Figure 3.

Does the smell of cooperation suffice to induce cooperative behaviour (experiment 3)? Focal rats provided food to a stooge earlier (a, b) and more often (c, d) while having access to smell of a cooperative individual (light green lines and symbols) than they did to a stooge while receiving olfactory information of a non-cooperative individual (dark blue lines and symbols). This applies in the experience phase (a, c) and in the test phase (b,d). Asterisks indicate a significant difference (p < 0.05), n.s. indicates a lack of a significant difference, a dot indicates a non-significant trend (p = 0.057). (a,b) Kaplan–Meier curves with 95% confident intervals. (c,d) mean numbers of pulls ± one standard error and the raw data points. For better visibility, overlapping data points were randomly offset horizontally. See electronic supplementary material, table S5 for statistical comparisons. (Online version in colour.)