[Campbell Biology P.605] In the initial phylogenetic tree presented, which group is the sist... | Practice Question

In the initial phylogenetic tree presented, which group is the sister taxon to Humans? Explain why their evolutionary relationship remains unchanged despite the rotations shown in the "Rotating Around Branch Points" section.

  • A: Chimps. Sister taxa are defined by sharing a common ancestor that is not shared by any other group, and rotation only alters the visual orientation, not the underlying branching pattern or common ancestry.
  • B: Lizards. Although rotations can change the visual layout, Lizards are not the sister group to Humans; they share a more distant common ancestor.
  • C: Frogs. The rotation concept applies to all branches, but Frogs are evolutionarily more distant from Humans than Chimps are.
  • D: Fishes. Fishes are the most distantly related group to Humans shown on the tree, and rotations do not alter the fundamental relationships.

Explanation

The initial tree clearly shows that Chimps and Humans share their most recent common ancestor with each other, making them sister taxa. The 'Rotating Around Branch Points' section explains that rotation only changes the visual arrangement of taxa at the tips but preserves the branching pattern and, crucially, the recency of common ancestors and thus the evolutionary relationships.