Evolution of cooperation without reciprocity.

A long-standing problem in biological and social sciences is to understand the conditions required for the emergence and maintenance of cooperation in evolving populations. For many situations, kin selection is an adequate explanation, although kin-recognition may still be a problem. Explanations of cooperation between non-kin include continuing interactions that provide a shadow of the future (that is, the expectation of an ongoing relationship) that can sustain reciprocity, possibly supported by mechanisms to bias interactions such as embedding the agents in a two-dimensional space or other context-preserving networks. Another explanation, indirect reciprocity, applies when benevolence to one agent increases the chance of receiving help from others. Here we use computer simulations to show that cooperation can arise when agents donate to others who are sufficiently similar to themselves in some arbitrary characteristic. Such a characteristic, or 'tag', can be a marking, display, or other observable trait. Tag-based donation can lead to the emergence of cooperation among agents who have only rudimentary ability to detect environmental signals and, unlike models of direct or indirect reciprocity, no memory of past encounters is required.     

Indirect reciprocity can stabilize cooperation without the second-order free rider problem

Models of large-scale human cooperation take two forms. 'Indirect reciprocity' occurs when individuals help others in order to uphold a reputation and so be included in future cooperation. In 'collective action', individuals engage in costly behaviour that benefits the group as a whole. Although the evolution of indirect reciprocity is theoretically plausible, there is no consensus about how collective action evolves. Evidence suggests that punishing free riders can maintain cooperation, but why individuals should engage in costly punishment is unclear. Solutions to this 'second-order free rider problem' include meta-punishment, mutation, conformism, signalling and group-selection. The threat of exclusion from indirect reciprocity can sustain collective action in the laboratory. Here, we show that such exclusion is evolutionarily stable, providing an incentive to engage in costly cooperation, while avoiding the second-order free rider problem because punishers can withhold help from free riders without damaging their reputations. However, we also show that such a strategy cannot invade a population in which indirect reciprocity is not linked to collective action, thus leaving unexplained how collective action arises.     

Reputation helps solve the 'tragedy of the commons'.

The problem of sustaining a public resource that everybody is free to overuse-the 'tragedy of the commons'-emerges in many social dilemmas, such as our inability to sustain the global climate. Public goods experiments, which are used to study this type of problem, usually confirm that the collective benefit will not be produced. Because individuals and countries often participate in several social games simultaneously, the interaction of these games may provide a sophisticated way by which to maintain the public resource. Indirect reciprocity, 'give and you shall receive', is built on reputation and can sustain a high level of cooperation, as shown by game theorists. Here we show, through alternating rounds of public goods and indirect reciprocity games, that the need to maintain reputation for indirect reciprocity maintains contributions to the public good at an unexpectedly high level. But if rounds of indirect reciprocation are not expected, then contributions to the public good drop quickly to zero. Alternating the games leads to higher profits for all players. As reputation may be a currency that is valid in many social games, our approach could be used to test social dilemmas for their solubility.     

合作进化模型综述

作者综述了合作进化模型的最新研究成果。合作进化模型以“囚徒困境”博弈模型为基础, 为合作中的个体提供了一种与个体本身无关的策略优化机制, 以此探讨合作策略能够稳定进化的条件。基于直接或间接互惠理论的合作进化模型验证了在小规模社会中建立声誉机制有助于实现稳定的互惠合作; 互惠可以看做是对合作行为的奖赏, 开放的社会网络有助于实现较大范围内的合作; 对非合作行为实施惩罚有助于实现多人合作, 在一定条件下, 由非合作者实施惩罚时的合作进化相较于由合作者实施时更稳定; 群组竞争有利于合作文化或制度的传播, 但无法解释群组融合后的合作问题。     

Image scoring and cooperation in a cleaner fish mutualism

Humans are highly social animals and often help unrelated individuals that may never reciprocate the altruist's favour. This apparent evolutionary puzzle may be explained by the altruist's gain in social image: image-scoring bystanders, also known as eavesdroppers, notice the altruistic act and therefore are more likely to help the altruist in the future. Such complex indirect reciprocity based on altruistic acts may evolve only after simple indirect reciprocity has been established, which requires two steps. First, image scoring evolves when bystanders gain personal benefits from information gathered, for example, by finding cooperative partners. Second, altruistic behaviour in the presence of such bystanders may evolve if altruists benefit from access to the bystanders. Here, we provide experimental evidence for both of the requirements in a cleaning mutualism involving the cleaner fish Labroides dimidiatus. These cleaners may cooperate and remove ectoparasites from clients or they may cheat by feeding on client mucus. As mucus may be preferred over typical client ectoparasites, clients must make cleaners feed against their preference to obtain a cooperative service. We found that eavesdropping clients spent more time next to 'cooperative' than 'unknown cooperative level' cleaners, which shows that clients engage in image-scoring behaviour. Furthermore, trained cleaners learned to feed more cooperatively when in an 'image-scoring' than in a 'non-image-scoring' situation.     

Human cooperation: second-order free-riding problem solved?

Panchanathan and Boyd describe a model of indirect reciprocity in which mutual aid among cooperators can promote large-scale human cooperation without succumbing to a second-order free-riding problem (whereby individuals receive but do not give aid). However, the model does not include second-order free riders as one of the possible behavioural types. Here I present a simplified version of their model to demonstrate how cooperation unravels if second-round defectors enter the population, and this shows that the free-riding problem remains unsolved.     

Behaviorial evolution: does similarity breed cooperation?

Reciprocity, whether direct or indirect, is thought to be the key to establishing cooperation among non-relatives. But Riolo et al. have presented a model in which cooperation is instead based on similarity: agents donate only when their partner's 'tag' lies within a 'tolerance' range around their own. Here we point out that their model requires individuals with identical tags to cooperate with each other, and show that cooperation tends to collapse when individuals bearing identical tags are given the option of not donating. We therefore question their mechanism for maintaining cooperation without reciprocity.     

基于二阶声誉测度的自组织网络合作激励机制

将二阶声誉测度Standing应用到自组织网络的合作激励机制中,设计了一种基于Standing的包括服务和声誉管理的分布式合作管理协议,克服了间接互惠所面临的二阶搭便车问题.数学分析和模拟实验表明,在二阶声誉作用下,区分策略是演化博弈惟一的进化稳定策略,从而促进了用户的合作.同时,采用完全的分布方式所构建的可信第三方架构能够有效应对合谋、虚假的声誉反馈与声誉提供等欺骗行为.该合作机制在一般的动态环境中具有良好的适应性.     

权函数支持域尺寸和场节点间距对移动最小二乘法拟合精度的影响

移动最小二乘法作为一种拟合插值方法,当其基函数采用非正交基时,移动最小二乘法中采样点支持域尺寸、节点间距大小将影响到力矩矩阵的可逆性.力矩矩阵可逆是移动最小二乘法拟合成功的必要条件.因此如何合理地选取节点间距及采样点支持域尺寸以确保力矩矩阵可逆,成为移动最小二乘法应用过程中的一个重要环节.其值的选取也是移动最小二乘法主要误差来源之一.理论上,至今仍无法推导出采样点支持域尺寸及节点间距最优取值.实践中,可通过拟合实验寻找支持域尺寸、节点间距的变化规律,给出具有建议性的取值范围.本文在节点均匀分布的情况下,对其变化规律进行研究并提出了可以保证插值精度的支持域尺寸、节点间距的建议取值.     

直流磁场的互易定理

电磁互易定理是一个在电磁场问题中很有用的定理.本文应用矢量分析方法,导出了直流磁场的互易定理和电流与磁通的互易关系.     

Emergence of cooperation and evolutionary stability in finite populations

To explain the evolution of cooperation by natural selection has been a major goal of biologists since Darwin. Cooperators help others at a cost to themselves, while defectors receive the benefits of altruism without providing any help in return. The standard game dynamical formulation is the 'Prisoner's Dilemma', in which two players have a choice between cooperation and defection. In the repeated game, cooperators using direct reciprocity cannot be exploited by defectors, but it is unclear how such cooperators can arise in the first place. In general, defectors are stable against invasion by cooperators. This understanding is based on traditional concepts of evolutionary stability and dynamics in infinite populations. Here we study evolutionary game dynamics in finite populations. We show that a single cooperator using a strategy like 'tit-for-tat' can invade a population of defectors with a probability that corresponds to a net selective advantage. We specify the conditions required for natural selection to favour the emergence of cooperation and define evolutionary stability in finite populations.     

n端口网络的互易定理

文章根据特勒根定理推导出n端口网络的互易定理，从而得到互易定理的普遍形式，推广了这一重要定理。     

Evolution of cooperative strategies from first principles

One of the greatest challenges in the modern biological and social sciences is to understand the evolution of cooperative behaviour. General outlines of the answer to this puzzle are currently emerging as a result of developments in the theories of kin selection, reciprocity, multilevel selection and cultural group selection. The main conceptual tool used in probing the logical coherence of proposed explanations has been game theory, including both analytical models and agent-based simulations. The game-theoretic approach yields clear-cut results but assumes, as a rule, a simple structure of payoffs and a small set of possible strategies. Here we propose a more stringent test of the theory by developing a computer model with a considerably extended spectrum of possible strategies. In our model, agents are endowed with a limited set of receptors, a set of elementary actions and a neural net in between. Behavioural strategies are not predetermined; instead, the process of evolution constructs and reconstructs them from elementary actions. Two new strategies of cooperative attack and defence emerge in simulations, as well as the well-known dove, hawk and bourgeois strategies. Our results indicate that cooperative strategies can evolve even under such minimalist assumptions, provided that agents are capable of perceiving heritable external markers of other agents.     

互易定理在复频域中的应用

本文将在时域中对线性电阻电路应用的互易定理,在有条件的前提下,推广到了复频域中对动态电路使用,并进行了证明,最后举例说明了其应用。     

广义静磁场互易定理在漏磁无损检测中的应用

应用微分几何语言导出了广义静磁场互易定理,并应用该定理推导了漏磁无损检测数值分析中的富内德和蒙积分方程和线圈电感增量公式     

Evolution and maintenance of cooperation via inheritance of neighborhood relationship

Cooperative behaviors are ubiquitous in nature and human society. It is very important to understand the internal mechanism of emergence and maintenance of cooperation. As we know now, the offsprings inherit not only the phenotype but also the neighborhood relationship of their parents. Some recent research results show that the interactions among individuals facilitate survival of cooperation through network reciprocity of clustering cooperators. This paper aims at introducing an inheritance mechanism of neighborhood relationship to explore the evolution of cooperation. In detail, a mathematical model is proposed to characterize the evolutionary process with the above inheritance mechanism. Theoretical analysis and numerical simulations indicate that high-level cooperation can emerge and be maintained for a wide variety of cost-to-benefit ratios, even if mutation happens during the evolving process.     

Testing the genetics underlying the co-evolution of mate choice and ornament in the wild

One of the most debated questions in evolutionary biology is whether female choice of males with exaggerated sexual displays can evolve as a correlated response to selection acting on genes coding for male attractiveness or high overall viability. To date, empirical studies have provided support for parts of this scenario, but evidence for all key genetic components in a natural population is lacking. Here we use animal-model quantitative genetic analysis on data from over 8,500 collared flycatchers (Ficedula albicollis) followed for 24 years to quantify all of the key genetic requirements of both fisherian and 'good-genes' models on sexual selection in the wild. We found significant additive genetic variances of all the main components: male ornament (forehead patch size), female mate choice for this ornament, male fitness and female fitness. However, when the necessary genetic correlations between these components were taken into account, the estimated strength of indirect sexual selection on female mate choice was negligible. Our results show that the combined effect of environmental influences on several components reduces the potential for indirect sexual selection in the wild. This study provides insight into the field of sexual selection by showing that genes coding for mate choice for an ornament probably evolve by their own pathways instead of 'hitchhiking' with genes coding for the ornament.     

A Comparative Analysis on Weibo and Twitter

Weibo is the Twitter counterpart in China that has attracted hundreds of millions of users. We crawled an almost complete Weibo user network that contains 222 million users and 27 billion links in 2013. This paper analyzes the structural properties of this network, and compares it with a Twitter user network. The topological properties we studied include the degree distributions, connected components, distance distributions, reciprocity,clustering coefficient, Page Rank centrality, and degree assortativity. We find that Weibo users have a higher diversity index, higher Gini index, but a lower reciprocity and clustering coefficient for most of the nodes. A surprising observation is that the reciprocity of Weibo is only about a quarter of the reciprocity of the Twitter user network. We also show that Weibo adoption rate correlates with economic development positively, and Weibo network can be used to quantify the connections between provinces and regions in China. In particular, point-wise mutual information is shown to be accurate in quantifying the strength of connections. We developed an interactive analyzing software framework for this study, and released the data and code online.     

Comments on scaling effect of reciprocity in BRDF study

Reciprocity principle is a common theory in electromagnetics and optics. It is also one of the general principles of the radiation transformation theory. However, in many remote sensing studies, this principle cannot be always supported by experimental data, especially when the scaling effect of the remote sensing image pixel is considered. The debate over the issue of whether the reciprocity principle can be used as a fundamental standard in evaluating the effectiveness of remote sensing observations has lasted for years. Using geometrical optics model, Li and Wan proved the existence of the scaling effect in applying the reciprocity principle to a remote sensing image pixel in 1998. In 2002, Snyder challenged Li's proof, and attempted to prove that reciprocity principle is universally valid without any scale limitation. In this paper, we will argue with Snyder's theory and point out that Snyder's theory had neglected an important condition used in Li's proof and, as a result, drawn the wrong conclusion. Here we will restate Li's condition in his demonstration and offer a further proof to verify that reciprocity principle cannot be applied unconditionally to the study of bi-directional reflectance distribution function (BRDF) of land surfaces in field or satellite remote sensing observation scale.