The left-hand cladogram is based on evidence from morphology, while the right-hand one is based on evidence from genetics. The two trees are similar, but they are not identical. See if you can identify how many ways these two cladograms differ. This is one of the main difficulties of phylogenetic systematics. The "true" evolutionary tree is lost in the distant past, and all that scientists can do is find evidence for the best evolutionary hypothesis. Sometimes different data sets do not give the exact same results. It should be noted here that Phylogenetic trees are so useful because they provide the historical narrative for explaining the similarities and differences among those entities placed on the tree. It should be noted here that a phylogenetic tree may change, for example, if new species are found and have to be included, or if new evidence shows that the species already 'in the tree' are related differently from that shown.
