Logical Reasoning

PT15 · S3 · Q18 In experiments in which certain kinds

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In experiments in which certain kinds of bacteria were placed in a generous supply of nutrients, the populations of bacteria grew rapidly, and genetic mutations occurred at random in the populations.

Conclusion (These show that)

All genetic mutation is random.

Evidence

In experiments where they put bacteria and nutrients in an area together, the populations of bacteria grew rapidly and genetic mutations occurred at random.

Evaluate

The evidence tells us that genetic mutation is random within these bacteria populations.

And the conclusion is claiming that all genetic mutation is random.

Goal

So we'll need some sort of idea like,

18.

Which one of the following, if true, enables the conclusion to be properly drawn?

  1. Correct

    Either all genetic mutations are

    Why this is right

    This performs the service we needed: "if bacteria's mutations are random, then all mutation is random." But it does so in a funky way. Whenever we say "either X or Y", we're saying at least one of those ideas is true. In the case of mutually exclusive options, such as "All A's are B / No A's are B", they can't both be true, so exactly one of them is true. It's impossible for "No genetic mutations are random" to be true, because we were told in the evidence that genetic mutations are random within populations of bacteria. So then it must be true that "All genetic mutations are random", which means the conclusion is proven true. This answer alone doesn't prove the conclusion, but this answer combined with our evidence proves the conclusion. Answer: mutations are X or Y Premise: mutations are not Y. Conclusion: mutations are X. X = all random Y = all not-random

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

    44% picked this

  2. The bacteria tested in the

    Too Weak

    Learning that this bacteria was an extremely common type makes us optimistic that "if these bacteria had random mutations, then most bacteria probably have random mutations". But it wouldn't get us anywhere close to proving that "all genetic mutation (in any species) is random".

    2% picked this

  3. If all genetic mutations in

    Bad Trigger Match

    This answer is very tempting, because it gives us a rule like this: If all genetic mutations → then all mutations in bacteria are random in other life forms are random If we could trigger that rule then we would certainly get an outcome that proves the conclusion. But can we trigger this rule? Do we know that all genetic mutations in bacteria are random? No, we only know that within experiments, certain kinds of bacteria showed random genetic mutations. Since we don't know yet whether all bacteria have nothing but random genetic mutations, we can't trigger this rule, and so it goes nowhere.

    32% picked this

  4. The kind of environment in

    Unrelated to Goal

    This has no language resembling our conclusion "all genetic mutation is random", and it does nothing to get us from "these bacteria had random genetic mutations" to our goal of "all genetic mutations are random".

    18% picked this

  5. The nutrients used were the

    Unrelated to Goal

    This has no language resembling our conclusion "all genetic mutation is random", and it does nothing to get us from "these bacteria had random genetic mutations" to our goal of "all genetic mutations are random".

    4% picked this

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