| Anagenesis | Change within a single lineage |
| Cladogenesis | Lineage splitting (speciation) |
| In order for two individuals to produce viable, fertile offspring there are a number of hurdles to cross (prezygotic and postzygotic barriers, see Campbell fig. 24.5). The study of speciation can be thought of as the study of how these barriers arise. |  |
Allopatric (= other land) speciation is when species divergence happens in geographically isolated areas
Sympatric (= same
land) when speciation occurs in the same area
