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Concept
Polyphylie
Résumé
A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of convergent evolution. The arrangement of the members of a polyphyletic group is called a polyphyly ˈpɒlɪˌfaɪli. It is contrasted with monophyly and paraphyly.
For example, the biological characteristic of warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds; "warm-blooded animals" is therefore a polyphyletic grouping. Other examples of polyphyletic groups are algae, C4 photosynthetic plants, and edentates.
Many taxonomists aim to avoid homoplasies in grouping taxa together, with a goal to identify and eliminate groups that are found to be polyphyletic. This is often the stimulus for major revisions of the classification schemes. Researchers concerned more with ecology than with systematics may take polyphyletic groups as legitimate subject matter; the similarities in activity within the fungus group Alternaria, for example, can lead researchers to regard the group as a valid genus while acknowledging its polyphyly. In recent research, the concepts of monophyly, paraphyly, and polyphyly have been used in deducing key genes for barcoding of diverse groups of species.
The term polyphyly, or polyphyletic, derives from the two Ancient Greek words, πολύς (), meaning "many, a lot of", and φῦλον (), meaning "genus, species", and refers to the fact that a polyphyletic group includes organisms (e.g., genera, species) arising from multiple ancestral sources.
Conversely, the term monophyly, or monophyletic, builds on the ancient Greek prefix μόνος (), meaning "alone, only, unique", and refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor.
By comparison, the term paraphyly, or paraphyletic, uses the ancient Greek prefix παρά (), meaning "beside, near", and refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor.
Source officielle
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