Cladogenesis describes evolution in which one ancestral species splits into two or more descendant lineages. The branching event increases the number of species in a lineage.
Cladogenesis can begin when populations become isolated by geography, ecology, behavior, or other barriers to gene flow. Over time, mutation, natural selection, genetic drift, and different environments can make the separated populations increasingly distinct. If reproductive isolation evolves, they are recognized as separate species.
Cladogenesis differs from anagenesis, in which a single lineage changes over time without branching into multiple species. A phylogenetic tree represents cladogenesis with branches and common ancestors at their points of separation. The exact speed of a split can vary greatly, and speciation may occur through several evolutionary routes.