Social Environment Shapes the Speed of Cooperation

Scientific Reports, Forthcoming

33 Pages Posted: 16 Jun 2016 Last revised: 17 Jun 2016

See all articles by Akihiro Nishi

Akihiro Nishi

Yale University

Nicholas A. Christakis

Yale University, Law School, Students

Anthony Evans

Tilburg University

Alistair O'Malley

Dartmouth College

David G. Rand

Massachusetts Institute of Technology (MIT)

Date Written: June 16, 2016


Are cooperative decisions typically made more quickly or slowly than non-cooperative decisions? While this question has attracted considerable attention in recent years, most research has focused on one-shot interactions. Yet it is repeated interactions that characterize most important real-world social interactions. As a result, the effect of the cooperativeness of one’s interaction partners (the “social environment”) on the speed of cooperation has been overlooked. We propose that reciprocal decisions (choices that mirror behavior observed in the social environment), rather than cooperative decisions per se, occur more quickly. We test this hypothesis by examining four independent decision time datasets with a total of 2,088 subjects making 55,968 decisions. We show that reciprocal decisions are consistently faster than non-reciprocal decisions: cooperation is faster than defection in cooperative environments, while defection is faster than cooperation in non-cooperative environments. These differences are further enhanced by subjects’ previous behavior – reciprocal decisions are faster when they are consistent with the subject’s previous choices. Finally, mediation analyses of a fifth dataset suggest that the speed of reciprocal decisions is explained, in part, by feelings of conflict – reciprocal decisions are less conflicted than non-reciprocal decisions, and less decision conflict appear to lead to shorter decision times.

Keywords: Decision time, Social environment, Evolution of cooperation, Reciprocal altruism, Prisoner’s Dilemma

JEL Classification: C7, C91, C70, C72, C79, C90, C92, D03, D63, D64, D69, D70, D79, D83, H41

Suggested Citation

Nishi, Akihiro and Christakis, Nicholas A. and Evans, Anthony and O'Malley, Alistair and Rand, David G., Social Environment Shapes the Speed of Cooperation (June 16, 2016). Scientific Reports, Forthcoming. Available at SSRN:

Akihiro Nishi (Contact Author)

Yale University ( email )

New Haven, CT 06520
United States

Nicholas A. Christakis

Yale University, Law School, Students ( email )

127 Wall Street
New Haven, CT 06511
United States

Anthony Evans

Tilburg University ( email )

P.O. Box 90153
Tilburg, DC 5000 LE

Alistair O'Malley

Dartmouth College ( email )

Department of Sociology
Hanover, NH 03755
United States

David G. Rand

Massachusetts Institute of Technology (MIT) ( email )

77 Massachusetts Avenue
50 Memorial Drive
Cambridge, MA 02139-4307
United States


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