The following inferences were made from this tree.
(A) Bacteria are more closely related to Eukarya than to Archaea.
(B) Bacteria and Archaea are more similar to each other than either is to Eukarya.
(C) Archaea and Eukarya diverged from each other after their common ancestor diverged from
bacteria.
Which of the following represents a combination of correct inferences?
(1) (A), (B) and (C) (2) (A) and (B) only
(3) (B) and (C) only (4) (A) and (C) only

Decoding the Evolutionary Relationships Among Bacteria, Archaea, and Eukarya: Insights from Phylogenetic Trees

Phylogenetic trees are powerful tools for visualizing the evolutionary relationships among the three domains of life: Bacteria, Archaea, and Eukarya. When tree branch lengths are proportional to the number of genetic changes, they offer even deeper insight into how these domains diverged from their common ancestor.

Evaluating the Inferences

Let’s examine the three inferences made from such a tree:

(A) Bacteria are more closely related to Eukarya than to Archaea.
This is incorrect. Molecular phylogenies, especially those based on ribosomal RNA and other conserved genes, consistently show that Archaea and Eukarya form a monophyletic group, meaning they share a more recent common ancestor with each other than either does with Bacteria. Bacteria are the most distantly related of the three domains.

(B) Bacteria and Archaea are more similar to each other than either is to Eukarya.
This is incorrect. While both Bacteria and Archaea are prokaryotes (lacking a nucleus), this is a superficial similarity. Genetically and evolutionarily, Archaea are more closely related to Eukarya than to Bacteria. The grouping of Bacteria and Archaea as “prokaryotes” does not reflect their true evolutionary relationships.

(C) Archaea and Eukarya diverged from each other after their common ancestor diverged from Bacteria.
This is correct. Phylogenetic trees rooted at the last universal common ancestor (LUCA) show that Bacteria split off first, followed by a later divergence between Archaea and Eukarya. This means Archaea and Eukarya share a more recent common ancestor with each other than with Bacteria.

Correct Combination of Inferences

The only correct inference based on current phylogenetic evidence is (C). None of the other statements accurately reflect the relationships shown by molecular phylogenetic trees.

Therefore, the correct answer is: (3) (B) and (C) only.

However, upon reviewing the options, only (C) is correct. If the question requires two correct inferences, and (B) is not supported by current science, the most accurate answer should focus on (C) alone. But if forced to choose from the listed options, (3) is the closest, though only (C) is truly correct.

Summary Table

Conclusion

Modern phylogenetic trees, based on molecular data, clearly show that Archaea and Eukarya are more closely related to each other than either is to Bacteria. The correct inference is that Archaea and Eukarya diverged from each other after their common ancestor diverged from Bacteria. This understanding has reshaped our view of the tree of life and the evolutionary history of all living organisms.