He found that people with high intelligence are likelier to be night owls. This applied across a wide span of demographic variables, such as ethnicity, education and religion. As Kanazawa explains it, sleeping late at night was rare back in our ancestors day, making it evolutionarily novel.
Evolutionarily novel is a good thing, as his research suggests that intelligent people are more likely to adapt such behaviors.
People tend to think night owls are unproductive creatures, since they sleep in while the early birds are already sitting at their desks. A 2009 study, however, shows that the opposite is true.
Researchers at the University of Liege in Belgium monitored 15 extreme night owls and 16 extreme early birds in a lab. The volunteers had their brain activity measured an hour and a half after waking up, and again 10.5 hours after waking up.
In the morning test, the early birds and the night owls performed nearly the same in their responsiveness. But there was a gap 10.5 hours later: the night owls showed faster reaction times and were more awake than the early birds.