Information AboutPolyphyletic |
| CATEGORIES ABOUT POLYPHYLY | |
| phylogenetics | |
| SHOPPER'S DELIGHT | |
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In Phylogenetics , a Taxon is polyphyletic ( Greek for "of many races") if the trait its members have in common evolved separately in different places in the phylogenetic tree. Equivalently, a polyphyletic taxon does not contain the most recent common ancestor of all its members. For example, the group of Warm-blooded animals is polyphyletic, because it contains both Mammals and Birds , but the most recent common ancestor of mammals and birds was cold-blooded. Warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds, so it is not a true genetic grouping. Scientific Classification aims to group Species together such that every group is descended from a single common ancestor, and the elimination of groups that are found to be polyphyletic is therefore a common goal, and is often the stimulus for major revisions of the classification schemes. A polyphyletic group can be "fixed" either by excluding Clade s or by adding the common ancestor. Opinions differ as to whether valid groups need to contain ''all'' the descendants of a common ancestor. Groups that do so are called Monophyletic , and according to Cladistics it should be the aim of classification to ensure that all groups have this property. However, many other taxonomists would argue that there is a valid place for groups that are Paraphyletic , i.e. contain only the descendants of a common ancestor, but do not contain all its descendants. |