Morning and evening-oriented people may follow other schedules, due to work, school and other demands, but their preferred schedule is more in sync with this internal clock, which may be partly determined by genetics.
Van Dongen told Discovery News that the finding about creativity and evening types is "certainly novel, and one I would not have expected on biological grounds."
He suggested that the observed differences in creativity might have to do with the fact that evening people also tend to be more extroverted than morning and intermediate types.
"One could reasonably envision a link between the personality trait of extraversion and the finding of creativity," Van Dongen said.
