels. Our results provide solid empirical evidence of conditional punishment strategies and illustrate their possible implications for the dynamics of human cooperation.     

Conditional expression of women's desires and men's mate guarding across the ovulatory cycle

Thirty-eight normally cycling women provided daily reports of sexual interests and feelings for 35 days. Near ovulation, both pair-bonded and single women reported feeling more physically attractive and having greater interest in attending social gatherings where they might meet men. Pair-bonded women who were near ovulation reported greater extra-pair flirtation and greater mate guarding by their primary partner. As predicted, however, these effects were exhibited primarily by women who perceived their partners to be low on hypothesized good genes indicators (low in sexual attractiveness relative to investment attractiveness). Ovulation-contingent increases in partner mate guarding were also moderated by female physical attractiveness; midcycle increases in mate guarding were experienced primarily by less attractive women, whereas more attractive women experienced relatively high levels of mate guarding throughout their cycle. These findings demonstrate ovulation-contingent shifts in desires and behaviors that are sensitive to varying fitness payoffs, and they provide support for the good genes hypothesis of human female extra-pair mating. The daily assessment method provides an important supplement to existing studies using scheduled laboratory visits as the purpose of the study (examining cycle-related variation) is not known by participants.     

Mate choice trade-offs and women’s preference for physically attractive men

Researchers studying human sexuality have repeatedly concluded that men place more emphasis on the physical attractiveness of potential mates than women do, particularly in long-term sexual relationships. Evolutionary theorists have suggested that this is the case because male mate value (the total value of the characteristics that an individual possesses in terms of the potential contribution to his or her mate’s reproductive success) is better predicted by social status and economic resources, whereas women’s mate value hinges on signals conveyed by their physical appearance. This pattern may imply that women trade off attractiveness for resources in mate choice. Here I test whether a trade-off between resources and attractiveness seems to be occurring in the mate choice decisions of women in the United States. In addition, the possibility that the risk of mate desertion drives women to choose less attractive men as long-term mates is tested. The results were that women rated physically attractive men as more likely to cheat or desert a long-term relationship, whereas men did not consider attractive women to be more likely to cheat. However, women showed no aversion to the idea of forming long-term relationships with attractive men. Evidence for a trade-off between resources and attractiveness was found for women, who traded off attractiveness, but not other traits, for resources. The potential meaning of these findings, as well as how they relate to broader issues in the study of sex differences in the evolution of human mate choice for physical traits, is discussed.     

Female Control of Offspring Sex Ratios Based on Male Attractiveness in the Guppy

The sex allocation hypothesis predicts that females manipulate the offspring sex ratios according to mate attractiveness. Although there is increasing evidence to support this prediction, it is possible that paternal effects may often obscure the relationship between female control of offspring sex ratios and male attractiveness. In the present study, we examined whether females played a primary role in the manipulation their offspring sex ratios based on male attractiveness, in the guppy Poecilia reticulata, a live‐bearing fish. We excluded the paternal effects by controlling the relative sexual attractiveness of the male by presenting them to the females along with a more attractive or less attractive stimulus male. The test male was perceived to be relatively more attractive by females when it was presented along with a less attractive stimulus male, or vice versa. Subsequently, test male was mated in two different roles (relatively more and less attractive) with two females. If females were responsible for offspring sex ratio manipulation, the sex ratio of the brood would be altered on the basis of the relative attractiveness of the test male. On the other hand, if males play a primary role in offspring sex ratio manipulation, the sex ratios would not differ with the relative attractiveness of the test male. We found that females gave birth to more male‐biased broods when they mated with test males in the attractive role than when they mated with males in the less attractive role. This finding suggests that females are responsible for the manipulation of offspring sex ratios based on the attractiveness of their mates.     

Dishonesty invites costly third-party punishment

Third-party punishment for norm violators is an evolvable enforcer of social norms. The present study, involving two experiments, examined whether violations of honesty norms would induce costly third-party punishments. In both experiments, participants in the third-party role observed a protocol of the trust game, in which the trustee solicited the trustor to transfer his/her endowment by stating that the trustee would return x units from the total resource. Dishonesty was defined such that the trustee in fact returned fewer than x units. Participants were asked about their willingness to incur some cost to reduce the trustee's payoff. In Experiment 1, x was exactly half of the total resource. Participants were willing to incur more cost to punish the dishonest trustee than the trustee who allocated the resource unequally but had not sent the dishonest message. In Experiment 2, x was more than half of the total resource and the dishonest trustee allocated the total resource equally. Therefore, the dishonest trustee was not unfair in Experiment 2. Approximately half of the participants (16 of 30) punished the dishonest but fair trustee, while few participants (1 of 30) punished the fair trustee who had not sent the dishonest message. These experiments together demonstrated that participants were willing to incur some cost to punish honesty-norm violators, even when the participants themselves were not harmed by the norm violation.     

Male facial attractiveness,perceived personality,and child-directed speech

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.     

The threat premium in economic bargaining

Costly punishment is thought to have evolved because it promotes cooperation and the equitable sharing of resources, but the costs associated with punishment – for both the punisher and the punished – limit the efficiency of this enforcement system in economic interactions. Reputation may also guide decision-making, but this information is not always available (e.g., in interactions involving strangers). Across several bargaining studies, we provide evidence of an efficient and flexible “threat-based” bargaining system that can influence the division of resources without the need for costly punishment and reputational information. We found that participants, without prompting, dynamically adjusted bargaining based on the perceived threat-potential (resource holding power and aggressiveness) of the bargaining partner, giving larger offers to individuals who appeared more threatening. These effects of perceived threat-potential were strongest among participants who were most vulnerable to harm in physical contests (women vs men and weaker men vs stronger men), despite that offers were made on-line and anonymously to photographs of the individuals rather than in face-to-face interactions. These results may reflect an overgeneralization of a real-world threat heuristic that allows low threat individuals to extract resources when possible, while avoiding physical retaliation and harm, and high threat individuals to appropriate larger shares of a resource through static facial cues of threat rather than by physically expressing their propensity to punish. Previously, researchers have highlighted the monetary advantages of attractiveness (the “beauty premium”), but the effects of threat either trumped, devalued, or were equivalent to those of attractiveness.     

How conception risk affects competition and cooperation with attractive women and men

We investigated competition and cooperation for resources across the menstrual cycle in the context of bargaining games. Although bargaining has been studied within an evolutionary framework, little attention has been paid specifically to the role of mating motives in economic behavior. To investigate how motives related to reproductive success affect bargaining, participants at high or low risk for conception or who were on oral contraceptives played ultimatum and dictator games with partners who varied in sex and facial attractiveness. In ultimatum games, women in the fertile phase were more competitive over resources with attractive women than with less attractive women. Intrasexual competition was not observed in dictator games. Women were more cooperative with attractive men than with less attractive men in both games, regardless of fertility status. Low fertility women were more cooperative with attractive members than with less attractive members of both sexes in both games. Results support the view that, during periods of high fertility, when women are most intrasexually competitive for mates, withholding resources from potential rivals would enable women to gain the means to enhance their attractiveness and weaken competitors' abilities to do the same at a time when relative advantages in appearance are most crucial to reproductive success. The lack of a fertility effect for cooperation with potential mates supports the view that displays of generosity accrue benefits for women across the cycle in their efforts to attract men who will invest in relationships.     

Beautiful parents have more daughters: a further implication of the generalized Trivers-Willard hypothesis (gTWH)

The generalized Trivers-Willard hypothesis (gTWH) [Kanazawa, S., 2005. Big and tall parents have more sons: further generalizations of the Trivers-Willard hypothesis. J. Theor. Biol. 235, 583-590) proposes that parents who possess any heritable trait which increases the male reproductive success at a greater rate than female reproductive success in a given environment will have a higher-than-expected offspring sex ratio, and parents who possess any heritable trait which increases the female reproductive success at a greater rate than male reproductive success in a given environment will have a lower-than-expected offspring sex ratio. One heritable trait which increases the reproductive success of daughters much more than that of sons is physical attractiveness. I therefore predict that physically attractive parents have a lower-than-expected offspring sex ratio (more daughters). Further, if beautiful parents have more daughters and physical attractiveness is heritable, then, over evolutionary history, women should gradually become more attractive than men. The analysis of the National Longitudinal Study of Adolescent Health (Add Health) confirm both of these hypotheses. Very attractive individuals are 26% less likely to have a son, and women are significantly more physically attractive than men in the representative American sample.     

Beyond species recognition: somatic state affects long-distance sex pheromone communication

Long-range sex pheromones have been subjected to substantial research with a particular focus on their biosynthesis, peripheral perception, central processing and the resulting orientation behaviour of perceivers. Fundamental to the research on sex attractants was the assumption that they primarily coordinate species recognition. However, especially when they are produced by the less limiting sex (usually males), the evolution of heightened condition dependence might be expected and long-range sex pheromones might, therefore, also inform about a signaller''s quality. Here we provide, to our knowledge, the first comprehensive study of the role of a male''s long-range pheromone in mate choice that combines chemical analyses, video observations and field experiments with a multifactorial manipulation of males'' condition. We show that the emission of the long-distance sex pheromone of the burying beetle, Nicrophorus vespilloides is highly condition-dependent and reliably reflects nutritional state, age, body size and parasite load—key components of an individual''s somatic state. Both, the quantity and ratio of the pheromone components were affected but the time invested in pheromone emission was largely unaffected by a male''s condition. Moreover, the variation in pheromone emission caused by the variation in condition had a strong effect on the attractiveness of males in the field, with males in better nutritional condition, of older age, larger body size and bearing less parasites being more attractive. That a single pheromone is influenced by so many aspects of the somatic state and causes such variation in a male''s attractiveness under field conditions was hitherto unknown and highlights the need to integrate indicator models of sexual selection into pheromone research.     

Cross-cultural consensus for waist–hip ratio and women's attractiveness

In women of reproductive age, a gynoid body fat distribution as measured by the size of waist–hip ratio (WHR) is a reliable indicator of their sex hormone profile, greater success in pregnancy and less risk for major diseases. According to evolutionary mate selection theory, such indicators of health and fertility should be judged as attractive. Previous research has confirmed this prediction. In this current research, we use the same stimulus for diverse racial groups (Bakossiland, Cameroon, Africa; Komodo Island, Indonesia; Samoa; and New Zealand) to examine the universality of relationships between WHR and attractiveness. As WHR is positively correlated with body mass index (BMI), we controlled BMI by using photographs of women who have gone through micrograft surgery for cosmetic reasons. Results show that in each culture participants selected women with low WHR as attractive, regardless of increases or decreases in BMI. This cross-cultural consensus suggests that the link between WHR and female attractiveness is due to adaptation shaped by the selection process.     

Choosy moral punishers

The punishment of social misconduct is a powerful mechanism for stabilizing high levels of cooperation among unrelated individuals. It is regularly assumed that humans have a universal disposition to punish social norm violators, which is sometimes labelled "universal structure of human morality" or "pure aversion to social betrayal". Here we present evidence that, contrary to this hypothesis, the propensity to punish a moral norm violator varies among participants with different career trajectories. In anonymous real-life conditions, future teachers punished a talented but immoral young violinist: they voted against her in an important music competition when they had been informed of her previous blatant misconduct toward fellow violin students. In contrast, future police officers and high school students did not punish. This variation among socio-professional categories indicates that the punishment of norm violators is not entirely explained by an aversion to social betrayal. We suggest that context specificity plays an important role in normative behaviour; people seem inclined to enforce social norms only in situations that are familiar, relevant for their social category, and possibly strategically advantageous.     

Head Tilt and Fertility Contribute to Different Aspects of Female Facial Attractiveness

Subjective attractiveness ratings of facial portraits of women taken at the fertile phase of the menstrual cycle are higher than those of portraits of the same women taken during non‐fertile periods. As female faces tilted downward are rated as more attractive and female courtship behaviours change across the menstrual cycle, we investigated whether systematic downward tilt of women's faces during the fertile phase might be responsible for increased attractiveness ratings. In the original study (Proc. R. Soc. Lond. B, 271, 2004, S272), the fertile‐phase portrait of each woman was deemed more attractive in 56–62% of cases. When the portraits were reclassified by head pitch, the more downward‐tilted portrait was preferred in 64–73% of cases. The fertile‐phase portrait was no more likely to be the downward‐tilted one, however, suggesting that effects of fertility on attractiveness are not simply due to changes in head position. We also had these portraits rated (N = 130) for physical attractiveness and behavioural allure. Fertile‐phase portraits were rated as more physically attractive than non‐fertile portraits, while more downward‐tilted portraits were rated as more behaviourally alluring than less downward‐tilted ones. These data not only confirm reported effects of head tilt and fertility on perceived female attractiveness, but also suggest that these factors influence different components of the attractiveness percept.     

Parental Care and Sexual Selection in the Bluethroat, Luscinia s. svecica: A Field-experimental Test of the Differential Allocation Hypothesis

One of the processes by which secondary sexual characters in monogamous species with biparental care may evolve is described by the differential allocation hypothesis. It predicts that mates adjust their parental effort to the attractiveness of their partner. The more attractive sex is expected to withhold parental effort while the less attractive sex is expected to compensate for the partner's decreased effort thus preventing a reduction in breeding success. Asymmetry in attractiveness then imposes costs on the less attractive sex which are thought to be exceeded by the indirect (i.e. genetic) benefits which result from sharing offspring with a highly attractive partner. This idea was tested with bluethroats, Luscinia s. svecica , a bird species in which the male is characterized by a complex multiple-coloured plumage ornament on the throat and chest. We manipulated male attractiveness by attaching conspicuous coloured leg bands which matched the blue and chestnut components of the male ornament. Control males were banded with green and yellow bands. The results from another field experiment on mate-guarding behaviour demonstrate the effectiveness of this treatment. As measures of parental effort we determined: 1. clutch size; 2. feeding rates by video recording feeding activity of both parents; and 3. brood mass up to day 9. The results do not support the differential allocation hypothesis. The experimental and control groups differed in none of the above variables. On the basis of these results we discuss the ecological factors which may influence the differential allocation process in monogamous birds.     

Dog Pups’ Attractiveness to Humans Peaks at Weaning Age

The domestic dog (Canis lupus familiaris) is characterized by greatly reduced parenting investment compared with the wild type wolf (C. l. lupus) from which it is descended. Unlike wolf pups, which are reared by both parents into their second year of life, dog pups are abandoned by their mother at weaning around eight weeks of age. This relatively small parental involvement may contribute to the high pup mortality observed in dogs not living as pets. We hypothesized that people would find dog pups most attractive around weaning age when conspecific parental care is significantly reduced and pup mortality rate is high. Younger and older pups would benefit less from human intervention because in the former case the mother is providing care, and in the latter their survival is already compromised. To test this hypothesis, 51 participants rated the attractiveness of 39 black and white headshot photographs presented on a computer screen of dog pups from three breeds (Jack Russell Terrier, Cane Corso, and White Shepherd), from birth to 7 months old. In line with our hypothesis, attractiveness of Cane Corsos peaked at 6.3 weeks of age; Jack Russell Terriers’ attractiveness peaked at 7.7 weeks; and White Shepherds were most attractive at 8.3 weeks. There were also differences in attractiveness between the breeds, with Cane Corsos rated less attractive than the other two breeds. If this attractiveness motivates humans to care for the dog pups and thereby improves pup survival, this could confer significant advantages to dogs, and may contribute to our understanding of the process of domestication.     

Mate Choice Copying in Humans

There is substantial evidence that in human mate choice, females directly select males based on male display of both physical and behavioral traits. In non-humans, there is additionally a growing literature on indirect mate choice, such as choice through observing and subsequently copying the mating preferences of conspecifics (mate choice copying). Given that humans are a social species with a high degree of sharing information, long-term pair bonds, and high parental care, it is likely that human females could avoid substantial costs associated with directly searching for information about potential males by mate choice copying. The present study was a test of whether women perceived men to be more attractive when men were presented with a female date or consort than when they were presented alone, and whether the physical attractiveness of the female consort affected women’s copying decisions. The results suggested that women’s mate choice decision rule is to copy only if a man’s female consort is physically attractive. Further analyses implied that copying may be a conditional female mating tactic aimed at solving the problem of informational constraints on assessing male suitability for long-term sexual relationships, and that lack of mate choice experience, measured as reported lifetime number of sex partners, is also an important determinant of copying.     

Intergenerational Perceptions of Body Image in Hispanics: Role of BMI,Gender, and Acculturation

Objective: To assess role of BMI, gender, and acculturation on maternal and children's perception of body size, body ideal, and attractiveness. Research Methods and Procedures: Eighty mothers and their 6‐ to‐ 12‐year‐old children (41 boys, 39 girls) participated. Maternal and children's perceptions of body size (actual and ideal) and attractiveness were assessed through a pictorial instrument. Mother and child height and weight, demographic, and acculturation characteristics were also assessed. Results: Seventy‐nine percent of the mothers were overweight, and 32% of the boys and 34% of the girls were overweight or at‐risk for overweight. BMI influenced the children's selection of perceived ideal size. Overweight or at‐risk for overweight children were more likely to select thinner figures as the ideal size than non‐overweight children. Gender and acculturation differences concerning children's perceptions of body size and attractiveness were also found. Girls perceived the obese figure as being less attractive than did the boys. More acculturated children were likely to select thinner figures as more attractive than their less acculturated counterparts. Maternal acculturation was associated positively with the girls’ choice of thinner figures as an ideal body size, but not with the boys. Mothers viewed their daughters’ actual body size and BMI as ideal, although 34% of the girls were at‐risk for overweight. Mothers perceived average body size figures as more attractive for their sons. Discussion: Findings from this study provide empirical data about the role of BMI, gender, acculturation, and familial influences on children's perceptions of actual and ideal body sizes and attractiveness.     

Negative peer perceptions of obese children in the classroom environment

Objective: It is asserted that the more immediate and observable consequences of pediatric obesity are psychosocial in nature. This study examines the peer relations of clinically referred obese youth compared to demographically comparable nonoverweight peers within the classroom environment. Methods and Procedures: Peer‐, teacher‐, and self‐reports of behavioral reputation (Revised Class Play (RCP)), and peer reports of social acceptance, nonsocial attributes (attractiveness, athleticism, academic competence), and health interference (school absence, illness, fatigue) were obtained regarding 90 obese youth (BMI > 95th percentile; 8–16 years, 57% girls, 50% African American) and 76 nonoverweight demographically similar comparison classmates. Results: Relative to comparison peers, obese children were nominated significantly less often as a best friend and rated lower in peer acceptance, although the two groups did not differ in the number of reciprocated friendships. Obese youth were described by peer, teacher, and self‐report as more socially withdrawn and by peers as displaying less leadership and greater aggressive‐disruptive behavior. Peers also described obese youth as less physically attractive, less athletic, more sick, tired, and absent from school. Being seen as less attractive and less athletic by peers helped to explain differences in obese and nonoverweight youth's levels of peer acceptance. Discussion: Clinically referred obese youth are characterized by peer relations that differ from those of nonoverweight youth. The peer environment provides a rich context to understand the social consequences of pediatric obesity as well as factors that could be targeted in intervention to promote more positive health and psychosocial outcomes.