Cladistics 17, 282–284 (2001) doi:10.1006/clad.2001.0174, available online at http://www.idealibrary.com on Majority Does Not Rule: The Trouble with Majority-Rule Consensus Trees Michael J. Sharkey* and Jason W. Leathers† *Department of Entomology, University of Kentucky, S-227 Ag. Sci. N., Lexington, Kentucky 40546-0091; and † Department of Entomology, Oregon State University, Corvallis, Oregon 97331-2907 Accepted May 20, 2001 The use of majority-rule consensus trees as a means of cladograms are independent and equally likely to be the correct tree. resolving ambiguity in phylogenetic analyses is investi- An example will show the lack of justification for gated. It is shown to be an inappropriate method for this this assumption. The cladograms A through C (Fig. 1) purpose.  2001 The Willi Hennig Society are the three minimum-length cladograms generated from the data set of Table 1. This data set is modified from the empirical data set of Hoplicnema species Accuracy has been the prime motivation for the (Pakaluk, 1987; Sharkey, 1989, 1994). The MRC and the development of character-weighting techniques (sum- strict consensus trees are illustrated in Fig. 2. Examina- marized in Kitching et al., 1998). More recently it has tion of the fundamental minimum-length cladograms become rather common practice to use majority-rule (Fig. 1) shows that there are two basal topologies. The consensus (MRC) as a method of weighting clades to first is found in cladograms A and C, both of which resolve ambiguous strict consensus trees (e.g., place darlingtoni as the sister-group of spiniventer + Swofford, 1991; Candall and Fitzpatrick, 1996; Colgan aquilonaria + cubensis + thomasi. The second basal and Flannery, 1995; Lutzoni, 1997; Titus and Larson, topology is found in cladogram B, which places darling- 1996). The purpose of this paper is to illustrate what toni in an unresolved trichotomy with woldai and a we perceive to be a critical weakness in these applica- large clade composed of eight species. tions of majority-rule consensus. Using the criterion of MRC the basal topology of MRC is a form of consensus that retains all clades cladograms A and C is preferred over the alternative that are found in more than 50% of the fundamental basal topology represented by cladogram B. An exami- cladograms (Margush and McMorris, 1981). The 50% nation of cladograms A and C reveals that the clade rule ensures that all included clades are compatible. A composed of spiniventer + aquilonaria + cubensis + more relaxed modification of MRC includes clades that thomasi is resolved in two different ways in the two are consistent with the basic MRC topology. The clades cladograms, but otherwise, they are identical. Each of that are repeated most often in the fundamental set of the two parsimonious reconstructions of this restricted minimum-length trees are preferred. This preference is clade supports the basal topology that they share. The alternative basal topology of cladogram B results in a based on the implicit assumption that all fundamental 0748-3007/01 $35.00 282 Copyright  2001 by The Willi Hennig Society All rights of reproduction in any form reserved