Make Entry -- Become an Editor -- Most Popular: (10, 25, 50, 75, 100)

   Help

Anagenesis

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. The ancestral population of a species that has changed through anagenesis is, by definition, extinct. (Cladogenetic evolution does not require the ancestor to be extinct.)

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. There is frequently disagreement among different taxonomists as to whether a population is indeed a distinct new species.

The one thing that most taxonomists agree on as a definition of species is that when a species has become reproductively unique – that is, individuals of one population cannot reproduce with individuals of a slightly different population and produce viable, fertile young – they are by definition a new species. In the case of anagenesis, the original population is extinct, making the fertility test impossible.

Web Resources On Anagenesis

Anagenesis Versus Cladogenesis
Absolute Astronomy: Anagenesis

Book Resources On Anagenesis

Schaums Outline of Biology by George H. Fried
What Evolution is by Ernst Mayr

Site Maps: Most Recent | Clusters | Browse
New: Graduate Student Job Opportunity