StrengthenDiff: Hardest
Logic Breakdown
Passage Summary: Because two different bird species have the same viral 'DNA scar' in the same spot, and they haven't been related for 25 million years, the virus must have infected their ancestor before they split.
Conclusion: The hepadnavirus has existed for at least 25 million years.
Reasoning: A specific fragment of the virus is found in the exact same location in the genomes of two bird species that split from a common ancestor 25 million years ago.
Analysis: The argument's strength hinges on the idea that the virus didn't just happen to land in the same spot in both birds by coincidence or through a later infection. To strengthen this, we need to eliminate the possibility of 'independent' events. Look for an answer that suggests the likelihood of a virus inserting itself into that exact chromosomal location more than once is extremely low. If it's a 'one-in-a-billion' spot, then the common ancestor explanation becomes much more certain.
Conclusion: The hepadnavirus has existed for at least 25 million years.
Reasoning: A specific fragment of the virus is found in the exact same location in the genomes of two bird species that split from a common ancestor 25 million years ago.
Analysis: The argument's strength hinges on the idea that the virus didn't just happen to land in the same spot in both birds by coincidence or through a later infection. To strengthen this, we need to eliminate the possibility of 'independent' events. Look for an answer that suggests the likelihood of a virus inserting itself into that exact chromosomal location more than once is extremely low. If it's a 'one-in-a-billion' spot, then the common ancestor explanation becomes much more certain.
Passage Stimulus
Passage Redacted
Unlock Full Passage22.Which one of the following, if true, most strengthens the argument?
Correct Answer
C
If insertion sites are random, it’s extremely unlikely that two independent, post-divergence insertions would land at the exact same chromosomal location in two species. That makes a single insertion in their common ancestor—at least 25 million years ago—the best explanation, thus strengthening the conclusion.
Upgrade Your Prep
Ready to go beyond free explanations?
LSAT Perfection is the #1 modern LSAT prep platform, trusted by thousands of students for comprehensive test strategies, advanced drilling, and full analytics on every PrepTest.
Detailed explanations for 59 PrepTests
Advanced drillset builder
Personalized analytics
Built-in Wrong Answer Journal