Figure 2.

Is olfactory information important for cooperative decisions (experiment 1)? Kaplan–Meier curves according to the experimental treatments, showing that rats provided food earlier to cooperators (light green) than to non-cooperator (dark blue) when olfactory information was present (solid lines) compared to when no olfactory information was available (dotted lines); shading represents the 95 confidence intervals. (a) Kaplan–Meier estimator for direct reciprocity and (b) for generalized reciprocity. Three asterisks indicate a significant difference (p < 0.001), whereas n.s. indicates a lack of a significant difference (non-significant). See electronic supplementary material, table S7 for all statistical comparisons. (Online version in colour.)