Can Monophyletic Groups be Polyphyletic?
In the context of cladistics, a school of thought in biological classification, consider the scenario where a group of organisms is divided into two distinct lineages that have evolved separately, yet still share a common ancestor. If these lineages exhibit significant differences in their morphology and physiology, would you consider this group to be monophyletic or polyphyletic? Explain your reasoning with respect to the cladistic criteria of common ancestry.
1 Answer
📌 CONCEPT: A monophyletic group is considered a group of organisms that shares a common ancestor and exhibits a shared characteristic, whereas a polyphyletic group does not share a common ancestor and is therefore not monophyletic.
📐 RULE / FORMULA: In cladistics, a group is considered monophyletic if it is united by a common ancestor and exhibits a shared characteristic, whereas a group is polyphyletic if it is divided into distinct lineages with separate common ancestors.
💡 WORKED EXAMPLE: Consider a group of organisms (A) that has two distinct lineages (B and C) with separate common ancestors. If lineage B exhibits a unique characteristic (X) that is not found in lineage C, then group A is polyphyletic because it does not share a common ancestor. However, if both lineages B and C exhibit characteristic X, then group A is monophyletic because it shares a common ancestor.
⚠️ COMMON MISTAKE: Students often mistakenly assume that a group is monophyletic if it shares a common characteristic, but not necessarily a common ancestor. This is incorrect because a polyphyletic group can share a common characteristic without sharing a common ancestor.
16 Sept 26
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