BIOL 1104 Lecture Notes - Lecture 4: Convergent Evolution, Cladistics, Ingroups And Outgroups
20 Apr 2020
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The taxa being classified form the ingroup. An outgroup is a taxa that is known to have diverged before the members of the ingroup have started to diverged. The outgroup acts as a reference point. Systematists compare each ingroup member with the outgroup to differentiate between shared derived and shared ancestral characteristics. Shared ancestral characters are shared by the outgroup and ingroup. Shared derived characters are shared only by some members of the ingroup. Character can be both ancestral and derived, depending on the context. For instance, when classifying vertebrates, the presence of hair is considered a shared derived character of mammals but when classifying only mammals, the presence of hair is considered a shared ancestral character. For a set of taxa, many different types are possible (ex for 50 taxa, Polytomies are used to illustrate uncertainty about relationships (pic below) Cladistics is an approach to systematics that groups organisms based on their common descent.
