A previous study found that evening people are smarter than morning people. In a new paper, Kanazawa replicates the finding and provides a theoretical grounding. Because the nocturnal lifestyle allowed by electricity didn't exist 10,000 years ago, we must now rely on general intelligence to override our early-to-bed instincts. So those with more of it stay up later. How much later? See below.

Night Lights

Bedtimes and wake-up times for Americans in their 20s by IQ.

Very Dull (IQ < 75)

Weekday: 11:41 P.M.-7:20 A.M.

Weekend: 12:35 A.M.-10:09 A.M.

Normal (90 < IQ < 110)

Weekday: 12:10 A.M.-7:32 A.M.

Weekend: 1:13 A.M.-10:14 A.M.

Very Bright (IQ > 125)

Weekday: 12:29 A.M.-7:52 A.M.

Weekend: 1:44 A.M.-11:07 A.M.