Analysis of mechanisms underlying adaptation processes

A system of elementary adaptation mechanisms is presented. The adaptations are considered as transients to a new homeostatic condition induced by an environmental change. We propose to distinguish adaptation mechanisms not directly related to gene expression (changes in the rate of synthesis and degradation of proteins, protein-ligand interactions, changes in viscosity of the membrane lipids) and the mechanisms relying on gene expression (changes in expression of already functioning genes, expression of new genes, mutations). Most of these mechanisms have phenotypic nature and just one (mutations) is genotypic. By the nature and time pattern of the environmental influence the adaptation processes can be divided into four types: phenotypic adaptations under rapidly (A) or gradually (B) alternating environmental factors, genotypic adaptations induced by an instant change (mutation) (C), and step adaptational changes (several or many mutations) (D). We propose a model based on a (second-order) linear differential equation qualitatively describing all four types of the adaptation processes.