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We present seven experiments exploring gender biases in GPT. Initially, GPT was asked to generate demographics of a potential writer of twenty phrases containing feminine stereotypes and twenty with masculine stereotypes. Results show a strong asymmetry, with stereotypically masculine sentences attributed to a female more often than vice versa. For example, the sentence "I love playing fotbal! Im practicing with my cosin Michael" was constantly assigned by ChatGPT to a female writer. This phenomenon likely reflects that while initiatives to integrate women in traditionally masculine roles have gained momentum, the reverse movement remains relatively underdeveloped. Subsequent experiments investigate the same issue in high-stakes moral dilemmas. GPT-4 finds it more appropriate to abuse a man to prevent a nuclear apocalypse than to abuse a woman. This bias extends to other forms of violence central to the gender parity debate (abuse), but not to those less central (torture). Moreover, this bias increases in cases of mixed-sex violence for the greater good: GPT-4 agrees with a woman using violence against a man to prevent a nuclear apocalypse but disagrees with a man using violence against a woman for the same purpose. Finally, these biases are implicit, as they do not emerge when GPT-4 is directly asked to rank moral violations. These results highlight the necessity of carefully managing inclusivity efforts to prevent unintended discrimination.

Over the last two decades, a growing body of experimental research has provided evidence that linguistic frames influence human behaviour in economic games, beyond the economic consequences of the available actions. This article proposes a novel framework that transcends the traditional confines of outcome-based preference models. According to the LENS model, the Linguistic description of the decision problem triggers Emotional responses and suggests potential Norms of behaviour, which then interact to shape an individual's Strategic choice. The article reviews experimental evidence that supports each path of the LENS model. Furthermore, it identifies and discusses several critical research questions that arise from this model, pointing towards avenues for future inquiry.

Understanding human behaviour in decision problems and strategic interactions has wide-ranging applications in economics, psychology, and artificial intelligence. Game theory offers a robust foundation for this understanding, based on the idea that individuals aim to maximize a utility function. However, the exact factors influencing strategy choices remain elusive. While traditional models try to explain human behaviour as a function of the outcomes of available actions, recent experimental research reveals that linguistic content significantly impacts decision-making, thus prompting a paradigm shift from outcome-based to language-based utility functions. This shift is more urgent than ever, given the advancement of generative AI, which has the potential to support humans in making critical decisions through language-based interactions. We propose sentiment analysis as a fundamental tool for this shift and take an initial step by analyzing 61 experimental instructions from the dictator game, an economic game capturing the balance between self-interest and the interest of others, which is at the core of many social interactions. Our meta-analysis shows that sentiment analysis can explain human behaviour beyond economic outcomes. We discuss future research directions. We hope this work sets the stage for a novel game theoretical approach that emphasizes the importance of language in human decisions.

Generative artificial intelligence has the potential to both exacerbate and ameliorate existing socioeconomic inequalities. In this article, we provide a state-of-the-art interdisciplinary overview of the potential impacts of generative AI on (mis)information and three information-intensive domains: work, education, and healthcare. Our goal is to highlight how generative AI could worsen existing inequalities while illuminating how AI may help mitigate pervasive social problems. In the information domain, generative AI can democratize content creation and access, but may dramatically expand the production and proliferation of misinformation. In the workplace, it can boost productivity and create new jobs, but the benefits will likely be distributed unevenly. In education, it offers personalized learning, but may widen the digital divide. In healthcare, it might improve diagnostics and accessibility, but could deepen pre-existing inequalities. In each section we cover a specific topic, evaluate existing research, identify critical gaps, and recommend research directions, including explicit trade-offs that complicate the derivation of a priori hypotheses. We conclude with a section highlighting the role of policymaking to maximize generative AI's potential to reduce inequalities while mitigating its harmful effects. We discuss strengths and weaknesses of existing policy frameworks in the European Union, the United States, and the United Kingdom, observing that each fails to fully confront the socioeconomic challenges we have identified. We propose several concrete policies that could promote shared prosperity through the advancement of generative AI. This article emphasizes the need for interdisciplinary collaborations to understand and address the complex challenges of generative AI., Comment: PNAS Nexus, in press

Generative artificial intelligence (AI) holds enormous potential to revolutionize decision-making processes, from everyday to high-stake scenarios. By leveraging generative AI, humans can benefit from data-driven insights and predictions, enhancing their ability to make informed decisions that consider a wide array of factors and potential outcomes. However, as many decisions carry social implications, for AI to be a reliable assistant for decision-making it is crucial that it is able to capture the balance between self-interest and the interest of others. We investigate the ability of three of the most advanced chatbots to predict dictator game decisions across 108 experiments with human participants from 12 countries. We find that only GPT-4 (not Bard nor Bing) correctly captures qualitative behavioral patterns, identifying three major classes of behavior: self-interested, inequity-averse, and fully altruistic. Nonetheless, GPT-4 consistently underestimates self-interest and inequity-aversion, while overestimating altruistic behavior. This bias has significant implications for AI developers and users, as overly optimistic expectations about human altruism may lead to disappointment, frustration, suboptimal decisions in public policy or business contexts, and even social conflict.

We review the literature on models that try to explain human behavior in social interactions described by normal-form games with monetary payoffs. We start by covering social and moral preferences. We then focus on the growing body of research showing that people react to the language in which actions are described, especially when it activates moral concerns. We conclude by arguing that behavioral economics is in the midst of a paradigm shift towards language-based preferences, which will require an exploration of new models and experimental setups., Comment: Forthcoming in the Journal of Economic Literature

Understanding the emergence of prosocial behaviours (e.g., cooperation and trust) among self-interested agents is an important problem in many disciplines. Network structure and institutional incentives (e.g., punishing antisocial agents) are known to promote prosocial behaviours, when acting in isolation, one mechanism being present at a time. Here we study the interplay between these two mechanisms to see whether they are independent, interfering or synergetic. Using evolutionary game theory, we show that punishing antisocial agents and a regular networked structure not only promote prosocial behaviours among agents playing the trust game, but they also interplay with each other, leading to interference or synergy, depending on the game parameters. Synergy emerges on a wider range of parameters than interference does. In this domain, the combination of incentives and networked structure improves the efficiency of incentives, yielding prosocial behaviours at a lower cost than the incentive does alone. This has a significant implication in the promotion of prosocial behaviours in multi-agent systems., Comment: 6 pages, 3 figures

Sender-receiver games are simple models of information transmission that provide a formalism to study the evolution of honest signaling and deception between a sender and a receiver. In many practical scenarios, lies often affect groups of receivers, which inevitably entangles the payoffs of individuals to the payoffs of other agents in their group, and this makes the formalism of pairwise sender-receiver games inapt for where it might be useful the most. We therefore introduce group interactions among receivers, and study how their interconnectedness in higher-order social networks affects the evolution of lying. We observe a number of counterintuitive results that are rooted in the complexity of the underlying evolutionary dynamics, which has thus far remained hidden in the realm of pairwise interactions. We find conditions for honesty to persist even when there is a temptation to lie, and we observe the prevalence of moral strategy profiles even when lies favor the receiver at a cost to the sender. We confirm the robustness of our results by further performing simulations on hypergraphs created from real-world data using the SocioPatterns database. Altogether, our results provide persuasive evidence that moral behaviour may evolve on higher-order social networks, at least as long as individuals interact in groups that are small compared to the size of the network., Comment: 12 two-column pages, 5 figures, supplementary information; accepted for publication in Physical Review E

We report on three pre-registered studies testing whether people in the position of describing a decision problem to decision-makers exploit this opportunity for their benefit, by choosing descriptions that may be potentially beneficial for themselves. In Study 1, recipients of an extreme dictator game (where dictators can either take the whole pie for themselves or give it entirely to the receiver) are asked to choose the instructions used to introduce the game to dictators, among six different instructions that are known from previous research to affect dictators' decisions. The results demonstrate that some dictator game recipients tend to choose instructions that make them more likely to receive a higher payoff. Study 2 shows that people who choose descriptions that make them more likely to receive a higher payoff indeed believe that they will receive a higher payoff. Study 3 shows that receivers are more likely than dictators to choose these descriptions. In sum, our work suggests that some people choose descriptions that are beneficial to themselves; we also found some evidence that deliberative thinking and young age are associated with this tendency., Comment: in press at Judgment and Decision Making

One-shot anonymous unselfishness in economic games is commonly explained by social preferences, which assume that people care about the monetary payoffs of others. However, during the last ten years, research has shown that different types of unselfish behaviour, including cooperation, altruism, truth-telling, altruistic punishment, and trustworthiness are in fact better explained by preferences for following one's own personal norms - internal standards about what is right or wrong in a given situation. Beyond better organising various forms of unselfish behaviour, this moral preference hypothesis has recently also been used to increase charitable donations, simply by means of interventions that make the morality of an action salient. Here we review experimental and theoretical work dedicated to this rapidly growing field of research, and in doing so we outline mathematical foundations for moral preferences that can be used in future models to better understand selfless human actions and to adjust policies accordingly. These foundations can also be used by artificial intelligence to better navigate the complex landscape of human morality., Comment: 34 pages; accepted for publication in Journal of the Royal Society Interface

We report three pre-registered studies (total N=1,799) exploring the effect of nudging personal and injunctive norms in decisions that involve a trade-off between objective equality and efficiency. The first two studies provide evidence that: (i) nudging the personal norm has a similar effect to nudging the injunctive norm; (ii) when both norms are nudged towards the same direction, there is no additive effect; (iii) when the personal norm and the injunctive norm are nudged towards opposite directions, some people tend to follow the personal norm, while others tend to follow the injunctive norm. Study 3 tests whether these two classes of people, those who tend to follow the injunctive norm and those who tend to follow the personal norm, map onto the two sub-dimensions of Aquino and Reed's moral identity scale. We find partial evidence of this hypothesis: people higher in the symbolisation dimension are weakly more likely to follow the injunctive norm; however, we do not find any evidence that people higher in the internalisation dimension are more likely to follow the personal norm.

Trust and trustworthiness form the basis for continued social and economic interactions, and they are also fundamental for cooperation, fairness, honesty, and indeed for many other forms of prosocial and moral behavior. However, trust entails risks, and building a trustworthy reputation requires effort. So how did trust and trustworthiness evolve, and under which conditions do they thrive? To find answers, we operationalize trust and trustworthiness using the trust game with the trustor's investment and the trustee's return of the investment as the two key parameters. We study this game on different networks, including the complete network, random and scale-free networks, and in the well-mixed limit. We show that in all but one case the network structure has little effect on the evolution of trust and trustworthiness. Specifically, for well-mixed populations, lattices, random and scale-free networks, we find that trust never evolves, while trustworthiness evolves with some probability depending on the game parameters and the updating dynamics. Only for the scale-free network with degree non-normalized dynamics, we find parameter values for which trust evolves but trustworthiness does not, as well as values for which both trust and trustworthiness evolve. We conclude with a discussion about mechanisms that could lead to the evolution of trust and outline directions for future work., Comment: 9 two-column pages, 7 figures; accepted for publication in Journal of the Royal Society Interface

Finding mechanisms to promote the use of face masks is fundamental during the second phase of the COVID-19 pandemic response, when shelter-in-place rules are relaxed and some segments of the population are allowed to circulate more freely. Here we report three pre-registered studies (total N = 1,920), using an heterogenous sample of people living in the USA, showing that priming people to "rely on their reasoning" rather than to "rely on their emotions" significantly increases their intentions to wear a face covering. Compared to the baseline, priming reasoning promotes intentions to wear a face covering, whereas priming emotion has no significant effect. These findings have theoretical and practical implications. Practically, they offer a simple and scalable intervention to promote intentions to wear a face mask. Theoretically, they shed light on the cognitive basis of intentions to wear a face covering.

Now that various countries are or will soon be moving towards relaxing shelter-in-place rules, it is important that people use a face covering, to avoid an exponential resurgence of the spreading of the coronavirus disease (COVID-19). Here we report a pre-registered online experiment (N=2,459) using a heterogenous, although not representative, sample of people living in the USA, where we test the relative effect of messages highlighting that the coronavirus is a threat to "you" vs "your family" vs "your community" vs "your country" on self-reported intentions to wear a face covering. Results show that focusing on "your community" promotes intentions to wear a face covering relative to the baseline; the trend is the same when comparing "your community" to the other conditions, but not significant. We also conducted pre-registered analyses of gender differences on intentions to wear a face covering. We find that men less than women intend to wear a face covering, but this difference almost disappears in counties where wearing a face covering is mandatory. We also find that men less than women believe that they will be seriously affected by the coronavirus, and this partly mediates gender differences in intentions to wear a face covering (this is particularly ironic because official statistics actually show that men are affected by the COVID-19 more seriously than women). Finally, we also find gender differences in self-reported negative emotions felt when wearing a face covering. Men more than women agree that wearing a face covering is shameful, not cool, a sign of weakness, and a stigma; and these gender differences also mediate gender differences in intentions to wear a face covering.

The new coronavirus disease (COVID-19) threatens the lives of millions of people around the world, making it the largest health threat in recent times. Billions of people around the world are asked to adhere to strict shelter-in-place rules, finalised to slow down the spread of the virus. Appeals and messages are being used by leaders and policy-makers to promote pandemic response. Given the stakes at play, it is thus important for social scientists to explore which messages are most effective in promoting pandemic response. In fact, some papers in the last month have explored the effect of several messages on people's intentions to engage in pandemic response behaviour. In this paper, we make two contributions. First, we explore the effect of messages on people's actual engagement, and not on intentions. Specifically, our dependent variables are the level of understanding of official COVID-19 pandemic response governmental informative panels, measured through comprehension questions, and the time spent on reading these rules. Second, we test a novel set of appeals built through the theory of norms. One message targets the personal norm (what people think is the right thing to do), one targets the descriptive norm (what people think others are doing), and one targets the injunctive norm (what people think others approve or disapprove of). Our experiment is conducted online with a representative (with respect to gender, age, and location) sample of Italians. Norms are made salient using a flier. We find that norm-based fliers had no effect on comprehension and on time spent on the panels. These results suggest that norm-based interventions through fliers have very little impact on people's reading and understanding of COVID-19 pandemic response governmental rules.

A growing body of work suggests that people are sensitive to moral framing in economic games involving prosociality, suggesting that people hold moral preferences for doing the "right thing". What gives rise to these preferences? Here, we evaluate the explanatory power of a reputation-based account, which proposes that people respond to moral frames because they are motivated to look good in the eyes of others. Across two pre-registered experiments (total N = 3,610), we investigated whether reputational incentives amplify sensitivity to framing effects. Both experiments manipulated (i) whether moral or neutral framing was used to describe a Trade-Off Game (in which participants chose between prioritizing equality or efficiency) and (ii) whether Trade-Off Game choices were observable to a social partner in a subsequent Trust Game. We find that framing effects are relatively insensitive to reputational incentives: observability did not significantly amplify sensitivity to moral framing. However, our results are not inconsistent with the possibility that observability has some amplification effect; quantitatively, the observed framing effect was 74% as large when decisions were private as when they were observable. These results suggest that moral frames may tap into moral preferences that are relatively deeply internalized, and that power of moral frames to promote prosociality may not be strongly enhanced by making the morally-framed behavior observable to others.

Do people discriminate between men and women when they have the option to punish defectors or reward cooperators? Here we report on four pre-registered experiments, that shed some light on this question. Study 1 (N=544) shows that people do not discriminate between genders when they have the option to punish (reward) defectors (cooperators) in a one-shot prisoner's dilemma with third-party punishment/reward. Study 2 (N=253) extends Study 1 to a different method of punishing/rewarding: participants are asked to rate the behaviour of a defector/cooperator on a scale of 1 to 5 stars. In this case too, we find that people do not discriminate between genders. Study 3a (N=331) and Study 3b (N=310) conceptually replicate Study 2 with a slightly different gender manipulation. These latter studies show that, in situations where they do not have specific beliefs about the gender of the defector/cooperator's partner, neither men nor women discriminate between genders., Comment: Forthcoming in the Journal of the Economic Science Association

In this paper we investigate the effect of moral suasion on ingroup favouritism. We report a well-powered, pre-registered, two-stage 2x2 mixed-design experiment. In the first stage, groups are formed on the basis of how participants answer to a set of questions, concerning non-morally relevant issues in one treatment (assorting on non-moral preferences), and morally relevant issues in another treatment (assorting on moral preferences). In the second stage, participants choose how to split a given amount of money between participants of their own group and participants of the other group, first in the baseline setting and then in a setting where they are told to do what they believe to be morally right (moral suasion). Our main results are: (i) in the baseline, participants tend to favour their own group to a greater extent when groups are assorted according to moral preferences, compared to when they are assorted according to non-moral preferences; (ii) the net effect of moral suasion is to decrease ingroup favouritism, but there is also a non-negligible proportion of participants for whom moral suasion increases ingroup favouritism; (iii) the effect of moral suasion is substantially stable across group assorting and four pre-registered individual characteristics (gender, political orientation, religiosity, pro-life vs pro-choice ethical convictions)., Comment: Forthcoming in Judgment and Decision Making

Lies can have a negating impact on governments, companies, and the society as a whole. Understanding the dynamics of lying is therefore of crucial importance across different fields of research. While lying has been studied before in well-mixed populations, it is a fact that real interactions are rarely well-mixed. Indeed, they are usually structured and thus best described by networks. Here we therefore use the Monte Carlo method to study the evolution of lying in the sender-receiver game in a one-parameter family of networks, systematically covering complete networks, small-world networks, and one-dimensional rings. We show that lies which benefit the sender at a cost to the receiver, the so-called black lies, are less likely to proliferate on networks than they do in well-mixed populations. Honesty is thus more likely to evolve, but only when the benefit for the sender is smaller than the cost for the receiver. Moreover, this effect is particularly strong in small-world networks, but less so in the one-dimensional ring. For lies that favor the receiver at a cost to the sender, the so-called altruistic white lies, we show that honesty is also more likely to evolve than it is in well-mixed populations. But contrary to black lies, this effect is more expressed in the one-dimensional ring, whereas in small-world networks it is present only when the cost to the sender is greater than the benefit for the receiver. Lastly, for lies that benefit both the sender and the receiver, the so-called Pareto white lies, we show that the network structure actually favors the evolution of lying, but this only when the benefit for the sender is slightly greater than the benefit for the receiver. In this case again the small-world topology acts as an amplifier of the effect, while other network topologies fail to do the same., Comment: 11 two-column pages, 6 figures

Recent work highlights that cooperation in the one-shot Prisoner's dilemma (PD) is primarily driven by moral preferences for doing the right thing, rather than social preferences for equity or efficiency. By contrast, little is known on what motivates cooperation in the Stag-Hunt Game (SHG). Cooperation in the SHG fundamentally differs from cooperation in the PD in that it is not costly, but risky: players have no temptation to deviate from the cooperative outcome, but cooperation only pays off if the other player cooperates. Here, we provide data from a large (N=436), pre-registered, experiment. Contrary to what has been observed for the PD, we find that SHG cooperation is primarily driven by preferences for efficiency, rather than preferences for doing the right thing.

Lies can have profoundly negative consequences for individuals, groups, and even for societies. Understanding how lying evolves and when it proliferates is therefore of significant importance for our personal and societal well-being. To that effect, we here study the sender-receiver game in well-mixed populations with methods of statistical physics. We use the Monte Carlo method to determine the stationary frequencies of liars and believers for four different lie types. We consider altruistic white lies that favor the receiver at a cost to the sender, black lies that favor the sender at a cost to the receiver, spiteful lies that harm both the sender and the receiver, and Pareto white lies that favor both the sender and the receiver. We find that spiteful lies give rise to trivial behavior, where senders quickly learn that their best strategy is to send a truthful message, whilst receivers likewise quickly learn that their best strategy is to believe the sender's message. For altruistic white lies and black lies, we find that most senders lie while most receivers do not believe the sender's message, but the exact frequencies of liars and non-believers depend significantly on the payoffs, and they also evolve non-monotonically before reaching the stationary state. Lastly, for Pareto white lies we observe the most complex dynamics, with the possibility of both lying and believing evolving with all frequencies between 0 and 1 in dependence on the payoffs. We discuss the implications of these results for moral behavior in human experiments., Comment: 10 two-column pages, 6 figures; accepted for publication in Journal of the Royal Society Interface

We experimentally study how redistribution choices are affected by positive and negative information regarding the behaviour of a previous participant in a dictator game with a taking option. We use the strategy method to identify behavioural "types", and thus distinguish "conformists" from "counter-conformists", and unconditional choosers. Unconditional choosers make up the greatest proportion of types (about 80%) while only about 20% of subjects condition their responses to social information. We find that both conformity and counter-conformity are driven by a desire to be seen as moral (the "symbolization" dimension of moral identity). The main difference is that, conformity is also driven by a sensitivity to what others think ("attention to social comparison"). Unconditional giving (about 30% of players) on the other hand is mainly driven by the centrality of moral identity to the self (the "internalization" dimension of moral identity). Social information thus seems to mainly affect those who care about being seen to be moral. The direction of effect however depends on how sensitive one is to what others think.

Which social decisions are influenced by intuitive processes? Which by deliberative processes? The dual-process approach to human sociality has emerged in the last decades as a vibrant and exciting area of research. Yet, a perspective that integrates empirical and theoretical work is lacking. This review and meta-analysis synthesizes the existing literature on the cognitive basis of cooperation, altruism, truth-telling, positive and negative reciprocity, and deontology, and develops a framework that organizes the experimental regularities. The meta-analytic results suggest that intuition favours a set of heuristics that are related to the instinct for self-preservation: people avoid being harmed, avoid harming others (especially when there is a risk of harm to themselves), and are averse to disadvantageous inequalities. Finally, this paper highlights some key research questions to further advance our understanding of the cognitive foundations of human sociality., Comment: Journal of Personality and Social Psychology (in press)

In this paper we investigate the evolution of cooperation when the interaction structure is strictly local, and hence fitness only depends on local behaviors, while the competition structure is partly global, and hence selection can happen also between distant agents. We explore this novel setup by means of numerical simulations in a model where agents are arranged in a one-dimensional ring. Preliminary results suggest that the extent of global comparison systematically favors defection under strong selection, while its effect under weak selection is less systematic, but overall still favors defection. Further, the extent of global comparison seems to reduce sensibly fixation times.

Gender differences in human behaviour have attracted generations of social scientists, who have explored whether males and females act differently in domains involving competition, risk taking, cooperation, altruism, honesty, as well as many others. Yet, little is known about gender differences in the equity-efficiency trade-off. It has been suggested that females are more equitable than males, but the empirical evidence is weak and inconclusive. This gap is particularly important, because people in power of redistributing resources often face a conflict between equity and efficiency, to the point that this trade-off has been named as "the central problem in distributive justice". The recently introduced Trade-Off Game (TOG) - in which a decision-maker has to unilaterally choose between being equitable or being efficient - offers a unique opportunity to fill this gap. To this end, I analyse gender differences on a large dataset including all N=5,056 TOG decisions collected by my research group since we introduced this game. The results show that females prefer equity over efficiency to a greater extent than males do. These findings suggest that males and females have different preferences for resource distribution, and point to new avenues for future research.

Understanding the cognitive underpinnings of moral judgment is one of most pressing problems in psychological science. Some highly-cited studies suggest that reliance on intuition decreases utilitarian (expected welfare maximizing) judgments in sacrificial moral dilemmas in which one has to decide whether to instrumentally harm (IH) one person to save a greater number of people. However, recent work suggests that such dilemmas are limited in that they fail to capture the positive, defining core of utilitarianism: commitment to impartial beneficence (IB). Accordingly, a new two-dimensional model of utilitarian judgment has been proposed that distinguishes IH and IB components. The role of intuition on this new model has not been studied. Does relying on intuition disfavor utilitarian choices only along the dimension of instrumental harm or does it also do so along the dimension of impartial beneficence? To answer this question, we conducted three studies (total N = 970, two preregistered) using conceptual priming of intuition versus deliberation on moral judgments. Our evidence converges on an interaction effect, with intuition decreasing utilitarian judgments in IH - as suggested by previous work - but failing to do so in IB. These findings bolster the recently proposed two-dimensional model of utilitarian moral judgment, and point to new avenues for future research., Comment: Forthcoming in: Journal of Experimental Social Psychology

Understanding whether preferences are sensitive to the frame has been a major topic of debate in the last decades. For example, several works have explored whether the dictator game in the give frame gives rise to a different rate of pro-sociality than the same game in the take frame, leading to mixed results. Here we contribute to this debate with two experiments. In Study 1 ($N=567$) we implement an extreme dictator game in which the dictator either gets \$0.50 and the recipient gets nothing, or the opposite (i.e., the recipient gets \$0.50 and the dictator gets nothing). We experimentally manipulate the words describing the available actions using six terms, from very negative (e.g., stealing) to very positive (e.g., donating) connotations. We find that the rate of pro-sociality is affected by the words used to describe the available actions. In Study 2 ($N=221$) we ask brand new participants to rate each of the words used in Study 1 from ``extremely wrong'' to ``extremely right'' . We find that these moral judgments explain the framing effect in Study 1. In sum, our studies provide evidence that framing effects in an extreme Dictator game can be generated using morally loaded language., Comment: Forthcoming in Judgment and Decision Making

Methods of statistical physics have proven valuable for studying the evolution of cooperation in social dilemma games. However, recent empirical research shows that cooperative behavior in social dilemmas is only one kind of a more general class of behavior, namely moral behavior, which includes reciprocity, respecting others' property, honesty, equity, efficiency, as well as many others. Inspired by these experimental works, we here open up the path towards studying other forms of moral behavior with methods of statistical physics. We argue that this is a far-reaching direction for future research that can help us answer fundamental questions about human sociality. Why did our societies evolve as they did? What moral principles are more likely to emerge? What happens when different moral principles clash? Can we predict the break out of moral conflicts in advance and contribute to their solution? These are amongst the most important questions of our time, and methods of statistical physics could lead to new insights and contribute towards finding answers., Comment: 5 two-column pages; accepted for publication in Frontiers in Physics [related work available at arXiv:1705.07161]

Previous experiments have found mixed results on whether honesty is intuitive or requires deliberation. Here we add to this literature by building on prior work of Capraro (2017). We report a large study (N=1,389) manipulating time pressure vs time delay in a deception game. We find that, in this setting, people are more honest under time pressure, and that this result is not driven by confounds present in earlier work., Comment: Journal of Behavioral and Experimental Economics, In press

Differences between men and women have intrigued generations of social scientists, who have found that the two sexes behave differently in settings requiring competition, risk taking, altruism, honesty, as well as many others. Yet, little is known about whether there are gender differences in cooperative behavior. Previous evidence is mixed and inconclusive. Here I shed light on this topic by analyzing the totality of studies that my research group has conducted since 2013. This is a dataset of 10,951 observations coming from 7,322 men and women living in the US, recruited through Amazon Mechanical Turk, and who passed four comprehension questions to make sure they understand the cooperation problem (a one-shot prisoner's dilemma). The analysis demonstrates that women are more cooperative than men. The effect size is small (about 4 percentage points, and this might explain why previous studies failed to detect it) but highly significant (p<.0001).

Previous experiments have explored the effects of gender and cognitive reflection on dishonesty separately. To the best of our knowledge, no studies have investigated potential interactions between these two factors. Exploring this interaction is important because previous work found that males tend to be both more deliberative than females. Therefore, it is possible that the gender effect on dishonesty is moderated by cognitive reflection. Here we report a large online experiment (N = 766) where subjects first have a chance to lie for their benefit and then take a Cognitive Reflection Test (CRT). We find a significant interaction between gender and CRT score such that lack of deliberation promotes honesty for men but not for women. Additional analyses highlight that this effect is mainly driven by men whose answers in the CRT are neither intuitive nor deliberative, who happen to be particularly honest in our deception game.

Prosociality is fundamental to human social life, and, accordingly, much research has attempted to explain human prosocial behavior. Capraro and Rand (Judgment and Decision Making, 13, 99-111, 2018) recently provided experimental evidence that prosociality in anonymous, one-shot interactions (such as Prisoner's Dilemma and Dictator Game experiments) is not driven by outcome-based social preferences - as classically assumed - but by a generalized morality preference for "doing the right thing". Here we argue that the key experiments reported in Capraro and Rand (2018) comprise prominent methodological confounds and open questions that bear on influential psychological theory. Specifically, their design confounds: (i) preferences for efficiency with self-interest; and (ii) preferences for action with preferences for morality. Furthermore, their design fails to dissociate the preference to do "good" from the preference to avoid doing "bad". We thus designed and conducted a preregistered, refined and extended test of the morality preference hypothesis (N=801). Consistent with this hypothesis, our findings indicate that prosociality in the anonymous, one-shot Dictator Game is driven by preferences for doing the morally right thing. Inconsistent with influential psychological theory, however, our results suggest the preference to do "good" was as potent as the preference to avoid doing "bad" in this case.

In the Ultimatum Game (UG) one player, named "proposer", has to decide how to allocate a certain amount of money between herself and a "responder". If the offer is greater than or equal to the responder's minimum acceptable offer (MAO), then the money is split as proposed, otherwise, neither the proposer nor the responder get anything. The UG has intrigued generations of behavioral scientists because people in experiments blatantly violate the equilibrium predictions that self-interested proposers offer the minimum available non-zero amount, and self-interested responders accept. Why are these predictions violated? Previous research has mainly focused on the role of social preferences. Little is known about the role of general moral preferences for doing the right thing, preferences that have been shown to play a major role in other social interactions (e.g., Dictator Game and Prisoner's Dilemma). Here I develop a theoretical model and an experiment designed to pit social preferences against moral preferences. I find that, although people recognize that offering half and rejecting low offers are the morally right things to do, moral preferences have no causal impact on UG behavior. The experimental data are indeed well fit by a model according to which: (i) high UG offers are motivated by inequity aversion and, to a lesser extent, self-interest; (ii) high MAOs are motivated by inequity aversion.

This paper studies lying in a novel context. Previous work has focused on situations in which people are either fully aware of the economic consequences of all available actions (e.g., die-under-cup paradigm), or they are uncertain, but this uncertainty cannot be cleared in any way (e.g., sender-receiver game). On the contrary, in reality, people oftentimes know that they will have a chance to lie, they are initially uncertain about the economic consequences of the available actions, but they can invest resources (e.g., time) to find them out. Here we capture the essence of this type of situations by means of a novel decision problem. Two experiments provide evidence of four empirical regularities regarding the distribution of choices, and suggest that participants vary along two dimensions: the moral cost of lying, and the cost of investing time to find out the payoffs associated to the available actions. Taking inspiration from these observations, we introduce a model that is consistent with the main empirical results.

The conflict between pro-self and pro-social behaviour is at the core of many key problems of our time, as, for example, the reduction of air pollution and the redistribution of scarce resources. For the well-being of our societies, it is thus crucial to find mechanisms to promote pro-social choices over egoistic ones. Particularly important, because cheap and easy to implement, are those mechanisms that can change people's behaviour without forbidding any options or significantly changing their economic incentives, the so-called "nudges". Previous research has found that moral nudges (e.g., making norms salient) can promote pro-social behaviour. However, little is known about whether their effect persists over time and spills across context. This question is key in light of research showing that pro-social actions are often followed by selfish actions, thus suggesting that some moral manipulations may backfire. Here we present a class of simple moral nudges that have a great positive impact on pro-sociality. In Studies 1-4 (total N = 1,400), we use economic games to demonstrate that asking subjects to self-report "what they think is the morally right thing to do" does not only increase pro-sociality in the choice immediately after, but also in subsequent choices, and even when the social context changes. In Study 5, we explore whether moral nudges promote charity donations to humanitarian organisations in a large (N=1,800) crowdfunding campaign. We find that, in this context, moral nudges increase donations by about 44 percent., Comment: Forthcoming in Scientific Reports

Whether there are gender differences in lying has been largely debated in the past decade. Previous studies found mixed results. To shed light on this topic, here I report a meta-analysis of 8,728 distinct observations, collected in 65 Sender-Receiver game treatments, by 14 research groups. Following previous work and theoretical considerations, I distinguish three types of lies: black lies, that benefit the liar at a cost for another person; altruistic white lies, that benefit another person at a cost for the liar; Pareto white lies, that benefit both the liar and another person. The results show that gender differences in lying significantly depend on the consequences of lying. Specifically: (i) males are significantly more likely than females to tell black lies (N=4,161); (ii) males are significantly more likely than females to tell altruistic white (N=2,940); (iii) results are inconclusive in the case of Pareto white lies (N=1,627)., Comment: Forthcoming in Judgment and Decision Making

The emergence and survival of cooperation is one of the hardest problems still open in science. Several factors such as the existence of punishment, fluctuations in finite systems, repeated interactions and the formation of prestige may all contribute to explain the counter-intuitive prevalence of cooperation in natural and social systems. The characteristics of the interaction networks have been also signaled as an element favoring the persistence of cooperators. Here we consider the invasion dynamics of cooperative behaviors in complex topologies. The invasion of a heterogeneous network fully occupied by defectors is performed starting from nodes with a given number of connections (degree) $k_0$. The system is then evolved within a Prisoner's Dilemma game and the outcome is analyzed as a function of $k_0$ and the degree $k$ of the nodes adopting cooperation. Carried out using both numerical and analytical approaches, our results show that the invasion proceeds following preferentially a hierarchical order in the nodes from those with higher degree to those with lower degree. However, the invasion of cooperation will succeed only when the initial cooperators are numerous enough to form a cluster from which cooperation can spread. This implies that the initial condition must be a suitable equilibrium between high degree and high numerosity, which usually takes place, when possible, at intermediate values of $k_0$. These findings have potential applications, as they suggest that, in order to promote cooperative behavior on complex networks, one should infect with cooperators \emph{high but not too high} degree nodes., Comment: 19 pages, 9 figures

Reputation plays a major role in human societies, and it has been proposed as an explanation for the evolution of cooperation. While the majority of previous studies equates reputation with a transparent and complete history of players' past decisions, in real life, reputations are often ambiguous and opaque. Using web-based experiments, we explore the extent to which opaque reputation works in isolating defectors, with and without partner selection opportunities. Our results show that low reputation works as a signal of untrustworthiness, whereas medium or high reputation are not taken into account by participants for orienting their choices. We also find that reputation without partner selection does not promote cooperative behavior; that is, defectors do not turn into cooperators only for the sake of getting a positive reputation. Finally, in a third study, we find that, when reputation is pivotal to selection, then a substantial proportion of would-be-defectors turn into cooperators. Taken together, these results provide insights on the characteristics of reputation and on the way in which humans make use of it when selecting partners but also when knowing that they will be selected., Comment: Forthcoming in Judgment and Decision Making