Figure 2.

Residuals of the number of pulls (A) and latency to first pull (B) in dependence of the pulling resistance and social experience. (A) The frequency of pulling food for previous cooperators and previous defectors declined with increasing costs (measured as resistance in newtons (N); mean ± standard error; n = 14 rats tested in both situations). The focal rat pulled more often for cooperators than for defectors (p < 0.001; see text). (B) The latency from the start of experiment to the donor's first pull increased with costs when the focal rat was paired with a social partner that had previously defected (p < 0.001; mean ± standard error; n = 14).