FIGURE 4. (a) In this cladogram of relationships among four taxa A, B, C, and D, (C, D) form a clade; (B, C, D) form a clade and (A, B, C, D) form a clade. C and D share a most recent common ancestor, and are therefore more closely related to each other than either is to A or B. The clade (C,D) is nested within the clade (B,C,D) which, in turn, is nested within the clade (A, B, C, D). C and D share a most recent common ancestor (3); B, C and D share a more recent common ancestor (2) than any of them do with A. Ancestor 1 gave rise to four descendants, A, B, C, D; ancestor 2 gave rise to three descendants, B, C, D; ancestor 3 gave rise to two descendants, C, D. (b) This cladogram shows that the relative positions of the taxa along the horizontal axis (along tips) is not relevant, but that the ancestor-descendant relationships are the same as in (a)