 In order to think about how lineages split or fuse, we have to first answer the question of what a lineage represents. In the case of a phylogeny where the tips are species, the natural answer is that the lineages are tracking species through time and the nodes represent speciation events. But consider the assumption that lineages split but do not fuse. For many readers, hybridization may be the most obvious counter-example. After all, hybridization is relatively familiar, especially for cases involving sexually reproducing charismatic mega-fauna and, even more frequently, plants.