Evolution of direct reciprocity in group-structured populations

People tend to have their social interactions with members of their owncommunity. Such group-structured interactions can have a profound impact on thebehaviors that evolve. Group structure affects the way people cooperate, andhow they reciprocate each other's cooperative actions. Past work has shown thatpopulation structure and reciprocity can both promote the evolution ofcooperation. Yet the impact of these mechanisms has been typically studied inisolation. In this work, we study how the two mechanisms interact. Using agame-theoretic model, we explore how people engage in reciprocal cooperation ingroup-structured populations, compared to well-mixed populations of equal size.To derive analytical results, we focus on two scenarios. In the first scenario,we assume a complete separation of time scales. Mutations are rare compared tobetween-group comparisons, which themselves are rare compared to within-groupcomparisons. In the second scenario, there is a partial separation of timescales, where mutations and between-group comparisons occur at a comparablerate. In both scenarios, we find that the effect of population structuredepends on the benefit of cooperation. When this benefit is small,group-structured populations are more cooperative. But when the benefit islarge, well-mixed populations result in more cooperation. Overall, our resultsreveal how group structure can sometimes enhance and sometimes suppress theevolution of cooperation.<br

Étude de quelques populations structurées : processus de coalescence et abondance d’une stratégie

Le fichiers qui accompagnent mon document ont été réalisés avec le logiciel MathematicaDans cette thèse, nous étudions la théorie des jeux évolutionnaires dans quelques exemples de populations structurées. En particulier, nous analysons l’évolution de la coopération en déterminant des conditions qui la favorisent dans le cas des interactions par paire. On s’intéresse à l’évolution de la coopération dans un espace phénotypique de dimension quelconque. Puis on étudie la coopération dans une population finie, subdivisée en groupes de même quelconques avec une hiérarchie entre les groupes. Finalement, on présente l’effet de l’aspiration sur le processus évolutif dans une population finie répartie sur un cercle où il y a des positions à occuper.In this thesis, we study some examples of structured populations. In particular, we analyze the evolution of cooperation in the sense of determining conditions that favor it. We study the evolution of cooperation in a phenotype space of any size. We study also the evolution of cooperation in a finite population subdivided into hierarchical groups of any size. Finally, we study the effect of aspiration on the evolutionary process in a finite population distributed on a circle with only a local interaction by pairwise

Cooperation in Microbial Populations: Theory and Experimental Model Systems

Cooperative behavior, the costly provision of benefits to others, is common across all domains of life. This review article discusses cooperative behavior in the microbial world, mediated by the exchange of extracellular products called public goods. We focus on model species for which the production of a public good and the related growth disadvantage for the producing cells are well described. To unveil the biological and ecological factors promoting the emergence and stability of cooperative traits we take an interdisciplinary perspective and review insights gained from both mathematical models and well-controlled experimental model systems. Ecologically, we include crucial aspects of the microbial life cycle into our analysis and particularly consider population structures where an ensemble of local communities (sub populations) continuously emerge, grow, and disappear again. Biologically, we explicitly consider the synthesis and regulation of public good production. The discussion of the theoretical approaches includes general evolutionary concepts, population dynamics, and evolutionary game theory. As a specific but generic biological example we consider populations of Pseudomonas putida and its regulation and utilization of pyoverdines, iron scavenging molecules. The review closes with an overview on cooperation in spatially extended systems and also provides a critical assessment of the insights gained from the experimental and theoretical studies discussed. Current challenges and important new research opportunities are discussed, including the biochemical regulation of public goods, more realistic ecological scenarios resembling native environments, cell to cell signalling, and multi-species communities.Comment: Review article, 88 pages, 14 figure

An analysis of the strategic, operational, and organizational differences between the Islamic State and al-Qa\u27ida

This project provides a comprehensive examination of the strategic, operational and organizational character of the Islamic State in Iraq and the Sham (ISIS). The purpose of the project is two fold: first, to challenge the perception that ISIS and al-Qā’ida are fundamentally “one and the same;” and, second, to offer policy makers a systematic and detailed description of ISIS on its own merits. Drawing on variables pertaining to three dimensions—strategy, operations, and organizational characteristics—and informed by both primary sources and secondary analyses, I investigate the qualitative differences between the two organizations. I find that, despite some similarities, ISIS and al-Qā’ida vary considerably in all facets. Accordingly, I offer targeted policy recommendations aimed at making current counter-strategy more effective and efficient

Four levers of reciprocity across human societies: concepts, analysis and predictions

This paper surveys five human societal types – mobile foragers, horticulturalists, pre-state agriculturalists, state-based agriculturalists and liberal democracies – from the perspective of three core social problems faced by interacting individuals: coordination problems, social dilemmas and contest problems. We characterise the occurrence of these problems in the different societal types and enquire into the main force keeping societies together given the prevalence of these. To address this, we consider the social problems in light of the theory of repeated games, and delineate the role of intertemporal incentives in sustaining cooperative behaviour through the reciprocity principle. We analyse the population, economic and political structural features of the five societal types, and show that intertemporal incentives have been adapted to the changes in scope and scale of the core social problems as societies have grown in size. In all societies, reciprocity mechanisms appear to solve the social problems by enabling lifetime direct benefits to individuals for cooperation. Our analysis leads us to predict that as societies increase in complexity, they need more of the following four features to enable the scalability and adaptability of the reciprocity principle: nested grouping, decentralised enforcement and local information, centralised enforcement and coercive power, and formal rules