Cladogenesis is an evolutionary splitting event in a species in which each branch and its smaller branches forms a "clade", an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of sister species. This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors. An example of cladogenesis today is the Hawaiian archipelago, to which stray organisms traveled across the ocean via ocean currents and winds. Most of the species on the islands are not found anywhere else on Earth due to evolutionary divergence.
Cladogenesis is often contrasted with anagenesis, in which gradual changes in an ancestral species lead to its eventual "replacement" by a novel form (i.e., there is no "splitting" of the phylogenetic tree).
Korotayev, Andrey (2004). World Religions and Social Evolution of the Old World Oikumene Civilizations: A Cross-cultural Perspective (First Edition ed.). Lewiston, New York: Edwin Mellen Press. ISBN0-7734-6310-0. (on the applicability of this notion to the study of social evolution).