In simply looking around, you can identify many rhythmic processes. Waves that form on the beach, tides that rise and fall each 12 and a half hours, the light dark cycle of each day and the seasons. These are all examples of rhythms that arise from physical forces. Other rhythms are of biological origin. Biological rhythms come in many different periods ranging from milliseconds to years and some have developed to help organisms cope with the environment's physical rhythms. In his introductory lecture, Till will guide you through the different biological rhythms and he'll explain why some of them are special. He'll introduce you to the concept of temporal niches and explain why an evolutionary adaptation to these niches is important for survival. You will need this knowledge to understand what's special about biological rhythms, about circa-rhythms, and most importantly for this course, about circadian rhythms. You'll begin to look at ecology through the eyes of a chronobiologist. [SOUND]