Logical Reasoning

PT1 · S4 · Q2 Only 1,000 to 2,000 species of fruit flies

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Only 1,000 to 2,000 species of fruit flies exist worldwide.

Information

1000 - 2000 species of FF globally.

Around 500 species in Hawaii (most of any place in the world.

106 of those are PWD's.

Any species in Hawaii currently is thought to be descended from the same one or two ancestral females.

Evaluate

The last sentence is a Conditional ("All"), so it piques our interest the most, since Must Be True is famous for using conditional logic.

We could apply this rule to the 500 species in Hawaii, including the 106 PWD's.

Apparently those are all thought to be descendants of the same 1 or 2 ancestral females.

Goal

It's hard to get a strong sense of where the correct answer is going. We have some quantitative ideas and a conditional.

Let's just stay flexible and find something we can prove.

2.

Which one of the following can be inferred from the passage?

  1. Correct

    All of the picture-winged drosophilids

    Why this is right

    Hey, this was basically one of our predictions. The final sentence gave us a conditional rule, whose trigger was "any fruit fly species now present in the Hawaiian archipelago". We were told about some fruit fly species present in Hawaii -- 500 species in general, with 106 of them being of a subtype called picture-winged drosophilids. We can apply that rule to that fact to derive that all 500 of those species, including the 106 drosophilids are "thought to be descendants of the same one or two ancestral females". (by the way, archipelago means "a chain of islands")

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

    84% picked this

  2. Picture-winged drosophilids are found only

    Too Strong: only

    This answer is trying to bait us with the famous "we only mentioned X in this context, so maybe you'll start thinking that X only occurs within this context." We heard that this species is "represented" in Hawaii by 106 species, but that doesn't meant that this species is only found in Hawaii. Alabama is represented in the U.S. Senate by two Alabamans, but that doesn't meant that people from Alabama are only found in the U.S. Senate.

    3% picked this

  3. All of the 1,000 to

    Too Strong: all

    The rule in the final sentence applies to "all of the fruit fly species present in Hawaii". We were never told that "all of the 1000 - 2000 species of fruit flies worldwide are present in Hawaii", so we can't apply the outcome of that rule to to fruit flies mentioned in the first sentence.

    4% picked this

  4. If 500 new species of

    Too Speculative: no longer be

    Being the most taxonomically diverse population means you have the highest number of fruit fly species in your area. It's possible that if 500 new species of fruit flies were all discovered in an area that previously had, say, 100 species of fruit fly, then this area would now have 600 species of fruit fly and be more taxonomically diverse than Hawaii. But it's possible that 500 new species of fruit flies were discovered across a bunch of different areas, so even though all those areas would become more taxonomically diverse, there might be no area that now tops Hawaii's record of having 500 species.

    3% picked this

  5. Some fruit flies originated in

    Out of Scope: originated

    This answer is lovably weak ("some"), but we have no information about the geographic origins of fruit flies, and no way to talk about a fruit fly from Hawaii ending up elsewhere. The fact that Hawaii has the most species of fruit fly doesn't guarantee that any fruit flies originated there. (They may have arrived in Hawaii because they started in Japan and got accidentally brought to Hawaii by boat).

    7% picked this

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