LSAT 117 | Section 2 | Logical Reasoning: Q4

LR Question 4 Explanation

QUESTION TEXT: The top 50 centimeters of soil on Tiliga …

QUESTION TYPE: Weaken

CONCLUSION: The arrival of humans significantly lowered the bird population and diversity on Tiliga.

REASONING:

• The top 50 cm of soil (the last 3,000 years, since humans arrived) contains evidence of fewer and less diverse bird populations.
• The lower 150 cm of soil (the previous 80,000 years) shows a much larger and more diverse bird population.

ANALYSIS: This is a causal argument. They’re arguing that humans caused the decline in bird populations on the island.

To weaken, we want an alternative explanation for why the bird population declined around the same time.

___________

1. If the birds eaten by islanders had few natural predators, this could make human predation look even more important.
2. This says many species survived on other islands until much later. That might suggest humans played some role on Tiliga, since the birds disappeared sooner there.
3. CORRECT. If a deadly microbe arrived immediately before humans immigrated and killed many bird species, then the observed decline may have been caused by the microbe rather than by humans. The timing that seemed to implicate humans is no longer persuasive.
4. Finding the same bird species in older soil simply means those species existed before humans arrived. That’s entirely expected and doesn’t undermine the argument.
5. Irrelevant. We’re not judging how skilled the birds were at flying.