Question 1
Multiple choiceHard1 markA museum’s catalogue covers many species and must organize them for comparative studies while reflecting inferred ancestry. The table gives the branching sequence, from earliest split to latest, and current class assignments. A clade contains a common ancestor and all its descendants. Which proposal meets both aims?
| Information | Data |
|---|---|
| Branching sequence | S separates from P, Q and R; then R separates from P and Q; then P separates from Q |
| Current classes | M: P and Q; N: R and S |
Show answer and explanation
Answer: B. A clade contains a common ancestor and all its descendants. The branching sequence gives nested clades P+Q and P+Q+R (and the full set); R+S is not a clade because their common ancestor also has P and Q as descendants. Classification can still organize extensive diversity for comparison, while unranked clades avoid implying that fixed taxonomic ranks measure evolutionary divergence.
A: It assumes both traditional classes are clades; class N excludes P and Q even though they descend from the same ancestor as R and S.
C: It treats the limitation of fixed ranks as a reason to discard classification, although classification facilitates comparative study.
D: It assigns rank by group size; the branching pattern does not require nested clades to have class and order ranks.
Remember: clades express common ancestry, whereas taxonomic ranks are fixed categories.