Anagenesis, also known as "phyletic change", is the evolution of species involving an entire population rather than a branching event, as in cladogenesis. When enough mutations have occurred and become stable in a population so that it is significantly differentiated 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 such that the ancestral population can be considered extinct. A series of such species is collectively known as an evolutionary lineage.
The various species along an evolutionary lineage are chronospecies. In the ancestral population of a chronospecies does not go extinct, the ancestral population represent a paraphyletic species or paraspecies,being an evolutionary grade. This situation is quite common in species with widespread populations.
It is easy to see from the preceding definition how controversy can arise among taxonomists as to when the differences are significant enough to warrant a new species classification. Anagenesis may also be referred to as "gradual evolution".
The philosopher of science Marc Ereshefsky argues that paraphyletic taxa are the result of anagenesis. The lineage leading to birds has diverged significantly from lizards and crocodiles, allowing evolutionary taxonomists to classify birds separately from lizards and crocodiles, which are grouped as reptiles.
Regarding social evolution, it has been suggested that social anagenesis/aromorphosis be viewed as universal or widely diffused social innovation that raises social systems' complexity, adaptability, integrity, and interconnectedness.
- The University of California, Berkeley resource on understanding evolution defines a lineage as "A continuous line of descent; a series of organisms, populations, cells, or genes connected by ancestor/descendent relationships." Understanding Evolution, Glossary of Terms
- The Oxford English Dictionary defines biological lineage as "a sequence of species each of which is considered to have evolved from its predecessor."OED definition of lineage
- Ereshefsky, M. (2001), "Philosophy of Biological Classification", Encyclopedia of Life Sciences, Wiley-Blackwell, doi:10.1038/npg.els.0003447, ISBN 0470016175
- Leonid Grinin & Andrey Korotayev. Social Macroevolution: Growth of the World System Integrity and a System of Phase Transitions. World Futures, Volume 65, Issue 7 October 2009 , pages 477 - 506; Aromorphoses in Biological аnd Social Evolution: Some General Rules for Biological and Social Forms of Macroevolution in Social Evolution & History (Vol. 8 No. 2, September 2009: 6-50).
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