During phylogenesis, new phylogenetic lines of organisms are formed from the original single line (denoted as the phylogenetic line, evolutionary line, monophylum or clade), i.e. from a branched or unbranched series of species that have a mutual relationship of ancestors and descendants, by splitting off in the process of branching speciation. These lines can then survive for long times in nature or disappear after a shorter or longer period of time. A phylogenetic line becomes extinct when all its members die out. Individual species are constantly formed and disappear within the individual phylogenetic lines, where the phenotype properties of the new species can differ from the phenotype properties of the older species. Just as the species composition of the individual phylogenetic lines changes during evolution, the phenotype composition of their living members also changes. The process of mutual splitting and, to the contrary, in isolated cases, merging of phylogenetic lines is termed cladogenesis, while the process of accumulation of phenotype changes within the line is termed anagenesis. The entire historical process of gradual splitting off of the individual phylogenetic lines and accumulation of their anagenetic changes is termed phylogenesis. It should be pointed out that the term anagenesis was used for some time in the past in different senses, for example in the narrower meaning of accumulation of progressive evolutionary changes, i.e. changes improving a certain structure and its functions (Rensch 1959).

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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