Anagenesis

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Anagenesis

Anagenesis, also known as "phyletic change", is the evolution

Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
of species involving a change in gene frequency in an entire population

Population

File:Population density.pngIn biology, a population is the collection of inter-breeding organisms of a particular species; in sociology, a collection of human beings....
rather than a branching event, as in cladogenesis

Cladogenesis

Cladogenesis is an evolutionary splitting event in which each branch and its smaller branches forms a "Cladistics", an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of sister organisms....
. When enough mutation

Mutation

In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or virus , or can be induced by the organism, itself, by cellular processes such as s...
s reach fixation in a population to significantly differentiate from an ancestral population, a new species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
name may be assigned. A key point is that the entire population is different from the ancestral population such that the ancestral population can be considered extinct.

It is easy to see from the preceding definition how controversy can arise among taxonomists

Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
when the differences are significant enough to warrant a new species classification.