Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

In modern animals, development is something like playing with an extremely complicated Lego building set with plastic building blocks.In contrast to real Lego, the individual building blocks cannot only be mutually exchanged and regrouped during evolution, but they can also change independently, for example, as a consequence of mutations.This is possible because the nature of epigenetic processes participating in ontogenesis simultaneously ensures that even the altered components will functionally fit into the whole as this adapts to them during ontogenesis, sometimes better, sometimes worse.This feature of developmental processes is of fundamental importance for the anagenesis of modern animals.New body structures can be formed by regrouping, multiplication or modification of older structures.Fundamental changes in organization of the body (bauplan) can occur, for example, even through a minor change in the order of establishing the individual organs.Simultaneously, the mechanisms of formation of the individual organs need not be evolutionarily created entirely anew, but the already finished Lego building blocks can be used, i.e. mechanisms active in phylogenetic ancestors.

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.

Table XII.2 Basic types of heterochronies. Progenesis and neoteny, in their consequences, are manifested as pedomorphosis, i.e. sexual maturity in individuals whose morphology corresponds to that of immature individuals of related species and their phylogenetic ancestors. The opposite phenomenon, i.e. reproduction in later developmental stages, which can occur through acceleration or hypermorphosis, is called recapitulation or peromorphosis.

Neotenyis apparently the best known heterochrony.Neoteny consists in delay of the development of some body organs compared to development of the sex organs (Wakahara 1996).Most authors now distinguish progenesis as special type of heterochrony, during which premature development occurs of the sexual organs without delay in the development of the somatic organs.An adult organism capable of reproduction thus frequently bears a number of traits characteristic for younger developmental stages, juveniles or larva of a related species of organisms.The best known example of a neotenic animal is the Mexican axolotl, a tailed amphibian, whose body structure differs drastically from related species and is remarkably similar to their larvae.Experimental intervention, specifically administration of a hormone, can induce metamorphosis in this species and the resultant organisms do not differ much from related species in which neoteny does not occur.Neoteny most probably played an important role in the anagenesis of humans (Gould 1978).A number of our body and other traits, e.g. the size of the cerebral cavity, shape of the facial part of the skull and, of nonanatomical traits, e.g. playfulness, are remarkably reminiscent of the traits of immature individuals of related species of anthropoids.s