Ongoing anagenesis in a certain phylogenetic line of an organism leads to changes in the phenotypes of the relevant species. These changes can occur from one generation to the next within a single species without splitting the original species into two new species. If a large number of changes have accumulated in such a species, from a certain moment the altered form can be designated as a new species formed by phyletic speciation. Thus phyletic speciation is caused by anagenesis alone. However, there is frequently a close connection between anagenesis and cladogenesis – the anagenetic change is connected with the formation of a new species. Anagenetic changes regularly occur in only some individuals of the original species that are reproductively isolated from the rest of the population. In this case, branching speciation occurs and the anagenetic changes in the phylogenetic line occur on the basis of gradual formation of new species, exhibiting new properties, and the extinction of the original species. Without anagenetic changes, the individual species would not differ phenotypically and we would not be capable of subsequently differentiating the individual events of cladogenesis. See also Phylogenesis.

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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