Final answer:
To calculate the distance between two species on a phylogenetic tree, you look at the path through their most recent common ancestor. Cladistics is used to group species into clades based on shared traits from a single ancestor. Species closer on the tree have more genetic similarities due to a more recent common ancestor.
Step-by-step explanation:
To calculate the distance between species A and species B on a phylogenetic tree, you would evaluate the path connecting them through their most recent common ancestor. The length of the path often corresponds to genetic changes, with longer paths indicating greater evolutionary divergence. Phylogenetic trees are constructed using methods like cladistics, which group organisms into clades based on a single ancestor and shared traits. Species that share a more recent common ancestor will be closer on the tree, showing fewer genetic differences. In a given tree where four species are displayed, if we focus on species D and E, we would likely find that these two species have more genetic similarities with each other than with species A and B. Similarly, species A and B would share more similarities with each other than with species D and E because of their respective positions on the tree, which suggest more recent common ancestry between each pair.