This book deals with general quantitative regularities of the alteration of evolutionary and reconstruction (critical) periods of development. An equation and a model of development are introduced which generalize a wide range of commonly accepted models, allowing the analysis of the characteristics of processes occurring on different structural levels of natural system organization. On the basis of this model, a hierarchy of critical constants has been established, applicable to, for example, geological history, cyclicity in the individual development of animals, structures of population and ecological systems, as well as to the perception of acoustical signals by man.