User:Abrower/sandbox

History of the word and the concept

Willi Hennig (1966, p. 196) said, "Our contention is generally true, that "family tree" and "written fixation of the system" correspond exactly only when the family tree clearly shows recognized or presumed sister-group relationships, and also makes clear which groups are undoubtedly monophyletic, and which are doubtfully so ... . By no means all of the family trees scattered through the literature  satisfy these criteria." Although Hennig's book was full of cladograms, Hennig did not describe them as such. Rather, it was Ernst Mayr (1965), and pheneticists Joseph Camin and Robert Sokal (1965) who independently proposed the term. Camin and Sokal said, "We suggest the term cladogram to distinguish a cladistic dendrogram from a phenetic one, which might be called a phenogram." Mayr (1965) did not provide a concise definition of the term, but in the glossary of his textbook (1969), Mayr defined a cladogram as "a dendrogram based on the principles of cladism; a strictly genealogical dendrogram in which rates of evolutionary divergence are ignored."

Three important post-Hennigian books about cladistics were published in 1980/81. Eldredge and Cracraft (1980) did not provide a succinct definition of cladogram, but offered the following considerations:  "Cladograms, as defined and discussed here, are specific kinds of hypotheses about the history of life.  They are hypotheses about pattern" (p. 20);   "Cladograms depict nested sets of synapomorphies, thereby defining monophyletic groups and simultaneously presenting a hypothesis of relationships among the taxa" (p. 113);  "... cladograms are hypotheses about the structure of that history, that is, not specifically about the history itself, but about the structure of the relationships of the organisms as expressed in their patterns of shared evolutionary novelties." (p. 212); and (notably), " ... cladograms, in themselves, are not phylogenies, but rather hypotheses about the pattern of nested evolutionary novelties." (p. 21). Wiley (1981, p. 97) defined cladogram as "a branching diagram of entities where the branching is based on the inferred historical connections between the entities as evidenced by synapomorphies", and also distinguished cladograms from phylogenetic trees. Nelson and Platnick (1981, p. 14) succinctly said, "phyletic trees depict aspects of evolutionary genealogies" while "cladograms depict structural elements of knowledge."

In more recent systematics textbooks, the following definitions of cladogram are found: The salient features of all of these definitions are that cladograms are dendrograms depicting relative recency of common ancestry, based on the presence of shared, derived characters (synapomorphies), and which do not take into account degree of difference or branch length.
 * "branching diagram[s] depicting the genealogical relationships between species or other suitable terminal taxa." (Minelli, 1993, p. 10) (Minelli also noted that "The differences between one tree-like diagram and another are not simply matters of aesthetics. Several conceptually different tree-like diagrams are possible and one
 * "a dendrogram (tree diagram) specifically depicting a phylogenetic hypothesis and therefore based on synapomorphies. A cladogram generally only indicates the branching pattern of the evolutionary history" (Quicke, 1993, p. 263)
 * "a branching diagram specifying hierarchical relationships among taxa based on homologies (synapomorphies). A cladogram includes no connotation of ancestry and has no implied time axis." (Kitching et al., 1998, p. 202)
 * "an evolutionary tree that has no information on branch lengths" (p. 24) and "simply shows relative recency of common ancestry" (p. 10) (Page and Holmes, 1998)
 * "a depiction of hierarchic relationships among taxa in the form of a treelike diagram, which shows relative recency of relationship and on which character-state transformations may be mapped, but without the connotation of the amount of difference or time since divergence." (Schuh and Brower, 2009, p. 259)
 * "a parsimony tree where the weight of the edges is not relevant" (Wiley and Lieberman, 2011, p. 104)

It is notable that three of the most important foundational sources of model-based phylogenetics, Swoffored et al. (1996), Nei and Kumar (2000) and Felsenstein (2004) do not define and barely mention cladograms at all.