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Mean percentage of prosocial choices (+s.e.) in the (a) Equal condition, (b) Unequal condition and (c) Equidistant condition of the Platforms task, as a function of species. Only gorillas made the prosocial choice significantly more in the experimental (grey bars) than in the control (white bars) Equal condition (p = 0.048). The black line represents chance performance (at 50%).
