People recognise when they are really anonymous in an economic game

Mounting evidence that cues of being watched can enhance cooperative behaviour questions the existence of ‘anonymous', one-shot, non-kin directed cooperation and the validity of using ‘anonymous' economic games to empirically measure such behaviour in humans. Here we investigate how sensitive people are to such cuing effects. We test whether people playing an ultimatum game can use explicit information about experimental anonymity to override any effects of cuing in a public context, when faced with both simultaneously. The aims of our study were to investigate whether, (1) individuals respond to experimentally imposed anonymity within a public context and (2) the presence of known others affects cooperative behaviour over and above merely the presence of others. We find that proposer offers did not vary with changes in context (i.e., there was no “eyes effect”) but did vary with the degree of actual anonymity and the specific presence of known others. Hence, we infer that people recognise when their decisions are anonymous or not and proposers respond to reputation concerns when they are not anonymous. Responder behaviour did not vary with changes in context, degree of actual anonymity or the specific presence of known others. Hence, responders do not respond to reputation concerns and use one uniform strategy, perhaps as long as the payoff structure remains constant. This latter finding may hint at selection in favour of strategies that uniformly ensure near-equal splits of resources in some environments, and thus manifest as strong fairness norms in a population.     

Fluctuating asymmetry and behavior in the ultimatum game in Jamaica

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).     

Testosterone administration does not affect men's rejections of low ultimatum game offers or aggressive mood

Correlative evidence suggests that testosterone promotes dominance and aggression. However, causal evidence is scarce and offers mixed results. To investigate this relationship, we administered testosterone for 48 h to 41 healthy young adult men in a within-subjects, double-blind placebo-controlled balanced crossover design. Subjects played the role of responders in an ultimatum game, where rejecting a low offer is costly, but serves to destroy the proposer's profit. Such action can hence be interpreted as non-physical aggression in response to social provocation. In addition, subjects completed a self-assessed mood questionnaire. As expected, self-reported aggressiveness was a key predictor of ultimatum game rejections. However, while testosterone affected subjective ratings of feeling energetic and interested, our evidence strongly suggests that testosterone had no effect on ultimatum game rejections or on aggressive mood. Our findings illustrate the importance of using causal interventions to assess correlative evidence.     

The Role of Cognitive and Emotional Perspective Taking in Economic Decision Making in the Ultimatum Game

We conducted a simple resource allocation game known as the ultimatum game (UG) with preschoolers to examine the role of cognitive and emotional perspective-taking ability on allocation and rejection behavior. A total of 146 preschoolers played the UG and completed a false belief task and an emotional perspective-taking test. Results showed that cognitive perspective taking ability had a significant positive effect on the proposer’s offer and a negative effect on the responder’s rejection behavior, whereas emotional perspective taking ability did not impact either the proposer’s or responder’s behavior. These results imply that the ability to anticipate the responder’s beliefs, but not their emotional state, plays an important role in the proposer’s choice of a fair allocation in an UG, and that children who have not acquired theory of mind still reject unfair offers.     

Kinship,Family, and Gender Effects in the Ultimatum Game

Kinship and reciprocity are two main predictors of altruism. The ultimatum game has been used to study altruism in many small-scale societies. We used the ultimatum game to examine effects of individuals’ family and kin relations on altruistic behavior in a kin-based horticultural community in rural Dominica. Results show sex-specific effects of kin on ultimatum game play. Average coefficient of relatedness to the village was negatively associated with women’s ultimatum game proposals and had little effect on men’s proposals. Number of brothers in the village was positively associated with men’s ultimatum game proposals and negatively associated with women’s proposals. Similarly, presence of father in the village was associated with higher proposals by men and lower proposals by women. We interpret the effect of brothers on men’s proposals as a consequence of local competition among brothers. We speculate that daughter-biased parental care in this community creates a sense of entitlement among women with brothers, which may explain the inverse relation between number of brothers and women’s ultimatum game proposals. The pattern of results may be consistent with how matrifocality affects cultural models of fairness differently along gender and family lines.     

Religious Pro-Sociality? Experimental Evidence from a Sample of 766 Spaniards

This study explores the relationship between several personal religion-related variables and social behaviour, using three paradigmatic economic games: the dictator (DG), ultimatum (UG), and trust (TG) games. A large carefully designed sample of the urban adult population in Granada (Spain) is employed (N = 766). From participants'' decisions in these games we obtain measures of altruism, bargaining behaviour and sense of fairness/equality, trust, and positive reciprocity. Three dimensions of religiosity are examined: (i) religious denomination; (ii) intensity of religiosity, measured by active participation at church services; and (iii) conversion out into a different denomination than the one raised in. The major results are: (i) individuals with “no religion” made decisions closer to rational selfish behaviour in the DG and the UG compared to those who affiliate with a “standard” religious denomination; (ii) among Catholics, intensity of religiosity is the key variable that affects social behaviour insofar as religiously-active individuals are generally more pro-social than non-active ones; and (iii) the religion raised in seems to have no effect on pro-sociality, beyond the effect of the current measures of religiosity. Importantly, behaviour in the TG is not predicted by any of the religion-related variables we analyse. While the results partially support the notion of religious pro-sociality, on the other hand, they also highlight the importance of closely examining the multidimensional nature of both religiosity and pro-social behaviour.     

Understanding Language Evolution: Beyond Pan-Centrism

Language does not fossilize but this does not mean that the language's evolutionary timeline is lost forever. Great apes provide a window back in time on our last prelinguistic ancestor's communication and cognition. Phylogeny and cladistics implicitly conjure Pan (chimpanzees, bonobos) as a superior (often the only) model for language evolution compared with earlier diverging lineages, Gorilla and Pongo (orangutans). Here, in reviewing the literature, it is shown that Pan do not surpass other great apes along genetic, cognitive, ecologic, or vocal traits that are putatively paramount for language onset and evolution. Instead, revived herein is the idea that only by abandoning single-species models and learning about the variation among great apes, there might be a chance to retrieve lost fragments of the evolutionary timeline of language.     

Local competition sparks concerns for fairness in the ultimatum game

Humans reject uneven divisions of resources, even at personal cost. This is observed in countless experiments using the ultimatum game, where a proposer offers to divide a resource with a responder who either accepts the division or rejects it (whereupon both earn zero). Researchers debate why humans evolved a psychology that is so averse to inequity within partnerships. We suggest that the scale of competition is crucial: under local competition with few competitors, individuals reject low offers, because they cannot afford to be disadvantaged relative to competitors. If one competes against the broader population (i.e. global competition), then it pays to accept low offers to increase one''s absolute pay-off. We support this intuition with an illustrative game-theoretical model. We also conducted ultimatum games where participants received prizes based on pay-offs relative to immediate partners (local competition) versus a larger group (global competition). Participants demanded higher offers under local competition, suggesting that local competition increases people''s demands for fairness and aversion to inequality.     

The spatial ultimatum game.

In the ultimatum game, two players are asked to split a certain sum of money. The proposer has to make an offer. If the responder accepts the offer, the money will be shared accordingly. If the responder rejects the offer, both players receive nothing. The rational solution is for the proposer to offer the smallest possible share, and for the responder to accept it. Human players, in contrast, usually prefer fair splits. In this paper, we use evolutionary game theory to analyse the ultimatum game. We first show that in a non-spatial setting, natural selection chooses the unfair, rational solution. In a spatial setting, however, much fairer outcomes evolve.     

The Relationship between Trait Emotional Intelligence and Interaction with Ostracized Others' Retaliation

Background

Regulation of emotions in others is distinct from other activities related to trait emotional intelligence in that only such behavior can directly change other people''s psychological states. Although emotional intelligence has generally been associated with prosociality, emotionally intelligent people may manipulate others'' behaviors to suit their own interests using high-level capabilities to read and manage the emotions of others. This study investigated how trait emotional intelligence was related to interacting with ostracized others who attempt retaliation.

Method

We experimentally manipulated whether two people were simultaneously ostracized or not by using an online ball-tossing game called Cyberball. Eighty university students participated in Cyberball for manipulating ostracism and a “recommendation game,” a variation of the ultimatum game for assessing how to interact with others who attempt retaliation, with four participants. After the recommendation game, participants rated their intention to retaliate during the game.

Results

People with higher interpersonal emotional intelligence were more likely to recommend that the ostracized other should inhibit retaliation and maximize additional rewards when they have a weaker intention to retaliate. However, they were more likely to recommend that the ostracized other should retaliate against the ostracizers when they have a stronger intention to retaliate.

Conclusion

This is the first laboratory study that empirically reveals that people with high interpersonal emotional intelligence influence others'' emotions based on their own goals contrary to the general view. Trait emotional intelligence itself is neither positive nor negative, but it can facilitate interpersonal behaviors for achieving goals. Our study offers valuable contributions for the refinement of the trait emotional intelligence concept in the respect of its social function.     

The SKX 1084 hominin patella from Swartkrans Member 2, South Africa: An integrated analysis of its outer morphology and inner structure

SKX 1084 is an isolated partial patella from Swartkrans Member 2, South Africa, attributed to a small-bodied Paranthropus robustus. This study provides complementary information on its outer conformation and, for the first time for a fossil hominin patella, documents its inner structure in the perspective of adding biomechanically-related evidence to clarify its identity. We used X-ray micro-tomography to investigate SKX 1084 and to extract homologous information from a sample of 12 recent human, one Neanderthal, and two adult Pan, patellae. We used geometric morphometrics to compare the outer equatorial contours. In SKX 1084, we identified two cancellous bony spots suitable for textural assessment (trabecular bone volume fraction, trabecular thickness, degree of anisotropy), and two related virtual slices for measuring the maximum cortico-trabecular thickness (CTT) of the articular surface. SKX 1084 shows a more complex articular shape than that for Pan, but still simpler than typical in Homo sapiens. At all sites, its CTT is thinner compared to Pan and approaches the condition in humans. This is also true for the expanded volume of the cancellous network. However, at both investigated spots, SKX 1084 is systematically intermediate between Homo and Pan for trabecular bone volume fraction and trabecular thickness, a pattern already shown in previous analyses on other Paranthropus postcranial remains. In the absence of any structural signal from patellae unambiguously sampling Paranthropus, as well as of comparable evidence extracted from specimens representing early Homo, our results do not allow rejection of the original taxonomic attribution of SKX 1084.     

Are Cape Ground Squirrels (Xerus inauris) Sensitive to Variation in the Pay‐offs from Their Caches?

For food caching to be adaptive, the benefits of recovery must outweigh the costs of storing an item. One of the costs to cachers is the risk of theft, and therefore, it is predicted that individuals may be sensitive to this theft and show various behavioural strategies to minimise it. In this study, we gave wild Cape ground squirrels (Xerus inauris) a choice between two different coloured items of the same food type: one item with a specific colour that was always artificially removed when cached and the other item with a different colour that was not removed when cached. During the choice presentations, subjects reduced the amount they consumed and cached of the food items with the colour that was experimentally removed when cached, despite the two items only differing in caching pay‐off. This avoidance to choose the food with the colour that was removed occurred over time, which suggests that subjects were using information about the item's pay‐off during cache recovery and this then impacted on successive decisions. This study highlights how the sensitivity to a food item's pay‐off can affect an individual's choice towards items that offer the greater overall reward.     

A dynamic over games drives selfish agents to win–win outcomes

Understanding human institutions, animal cultures and other social systems requires flexible formalisms that describe how their members change them from within. We introduce a framework for modelling how agents change the games they participate in. We contrast this between-game ‘institutional evolution’ with the more familiar within-game ‘behavioural evolution’. We model institutional change by following small numbers of persistent agents as they select and play a changing series of games. Starting from an initial game, a group of agents trace trajectories through game space by navigating to increasingly preferable games until they converge on ‘attractor’ games. Agents use their ‘institutional preferences'' for game features (such as stability, fairness and efficiency) to choose between neighbouring games. We use this framework to pose a pressing question: what kinds of games does institutional evolution select for; what is in the attractors? After computing institutional change trajectories over the two-player space, we find that attractors have disproportionately fair outcomes, even though the agents who produce them are strictly self-interested and indifferent to fairness. This seems to occur because game fairness co-occurs with the self-serving features these agents do actually prefer. We thus present institutional evolution as a mechanism for encouraging the spontaneous emergence of cooperation among small groups of inherently selfish agents, without space, reputation, repetition, or other more familiar mechanisms. Game space trajectories provide a flexible, testable formalism for modelling the interdependencies of behavioural and institutional evolutionary processes, as well as a mechanism for the evolution of cooperation.     

Trust and cooperation among economic agents

The units that are subject to selection pressure in evolutionary biology are ‘strategies’, which are conditional actions (‘Do P if X occurs, otherwise do Q’). In contrast, the units in economics select strategies from available menus so as to further their projects and purposes. As economic agents do not live in isolation, each agent''s optimum choice, in general, depends on the choices made by others. Because their projects and purposes involve the future, not just the present, each agent reasons about the likely present and future consequences of their respective choices. That is why beliefs, about what others may do and what the consequences of those choices could be, are at the basis of strategy selection. A catalogue of social environments is constructed in which agents not only promise each other''s cooperation, but also rationally believe that the promises will be kept. Unfortunately, non-cooperation arising from mistrust can be the outcome in those same environments: societies harbour multiple ‘equilibria’ and can skid from cooperation to non-cooperation. Moreover, a pre-occupation among analysts with the Prisoners'' Dilemma game has obscured the fact that cooperative arrangements can harbour not only inequality, but also exploitation. The analysis is used to discuss why international cooperation over the use of global public goods has proved to be so elusive.     

Statistical fluctuations in population bargaining in the ultimatum game: Static and evolutionary aspects

We explore the emergent behavior in heterogeneous populations where players negotiate via an ultimatum game: two players are offered a gift, one of them (the proposer) suggests how to divide the offer while the other player (the responder) can either accept or reject the deal. Rejection is detrimental to both players as it results in no earnings. In this context, our contribution is twofold: (i) we consider a population where the distribution of used strategies is constant over time and properties of the random payoff received by the players (average and higher moments) are reported from simple exact methods and corroborated by computer simulations; (ii) the evolution of a population is analyzed via Monte Carlo simulations where agents may change independently the proposing and accepting parameters of their strategy depending on received payoffs. Our results show that evolution leads to a stationary state in which wealth (accumulated payoff) is fairly distributed. As time evolves, an increase in average payoff and a simultaneous variance decrease is observed when we use a dynamics based on a probabilistic version of the saying: “One should not comply with small earnings, but one's greed must be limited.”     

How Much Is Our Fairness Worth? The Effect of Raising Stakes on Offers by Proposers and Minimum Acceptable Offers in Dictator and Ultimatum Games

Background

The aim of this study was to determine whether people respond differently to low and high stakes in Dictator and Ultimatum Games. We assumed that if we raised the stakes high enough, we would observe more self-orientated behavior because fairness would become too costly, in spite of a possible risk of a higher punishment.

Methods

A questionnaire was completed by a sample of 524 university students of biology. A mixed linear model was used to test the relation between the amount at stake (CZK 20, 200, 2,000, 20,000 and 200,000, i.e., approximately $1–$10,000) and the shares, as well as the subjects’ gender and the design of the study (single vs. multiple games for different amounts).

Results

We have discovered a significant relationship between the amount at stake and the minimum acceptable offer in the Ultimatum Game and the proposed shares in both Ultimatum and Dictator Games (p = 0.001, p<0.001, p = 0.0034). The difference between playing a single game or more games with several amounts at stake did not influence the relation between the stakes and the offered and minimum acceptable shares. Women proved significantly more generous than men in their offers in the Dictator Game (p = 0.007).

Conclusion

Our results suggest that people’s behavior in the Dictator and Ultimatum Games depends on the amount at stake. The players tended to lower their relative proposed shares, as well as their relative minimum acceptable offers. We propose that the Responders’ sense of equity and fair play depends on the stakes because of the costs of maintaining fairness. However, our results also suggest that the price of fairness is very high and that it is very difficult, probably even impossible, to buy the transition of Homo sociologicus into Homo economicus.     

Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes’ Hearing Evolution

Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species’ sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the “hypertrophied” cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.     

Body size and its consequences: Allometry and the lower limb length of Liang Bua 1 (Homo floresiensis)

Bivariate femoral length allometry in recent humans, Pan, and Gorilla is investigated with special reference to the diminutive Liang Bua (LB) 1 specimen (the holotype of Homo floresiensis) and six early Pleistocene femora referred to the genus Homo. Relative to predicted body mass, Pan and Gorilla femora show strong negative length allometry while recent human femora evince isometry to positive allometry, depending on sample composition and line-fitting technique employed. The allometric trajectories of Pan and Homo show convergence near the small body size range of LB 1, such that LB 1 manifests a low percentage deviation (d_yx of Smith [1980]) from the Pan allometric trajectory and falls well within the 95% confidence limits around the Pan individuals (but also outside the 95% confidence limits for recent Homo). In contrast, the six early Pleistocene Homo femora, belonging to larger individuals, show much greater d_yx values from both Pan and Gorilla and fall well above the 95% confidence limits for these taxa. All but one of these Pleistocene Homo specimens falls within the 95% confidence limits of the recent human sample. Similar results are obtained when femoral length is regressed on femoral head diameter in unlogged bivariate space. Regardless of the ultimate taxonomic status of LB 1, these findings are consistent with a prediction made by us (Franciscus and Holliday, 1992) that hominins in the small body size range of A.L. 288-1 (“Lucy”), including members of the genus Homo, will tend to possess short, ape-like lower limbs as a function of body size scaling.     

Does Invasion Success Reflect Superior Cognitive Ability? A Case Study of Two Congeneric Lizard Species (Lampropholis,Scincidae)

A species'' intelligence may reliably predict its invasive potential. If this is true, then we might expect invasive species to be better at learning novel tasks than non-invasive congeners. To test this hypothesis, we exposed two sympatric species of Australian scincid lizards, Lampropholis delicata (invasive) and L. guichenoti (non-invasive) to standardized maze-learning tasks. Both species rapidly decreased the time they needed to find a food reward, but latencies were always higher for L. delicata than L. guichenoti. More detailed analysis showed that neither species actually learned the position of the food reward; they were as likely to turn the wrong way at the end of the study as at the beginning. Instead, their times decreased because they spent less time immobile in later trials; and L. guichenoti arrived at the reward sooner because they exhibited “freezing” (immobility) less than L. delicata. Hence, our data confirm that the species differ in their performance in this standardized test, but neither the decreasing time to find the reward, nor the interspecific disparity in those times, are reflective of cognitive abilities. Behavioural differences may well explain why one species is invasive and one is not, but those differences do not necessarily involve cognitive ability.     

Digit ratio (2D:4D) moderates the impact of sexual cues on men's decisions in ultimatum games

Three experimental studies demonstrate that 'sex-related cues' impact human decision-making in ultimatum games. In the ultimatum game, two individuals divide a sum of money. The proposer offers a portion of the money to the other player, the responder. If the responder accepts the offer, the money is distributed in agreement with the proposer's offer. If the responder rejects the offer, neither player receives anything. Our studies show that exposure to pictures of sexy women or lingerie increases the likelihood of accepting unfair offers. Digit ratios of responders are reliably associated with their behaviour: males with lower digit ratios are more likely to reject an unfair split in neutral contexts, but more likely to accept unfair offers in sex-related contexts.