“Tokogeny versus phylogeny. (a) Processes occurring among sexual species (phylogenetic
processes) are hierarchical. That is, an ancestral species gives rise to two descendant species.
(b) Processes occurring within sexual species (tokogenetic processes) are nonhierarchical. That is,
two parentals combine their genes to give rise to the offspring. (c) The split of two species defines a
phylogenetic relationship among species (thick lines) but, at the same time, relationships among
individuals within the ancestral species (species 1) and within the descendant species (species 2 and
3) are tokogenetic (arrows).” Source: Posada, David, and Keith A. Crandall. “Intraspecific gene genealogies: trees grafting into networks.” Trends in Ecology & Evolution 16, no. 1 (2001): 37-45.