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📝 Evolutionary relationships and phylogeny (7 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 7 questions available

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What is Evolutionary relationships and phylogeny?

Definition:
Evolutionary relationships and phylogeny refer to the historical connections between species based on their shared ancestry, represented by phylogenetic trees or cladograms that depict the branching patterns of divergence from common ancestors over time, and these relationships are inferred from morphological, molecular, and fossil data, providing a framework for understanding the diversification and unity of life.

Working:
Phylogeny works by using characters (traits) and DNA sequences to construct trees, where nodes represent speciation events and branch lengths may indicate evolutionary change, and the relationships are estimated using methods like maximum parsimony and maximum likelihood, with the molecular clock providing divergence times via the equation $t = \frac{d}{2\mu}$ , where $d$ is genetic distance and $\mu$ is mutation rate, allowing scientists to trace evolutionary history.

Example:
A simple example is the phylogeny of primates, where DNA sequencing shows that humans and chimpanzees share about 98.8% of their DNA, indicating a common ancestor about 6 million years ago, while gorillas and orangutans are more distantly related, and this tree helps explain the evolutionary relationships among apes, illustrating how phylogeny organizes biodiversity.

Reason:
Understanding phylogeny is essential for classification, comparative biology, and predicting the characteristics of newly discovered species, and it has applications in conservation, medicine (e.g., tracing disease origins), and evolutionary biology, making it a cornerstone of modern biology.

Easy

Medium

Hard

📝 All Evolutionary relationships and phylogeny MCQs

Q1. Researchers compare DNA sequences from four species. Species A and B differ at 4% of the examined sites, A and C differ at 9%, A and D differ at 18%, and B and C differ at 8%. Assuming the sequences evolve at comparable rates, which inference is best supported?

A.A and D are the closest relatives because their difference is largest

B.A and B are likely more closely related than A and D ✅

C.B and D must be identical in evolutionary history

D.The species with the greatest DNA difference must be the most recently evolved

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Smaller genetic differences generally indicate fewer accumulated changes since divergence when comparable evolutionary rates are assumed. Therefore, A and B are more likely to share a more recent common ancestor than A and D.

Q2. Two species have very similar body structures, but genetic analysis shows that one is more closely related to a third species with a very different body form. Which explanation best accounts for this result?

A.Similar structures always prove the species share the most recent ancestor

B.The similar structures may have evolved independently under similar environmental pressures ✅

C.Genetic evidence cannot be used to infer evolutionary relationships

D.Differences in body form prove that the species cannot share any common ancestor

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Similar structures can arise independently when unrelated organisms experience comparable selective pressures. Genetic evidence may reveal a closer evolutionary relationship between species whose outward appearances differ because inherited changes can accumulate differently across lineages.

Q3. A biologist proposes that species X and Y diverged recently because they share several molecular characteristics. Later, a larger dataset shows that X and Z share even more derived molecular features. What should the biologist conclude?

A.The original hypothesis should be retained because the first dataset was smaller

B.X and Y must have gone extinct at different times

C.The expanded evidence supports X and Z as the more closely related pair ✅

D.Molecular characteristics are irrelevant when organisms look different

💡 Difficulty: hard | ✅ Correct: C

📖 Explanation: A phylogenetic hypothesis should be revised when stronger or broader evidence provides a better explanation. If X and Z share more informative derived characteristics, the data support a more recent common ancestor between X and Z.

Q4. A student argues, "Species P is more evolved than species Q because P has more complex organs and therefore must have appeared later in evolutionary history." Which correction is most scientifically appropriate?

A.Evolution always produces increasing complexity, so the student is correct

B.Complexity alone does not determine evolutionary relatedness or imply that one living species is more evolved ✅

C.The oldest species is always the most complex

D.A species with fewer structures cannot have undergone natural selection

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Evolution does not follow a ladder from simple organisms toward increasingly advanced ones. Living species have independent evolutionary histories, and complexity is not a reliable measure of how recently a species diverged from another.

Q5. A phylogenetic analysis produces the following pattern of branching: species A and B join at one node, species C joins that lineage at the next node, and species D branches off earlier. Which pair is most strongly supported as having the most recent common ancestor?

A.A and B ✅

B.A and D

C.B and D

D.C and D

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: In a branching evolutionary model, the pair connected by the most recent shared branch point is inferred to have the most recent common ancestor. Because A and B join directly at a later node, they are the closest pair.

Q6. A researcher compares two competing evolutionary models. Model 1 requires 12 evolutionary changes to explain the observed characteristics, whereas Model 2 requires 7 changes. If all other assumptions are comparable, which interpretation is most reasonable?

A.Model 1 is automatically better because it contains more changes

B.Model 2 is preferred because it explains the observations with fewer assumed evolutionary changes ✅

C.Both models must be rejected because evolutionary change cannot be counted

D.Model 1 is preferred because more evolutionary changes indicate greater accuracy

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: When competing evolutionary explanations are otherwise comparable, a model requiring fewer independent evolutionary changes is generally more economical. This does not prove the model is correct, but it provides a rational basis for preferring it.

Q7. A graph shows genetic similarity on the vertical axis and time since divergence on the horizontal axis. The similarity between two lineages decreases steadily as divergence time increases. A newly sampled species has very high similarity to lineage M but much lower similarity to lineage N. What prediction is most consistent with the graph?

A.The new species probably shares a more recent common ancestor with M than with N ✅

B.The new species must have evolved directly from M

C.The new species cannot share any ancestor with N

D.N must have evolved after the new species

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The graph indicates that greater genetic similarity corresponds to shorter divergence time. Therefore, the new species is most consistent with a more recent common ancestor with M. However, similarity alone does not mean one living species directly descended from another.

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