Evolutionary game theory: Temporal and spatial effects beyond replicator dynamics

Evolutionary game dynamics is one of the most fruitful frameworks for studying evolution in different disciplines, from Biology to Economics. Within this context, the approach of choice for many researchers is the so-called replicator equation, that describes mathematically the idea that those individuals performing better have more offspring and thus their frequency in the population grows. While very many interesting results have been obtained with this equation in the three decades elapsed since it was first proposed, it is important to realize the limits of its applicability. One particularly relevant issue in this respect is that of non-mean-field effects, that may arise from temporal fluctuations or from spatial correlations, both neglected in the replicator equation. This review discusses these temporal and spatial effects focusing on the non-trivial modifications they induce when compared to the outcome of replicator dynamics. Alongside this question, the hypothesis of linearity and its relation to the choice of the rule for strategy update is also analyzed. The discussion is presented in terms of the emergence of cooperation, as one of the current key problems in Biology and in other disciplines.Comment: Review, 48 pages, 26 figure

- FIRM-SPECIFIC TEMPORAL VARIATION IN TECHNICAL EFFICENCY RESULTS OF: A STOCHASTIC OUTPUT DISTANCE FUNCTION

The aim of this paper is to test the temporal variation of technical efficiency of the Spanish Savings Banks during the period 1985-1994. Furthermore, a stochastic output distance function (Shephard, 1970) is employed to accommodate multiple output technology. The distance function provides the advantage that it does not need information about prices, so it can accommodate the multiproduct nature of the financial sector only using the quantitiesas data. The temporal variation of efficiency is modeled using an extension of Battese and Coelli (1992), allowing for firm-specific patterns of temporal change. El objetivo de este trabajo es contrastar la variación temporal de la eficiencia técnica de las Cajas de Ahorros españolas durante el periodo 1985-1994. Para ello la tecnología se modeliza a través de la función de distancia (Shephard, 1970) y el término de ineficiencia se especifica mediante una generalización del modelo propuesto por Battese y Coelli (1992). La función de distancia tiene la ventaja de que puede recoger tecnologías multiproducto sin precisar de información acerca de precios. Esta ventaja es mayor en un sector como el bancario en el que, generalmente, los precios se construyen a partir de gastos, lo cual podría suponer un problema. Por último, el modelo propuesto permite que el término de ineficiencia varíe con el tiempo de forma particular para cada empresa.Eficiencia técnica variante en el tiempo, Funciones de distancia estocásticas Time-varying Technical Efficiency, Stochastic Distance Functions, Panel Data.

Time Scales in Evolutionary Dynamics

Evolutionary game theory has traditionally assumed that all individuals in a population interact with each other between reproduction events. We show that eliminating this restriction by explicitly considering the time scales of interaction and selection leads to dramatic changes in the outcome of evolution. Examples include the selection of the inefficient strategy in the Harmony and Stag-Hunt games, and the disappearance of the coexistence state in the Snowdrift game. Our results hold for any population size and in the presence of a background of fitness.Comment: Final version with minor changes, accepted for publication in Physical Review Letter

El hombre como «ser-proyecto», objeto formal de la antropología filosófica.

Sin resume

Imperfect Imitation Can Enhance Cooperation

The promotion of cooperation on spatial lattices is an important issue in evolutionary game theory. This effect clearly depends on the update rule: it diminishes with stochastic imitative rules whereas it increases with unconditional imitation. To study the transition between both regimes, we propose a new evolutionary rule, which stochastically combines unconditional imitation with another imitative rule. We find that, surprinsingly, in many social dilemmas this rule yields higher cooperative levels than any of the two original ones. This nontrivial effect occurs because the basic rules induce a separation of timescales in the microscopic processes at cluster interfaces. The result is robust in the space of 2x2 symmetric games, on regular lattices and on scale-free networks.Comment: 4 pages, 4 figure

Miguel de Unamuno: Epistolario y hermenéutica.

Sin resume

Rewarding cooperation in social dilemmas

One of the most direct human mechanisms of promoting cooperation is rewarding it. We study the effect of sharing a reward among cooperators in the most stringent form of social dilemma. Thus, individuals confront a new dilemma: on the one hand, they may be inclined to choose the shared reward despite the possibility of being exploited by defectors; on the other hand, if too many players do that, cooperators will obtain a poor reward and defectors will outperform them. By appropriately tuning the amount to be shared we can cast a vast variety of scenarios, including traditional ones in the study of cooperation as well as more complex situations where unexpected behavior can occur. We provide a complete classification of the equilibria of the nplayer game as well as of the evolutionary dynamics. Beyond, we extend our analysis to a general class of public good games where competition among individuals with the same strategy exists

Altruism may arise from individual selection

The fact that humans cooperate with non-kin in large groups, or with people they will never meet again, is a long-standing evolutionary puzzle. Altruism, the capacity to perform costly acts that confer benefits on others, is at the core of cooperative behavior. Behavioral experiments show that humans have a predisposition to cooperate with others and to punish non-cooperators at personal cost (so-called strong reciprocity) which, according to standard evolutionary game theory arguments, cannot arise from selection acting on individuals. This has led to the suggestion of group and cultural selection as the only mechanisms that can explain the evolutionary origin of human altruism. We introduce an agent-based model inspired on the Ultimatum Game, that allows us to go beyond the limitations of standard evolutionary game theory and show that individual selection can indeed give rise to strong reciprocity. Our results are consistent with the existence of neural correlates of fairness and in good agreement with observations on humans and monkeys.We acknowledge financial support from Ministerio de Ciencia y Tecnología (Spain) through grants BFM2003-07749-C05-01 (AS) and BFM2003-0180 (JAC).Publicad

Differences in the biomechanical response between healthy and low back pain patients from a isometric extension test

Purpose: To compare, in healhty subjects and low back pain patients, the erector spinal muscle response in a máximum isometric contraction intensities using simultaneously electromyography and ultrasonography. Participants: 59 subjects: 33 Healthy persons (45% ♀). 26 LBP patients (39% ♀) with a mean age of 30.39 (±7.785). Methods: Cross sectional study. Participants, following a maximal strength test as measured by a load cell, perform an isometric contraction of maximum strength. From sitting, each subject develops a maximum isometric lumbar extension, locked at 45 degrees from vertical. The hip and this of the subject were attached by a strap. After preliminary training, each subject performed three repetitions of described gesture resting for a minute and a half between each attempt. Records were taken throughout the maximum contraction, EMG signal and a ultrasonography image, for each ES (right and left). Measured torque, inclination angle, thickness and electromyography activation (MVC). Analysis: We performed a descriptive analysis of both groups and subsequently made T-Student test for independent data in each of the variables measured. Results: Mean values for groups of healthy subjects and low back pain patients were, respectively: Torque: 61.652 (±20.137); 70.298 (±25.053). Right Angle: 6.48 (±2.181); 7.15 (±2.53). Left Angle: 5.36 (±2.26); 6.38 (±1.86). Right Thickness: 0.031 (±0.005); 0.033 (±0.008). Left Thickness: 0.032 (±0.006); 0.034 (±0.006). Right MVC: 558.64 (±211.029); 576.15 (±267.69). Left MVC: 589.21 (±257.739); 671.15 (±370.722). No significant differences were found in any variable when comparing the results between healthy subjects and low back pain patients. Torque: −8.65 (±9.02) (p = 0.347). Angle: Right: −0.659 (±0.613) (p = 0.280); Left: −1.021 (±0.549) (p = 0.068). Thick-ness: Right: 0.00 (±0.00) (p=0.259); Left: 0.00 (±0.00) (p=0.069). MVC: Right: -17.52 (±62.29) (p=0.780). Left: −81.84 (±81.91) (p = 0.321). Conclusions: Knowing how the erector spinal muscle behaves in a isometric back extension test, noting that biomechanically there are not significant differences in the responses with respect to a healthy subject, physical therapists could perform planning treatment which is the biopsychosocial model supported by the biomechanical model.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Functional and structural of the erector spinae muscle during iso-metric lumbar extension

Study Design: cross-sectional study. Objectives: to compare erector spinae (ES) muscle fatigue between chronic non-specific lower back pain (CNLBP) sufferers and healthy subjects from a biomechanical perspective during fatiguing isometric lumbar extensions. Background: paraspinal muscle maximal contraction and fatigue are used as a functional predictor for disabilities. The simplest method to determine muscle fatigue is by evaluating the evolution during specific contractions, such as isometric contractions. There are no studies that evaluate the evolution of the ES muscle during fatiguing isometric lumbar extensions and analyse functional and architectural variables. Methods: In a pre-calibrated system, participants performed a maximal isometric extension of the lumbar spine for 5 and 30 seconds. Functional variables (torque and muscle activation) and architecture (pennation angle and muscle thickness) were measured using a load cell, surface electromyography and ultrasound, respectively. The results were normalised and a reliability study of the ultrasound measurement was made. Results: The ultrasound measurements were highly reliable, with Cronbach's alpha values ranging from 0.951 0.981. All measured variables shown significant differences before and after fatiguing isometric lumbar extension. Conclusion: During a lumbar isometric extension test, architecture and functional variables of the ES muscle could be analised using ultrasound, surface EMG and load cell. In adition, during an endurance test, ES muscle suffers an acute effect on architectural and functional variables.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. 25 September 2013 through 28 September 2013; Code 10172