Phylogenetic trees with >2 branches on a node are polytomic, and polytomy can appear on trees for two reasons. Firstly a lack of information in the data prevents proper resolution within a clade, called soft polytomy. Alternatively, hard polytomy may exist, this is when there truly is a simultaneous split from one lineage (species) in to more than two. Yang states that "it may be argued that hard polytomies do not exist" but makes no citation or attempts at theoretical discussion. Are there any papers which discuss the theoretical possibility of hard polytomy and any evidence of it occurring?