Cladistics and Cladogram1

Cladistics and Cladogram1 - the evaluation) of multiple...

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Cladistics and Cladograms Cladistics is a type of systematics developed by the late German biologist Willi Hennig, who attempted to formulate a more objective method of classifying organisms. Cladists group organisms based on the presence of shared derived characters, not the overall similarity of potential group members. In the example cited in Figure 3, the amniotic egg would be used to unite a group sharing common ancestry, since it would NOT be present in a group that was not in the lineage. The use of feathers and hair to separate birds and mammals from reptiles would NOT factor into a cladistic hypothesis, or cladogram, since these are characters unique to only one taxon in our group. Such an approach is shown in Figure 4. The value of cladistics lies in its capacity to generate (and provide a set of criteria for
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Unformatted text preview: the evaluation) of multiple hypotheses (alternate cladograms) that can be evaluated with additional data. Almost always the "correct" cladogram employs the principle of parsimony, which proposes that the shortest number of steps or character state changes is most likely correct. An important question. ...is evolution always parsimonmious? However the ultimate answer to that question unfolds, the rigor cladistics introduces to systematics is useful in getting traditional systematists to look at their subjective classifications in a new light. On the diagram shown in Figure 5, shared derived characters are indicated as hauchers across the lines. The mammal clade (in this case represented by mouse and chimpanzee) is united by fur, the lizard, pigeon, mouse-chimp clade is united by claws or nails, etc....
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