Fig. 1: Setup used for the five tasks.

a, For gaze following, the experimenter looked to the ceiling. We coded if the ape followed gaze. b, For direct causal inference, food was hidden in one of two cups, the baited cup was shaken (food produced a sound) and apes had to choose the shaken cup to get food. For inference by exclusion, food was hidden in one of two cups. The empty cup was shaken (no sound), so apes had to choose the non-shaken cup to get food. c, For quantity discrimination, small pieces of food were presented on two plates (five versus seven items); we coded if subjects chose the larger amount. d, For delay of gratification (only phase 2), to receive a larger reward, the subject had to wait and forgo a smaller, immediately accessible reward. e, Order of task presentation, trial numbers and organization of tasks into sessions. In both phases, we ran the two sessions on two separate days.