LR Question 22 Explanation
QUESTION TEXT: Fish with teeth specialized for scraping algae…
QUESTION TYPE: Flawed Reasoning
CONCLUSION: The specialized algae scraping ability evolved more than once.
REASONING: One possible sufficient condition for single evolution didn’t happen.
ANALYSIS: This is a very bad argument. It talks about fish that live in Blue Lake and Flower Lake. The argument presents this single conditional statement:
closely related ➞ evolved once
The argument then negates the sufficient condition: scientists have shown that the fish aren’t closely related.
But negating the sufficient doesn’t negate the necessary. It’s perhaps possible that the ability evolved only once even though the fish aren’t closely related. Perhaps the fish are loosely related.
___________
- This is a different flaw.
Example of flaw: Algae-scraping is correlated with the two lakes. So the two lakes must have caused the algae scraping ability. - This is a different flaw.
Example of flaw: John says he will get the job. But since we don’t know if that’s true yet, clearly John will not get the job. - CORRECT. This is it. See the analysis above. The author assumed that being closely related was a necessary condition for single evolution.
- This is a different flaw.
Example of flaw: Algae scraping fish will probably go extinct soon. So they definitely will go extinct soon, with 100% certainty. - This is a different flaw. For this to be correct, we’d need to know there was some reason to suspect that the opinion of the biologists was not universal. Here, we have no reason to believe that other biologists would disagree.
Example of flaw: Dr. Jones, famous for his disagreements with the biological community, believes that the algae-scraping ability evolved many times. So Jones must be right.
More Resources for Flaw Questions
- Flaw drills: Use these to practice making examples of abstract flaws.
- Intro Course lesson: This intro course lesson covers Flaw questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers flaw questions.
Hi Graeme, thanks for the explanations!
I have one major issue with this question that I was hoping you could address further. I incorrectly chose choice E because the question stem said “some biologists”. I understand why C is the correct answer, but I don’t understand why “some biologists” isn’t enough to call this argument into question. It is very possible that “some biologists” are unrepresentative of all biologists with relevant expertise or even the general biological consensus on the issue.
That’s true, it is possible. But we have no evidence in the stimulus that points to a reason to suspect them of being unrepresentative. For this to be the correct answer, we’d need the stimulus to give us some potential reason to question the authority, or representativeness, of these biologists. (C), on the other hand, is very clearly evidenced in the stimulus.