Our hypothesis holds that the left hemisphere of the vertebrate brain was originally specialized for the control of well-established patterns of behavior under ordinary and familiar circumstances. In contrast, the right hemisphere, the primary seat of emotional arousal, was at first specialized for detecting and responding to unexpected stimuli in the environment.
Humans' ability to create new environments, like factories or cities, is fairly recent on the evolutionary time scale. Nevertheless, human creativity itself must have ancient origins because even small children can generate counterfactual "what if" scenarios. Assuming that one hemisphere is responsible for well established patterns and the other for reacting to unexpected stimuli, both of them need to work together to imagine environments with new stimuli and realize that old reactions might not work.