Survival curve of the probability of chimpanzee subjects to pull from their rope across time as a function of the condition presented (non-social control trials in green and test trials in red).

A lower probability of acting means that chimpanzees waited longer to pull from their rope. The horizontal whiskers represent the censored-data (the events that were terminated either by the partner acting before them or by the experimenter). Chimpanzees waited longer to pull in the presence of a partner.