Ever wonder why some people are night owls and others crash by 8PM? Well – blame it on their GENES. According to the journal Science, a genetic mutation called the “after-hours gene” – or Afh, may explain the phenomenon. In a study, scientists from the UK and New York University monitored when and how often mice chose to run on an exercise wheel. They noticed that instead of following the typical 24 hour pattern, some of the mice had body clocks that stretched to a 27-hour day. When they studied the mice’s DNA, they found that those on a 27-hour-cycle had the “after hours” gene.

Dr. Patrick Nolan led the study and he said the internal body clocks of mice with the Afh gene run on a longer cycle than those with a normal copy of the gene - who like most of us, live on a 24 hour schedule. This unique gene slows the breakdown of specific proteins in the body, keeping them awake longer and essentially – lengthening their body clock. Scientists have yet to translate this study to humans, but it’s likely that we have a similar gene. Which may explain why some people can stay up much later than others.