Final answer:
The method used to plot the divergence between sister species is termed phylogenetically independent contrasts. Therefore, the correct option is 4.
Step-by-step explanation:
The method used to plot the divergence that arises between sister species as they evolve farther and farther from their common ancestor is termed phylogenetically independent contrasts. It allows scientists to compare traits or characteristics between different species while accounting for their shared ancestry. Phylogenetically independent contrasts allow scientists to compare traits or characteristics between different species, while accounting for their shared ancestry. By analyzing these contrasts, scientists can better understand how species change over time and the relationships between different species.