Cooperation in the Prisoner's Dilemma Game Based on the Second-Best Decision

In the research addressing the prisoner's dilemma game, the effectiveness and accountableness of the method allowing for the emergence of cooperation is generally discussed. The most well-known solutions for this question are memory based iteration, the tag used to distinguish between defector and cooperator, the spatial structure of the game and the either direct or indirect reciprocity. We have also challenged to approach the topic from a different point of view namely that temperate acquisitiveness in decision making could be possible to achieve cooperation. It was already shown in our previous research that the exclusion of the best decision had a remarkable effect on the emergence of an almost cooperative state. In this paper, we advance the decision of our former research to become more explainable by introducing the second-best decision. If that decision is adopted, players also reach an extremely high level cooperative state in the prisoner's dilemma game and also in that of extended strategy expression. The cooperation of this extended game is facilitated only if the product of two parameters is under the criticality. In addition, the applicability of our model to the problem in the real world is discussed.Cooperation, Altruism, Agent-Based Simulation, Evolutionary Game Theory

Think global, act local: Preserving the global commons

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordPreserving global public goods, such as the planet’s ecosystem, depends on large-scale cooperation, which is difficult to achieve because the standard reciprocity mechanisms weaken in large groups. Here we demonstrate a method by which reciprocity can maintain cooperation in a large-scale public goods game (PGG). In a first experiment, participants in groups of on average 39 people play one round of a Prisoner’s Dilemma (PD) with their two nearest neighbours on a cyclic network after each PGG round. We observe that people engage in “local-to-global” reciprocity, leveraging local interactions to enforce global cooperation: Participants reduce PD cooperation with neighbours who contribute little in the PGG. In response, low PGG contributors increase their contributions if both neighbours defect in the PD. In a control condition, participants do not know their neighbours’ PGG contribution and thus cannot link play in the PD to the PGG. In the control we observe a sharp decline of cooperation in the PGG, while in the treatment condition global cooperation is maintained. In a second experiment, we demonstrate the scalability of this effect: in a 1,000-person PGG, participants in the treatment condition successfully sustain public contributions. Our findings suggest that this simple “local-to-global” intervention facilitates large-scale cooperation.This work was supported by Office of Naval Research grant N00014-16-1-2914 and by the John Templeton Foundation. The Program for Evolutionary Dynamics is supported in part by a gift from B Wu and Eric Larson

Coevolution of risk aversion, trust and trustworthiness: an agent-based approach

The research presented here deals with the evolution of personality features of humans engaged in strategic interactions. The evolution of risk aversion and trustworthiness is modelled and simulated in the context of a binary trust game, seeking the origin and end-points of an evolutionary process, accounting for different degrees of locality. This research has employed computer simulations in order to get dynamic equilibria in populations of players that keep evolving. The locality or global nature of interaction plays an important role. Risk aversion evolves together with trust and trustworthiness. Trust behaviour follows reciprocation attributes. Results of the simulations are equal to the ones elicited in empirical studies

Evolution of cooperation in multilayer networks

Dissertation presented as the partial requirement for obtaining a Master's degree in Information Management, specialization in Information Systems and Technologies ManagementIndividuals take part in multiple layers of networks of interactions simultaneously. These interdependent networks account for the different sort of social ties individuals maintain per layer. In each layer individuals participate in N-Player Public Goods Games where benefits collected increase with amounts invested. It is, however, tempting to be a free-rider, i.e., to take advantage of the common pool without contributing to it, a situation from which a social dilemma results. This thesis offers new insights on how cooperation dynamics is shaped by multiple layers of social interactions and diversity of contributions invested per game. To this end, we resort to Evolutionary Game Theory and Network Science to provide a convenient framework to address the most important prototypical social conflicts and/or dilemmas in large networked populations. In particular, we propose a novel mean-field approach capable of tracking the self-organization of Cooperators when co-evolving with Defectors in a multilayer environment. We show that the emerging collective dynamics, which depends (i) on the underlying layer networks of interactions and (ii) on the criteria to share a finite investment across all games, often does not bear any resemblance with the local processes supporting them. Our findings suggest that, whenever individual investments are distributed among games or layers, resilience of cooperation against free-riders increases with the number of layers, and that cooperation emerges from a non-trivial organization of cooperation across the layers. In opposition, under constant, non-distributed investments, the level of cooperation shows little sensibility to variations in the number of layers. These findings put in evidence the importance of asymmetric contributions across games and social contexts in the emergence of human cooperation

Game theoretic modeling and analysis : A co-evolutionary, agent-based approach

Ph.DDOCTOR OF PHILOSOPH

COOPERATION AND SOCIAL BONDS IN COMMON VAMPIRE BATS

Regurgitated food sharing among vampire bats is a classic textbook example of reciprocity ("reciprocal altruism"). But many authors have contested both the notion that reciprocity explains vampire bat food-sharing and the importance of reciprocity more generally. In Chapter 1, I review the literature on evolutionary explanations of cooperation. I show why reciprocity was once considered important but is now considered rare: overly literal translations of game theory strategies have resulted in problems for both defining and testing reciprocity. In Chapter 2, I examine the relative roles of social predictors of food-sharing decisions by common vampire bats (Desmodus rotundus) under controlled conditions of mixed relatedness and equal familiarity by fasting 20 individuals in 48 trials over two years. The food-sharing network was consistent, symmetrical, and correlated with mutual allogrooming. Non- kin food-sharing patterns were not consistent with harassment or byproduct explanations. I next attempted to manipulate food-sharing decisions in two ways. In Chapter 3, I administered intranasal oxytocin to test for effects on allogrooming and food sharing. I observed that inhaled oxytocin slightly increased the magnitude of food donations within dyads, and the amount of female allogrooming within and across all partners, without increasing number of partners. In Chapter 4, I assessed contingency of food-sharing in 7 female dyads (including four pairs of mother and adult daughters) with prior histories of sharing. To test for evidence of partner switching, I measured dyadic levels of food sharing before and after a treatment period where I prevented dyadic sharing (each bat could only be fed by others). A bat's sharing network size predicted how much food it received in the experiment. When primary donors were excluded, subjects did not compensate with donations from other partners. Yet, food-sharing bonds appeared unaffected by the non-sharing treatment. In particular, close maternal kin were clearly not enforcing cooperation using strict contingency. I argue that any contingencies within such bonds are likely to involve multiple services and long timescales, making them difficult to detect. Simple and dyadic `tit-for-tat' models are unlikely to predict cooperative decisions by vampire bats or other species with stable, mixed kinship, social bonds

Cooperation and Punishment in Humans: Exploring the Effect of Power Asymmetries and the Motivations Underpinning Punishment

People willingly pay to harm cheats in economic games. Although, punishment ostensibly increases cooperation levels, consensus is lacking over when punishment can increase individual or group payoffs and what motivates punishment decisions. Most previous studies have assumed that all individuals are equal. However, in reality individuals often vary in terms of power, such that some players are able to inflict a greater cost on their partner than their partner is able to reciprocate. I investigated the effect of power asymmetries on cooperation and punishment in repeated prisoner's dilemma games with punishment both where cooperation investment was binary and where cooperation investment was variable. I found that punishment did not promote cooperation from targets in any conditions. Several studies have suggested that punishment may be motivated by disadvantageous inequality aversion. These findings raise the possibility that individuals use punishment to restore equality. However, the alternative that punishment is simply motivated by a desire for revenge and is not tailored to achieve equality, cannot be ruled out. I used a modified dictator game with punishment to disentangle these two possibilities. I found evidence that punishment was motivated by both a desire for revenge and a desire for equality. Individuals often punish those who deviate from social norms. Why atypical behaviour is more likely to be punished than typical behaviour remains unclear. One possibility is that individuals simply dislike norm violators. Alternatively, individuals may be more likely to punish atypical behaviour because the cost of punishment generally increases with the number of individuals punished. To test these hypotheses, I used a modified public goods game with third party punishment. My results suggest that punishment of atypical behaviour might often be explained in terms of the costs to the punisher, rather than responses to norm violators. In summary, my thesis sheds light on the conditions in which punishment is most likely to promote cooperation and on the motivations underpinning punishment decisions

Behaviour from an evolutionary point of view: experimental studies on fish and humans

Evolutionary theory based on natural selection states that individuals of a population vary in certain traits and pass these traits on to their offspring. Furthermore, individuals continuously compete with each other for limited resources, such as food items, mating partners, and territories. As a consequence, those individuals that feature traits enabling them to cope better with the current environmental conditions have an advantage in accessing and exploiting these resources and can, therefore, allocate more resources to reproduction. Thus, they will outcompete those individuals not having such advantageous traits and the respective traits will spread in the population. Disadvantageous traits will diminish. The result of evolution is ever better adapted organisms. However, there are many traits that do not seem to be advantageous to the individual, but they still have evolved. The present work focuses on two such phenomena that are disadvantageous and costly at the first sight: sexual reproduction and human cooperation. Sexual reproduction is disadvantageous, because only one half of the population can bear offspring. Furthermore, it is costly to the individual, because, among other things, individuals have to search for mates. It has been suggested that sexually reproducing organisms have an advantage due to a higher genetic recombination rate. Thus, they are supposed to have an increased ability to adapt to environmental changes. A potential source of such changes are parasites: Organisms potentially need to continuously develop better adapted immune defence (e.g., genes of the major histocompatibility complex, MHC) to successfully fight parasites. This exerts selection pressure on the parasites which have to adapt subsequently. The result is an arms race between host and parasites in which it would be advantageous for the host to achieve a high genetic recombination rate and, hence, a high adaptability by sexual reproduction. A crucial behaviour connected to sexual reproduction is mate choice, and the threespined stickleback is a perfectly suited model organism to investigate this behaviour in more detail. It is known that female sticklebacks base their mating decision on various visual and olfactory male cues, such as red breeding colouration (visual cue) and MHC peptides (olfactory cue). Adding on to previous work, Chapter 1 deals with seasonal variation of male olfactory attractiveness to female sticklebacks. Our results document that, besides the MHC signal, a further cue conveys information about potential mates; male olfactory attractiveness to females peaked in summer while the males maintained a nest. This finding suggests that males release special substances during nest maintenance that indicate male reproductive status to females. Evidently, female olfactory mate choice is not only based on the MHC signal, but on a combination of at least two cues. A second experiment (Chapter 2) examined the evolutionary consequences of mate choice in sticklebacks under semi-natural conditions. Thereby, the focus was on MHC-based mate choice, and actual matings were analysed in six enclosure facilities in the lake Großer Plöner See. The obtained results are consistent with previous studies that linked MHC genetics with fitness related traits, and show that individuals with an intermediate number of MHC variants ultimately achieve the highest reproductive output. Consequently, choosing the right mate bearing the best MHC genotype might confer the individual advantage needed to cope with an ever changing environment of parasites. This finding is in line with the hypothesis that parasite pressure is a potential cause of the evolution and maintenance of sexual reproduction. Another seemingly paradoxical phenomenon for evolutionary biologists is the evolution and maintenance of cooperation. Cooperation describes behaviour that is beneficial for another individual, but costly for the cooperator. Thus, a cooperator is someone who invests his own resources in order to help others. Evidently, a defector (i.e., someone who does not cooperate) does not bear the costs of cooperation and, therefore, has more resources to himself. But why is cooperative behaviour so abundant if it is costly? This is especially puzzling in the case of humans which tend to cooperate even with unrelated individuals in one-shot encounters. In general, university students played computer-based games that served as experimental setup for the research presented in the second part of this thesis. Analysing the participants’ behaviour provided further insight into the phenomenon of human cooperation. A first study (Chapter 3) has elucidated whether the evolved strategies also enable humans to solve modern social dilemmas. Thereby, we focused in Chapter 3 on a global dilemma that we characterised as a collective-risk social dilemma: the prevention of dangerous climate change. To reduce the risk of dangerous climate change, greenhouse gas emissions need to be reduced to ~50% of the present level by 2050. Thus, states, companies, but also private individuals need to invest in environmentally friendly technologies and practices. In order to reduce greenhouse gas emissions down to a certain threshold, we need to invest in climate protection up to a certain threshold. Otherwise we will face substantial human, ecological, and economic losses. This scenario was simulated in an experimental game with 30 groups of six students each. The participants’ investments in climate protection had to reach a known threshold to prevent dangerous climate change. Participants only reached this threshold if the risk of personal loss was high. Thus, we conclude that humans are able to solve the real climate dilemma if they are convinced about the extreme risk of losses. Further experiments on cooperation (Chapters 4 and 5) are based on the finding that humans tend to direct their help towards people that have previously helped others. This so called indirect reciprocity can explain high levels of cooperation and is based on the reputation of the other person. But how do people get to know the reputation of others? Evidently, we cannot observe all the people we possibly interact with during our entire life, therefore various scientists proposed gossip as a possible means of spreading and gathering this information. In this thesis, this proposed function of gossip has been investigated experimentally. The first study in this context (Chapter 4) has shown that gossip indeed can serve as a vector for social, reputation-relevant information. Participants described the observed behaviour of others truthfully; this gossip was perceived as positive or negative in accordance with the author’s intention; and, last, participants reacted on positive gossip with cooperative behaviour, and on negative gossip with defection towards the person who was described by that gossip. Yet, gossip also seems to have a strong manipulative potential; people’s decisions were influenced by gossip designed by the experimenter even if they knew hard facts (i.e., past behaviour) about the other person. In a follow-up study (Chapter 5), this effect was examined in more detail. The effect of multiple gossip statements was examined with respect to elicited cooperation from the people encountering them. The participants’ response was compared to the same people’s response based on a single gossip statement or direct observation. The results indicate that an increased number of gossip statements helps to reduce the risk of manipulation and to direct cooperative behaviour towards cooperators. Furthermore, this study suggests a strong connection between reputation, reciprocity, and trust: Participants who gained a high reputation through reciprocating were also perceived as more trustworthy. This connection might have fostered cooperative behaviour up to the present level in modern human societies. These findings support the hypothesis that gossip and, hence, the use of language, is connected to the high level of human cooperation.Summary__________________________________________________________________ 7 Zusammenfassung _________________________________________________________ 10 Introduction ______________________________________________________________ 13 Sexual reproduction ____________________________________________________________ 14 Human Cooperation ____________________________________________________________ 17 Outline __________________________________________________________________ 21 Mate choice in the three-spined stickleback __________________________________________ 21 Human cooperation_____________________________________________________________ 22 Chapter 1 Seasonal Variation of Male Attractiveness in Sticklebacks ________________ 24 Abstract______________________________________________________________________ 24 Introduction___________________________________________________________________ 25 Materials and Methods __________________________________________________________ 26 Results_______________________________________________________________________ 28 Discussion____________________________________________________________________ 30 Acknowledgements_____________________________________________________________ 31 Chapter 2 Lifetime Reproductive Success and the MHC __________________________ 32 Abstract______________________________________________________________________ 32 Introduction___________________________________________________________________ 33 Material and methods ___________________________________________________________ 34 Results_______________________________________________________________________ 37 Discussion____________________________________________________________________ 41 Acknowledgments______________________________________________________________ 43 Chapter 3 Preventing Dangerous Climate Change: a Collective-Risk Social Dilemma __ 44 Abstract______________________________________________________________________ 44 Introduction___________________________________________________________________ 45 Results and Discussion __________________________________________________________ 47 Methods______________________________________________________________________ 51 Acknowledgements_____________________________________________________________ 51 Chapter 4 Gossip as an Alternative for Direct Observation ________________________ 52 Abstract______________________________________________________________________ 52 Introduction___________________________________________________________________ 53 Results_______________________________________________________________________ 55 Discussion____________________________________________________________________ 59 Materials and Methods __________________________________________________________ 61 Acknowledgements_____________________________________________________________ 63 Chapter 5 Multiple Gossip Statements, Reputation, and Trust ______________________ 64 Abstract______________________________________________________________________ 64 Introduction___________________________________________________________________ 65 Materials and Methods __________________________________________________________ 66 Results_______________________________________________________________________ 68 Discussion____________________________________________________________________ 72 Acknowledgements_____________________________________________________________ 75 Conclusion _______________________________________________________________ 76 Acknowledgements _________________________________________________________ 78 References________________________________________________________________ 80 Appendix A ______________________________________________________________ 104 Appendix B ______________________________________________________________ 106 Appendix C ______________________________________________________________ 111 Appendix D ______________________________________________________________ 122 Appendix E ______________________________________________________________ 128 Curriculum vitae__________________________________________________________ 13

Behaviour from an evolutionary point of view: experimental studies on fish and humans

Evolutionary theory based on natural selection states that individuals of a population vary in certain traits and pass these traits on to their offspring. Furthermore, individuals continuously compete with each other for limited resources, such as food items, mating partners, and territories. As a consequence, those individuals that feature traits enabling them to cope better with the current environmental conditions have an advantage in accessing and exploiting these resources and can, therefore, allocate more resources to reproduction. Thus, they will outcompete those individuals not having such advantageous traits and the respective traits will spread in the population. Disadvantageous traits will diminish. The result of evolution is ever better adapted organisms. However, there are many traits that do not seem to be advantageous to the individual, but they still have evolved. The present work focuses on two such phenomena that are disadvantageous and costly at the first sight: sexual reproduction and human cooperation. Sexual reproduction is disadvantageous, because only one half of the population can bear offspring. Furthermore, it is costly to the individual, because, among other things, individuals have to search for mates. It has been suggested that sexually reproducing organisms have an advantage due to a higher genetic recombination rate. Thus, they are supposed to have an increased ability to adapt to environmental changes. A potential source of such changes are parasites: Organisms potentially need to continuously develop better adapted immune defence (e.g., genes of the major histocompatibility complex, MHC) to successfully fight parasites. This exerts selection pressure on the parasites which have to adapt subsequently. The result is an arms race between host and parasites in which it would be advantageous for the host to achieve a high genetic recombination rate and, hence, a high adaptability by sexual reproduction. A crucial behaviour connected to sexual reproduction is mate choice, and the threespined stickleback is a perfectly suited model organism to investigate this behaviour in more detail. It is known that female sticklebacks base their mating decision on various visual and olfactory male cues, such as red breeding colouration (visual cue) and MHC peptides (olfactory cue). Adding on to previous work, Chapter 1 deals with seasonal variation of male olfactory attractiveness to female sticklebacks. Our results document that, besides the MHC signal, a further cue conveys information about potential mates; male olfactory attractiveness to females peaked in summer while the males maintained a nest. This finding suggests that males release special substances during nest maintenance that indicate male reproductive status to females. Evidently, female olfactory mate choice is not only based on the MHC signal, but on a combination of at least two cues. A second experiment (Chapter 2) examined the evolutionary consequences of mate choice in sticklebacks under semi-natural conditions. Thereby, the focus was on MHC-based mate choice, and actual matings were analysed in six enclosure facilities in the lake Großer Plöner See. The obtained results are consistent with previous studies that linked MHC genetics with fitness related traits, and show that individuals with an intermediate number of MHC variants ultimately achieve the highest reproductive output. Consequently, choosing the right mate bearing the best MHC genotype might confer the individual advantage needed to cope with an ever changing environment of parasites. This finding is in line with the hypothesis that parasite pressure is a potential cause of the evolution and maintenance of sexual reproduction. Another seemingly paradoxical phenomenon for evolutionary biologists is the evolution and maintenance of cooperation. Cooperation describes behaviour that is beneficial for another individual, but costly for the cooperator. Thus, a cooperator is someone who invests his own resources in order to help others. Evidently, a defector (i.e., someone who does not cooperate) does not bear the costs of cooperation and, therefore, has more resources to himself. But why is cooperative behaviour so abundant if it is costly? This is especially puzzling in the case of humans which tend to cooperate even with unrelated individuals in one-shot encounters. In general, university students played computer-based games that served as experimental setup for the research presented in the second part of this thesis. Analysing the participants’ behaviour provided further insight into the phenomenon of human cooperation. A first study (Chapter 3) has elucidated whether the evolved strategies also enable humans to solve modern social dilemmas. Thereby, we focused in Chapter 3 on a global dilemma that we characterised as a collective-risk social dilemma: the prevention of dangerous climate change. To reduce the risk of dangerous climate change, greenhouse gas emissions need to be reduced to ~50% of the present level by 2050. Thus, states, companies, but also private individuals need to invest in environmentally friendly technologies and practices. In order to reduce greenhouse gas emissions down to a certain threshold, we need to invest in climate protection up to a certain threshold. Otherwise we will face substantial human, ecological, and economic losses. This scenario was simulated in an experimental game with 30 groups of six students each. The participants’ investments in climate protection had to reach a known threshold to prevent dangerous climate change. Participants only reached this threshold if the risk of personal loss was high. Thus, we conclude that humans are able to solve the real climate dilemma if they are convinced about the extreme risk of losses. Further experiments on cooperation (Chapters 4 and 5) are based on the finding that humans tend to direct their help towards people that have previously helped others. This so called indirect reciprocity can explain high levels of cooperation and is based on the reputation of the other person. But how do people get to know the reputation of others? Evidently, we cannot observe all the people we possibly interact with during our entire life, therefore various scientists proposed gossip as a possible means of spreading and gathering this information. In this thesis, this proposed function of gossip has been investigated experimentally. The first study in this context (Chapter 4) has shown that gossip indeed can serve as a vector for social, reputation-relevant information. Participants described the observed behaviour of others truthfully; this gossip was perceived as positive or negative in accordance with the author’s intention; and, last, participants reacted on positive gossip with cooperative behaviour, and on negative gossip with defection towards the person who was described by that gossip. Yet, gossip also seems to have a strong manipulative potential; people’s decisions were influenced by gossip designed by the experimenter even if they knew hard facts (i.e., past behaviour) about the other person. In a follow-up study (Chapter 5), this effect was examined in more detail. The effect of multiple gossip statements was examined with respect to elicited cooperation from the people encountering them. The participants’ response was compared to the same people’s response based on a single gossip statement or direct observation. The results indicate that an increased number of gossip statements helps to reduce the risk of manipulation and to direct cooperative behaviour towards cooperators. Furthermore, this study suggests a strong connection between reputation, reciprocity, and trust: Participants who gained a high reputation through reciprocating were also perceived as more trustworthy. This connection might have fostered cooperative behaviour up to the present level in modern human societies. These findings support the hypothesis that gossip and, hence, the use of language, is connected to the high level of human cooperation.Summary__________________________________________________________________ 7 Zusammenfassung _________________________________________________________ 10 Introduction ______________________________________________________________ 13 Sexual reproduction ____________________________________________________________ 14 Human Cooperation ____________________________________________________________ 17 Outline __________________________________________________________________ 21 Mate choice in the three-spined stickleback __________________________________________ 21 Human cooperation_____________________________________________________________ 22 Chapter 1 Seasonal Variation of Male Attractiveness in Sticklebacks ________________ 24 Abstract______________________________________________________________________ 24 Introduction___________________________________________________________________ 25 Materials and Methods __________________________________________________________ 26 Results_______________________________________________________________________ 28 Discussion____________________________________________________________________ 30 Acknowledgements_____________________________________________________________ 31 Chapter 2 Lifetime Reproductive Success and the MHC __________________________ 32 Abstract______________________________________________________________________ 32 Introduction___________________________________________________________________ 33 Material and methods ___________________________________________________________ 34 Results_______________________________________________________________________ 37 Discussion____________________________________________________________________ 41 Acknowledgments______________________________________________________________ 43 Chapter 3 Preventing Dangerous Climate Change: a Collective-Risk Social Dilemma __ 44 Abstract______________________________________________________________________ 44 Introduction___________________________________________________________________ 45 Results and Discussion __________________________________________________________ 47 Methods______________________________________________________________________ 51 Acknowledgements_____________________________________________________________ 51 Chapter 4 Gossip as an Alternative for Direct Observation ________________________ 52 Abstract______________________________________________________________________ 52 Introduction___________________________________________________________________ 53 Results_______________________________________________________________________ 55 Discussion____________________________________________________________________ 59 Materials and Methods __________________________________________________________ 61 Acknowledgements_____________________________________________________________ 63 Chapter 5 Multiple Gossip Statements, Reputation, and Trust ______________________ 64 Abstract______________________________________________________________________ 64 Introduction___________________________________________________________________ 65 Materials and Methods __________________________________________________________ 66 Results_______________________________________________________________________ 68 Discussion____________________________________________________________________ 72 Acknowledgements_____________________________________________________________ 75 Conclusion _______________________________________________________________ 76 Acknowledgements _________________________________________________________ 78 References________________________________________________________________ 80 Appendix A ______________________________________________________________ 104 Appendix B ______________________________________________________________ 106 Appendix C ______________________________________________________________ 111 Appendix D ______________________________________________________________ 122 Appendix E ______________________________________________________________ 128 Curriculum vitae__________________________________________________________ 13