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Difficulty: MediumWeaken

Ornithologist: A recent study found that urban crows living in close proximity to fast-food restaurants have significantly higher average body weights than crows living in rural habitats. The diet of these urban crows consists heavily of discarded processed foods, which are notoriously high in calories. Therefore, it is clear that the consumption of these high-calorie processed foods is the primary cause of the increased body weight in these urban crows.

Which of the following, if true, most seriously weakens the ornithologist's argument?

  1. Due to the high concentration of readily available food, urban crows near fast-food restaurants expend significantly fewer calories daily flying and foraging than rural crows do.Answer
  2. B
    Urban crows actually consume very little discarded processed food, instead preferring to hunt for natural insects in nearby parks.
  3. C
    Urban crows that live in residential neighborhoods far from fast-food restaurants have average body weights that are almost identical to those of rural crows.
  4. D
    Mammalian scavengers, such as raccoons, also tend to have significantly higher average body weights when living in urban environments.
  5. E
    The total population of crows in urban environments is substantially smaller than the total population of crows in rural environments.

Answer

The option stating that urban crows near fast-food restaurants expend significantly fewer calories daily flying and foraging than rural crows do.
The argument concludes that a high-calorie diet is the primary cause of the urban crows' higher body weight. However, body weight depends on both caloric intake and caloric expenditure. By pointing out that these urban crows expend significantly fewer calories because their food is highly concentrated, this statement introduces a compelling alternate explanation for their increased weight. This severs the assumed direct link between the high-calorie food itself and the weight gain, thereby severely weakening the conclusion.

Step-by-Step Solution

1
Identify the argument's premises and main conclusion.
Premises: Urban crows near fast food weigh more than rural crows, and they eat a high-calorie processed diet. Conclusion: The high-calorie diet causes the increased body weight.
Deconstructing the argument is necessary to spot the logical gap.
2
Determine the type of reasoning and its inherent vulnerabilities.
The argument uses causal reasoning based on a correlation. A vulnerability is that there might be an alternate cause for the effect (increased body weight).
Understanding the flaw type directs the search for the correct weakening statement.
3
Evaluate the options to find the one that exploits this vulnerability.
The correct option points out that urban crows burn fewer calories. Since weight is determined by calories in minus calories out, a lower expenditure of calories is a plausible alternate explanation for the higher weight.
Introducing a viable alternate explanation is the standard method for weakening a causal argument on the LSAT.

Key Concept

Weakening causal arguments by identifying alternate explanations
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