LSAT 123 | Section 3 | Logical Reasoning: Q25

LR Question 25 Explanation

QUESTION TEXT: Some anthropologists argue that the human species could not…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: The anthropologists are wrong to say that prehistoric human survival required the ability to cope with diverse environments.

REASONING: One prehistoric species related to humans had the ability to thrive in different environments, but became extinct.

ANALYSIS: This argument mixes up sufficient and necessary conditions. The anthropologists argued that coping with diverse environments was necessary: “Survive ➞ ability to cope”. Contrapositive: ability to cope ➞ survive

The author gets things backwards with their evidence. The author mistakenly assumed the statement was “ability to cope ➞ survive”, and that Australopithecus afarensis was a counterexample disproving the statement.

But in the anthropologists’ version, the ability to cope was necessary, but not sufficient. So a species failing to survive doesn’t disprove the claim. (You’d instead need to show a human species surviving without the ability to thrive in a diverse array of environments)

___________

1. CORRECT. See the analysis above. The ability to cope was a necessary condition for survival. The author got confused and assumed it was a sufficient condition.
2. This didn’t happen, and this assumption doesn’t make sense: why would someone assume this?
    
   Example of flaw: Humans have ears, and these helped us survive. That means at least some of our extinct relatives had ears.
3. Like B, this didn’t happen. Instead, the author was assuming that not all species survived.
    
   Example of flaw: Humans had bones, and survived an ice age. So all of humanity’s relatives with bones must also have survived ice ages.
4. In a conditional statement, fulfilling or not fulfilling the condition is what’s important. If I say “To buy a house, you need money”, I don’t care why you do or don’t have money. In terms of fulfilling the necessary condition, only having the money matters.
    
   “Survive” was the (implied) sufficient condition in the author’s argument. So, the important point was that Australopithecus afarensis didn’t survive. Why it didn’t is unimportant.
    
   The author’s actual flaw was mistaking a necessary condition for a sufficient one. “Survive” was actually the anthropologists’ necessary condition, not sufficient.
5. This is a different flaw. The example below shows a flawed argument using the method described in this answer.
    
   Example of flaw: A police officer was shot by a bank robber yesterday. The bank robber had surprised the police officer using a bank security guard’s uniform.
    
   Therefore, in all cases of shootings of police by bank robbers, the bank robber must have a bank security guard’s uniform.