Before revision: Evolutionary events like hybridization and horizontal gene transfer cannot be represented by a tree but require a phylogenetic network instead. Nonetheless, it has been argued that evolution is fundamentally tree-like , in the sense that it can be modeled by a tree with additional arcs.
After revision: Tree-based networks are a class of phylogenetic networks that attempt to formally capture what is meant by `` tree-like , in the sense that it can be modeled by a tree with additional arcs.