The role of epigenetic processes is of fundamental importance for the development of multicellular organisms. If these processes did not participate, the results of individual development would be extremely sensitive to various random internal and external disturbances. For example, if the length of a vein that is intended to supply the brain with blood were determined by the number of times that its cells divided during embryogenesis, where the number of cell divisions would be determined genetically, any mutation or intervention from the environment affecting the length of the individual would have catastrophic consequences for the viability of the organism. In such a case, the relevant vein would not reach to the brain or it would be narrowed or interrupted, the brain would not be supplied with blood and its tissues would die. In contrast, if the length of the vein is determined epigenetically, for example, by the fact that its cells should renew division when the mechanical strain on a forming vein, fixed at one end to the heart and at the other to the head part of the embryo, exceeds a certain value, it will be ensured that the vein will always reach from the heart to the brain regardless of whether, under the effect of a mutation or unusual external conditions, a very short or long neck were to form in the particular embryo. The existence of self-regulation epigenetic processes is probably the most important source of developmental canalization (directing), i.e. the resistance of developmental processes to the action of genetic and environmental disturbances (Wilkins 1997; Wagner 1996; Hartman, Garvik, & Hartwell 2001). The term developmental canalization is understood by various authors as both the actual resistance of developmental processes against disturbances and also the process of evolutionary accumulation of alleles that determine this resistance through their effects. C.H. Waddington studied canalization by genetic methods in the 1950’s and 1960’s. At the present time, this phenomenon is also being studied at a molecular level primarily on organisms into whose genome a certain gene has been inserted (transgenic organisms) or on organisms with targeted removal or inactivation of genes (knock-out organisms). It was found that similar interventions frequently have only a surprisingly small effect on the phenotype of the organism. Thus, development is generally well buffered against drastic changes in the external environment. If, on the other hand, the phenotype of organisms differs substantially according to the conditions under which they developed, which frequently occurs especially in plants (Pigliucci 1998) and somewhat less frequently in some animals (Gotthard & Nylin 1995; Brönmark & Miner 1992), then this developmental plasticity is mostly genetically programmed in advance; from the standpoint of the viability of the organisms in the particular environment, it is usually useful and the relevant mechanisms of its formation and functioning arose in the course of evolution through natural selection.