Circadian clocks and a revolving planet go hand-in-hand. But why so many plants and animals have a circadian clock from an evolutionary perspective is relatively unknown. One way to find out is to study animals that live in non-rhythmic environments. And at the end of 2013, my team published a study on exactly that: the circadian clock of the Mexican blind cavefish, Astyanax mexicanus, from data collected in the laboratory and in the fishes’ natural habitat. We showed that these cavefish fish shows wonderful daily patterns of behaviour and gene expression, confirming that it has a functional circadian clock.