**THE 5th GLOBAL ISSUES COLLOQUIUM **

Institute for International Trade and Cooperation would like to invite you to our fifth faculty colloquium.

Core-periphery Segregation in Evolving Prisoner’s Dilemma Networks

Presenter: Prof. T. K. Ahn (Seoul National University)

Monday, Dec. 12th, 2011
4:30pm-6:00pm (Dinner will be provided)
#1002 Seminar Room, International Education Building

* RSVP BY Dec. 9th FOR DINNER PREPARATION 

Professor T. K. Ahn

Professor T. K. Ahn is Associate Professor in the Department of Political Science and International Relations at Seoul National University. He received his B.A (1990) and M.A (1994) in Political Science, Seoul National University, and his Ph.D. in Political Science, Indiana University (2001). Prior to joining the Seoul National University, Professor T. K. Ahn taught at the Florida State University (2003-2006) and Korea University (2006-2010).

His research focuses on the problem of institutions and collective action using diverse methods including game theory and experiments. He works have been published in Journal of Politics, Journal of Theoretical Politics, Political Psychology, Public Choice, Journal of Public Economics, Journal of Public Economic Theory, Ecological Economics, Journal of Economic Behavior and Organization, etc. He co-edited Foundations of Social Capital (2003) with Elinor Ostrom and translated Anthony Downs’s An Economic Theory of Democracy and Elinor Ostrom’s Governing the Commons: The Evolution of Institutions for Collective Action.

Abstract

Dense cooperative networks are an essential element of the social capital for a democratic and prosperous society. Yet, it remains unclear how these structures emerge. Many studies show how network structures affects the evolution of cooperation, But in many biological and social settings, network structures are not fixed but evolve endogenously as agents exit from current relationships and build new ones. The ability to exit may hinder cooperation by allowing an advantage for the roving defectors. On the other hand, partner selection may promote cooperation by enabling cooperators to cluster with each other. By conducting controlled laboratory experiments using large groups of subjects between 35 to 40 per session, we show that partner-selection can facilitate evolution of cooperation in the absence of social exchange of reputation. Positive assortation of similar strategic types emerged as cooperators cut links with defectors and build links with other cooperators. Cooperators used the Quit-for-Tat strategy, cutting links with defectors, and formed stable clusters at the structural core of the global network. Most defectors were ‘rovers’ who try to find new ‘suckers’ every round. But the roving strategy failed as cooperators locked in with other cooperators and stopped searching for new partners. Cooperators accumulated more links than defectors and clustered at the structural core of the evolving network whereas defectors scattered around the periphery. With more relationships and larger returns per relationship, cooperators earned much larger payoffs than defectors and this gap increased over rounds.

Viewed from the evolutionary perspective, our results suggest that endogenous network formation can be a powerful mechanism for the evolution of cooperation. Equally importantly, the dynamic process of co-evolution unveils the generative mechanism of social capital specified by the topological characteristics of behavioral type clusters.

* This colloquium is supported by the Ewha Global Top 5 Grant 2011 of Ewha Womans University and Ewha GSIS