History graphs. (A) A history graph representing homology relationships between the vertices in Figure 1. Due to space, colours are used as labels (and match those in Figure 1), with unlabeled vertices shaded grey. Two vertices have the same colour shade if they have identical labels. The dotted arrows represent branches. Four ancestral vertices are added relative to Figure 1 to represent the common ancestral vertices of the subsets of homologous vertices in Figure 1. (B) An extension of (A). (C) The event graph for (B). (D) A simple history with four epochs (1 - 4), and rearrangements given names corresponding to their type. It is a realisation for the graphs in (A) and (B).