Types of Evolution
We can differentiate between two types of evolution that take place within a group of organisms connected by reproduction. Anagenesis refers to evolution taking place in a single lineage (a group of organisms connected by ancestry) over time (Figure 18.9). Another type of evolution is cladogenesis, the splitting of one lineage into two. When a lineage splits, the two branches no longer have a common gene pool and evolve independently of each other. New species arise through cladogenesis. 
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Figure 18.9: Anagenesis and cladogenesis are two different types of evolutionary change. Anagenesis is change within an evolutionary lineage; cladogenesis is the splitting of lineages.
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CONCEPTS
Biological evolution is genetic change that takes place within a group of organisms. Anagenesis is evolution that takes place within a single lineage; cladogenesis is the splitting of one lineage into two.