 While most occurrences of hybridization do not lead to new species, many often lead to introgression–that is, the introduction of genetic information from one lineage to another. If we model this as one lineage connecting to another, we violate the assumption that a phylogeny is a strictly branching tree diagram. But if we instead do not depict these lineages as directly connected, then we violate another background assumption in phylogenetics, namely, that changes along one branch do not affect any other branches. In either case, we now have a situation where the branching history of some characters is not the same as the history of others or of the history of the species as a whole. In the case of genetic history, this is known as genealogical discordance.