A simpler explanation seems to be that morning people are more in line with the regular 9-5 schedule of businesses and schools, and that 9-5 schedule was set fr

A simpler explanation seems to be that morning people are more in line with the regular 9-5 schedule of businesses and schools, and that 9-5 schedule was set from the days when natural light was an important factor in when work could be conducted. Thus, biology may be less of a factor than social structures. These days, I'm noticing a shift toward later schedules--college professors are realizing they get better attendance if they hold classes in the afternoons, for example. So perhaps a gradual cultural shift will come to better accommodate evening people.