Anagenetic

Anagenetic evolution refers to the evolution of an ancestral species to a descendant species without a split of lineage.

There are two views of how evolution works. The first is called anagenetics. This is where one type gradually evolves into another type along a single line. The second is cladogenetics. This is where a population splits and each part evolves separately along a different line from the other. In the first case one species literally replaces another as the parent species evolves into the daughter species. In the second case the new and old species live side by side until one or both becomes extinct. The new species does not replace the old one, and sometimes the old species can outlive the new species.

It should be noted that nothing in these definitions assumes that the new species drives the old species to extinction.