Circadian rhythms in physiology and behavior provide a selective advantage by enabling
organisms to anticipate rhythmic changes in their environment. These rhythms are based
upon a molecular clock generated via an intracellular transcriptional–translational feedback
loop involving a number of key clock genes. However, to be of practical use, circadian
rhythms need to be entrained to the external environment. In mammals, the primary signal
for entrainment is light detected by the photoreceptors of the eye. Research on the …