Logical Reasoning

PT1 · S4 · Q22 A fourteen-year study of finches

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A fourteen-year study of finches on the Galapagos islands concluded that there is a definite relationship between climate and the population size of finch species that thrive at various times.

Conclusion (in question stem)

Climatic variations cause a major difference in survival rates of small and large finches.

Evidence

During droughts, large finches survive better because their large bills can crack the large, hard seeds that smaller finches can't access. In rainy years, large finches survive worse because the moisture fosters plants that produce small seeds, and large finches must consume enormous numbers of small seeds to meet their energy demands — too many to eat fast enough.

Evaluate

The general storyline here is that droughts favor the survival rates of large finches (because of large, hard seeds) whereas rainy years favor the survival rates of small finches (because of small seeds).

It's established that the small finches can't survive on the large seeds (because they can't crack them open) and the large finches can't survive on the small seeds (because you they just can't eat them fast enough to satisfy their huge energy demands).

Goal

The only thing that seems to be missing is the unstated idea that during droughts, the small finches can't find enough of their small seeds to survive. And that during rainy seasons, the large finches can't find enough of their large seeds to survive.

22.

Which one of the following must be assumed in order to justify the conclusion that climatic variations cause a major difference in survival rates of small and large finches?

  1. During drought conditions, the weather

    Bad Assumption

    The passage says droughts produce large, hard seeds, not small hard seeds. Small and hard is just a word salad combo we never talked about.

    3% picked this

  2. Correct

    A lengthy period of rainy

    Why this is right

    This is one of the Assumed Differences the author was making: during drought, there aren't enough small seeds for the small finches. during rainy season, there aren't enough large hard seeds for the large finches. If we negated this and said that rainy weather doesn't result in any fewer large, hard seeds, then we wouldn't have any reason to think that large finches would struggle to survive in rainy climates.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    73% picked this

  3. In rainy periods, the small

    Bad Assumption

    The argument doesn't need small finches to grow larger in rainy years. The argument is about survival rates, not about size changes. If we negated this and said that small finches don't grow larger and heavier, that wouldn't hurt the argument. The author's only committed belief about rainy periods is that large finches would find it harder to survive and small finches would find it easier to survive.

    6% picked this

  4. The Galapagos climate during this

    Bad Assumption

    The argument doesn't need the climate to be balanced between dry and wet. It only needs both kinds of weather to occur and to produce the described effects on survival. The author isn't saying that climate spends about equal time favoring the large ones vs. favoring the small ones. The conclusion is merely saying that different climates affect the survival rates of large vs. small finches differently. It doesn't make any different if one type of climate occurs more frequently than the other.

    10% picked this

  5. Small seeds do not have

    Bad Assumption

    This does have the lovable Defender "not". If we negate this, does it weaken to say, "hey author - small seeds ALSO need to be cracked open!" No. The small seeds might be totally manageable for the small finches. Their bills are too small to crack something large and hard, but might be fine cracking something smaller and moister.

    7% picked this

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