During phylogenesis, not only individual species, but entire higher taxa very rapidly emerge and develop to their typical form. G.G. Simpson pointed out this fact in the middle of the last century and proposed the name quantum evolution for this phenomenon, in contrast to phyletic evolution (Simpson 1944). In modern terminology, we would most probably speak of quantum or phyletic anagenesis. While the punctualist model of evolution refers to the fact that a species changes only immediately after the time of its formation, the quantum evolution model refers to the fact that fundamental anagenetic changes typical for the members of a particular taxon also occur very rapidly, almost in a jump on a paleontological scale, in sequences of (punctualistically or gradualistically evolving) species forming a certain phylogenetic line. Simpson explained this by suggesting that the formation of a new taxon is dependent primarily on key anagenetic changes that enable the hosts to occupy a new adaptive zone. However, passage to a new zone frequently has the character of “all or nothing”, so that organisms with transition forms of the particular traits are exposed to very strong selection pressures that cause a very rapid passage to a new adaptive zone. Consequently, species with transition traits practically do not occur in nature or have such short lives that they are not even observed in the paleontological record.
At the present time, it is not clear whether the quantitative character of anagenesis requires separate explanation or whether it can also be a consequence of the punctualist character of anagenesis of the species.