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Reputation and Cooperation in Defence

36 Pages Posted: 23 Jul 2011  

David Hugh-Jones

University of East Anglia (UEA)

Ro'i Zultan

University College London

Date Written: September 22, 2010


In experiments, people behave more cooperatively when they are aware of an external threat, while in the field, we observe surprisingly high levels of within - group cooperation in conflict situations such as civil wars. We provide an explanation for these phenomena. We introduce a model in which different groups vary in their willingness to help each other against external attackers. Attackers infer the cooperativeness of a group from its members’ behavior under attack, and may be deterred by a group that bands together against an initial attack. Then, even self-interested individuals may defend each other when threatened, so as to mimic more cooperative groups. By doing so, they drive away attackers and increase their own future security. We argue that a group’s reputation is a public good with a natural weakest - link structure. We extend the model from cooperation in defence to cooperative and altruistic behavior in general.

Keywords: cooperation, conflict, signaling, groups

JEL Classification: C90, D74

Suggested Citation

Hugh-Jones, David and Zultan, Ro'i, Reputation and Cooperation in Defence (September 22, 2010). Available at SSRN: or

David Hugh-Jones (Contact Author)

University of East Anglia (UEA) ( email )

Norwich Research Park
Norwich, Norfolk NR4 7TJ
United Kingdom

Ro'i Zultan

University College London ( email )

Gower Street
London, WC1E 6BT
United Kingdom

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