Which statement best distinguishes a monophyletic group from a polyphyletic group?

Which statement best distinguishes a monophyletic group from a polyphyletic group?

• A. Monophyletic includes an ancestor and all descendants; polyphyletic includes organisms without a recent common ancestor.
• B. Monophyletic is based on convergent traits; polyphyletic on homologous traits.
• C. Monophyletic excludes some descendants.
• D. Polyphyletic includes a single lineage.

Answer: (A)

A monophyletic group is a true clade: it includes the most recent common ancestor and every descendant that comes from that ancestor. A polyphyletic group, on the other hand, gathers organisms from different lineages and does not include the most recent common ancestor of all members within the group. That’s why the statement that a monophyletic group includes an ancestor and all descendants, while a polyphyletic group includes organisms without a recent common ancestor within the group, best captures the distinction. Context helps: monophyly reflects shared evolutionary history, so a clade represents one branch of the tree of life. Conversely, polyphyletic groupings arise from grouping species by superficial similarities (convergent traits) rather than by descent, which is why they don’t track the true common ancestry. The other ideas mix up these concepts—for example, monophyly is not defined by convergent traits, and polyphyletic groups are built from multiple lineages, not a single one.

A monophyletic group is a true clade: it includes the most recent common ancestor and every descendant that comes from that ancestor. A polyphyletic group, on the other hand, gathers organisms from different lineages and does not include the most recent common ancestor of all members within the group. That’s why the statement that a monophyletic group includes an ancestor and all descendants, while a polyphyletic group includes organisms without a recent common ancestor within the group, best captures the distinction.

Context helps: monophyly reflects shared evolutionary history, so a clade represents one branch of the tree of life. Conversely, polyphyletic groupings arise from grouping species by superficial similarities (convergent traits) rather than by descent, which is why they don’t track the true common ancestry. The other ideas mix up these concepts—for example, monophyly is not defined by convergent traits, and polyphyletic groups are built from multiple lineages, not a single one.