Figure 4.

Does the performance of cooperation trigger cooperative responses (experiment 4)? Focal rats pulled earlier (a) and more often (b) for a stooge if receiving the smell from a cooperating conspecific (light green) acting in a different room than if receiving the smell of the same individual when it was not cooperating (dark grey). (a) Kaplan–Meier curves with 95% confident intervals. (b) Raw data and the mean number of pulls ± one standard error. For better visibility, overlapping raw data points were randomly offset horizontally. One asterisk indicates a significant difference at p < 0.05, two asterisks at p < 0.01. See electronic supplementary material, table S6 for statistical comparisons. (Online version in colour.)