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Inheritance patterns in citation networks reveal scientific memes
Tobias Kuhn, Matjaž Perc, Dirk Helbing, 2014, original scientific article

Abstract: Memes are the cultural equivalent of genes that spread across human culture by means of imitation. What makes a meme and what distinguishes it from other forms of information, however, is still poorly understood. Our analysis of memes in the scientific literature reveals that they are governed by a surprisingly simple relationship between frequency of occurrence and the degree to which they propagate along the citation graph. We propose a simple formalization of this pattern and validate it with data from close to 50 million publication records from the Web of Science, PubMed Central, and the American Physical Society. Evaluations relying on human annotators, citation network randomizations, and comparisons with several alternative approaches confirm that our formula is accurate and effective, without a dependence on linguistic or ontological knowledge and without the application of arbitrary thresholds or filters.
Keywords: memes, inheritance, genes, network science, complex systems
Published: 03.08.2017; Views: 636; Downloads: 328
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Punish, but not too hard: how costly punishment spreads in the spatial public goods game
Dirk Helbing, Attila Szolnoki, Matjaž Perc, György Szabó, 2010, original scientific article

Abstract: We study the evolution of cooperation in spatial public goods games where, besides the classical strategies of cooperation (C) and defection (D), we consider punishing cooperators (PC) or punishing defectors (PD) as an additional strategy. Using a minimalist modeling approach, our goal is to separately clarify and identify the consequences of the two punishing strategies. Since punishment is costly, punishing strategies lose the evolutionary competition in case of well-mixed interactions. When spatial interactions are taken into account, however, the outcome can be strikingly different, and cooperation may spread. The underlying mechanism depends on the character of the punishment strategy. In the case of cooperating punishers,increasing the fine results in a rising cooperation level. In contrast, in the presence of the PD strategy, the phase diagram exhibits a reentrant transition as the fine is increased. Accordingly, the level of cooperation shows a non-monotonous dependence on the fine. Remarkably, punishing strategies can spread in both cases, but based on largely different mechanisms, which depend on the cooperativeness (or not) of punishers.
Keywords: evolutionary game theory, public goods, spatial games, punishment, social systems, moral
Published: 03.07.2017; Views: 786; Downloads: 305
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Stability of cooperation under image scoring in group interactions
Heinrich H. Nax, Matjaž Perc, Attila Szolnoki, Dirk Helbing, 2015, original scientific article

Abstract: Image scoring sustains cooperation in the repeated two-player prisoner's dilemma through indirect reciprocity, even though defection is the uniquely dominant selfish behaviour in the one-shot game. Many real-world dilemma situations, however, firstly, take place in groups and, secondly, lack the necessary transparency to inform subjects reliably of others' individual past actions. Instead, there is revelation of information regarding groups, which allows for "group scoring" but not for image scoring. Here, we study how sensitive the positive results related to image scoring are to information based on group scoring. We combine analytic results and computer simulations to specify the conditions for the emergence of cooperation. We show that under pure group scoring, that is, under the complete absence of image-scoring information, cooperation is unsustainable. Away from this extreme case, however, the necessary degree of image scoring relative to group scoring depends on the population size and is generally very small. We thus conclude that the positive results based on image scoring apply to a much broader range of informational settings that are relevant in the real world than previously assumed.
Keywords: public goods, group interactions, phase transition, social dilemma, physics of social systems
Published: 23.06.2017; Views: 846; Downloads: 373
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Understanding recurrent crime as system-immanent collective behavior
Matjaž Perc, Karsten Donnay, Dirk Helbing, 2013, original scientific article

Abstract: Containing the spreading of crime is a major challenge for society. Yet, since thousands of years, no effective strategy has been found to overcome crime. To the contrary, empirical evidence shows that crime is recurrent, a fact that is not captured well by rational choice theories of crime. According to these, strong enough punishment should prevent crime from happening. To gain a better understanding of the relationship between crime and punishment, we consider that the latter requires prior discovery of illicit behavior and study a spatial version of the inspection game. Simulations reveal the spontaneous emergence of cyclic dominance between criminals, inspectors, and ordinary people as a consequence of spatial interactions. Such cycles dominate the evolutionary process, in particular when the temptation to commit crime or the cost of inspection are low or moderate. Yet, there are also critical parameter values beyond which cycles cease to exist and the population is dominated either by a stable mixture of criminals and inspectors or one of these two strategies alone. Both continuous and discontinuous phase transitions to different final states are possible, indicating that successful strategies to contain crime can be very much counter-intuitive and complex. Our results demonstrate that spatial interactions are crucial for the evolutionary outcome of the inspection game, and they also reveal why criminal behavior is likely to be recurrent rather than evolving towards an equilibrium with monotonous parameter dependencies.
Keywords: crime, evolutionary games, collective phenomena, phase transitions, statistical physics
Published: 19.06.2017; Views: 786; Downloads: 382
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Evolutionary establishment of moral and double moral standards through spatial interactions
Dirk Helbing, Attila Szolnoki, Matjaž Perc, György Szabó, 2010, original scientific article

Abstract: Situations where individuals have to contribute to joint efforts or share scarce resources are ubiquitous. Yet, without proper mechanisms to ensure cooperation, the evolutionary pressure to maximize individual success tends to create a tragedy of the commons (such as over-fishing or the destruction of our environment). This contribution addresses a number of related puzzles of human behavior with an evolutionary game theoretical approach as it has been successfully used to explain the behavior of other biological species many times, from bacteria to vertebrates. Our agent-based model distinguishes individuals applying four different behavioral strategies: non-cooperative individuals ('defectors'), cooperative individuals abstaining from punishment efforts (called 'cooperators' or 'second-order free-riders'), cooperators who punish non-cooperative behavior ('moralists'), and defectors, who punish otherdefectors despite being non-cooperative themselves ('immoralists'). By considering spatial interactions with neighboring individuals, our model reveals several interesting effects: First, moralists can fully eliminate cooperators. This spreading of punishing behavior requires a segregation of behavioral strategies and solves the 'second-order free-rider problem'. Second, the system behavior changes its character significantly even after very long times ('who laughs last laughs best effect'). Third, the presence of a number of defectors can largely accelerate the victory of moralists over non-punishing cooperators. Fourth, in order to succeed, moralists may profit from immoralists in a way that appears like an 'unholy collaboration'. Our findings suggest that the consideration of punishment strategies allows one to understand the establishment and spreading of 'moral behavior' by means of game-theoretical concepts. This demonstrates that quantitative biological modeling approaches are powerful even in domains that have been addressed with non-mathematical concepts so far. The complex dynamics of certain social behaviors become understandable as the result of an evolutionary competition between different behavioral strategies.
Keywords: evolutionary game theory, social dilemmas, spatial games, moral, cooperation
Published: 16.06.2017; Views: 674; Downloads: 334
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