Question

a phylogenetic tree shows four species: p, q, r, and s. species p and q share a node (common ancestor) that is more recent than the node shared by q and r. which of the following statements is true?
species p and q are more closely related to each other than either is to species r.
species s is the outgroup for the clade containing p, q, and r.
species p is an ancestor of species q.
species r is the most recent common ancestor of all four species.

Explanation:

• In a phylogenetic tree, the closer the common ancestor (node), the more closely related the species. Since P and Q share a more recent common ancestor than Q and R, P and Q are more closely related to each other than either is to R.
• For the out - group: An out - group is a species that is less closely related to the other species in the clade. Here, we cannot be sure that S is the out - group for the clade containing P, Q, and R without more information about the branching patterns and evolutionary distances.
• Just because P and Q share a common ancestor does not mean P is an ancestor of Q. They could be sister species (evolved from the same immediate ancestor).
• R is not the most recent common ancestor of all four species. The most recent common ancestor of all four species would be at a deeper (more ancestral) node in the tree.

Answer:

Species P and Q are more closely related to each other than either is to Species R.