Organisms are in a constant interaction with abiotic and biotic components of their surroundings. Whereas many and perhaps most of the encounters pass with transient changes at the molecular and metabolic levels, some have a profound impact on the phenotypic appearance of an organism and, more importantly, on the phenotypic appearance of their progeny. Since genetic changes are rare and random in nature, their influence on species or/and population evolution, especially in higher eukaryotes, may not be as dramatic and important as it was believed to be. In contrast, environmentally induced transgenerational phenotypic changes, that is what epigenetics in its narrow sense is, are more likely to have an appreciable effect on stress adaptation and the process of microevolution.