PrepTest 116

Incorrect. This trait wouldn't be favored in natural selection, but that doesn't mean that it wouldn't be present. It might be riding along with a trait that does have positive effects.

Incorrect. If this were the case, then that mutation would be favored by natural selection. There's nothing preventing all effects from being positive, just a consideration if they're not.

Incorrect. Again, this trait wouldn't be favored by natural selection, but it could still exist (and might be on its way out of the gene pool, or riding along with a very beneficial trait).

Incorrect. As long as the positives outweigh these negatives, this mutation could still be carried along.

Correct. Argument or Facts:
Facts

Question Type:
Cannot Be True

Stimulus Summary:
Effect of genetic mutation contributes to survival ←→* Mutation favored in natural selection
*Any negative traits carried along with it can't be so bad as to cancel out the benefit

Answer Anticipation:
This Cannot Be True question presents almost as a Principle question—it gives us a conditional that we can apply to situations. Here in this Cannot Be True question, however, we're looking for one that violates the principle.

Two things to deal with.

First, this is a biconditional, which we can see from the language then, and only then, which sets up both terms as sufficient and necessary. Biconditionals mean you either have both conditions or neither.

Second, there's a caveat, or exception. The rule breaks down when a would—be favored trait carries along another trait so bad that it outweighs the positive.

Again, we're looking for an answer that contradictions/violates the rule—so we're looking for a situation that has one of the conditions in the biconditional but not the other, or that falls into the exception but still follows the rule.

Answer Explanation:
The biconditional establishes that only genetic mutations with an effect that substantially contributes to survival is favored in natural selection. A neutral effect doesn't contribute to survival at all, so the conditional allows us to say that it won't be favored by natural selection. Since this answer contradicts the rule, it's correct.

Key Takeaway:
Remember that Cannot Be True questions that feature a conditional look for answers that contradict that conditional—that they establish the sufficient condition without the necessary condition.