This mammal phylogenetic tree is based on morphological evidence, whereas the one on the right is based on genetic evidence. Although the two trees are similar, they are not identical. Try to figure out how many ways these two cladograms differ. One of the most difficult aspects of phylogenetic systematics is this. The "true" evolutionary tree has been lost in the distant past, and scientists can only look for evidence to support the best evolutionary hypothesis. Different data sets do not always produce the same results. Although we will never know what the true evolutionary tree of any particular clade is, probability suggests that as more evidence is gathered, the resulting cladograms will become more similar. Go ahead and start using EdrawMax to create phylogenetic trees for your class.