What is polyphyly in cladistics?
Q: What is polyphyly in cladistics?
A: Polyphyly is a term in cladistics that describes a group of organisms whose last common ancestor is not a member of the group.
Q: How can polyphyly be expressed?
A: Polyphyly can be expressed by saying that it includes groups some members of which are descended from ancestral populations.
Q: Are birds and mammals related?
A: Yes, birds and mammals are related, but only at the level of the early amniotes. In terms of evolution, there is a vast gulf between them.
Q: Why do traditional taxonomies make mammals polyphyletic?
A: Traditional taxonomies make mammals polyphyletic by including all descendants (say, living mammals) without the group they evolved from (which would be some clade in the therapsida) for convenience.
Q: What is the aim of biological classification?
A: The aim of biological classification is to group species together such that every group is descended from a single common ancestor.
Q: How can a polyphyletic group be "fixed"?
A: A polyphyletic group can be "fixed" either by excluding clades or by adding the common ancestor.
Q: Do all taxonomists agree on the validity of polyphyletic groups?
A: No, not all taxonomists agree on the validity of polyphyletic groups. While cladistics argues that the aim of classification should be to ensure that all groups are monophyletic, some taxonomists argue that there is a valid place for groups that are paraphyletic. These would contain their most recent common ancestor but not all the descendants of that ancestor.
