2. Linnaean Classification This system was created long before scientists understood that organisms evolved. Because the Linnaean system is not based on evolution, most biologists are switching to a classification system that reflects the organisms' evolutionary history. K ing P hilip C ame O ver F or G ood S oup.
6. Different ways of drawing trees All of these state the same relationships!
7. When a lineage splits (speciation), it is represented as branching on a phylogeny.
8. Clades A clade is a grouping that includes a common ancestor and all the descendents (living and extinct) of that ancestor. Using a phylogeny, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny—all of the organisms on that pruned branch make up a clade.
9. Identifying Clades Are reptiles a clade? No! That means that either "reptile" is not a valid phylogenetic grouping or we have to start thinking of birds as reptiles.
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11. Practice Question* Note that the previous example gives four statements about the relationships: one for each ancestral species on the tree. See if you can give the same kind of description of relationships for each of the phylogenies pictured above. * Information for this practice question comes from: http://www.utm.edu/departments/cens/biology/rirwin/391/391Phylog.htm