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Lookup NU author(s): Dr Gilbert Roberts
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The iterated Prisoner's Dilemma reflects the essence of repeated cooperative interactions with selfish incentives. However, the classical form of this game assumes that individuals either cooperate or defect, whereas in practice different degrees of cooperation are usually possible. To overcome this limitation, we present a model of alternating cooperative trade in which individuals controlled the costs they incurred in benefiting their partners. Since the range of possible strategies is enormous, competitively successful solutions were identified using a genetic algorithm, a powerful search technique in which good performers are iteratively selected and recombined from an initial 'strategy soup'. Beginning with a population;If asocial individuals, altruistic behaviour readily emerged. Like the pre-defined strategy of 'Raise-theStakes', the emerging strategies evolved protection from cheats by investing relatively little in strangers and subsequently responding quantitatively to a partner's altruism. Unlike 'Raise-the-Stakes', they began trading relations at intermediate levels and, when the benefit-to-cost ratio of cooperation was relatively low, mean investment was considerably below the maximum level. Our approach is novel in allowing us to predict not just whether cooperation will occur, but how cooperative individuals will be, in relation to factors such as the number of rounds and the cost effectiveness of cooperative trade.
Author(s): Sherratt TN, Roberts G
Publication type: Article
Publication status: Published
Journal: Journal of Theoretical Biology
Year: 1999
Volume: 200
Issue: 4
Pages: 419-426
Print publication date: 21/10/1999
ISSN (print): 0022-5193
ISSN (electronic): 1095-8541
Publisher: Academic Press
URL: http://dx.doi.org/10.1006/jtbi.1999.1005
DOI: 10.1006/jtbi.1999.1005
PubMed id: 10525400
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