Since de Mairan‘s discovery nearly three centuries ago, scientists have established that nearly all living things—from singlecell organisms that lurk in ponds to multicellular organisms that drive minivans—have biological clocks. These internal time keepers play an essential role in proper functioning. They govern a collection of what are called circadian rhythms (from the Latin circa [around) and diem [day]) that set the daily backbeat of every creature‘s life.