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By Ethan Cochrane

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If a bird, bat, and a winged insect were scored for the character, "presence of wings", a homoplasy would be introduced into the dataset, and this would confound the analysis, possibly resulting in a false evolutionary scenario. Phylogenetic-Groups-... Phylogenetic-Groups Polytomies PrimitivePlanterClad... Ranunculaceae APGII Homoplasies can often be avoided outright in morphological datasets by defining characters more precisely and increasing their number. When analyzing "supertrees" (datasets incorporating as many taxa of a suspected clade as possible), it may become unavoidable to introduce character definitions that are imprecise, as otherwise the characters might not apply at all to a large number of taxa; to continue with the "wings" example, the presence of wings would hardly be a useful character if attempting a phylogeny of all Metazoa, as most of these don't have wings at all.

Many cladistic programs then continue the search with the following repetitive steps: 1. Evaluate the candidate cladograms by comparing them to the characteristic data 2. Identify the best candidates that are most consistent with the characteristic data 3. Create additional candidates by creating several variants of each of the best candidates from the prior step 4. Use heuristics to create several new candidate cladograms unrelated to the prior candidates 5. Repeat these steps until the cladograms stop getting better Computer programs that generate cladograms use algorithms that are very computationally intensive, because the cladogram problem is NP-hard.

In an attempt to avoid a schism in the biologist community, "Gauthier suggested to two members of the ICZN to apply formal taxonomic names ruled by the zoological code only to clades (at least for supraspecific taxa) and to abandon Linnean ranks, but these two members promptly rejected these ideas" (Laurin, 2008: 224). This led him, Kevin de Queiroz, and the botanist Philip Cantino to start drafting their own code of nomenclature, the PhyloCode, for regulating phylogenetic nomenclature. Chapter- 5 Cladogram A horizontal cladogram, with the ancestor (not named) to the left A vertical cladogram, with the ancestor at the top Two vertical cladograms, the ancestor at the bottom A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life.

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