The cellular switch that explains why humans aren’t nocturnal

Differences in cellular pathway activity flip the switch from nocturnality to diurnality and explain a major evolutionary change humans have undergone.

Early mammals were nocturnal, sleeping during the day while large predators were active. However, after the extinction of dinosaurs, several different lineages of mammals independently transitioned to become active during the day. Exactly how this dramatic change occurred has proved elusive. A new study, published in the journal Science, has revealed a cellular switch which holds the answer.