The Evolution of Extortion in Iterated Prisoner's Dilemma Games

Iterated games are a fundamental component of economic and evolutionary game theory. They describe situations where two players interact repeatedly and have the possibility to use conditional strategies that depend on the outcome of previous interactions. In the context of evolution of cooperation, repeated games represent the mechanism of reciprocation. Recently a new class of strategies has been proposed, so called 'zero determinant strategies'. These strategies enforce a fixed linear relationship between one's own payoff and that of the other player. A subset of those strategies are 'extortioners' which ensure that any increase in the own payoff exceeds that of the other player by a fixed percentage. Here we analyze the evolutionary performance of this new class of strategies. We show that in reasonably large populations they can act as catalysts for the evolution of cooperation, similar to tit-for-tat, but they are not the stable outcome of natural selection. In very small populations, however, relative payoff differences between two players in a contest matter, and extortioners hold their ground. Extortion strategies do particularly well in co-evolutionary arms races between two distinct populations: significantly, they benefit the population which evolves at the slower rate - an instance of the so-called Red King effect. This may affect the evolution of interactions between host species and their endosymbionts.Comment: contains 4 figure

The Other January Effect: International Evidence

This paper investigates the predictive power of stock market returns in January for the subsequent eleven months' returns across 19 countries, thereby contributing to the literature on stock market seasonalities. Only two out of 19 countries' stock markets exhibit a robust Other January Eect. In light of this evidence, we conclude that the Other January Eect is not an international phenomenon.Stock market efciency, Other January Efect, Stock market anomalies

The case for international coordination of electricity regulation : evidence from the measurement of efficiency in South America

A decade long experience shows that monitoring the performance of public and private monopolies in South America is proving to be the hard part of the reform process. The operators who control most of the information needed for regulatory purposes have little interest in volunteering their dissemination unless they have an incentive to do so. The authors argue that, in spite of, and maybe because of, a much weaker information base and governance structure, South America's electricity sector could pursue an approach that relies on performance rankings based on comparative efficiency measures. The authors show that with the rather modest data currently available publicly, such an approach could yield useful results. They provide estimates of efficiency levels in South America's main distribution companies between 1994 and 2000. Moreover, the authors show how relatively simple tests can be used by regulators to check the robustness of their results and strengthen their position at regulatory hearings.Economic Theory&Research,Environmental Economics&Policies,Enterprise Development&Reform,Labor Policies,Health Monitoring&Evaluation,Environmental Economics&Policies,Economic Theory&Research,Geographical Information Systems,Health Monitoring&Evaluation,Educational Technology and Distance Education

Do Individual Index Futures Investors Destabilize the Underlying Spot Market?

This paper investigates the impact of introducing index futures trading on the volatility of the underlying stock market. We exploit a unique institutional setting in which presumably uninformed individuals are the dominant trader type in the futures markets. This enables us to investigate the destabilization hypothesis more accurately than previous studies do and to provide evidence for or against the in uence of individuals trading in index futures on spot market volatility. To overcome econometric shortcomings of the existing literature we employ a Markov-switching-GARCH approach to endogenously identify distinct volatility regimes. Our empirical evidence for Poland surprisingly suggests that the introduction of index futures trading does not destabilize the spot market. This nding is robust across 3 stock market indices and is corroborated by further analysis of a control group.Individual Investors, Uninformed Trading, Stock Index Futures, Emerging Capital Markets, Stock Market Volatility, Markov-Switching-GARCH Model

Comparing reactive and memory-one strategies of direct reciprocity

Direct reciprocity is a mechanism for the evolution of cooperation based on repeated interactions. When individuals meet repeatedly, they can use conditional strategies to enforce cooperative outcomes that would not be feasible in one-shot social dilemmas. Direct reciprocity requires that individuals keep track of their past interactions and find the right response. However, there are natural bounds on strategic complexity: Humans find it difficult to remember past interactions accurately, especially over long timespans. Given these limitations, it is natural to ask how complex strategies need to be for cooperation to evolve. Here, we study stochastic evolutionary game dynamics in finite populations to systematically compare the evolutionary performance of reactive strategies, which only respond to the co-player's previous move, and memory-one strategies, which take into account the own and the co-player's previous move. In both cases, we compare deterministic strategy and stochastic strategy spaces. For reactive strategies and small costs, we find that stochasticity benefits cooperation, because it allows for generous-tit-for-tat. For memory one strategies and small costs, we find that stochasticity does not increase the propensity for cooperation, because the deterministic rule of win-stay, lose-shift works best. For memory one strategies and large costs, however, stochasticity can augment cooperation.Comment: 18 pages, 7 figure

Physical properties and lattice dynamics of bixbyite-type V2O3

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Some time ago, we reported the synthesis of bixbyite-type V2O3, a new metastable polymorph of vanadium sesquioxide. Since, a number of investigations followed, dealing with different aspects like electronic and magnetic properties of the material, the deviation from ideal stoichiometry or the preparation of nanocrystals as oxygen storage material. However, most of the physical properties were only evaluated on a theoretical basis. Here, we report the lattice dynamics and physical properties of bixbyite-type V2O3 bulk material, which we acquired from physical property measurements and neutron diffraction experiments over a wide temperature range. Besides attributing different possible orientations of the magnetic moments for V1 and V2 to the identified antiferromagnetic (AFM) ground state with a Néel temperature of 38.1(5) K, we use a first order Grüneisen approximation to determine lattice-dependent parameters for the relatively stiff cubic lattice, and, amongst others identify the Debye temperature to be as low as 350 ± 65 K.DFG, 73789094, SPP 1415: Kristalline Nichtgleichgewichtsphasen - Präparation, Charakterisierung und in situ-Untersuchung der Bildungsmechanisme