Anagenesis

Anagenesis is the gradual evolutionary change of a species that continues to exist as a single interbreeding population, as opposed to cladogenesis, in which a lineage branches and splits into separate species. It does not necessarily produce a new species: a population can transform substantially over time while remaining one continuous lineage. Where speciation does occur, with different lineages branching off and ceasing to interbreed, a core group can continue to be defined as the original species, and the ongoing evolution of that core group, without extinction or the branching off of the divergent lineages counting against it, is what is called anagenesis. The concept matters in paleontology, where it helps address the difficulty of telling, from fossil evidence alone, whether a change was gradual transformation within one lineage or the replacement of one species by another. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/