How chimpanzees solve collective action problems

We presented small groups of chimpanzees with two collective action situations, in which action was necessary for reward but there was a disincentive for individuals to act owing to the possibility of free-riding on the efforts of others. We found that in simpler scenarios (experiment 1) in which group size was small, there was a positive relationship between rank and action with more dominant individuals volunteering to act more often, particularly when the reward was less dispersed. Social tolerance also seemed to mediate action whereby higher tolerance levels within a group resulted in individuals of lower ranks sometimes acting and appropriating more of the reward. In more complex scenarios, when group size was larger and cooperation was necessary (experiment 2), overcoming the problem was more challenging. There was highly significant variability in the action rates of different individuals as well as between dyads, suggesting success was more greatly influenced by the individual personalities and personal relationships present in the group.     

我国器官移植中的伦理困境及解决思路

我国的器官移植近10年来有了发展,无论从技术层面、移植数量和质量、临床管理以及法规建设上都有了长足的进步。然而,由于我们在开展器官移植方面的先天不足,例如从事器官移植的技术队伍主要是来自海外学成归来的专家;技术主要靠引进西方的临床技术,在基础研究和创新方面相对薄弱;在法律和管理制度的建设方面相对滞后,没有建立一个从制度上保证器官移植健康开展的系统,使得在器官供体来源和器官的公正分配上存在许多欠缺。因此有必要对我国的器官移植历史进行回顾和总结,对我国在器官移植中存在的错误观念和伦理困境进行剖析,寻找适合我国开展器官移植的正确途径,促进我国的器官移植事业健康发展。     

Evolving learning rules and emergence of cooperation in spatial prisoner's dilemma

In the evolutionary Prisoner's dilemma (PD) game, agents play with each other and update their strategies in every generation according to some microscopic dynamical rule. In its spatial version, agents do not play with every other but, instead, interact only with their neighbours, thus mimicking the existing of a social or contact network that defines who interacts with whom. In this work, we explore evolutionary, spatial PD systems consisting of two types of agents, each with a certain update (reproduction, learning) rule. We investigate two different scenarios: in the first case, update rules remain fixed for the entire evolution of the system; in the second case, agents update both strategy and update rule in every generation. We show that in a well-mixed population the evolutionary outcome is always full defection. We subsequently focus on two-strategy competition with nearest-neighbour interactions on the contact network and synchronised update of strategies. Our results show that, for an important range of the parameters of the game, the final state of the system is largely different from that arising from the usual setup of a single, fixed dynamical rule. Furthermore, the results are also very different if update rules are fixed or evolve with the strategies. In these respect, we have studied representative update rules, finding that some of them may become extinct while others prevail. We describe the new and rich variety of final outcomes that arise from this co-evolutionary dynamics. We include examples of other neighbourhoods and asynchronous updating that confirm the robustness of our conclusions. Our results pave the way to an evolutionary rationale for modelling social interactions through game theory with a preferred set of update rules.     

Replicator dynamics of reward & reputation in public goods games

Public goods games have become the mathematical metaphor for game theoretical investigations of cooperative behavior in groups of interacting individuals. Cooperation is a conundrum because cooperators make a sacrifice to benefit others at some cost to themselves. Exploiters or defectors reap the benefits and forgo costs. Despite the fact that groups of cooperators outperform groups of defectors, Darwinian selection or utilitarian principles based on rational choice should favor defectors. In order to overcome this social dilemma, much effort has been expended for investigations pertaining to punishment and sanctioning measures against defectors. Interestingly, the complementary approach to create positive incentives and to reward cooperation has received considerably less attention—despite being heavily advocated in education and social sciences for increasing productivity or preventing conflicts. Here we show that rewards can indeed stimulate cooperation in interaction groups of arbitrary size but, in contrast to punishment, fail to stabilize it. In both cases, however, reputation is essential. The combination of reward and reputation result in complex dynamics dominated by unpredictable oscillations.     

Overlapping generations can promote altruistic behavior

Abstract. We use an inclusive fitness model to study the evolution of altruism in a patch-structured population in which there is positive probability of breeder survival from one generation to the next. We find first that breeder survival promotes altruism and second that there is a marked difference between benefits of fecundity and benefits of survival. Under the first altruism is more strongly favored, and under the second altruism is less strongly favored than in a randomly mixing population.     

Social observation increases deontological judgments in moral dilemmas

A concern for positive reputation is one of the core motivations underlying various social behaviors in humans. The present study investigated how experimentally induced reputation concern modulates judgments in moral dilemmas. In a mixed-design experiment, participants were randomly assigned to the observed vs. the control group and responded to a series of trolley-type moral dilemmas either in the presence or absence of observers, respectively. While no significant baseline difference in personality traits and moral decision tendency were found across two groups of participants, our analyses revealed that social observation promoted deontological judgments especially for moral dilemmas involving direct bodily harm (i.e., personal moral dilemmas), yet with an overall decrease in decision confidence and significant prolongation of reaction time. Moreover, participants in the observed group, but not in the control group, showed the increased sensitivities towards warmth vs. competence traits words in the lexical decision task performed after the moral dilemma task. Our findings suggest that reputation concern, once triggered by the presence of potentially judgmental others, could activate a culturally dominant norm of warmth in various social contexts. This could, in turn, induce a series of goal-directed processes for self-presentation of warmth, leading to increased deontological judgments in moral dilemmas. The results of the present study provide insights into the reputational consequences of moral decisions that merit further exploration.     

Economic game theory for mutualism and cooperation

We review recent work at the interface of economic game theory and evolutionary biology that provides new insights into the evolution of partner choice, host sanctions, partner fidelity feedback and public goods. (1) The theory of games with asymmetrical information shows that the right incentives allow hosts to screen-out parasites and screen-in mutualists, explaining successful partner choice in the absence of signalling. Applications range from ant-plants to microbiomes. (2) Contract theory distinguishes two longstanding but weakly differentiated explanations of host response to defectors: host sanctions and partner fidelity feedback. Host traits that selectively punish misbehaving symbionts are parsimoniously interpreted as pre-adaptations. Yucca-moth and legume-rhizobia mutualisms are argued to be examples of partner fidelity feedback. (3) The theory of public goods shows that cooperation in multi-player interactions can evolve in the absence of assortment, in one-shot social dilemmas among non-kin. Applications include alarm calls in vertebrates and exoenzymes in microbes.     

Co-evolution of behaviour and social network structure promotes human cooperation

The ubiquity of cooperation in nature is puzzling because cooperators can be exploited by defectors. Recent theoretical work shows that if dynamic networks define interactions between individuals, cooperation is favoured by natural selection. To address this, we compare cooperative behaviour in multiple but independent repeated games between participants in static and dynamic networks. In the latter, participants could break their links after each social interaction. As predicted, we find higher levels of cooperation in dynamic networks. Through biased link breaking (i.e. to defectors) participants affected their social environment. We show that this link-breaking behaviour leads to substantial network clustering and we find primarily cooperators within these clusters. This assortment is remarkable because it occurred on top of behavioural assortment through direct reciprocity and beyond the perception of participants, and represents a self-organized pattern. Our results highlight the importance of the interaction between ecological context and selective pressures on cooperation.