Anagenetic evolution refers to the evolution of an ancestral species to a descendant species without a split of lineage. Charles Darwin, the father of modern evolutionary theory In the life sciences, evolution is a change in the traits of living organisms over generations, including the emergence of new species. ... In biology, a species is a kind of organism. ...
Conventional anagenetic change may occur within populations (Sheldon, 1987; Bown and Rose, 1987), but most reported cases are dubious (Gould and Eldredge, in press), and I do not believe that this mode accounts for much in the total pattern of evolution.
Valid cases tend to add a rib, a bump, or a millimeter over millions of years--and such changes simply do not extrapolate to the evolutionary patterns that historians of life are charged to explain (they are also too slow to ascribe to conventional directional selection--see Gould and Eldredge, 1977).
On the theme of hierarchy, we must recognize that many trends formerly interpreted as anagenetic movement of an entity are actually generated by the higher-level process of species sorting (Vrba and Gould, 1986)--that is, by differential success of species leading to expansions or contractions of variance.
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