One of the very important possibilities that has been applied many times in anagenesis consists in heterochrony (Wakahara 1996; Klingenberg 1998; Richardson 1995), the evolutionary modification of the rate of formation and development of the individual organs and organ systems (Tab. XII.2). A very small genetic change is sufficient for a certain organ to begin to be formed in the ontogenesis of an individual of a certain species sooner or, to the contrary, later and thus arrive at a different state during ontogenesis than in its phylogenetic ancestors. Consequently, a small change in the timing of the individual ontogenetic events can be of fundamental importance for the phenotype of the members of a particular species. An individual with altered phenotype can, again, fundamentally alter its life niche and this change in life niche again fundamentally changes the selection pressures to which the particular species is exposed. Thus, fundamental changes can occur in the body structure as a consequence of minimal genetic changes, for example changes in the regulation region of a single gene.