Supplementary material from "Preparatory responses to socially determined, mutually exclusive possibilities in chimpanzees and children"

Recent research suggests that between age 2 and 4 children gradually begin to demonstrate a capacity to prepare for two simple, mutually exclusive alternatives of an immediate future event. When children were given the opportunity to catch a target an experimenter dropped into an inverted Y-shaped tube, 2-year olds—as well as great apes—tended to cover only one of the exits, whereas 4-year-olds spontaneously and consistently prepared for both possible outcomes.

Here we gave children, age 2 to 4 years, and chimpanzees a different opportunity to demonstrate potential competence. Given that social behaviour is particularly full of uncertainty, we developed a version of the task where the outcome was still unpredictable yet obviously controlled by an experimenter. Participants could ensure they would catch the target by simply covering two tube exits.