Logical Reasoning

PT116 · S3 · Q17 If one of the effects of

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If one of the effects of a genetic mutation makes a substantial contribution to the survival of the species, then, and only then, will that mutation be favored in natural selection.

Statements

bi-conditional (then and only then)

if, then, effect of mutation favored in natural makes substantial selection contribution

if, then, effect of mutation not favored in doesn't make a natural selection substantial contribution

The second sentence is giving a potential exception to the first statement, saying that a mutation that leads to some good stuff (favored) and some bad stuff (not favored) can't be so negative that it cancels out the positive.

So if we were trying to amend the original rule to capture that proviso, I would just qualify the wording of the rule so that we capture this idea of .

Goal

Since this is a Must Be False question, we're anticipating that it will contradict the conditional we were provided. Contradicting a conditional usually means saying the Left side is true but the Right side is false.

But contradicting a bi-conditional works either way.

We know: if a mutation offers a net gain, it's favored. if it doesn't offer a net gain, it's not favored.

So a must be false would be either of these: - this mutation is favored / doesn't offer a net gain - this mutation is favored / does offer a net gain

17.

If the statements above are true, each of the following could be true EXCEPT:

  1. A species possesses a trait

    Compatible

    There aren't any rules provided about "possessing" a trait, just whether a trait is favored or not. It's certainly possible for a species to have a mutation whose effects are all neutral. We would say "that is NOT a favored mutation", but it's still possible for the species to possess it.

    3% picked this

  2. All the effects of some

    Compatible

    This doesn't contradict anything we heard about. We would certainly call these mutations favored.

    7% picked this

  3. A species possesses a trait

    Compatible

    There aren't any rules provided about "possessing" a trait, just whether a trait is favored or not. It's certainly possible for a species to have a mutation whose effects are negative. We would say "that is NOT a favored mutation", but it's still possible for the species to possess it.

    12% picked this

  4. A genetic mutation that carries

    Compatible

    This is the first tempting answer, because it deals with "whether or not favored". We were looking for an answer to either say: mutation is a net gain + not favored or mutation is not a net gain + favored This says that the mutation carries several negative traits, yet is favored. That's possible, since the mutation may also carry along some positive traits. If the positive outweighs the negative, then it would be a net gain, and so it would be favored. In other words, this answer doesn't clearly establish whether this mutation is a net gain, or not a net gain, so there's no way to apply the rule we were given.

    13% picked this

  5. Correct

    A genetic mutation whose effects

    Why this is right

    We were looking for an answer to either say: mutation is a net gain + not favored or mutation is not a net gain + favored This does the 2nd one. If the effects are all neutral, then the mutation does not make a net gain, so it should not be considered favored. If we go back to the original text of the rule, it says that if a genetic mutation makes a substantial contribution to the survival of the species (this mutation does not, since it's all neutral), then and only then can it be favored. So this answer is contradicting that first sentence.

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

    65% picked this

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