Fig. 17

The number of intervening nodes does not indicate overall relatedness between lineages. The tree in a is the same in topology as the one used in the study of Meir et al. (2007), which showed that many readers have a tendency misread the directionality of time on phylogenies and to count nodes when asked to determine evolutionary relatedness among species. Confusion may arise in this particular case because many people maintain the erroneous assumption that mammals are the most “advanced” and therefore must be the youngest group. More generally, because the tree is unbalanced, students may tend to consider birds and mammals (separated by four internal nodes on this tree, Z, Y, X, and W) as more distantly related than turtles and mammals (separated by two internal nodes, X and W). However, this is simply an artifact of the species chosen for inclusion on the tree. All species descended from ancestor X are equally related to kangaroos, with which they all share the same last common ancestor, W. To demonstrate this, b illustrates the same tree with different patterns for each branch, which are then spliced together in c to reveal the identical total distance from the common ancestor W to all of the terminal nodes