XXV.2.2 Both cladistics and evolutionary systematics base the hierarchical system of taxa on the fact that cladogenesis progressed as a gradual branching of evolutionary lines

In the vast majority of evolutionary lines, cladogenesis occurs as a gradual branching off of new phylogenetic lines within already existing lines. Thus, it is natural to order the species in a hierarchical system of groups, i.e. to delimit and specify, within the entire system of species, mutually immersed groups of taxa.  Lower taxa encompass a narrow range of mutually more related organisms, while higher taxa gradually extend this range to include relatedness with more distant organisms. This approach has the great advantage that, objectively, there exists only one cladogenesis of organisms on the Earth (the result of the real history of evolution on the Earth) and thus the systems created on this basis should, under ideal conditions, be independent of the taxonomist. Only cladists attempt to fully utilize this advantage and base their systems exclusively on cladogenesis. In creating their system, evolutionary systematists take into account both cladogenesis and anagenesis. The main drawback of this procedure is that the choice of criteria according to which the achieved level of anagenesis should be evaluated cannot basically be made objective.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.