Epigenetic Mechanisms: Reflections on Evolutionary Processes

Abstract

Evolutionary trends leading to certain patterns call for reflection on possible processes which maintain the stability of these patterns and facilitate their changes. Epigenetic processes (like heterochrony) operate mainly in early ontogeny and trigger a chain reaction of changes in induction, regulation and control of the formation of vital structures and functions. Genetic variation maintained by reproduction via supernumerous despecialized zygotes is enhanced by epigenesis. The tendency to optimize, especially in stable and competitive environments, is resisted by a barrier against easy inheritance of selected phenotypic characters, and by juvenilization. If optimization would be allowed to succeed, any new unpredictable perturbation would cause extinction; therefore variations must constantly oscillate around two steady states needed to address any survival goal. This oscillatory process is explained, and named, the Chen principle. The generalist's homeostatic state can be termed altricial and the specialist's precocial. Consequently, "altricial [Formula: see text] precocial dynamic states" form a dichotomy reflected in most evolutionary patterns. Both theories explain the processes we came to perceive as a result of partly closed thermodynamic systems within the open-ended system of nonequilibrium thermodynamics.