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Encyclopedia > Anagenesis

Anagenesis is the progressive evolution of species involving a change in gene frequency in an entire population rather than a cladogenetic branching event. When enough mutations reach fixation in a population to significantly differentiate from an ancestral population a new species name may be assigned. A key point is that the entire population is different from the ancestral population so that the ancestral population can be considered extinct. It is easy to see from the preceding definition how controversy can arise among taxonomists regarding when the differences are significant enough to warrant a new species classification. Anagenesis may also be referred to as phyletic evolution.

Basic topics in evolutionary biology
Processes of evolution: macroevolution - microevolution _ speciation
Mechanisms: selection - genetic drift - gene flow - mutation
Modes: anagenesis - catagenesis - cladogenesis
History: Charles Darwin _ The Origin of Species - modern evolutionary synthesis
Subfields: population genetics _ ecological genetics - human evolution - molecular evolution - phylogenetics - systematics - evo_devo
List of evolutionary biology topics | Timeline of evolution

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Anagenesis (215 words)
When the population of an entire species changes on a genetic level without a split, it is called anagenesis, phyletic evolution, or simply evolution.
The opposite of anagenesis, cladogenesis, is when a species splits into two genetically-distinct populations adapted to different ecosystems or survival strategies.
Taxonomists, when determining whether a species has indeed drifted enough from the ancestral population through anagenesis to be considered a new species, may look for differences in both behavior and structure of an organism, especially on a genetic level.
Anagenesis Summary (575 words)
Evolutionary taxonomists such as Simpson use both cladogenesis and anagenesis in their classifications, arguing that taxonomic groups should be based on the branching points in evolution and the degree of difference between groups.
Anagenesis also know as "Phyletic change" is the progressive evolution of species involving a change in gene frequency in an entire population rather than a cladogenetic branching event.
Diagram contrasting Anagenesis and Cladogenesis from the University of Newfoundland
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