Physica A 343 (2004) 669–676 Emergence of cooperation in an evolutionary game with two-level decisions G. Acosta , S. Guala, J. Marenco Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires, Argentina Received 8 March 2004; received in revised form 29 April 2004 Available online 23 July 2004 Abstract We introduce an extended version of the classical minority game model, with two groups of agents: a group of leading players and a group of following players. The members of the first group can be related to the financial ‘‘gooroos’’, who define market trends and are imitated by the members of the second group. This extension implements a two-level decision process, modelling a typical leadership behaviour of financial markets. We show by means of numerical experiments that the dynamics of this model leads to the emergence of coordination and organization patterns. r 2004 Elsevier B.V. All rights reserved. PACS: 89.65.Gh; 82.20.Wt Keywords: Minority game; Two-level decision 1. Introduction In recent years, discrete adaptive games have attracted much attention because of their relation to economic and financial markets. This kind of games generally involves a set of decision makers who, at discrete moments in time, independently choose an action from a finite set of available actions according to decision rules ARTICLE IN PRESS www.elsevier.com/locate/physa 0378-4371/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physa.2004.06.101 Corresponding author. E-mail address: gacosta@ungs.edu.ar (G. Acosta).