Number : ENDO : 0196

p0010 As most people have experienced throughout their lifetimes, timing is everything. The ability to modify one’s behavior or physiology on a regular basis, be it daily, monthly, or yearly, is arguably one of the most adaptive responses of life and occurs in virtually all organisms, ranging from single-celled algae to complex humans. But why have biological rhythms evolved, and what functions do they serve? All physiological systems require proper coordination and synchronization with one another to ensure that a wide variety of rhythmic events can occur during an optimal time of the day or year. For example, for the body to prepare appropriately to digest a meal, numerous physiological processes must occur in anticipation of eating. Many species must also predict the time of year to coordinate breeding activities. These daily and yearly changes require critical coordination among numerous internal processes necessary to maintain homeostasis. Furthermore, for biological rhythms in behavior and physiology to be coordinated with the appropriate time, these rhythms need to be synchronized to external time cues within the environment. The means by which intrinsic rhythms are generated by a clock in the brain, and how these rhythms are synchronized to local time, is the primary focus of the study of biological rhythms.