 A monophyletic group consists of an ancestor and all of its descendants. Some familiar groups turn out not to be monophyletic. For example, if we tried to unite pufferfish and sharks into a single group that excluded frogs and other tetrapods (such as the traditional Pisces) we get what is called a paraphyletic group. Individuals in paraphyletic groups all share a single common ancestor, but exclude some descendants of that ancestor. Artificial groups like “flying tetrapods” (birds plus the bats) would be called polyphyletic since they have multiple, distinct origins. Because paraphyletic and polyphyletic groups do not share a single history that is unique just to them (i.e., there is no branch on the tree that leads just to this group), they cannot feature in explanations in the same way that monophyletic groups can, i.e., they lack the utility and explanatory power of monophyletic groups (Velasco 2008a). For example, biologists might be interested in studying whether flower diversity is driven by pollinator syndrome (i.e., moth, bird, or bee) or vice-versa. Phylogenetic principles predict different patterns of monophyly on these competing hypotheses, which can be tested empirically and used by biologists as they design experiments to test for the evidence of selection in cases like these (Whittall &amp; Hodges 2007). This is simply unavailable without the explanatory and organizing principles of monophyly, and one reason it has grown to dominate systematics.