Actors' choices by first approach, condition, and sex of actors.

In actor-first trials actors approached the boxes first and made their choice prior to the arrival of the recipient. In recipient-first trials recipients approached the boxes first and the later arriving actors made their choice with the recipients present at their baited box. White bars depict male actors, grey bars depict female actors. Plain bars illustrate the prosocial condition, striped bars illustrate the altruistic condition. The Y-axis displays the proportion of selfish versus cooperative choices and ranges from 0 to 1. 0 represents solely selfish and 1 represents solely cooperative choices. Bars constitute mean values ± SE. P-values derive from pairwise tests of the final model.