peciation Can Occur by Transformation or by Splitting Gene Pools
Figure 26-1 shows an evolutionary tree, or phylogeny, that describes the history of several hypothetical lizard species. The passage of time is plotted horizontally as changes in the phenotype of the lizards occur and the lineages diverge or separate.
Figure 26-1. In phyletic evolution, or anagenesis, one species is transformed over time into another species. At all times, only one species exists. In cladogenesis, one species splits into two or more species.