title: Meeting now suggests we will meet again: implications for debates on the evolution of cooperation.
abstract: Humans are often generous, even towards strangers encountered by chance and even in the absence of any explicit information suggesting they will meet again. Because game theoretic analyses typically conclude that a psychology designed for direct reciprocity should defect in such situations, many have concluded that alternative explanations for human generosity--explanations beyond direct reciprocity--are necessary. However, human cooperation evolved within a material and informational ecology: Simply adding consideration of one minimal ecological relationship to the analysis of reciprocity brings theory and observation closer together, indicating that ecology-free analyses of cooperation can be fragile. Using simulations, we show that the autocorrelation of an individual's location over time means that even a chance encounter with an individual predicts an increased probability of a future encounter with that same individual. We discuss how a psychology designed for such an ecology may be expected to often cooperate even in apparently one-shot situations.
authors.affiliation: Department of Psychological & Brain Sciences, University of California-Santa Barbara, CA, USA. max.krasnow@gmail.com
authors.forename: Max M
authors.initials: MM
authors.lastname: Krasnow
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Delton
authors.forename: John
authors.initials: J
authors.lastname: Tooby
authors.forename: Leda
authors.initials: L
authors.lastname: Cosmides
mesh_terms: D005075:Biological Evolution; D003142:Communication; D003198:Computer Simulation; D003299:Cooperative Behavior; D005716:Game Theory; D006801:Humans; D007398:Interpersonal Relations; D011336:Probability; D012919:Social Behavior; D013995:Time