An evolutionary biologist analysed the sequence of amino acids in the respiratory protein cytochrome c from four different eukaryotic species: PPP, QQQ, RRR, and SSS. The table below shows the number of amino acid differences between each pair of species:
| Species | PPP | QQQ | RRR | SSS |
|---|---|---|---|---|
| PPP | 0 | 12 | 3 | 19 |
| QQQ | 12 | 0 | 11 | 24 |
| RRR | 3 | 11 | 0 | 18 |
| SSS | 19 | 24 | 18 | 0 |
Based on this biochemical evidence, which of the phylogenetic trees (A, B, C, or D) represents the correct natural classification of these species?
Tree A, because species PPP and RRR share the most recent common ancestor, whilst species SSS shared a common ancestor with the other species least recently.
Tree B, because species RRR and SSS have only 18 amino acid differences, indicating they are more closely related than species PPP and RRR.
Tree C, because species QQQ and SSS have the greatest number of amino acid differences (24), which places them at the most recent divergence point.
Tree D, because natural classification systems always display symmetric bifurcations to show balanced rates of evolutionary mutation.