Biologist: Some speculate that the unusually high frequency of small goats found in island populations is a respon...

Naz on August 13, 2013

The Biologist's conclusion is "the only kind of evolutionary pressure that can reduce the average size of the members of a goat population is that resulting from small goats achieving greater reproductive success than their larger cousins." His premise stands, even though "Some speculate that the unusually high frequency of small goats found in island populations is a response to evolutionary pressure to increase the number of goats so as to ensure a diverse gene pool," they are wrong because "only the reproductive success of a trait influences its frequency in a population."

We are asked then to see which one of the answer choices we can infer. So, our correct answer choice must be true.

(A) is incorrect because it goes against the passage. The biologist states that the high frequency of small goats is not a response to evolutionary pressure to increase the number of goats.

(B) is incorrect because of the phrase "when space is limited." We do not know what happens when space is limited. Therefore, we cannot infer answer choice (B).

(C) is incorrect not only because of the phrase "when space is limited," but also because it weakens the passage. If large goats do achieve greater reproductive success, even when space is limited, then the Biologist's conclusion is less sound.

(D) is CORRECT because if "The evolutionary pressure to ensure a diverse gene pool" does "have the effect of increasing the frequency of a gene for small size," then the conclusion is incorrect because it would not be the case that the ONLY kind of evolutionary pressure that can reduce the average size of the members of a goat population is that resulting from small goats achieving greater reproductive success than their larger cousins. (D) is basically invoking the contrapositive of the statement only the reproductive success of a trait influences its frequency in a population. So:

IFP ==> RS

Contrapositive:

Not RS ==> not IFP

The evolutionary pressure is "not the reproductive success," so it leads to not influencing frequency in population.

(E) is incorrect because we do not know that the only way to reduce the average size of the members in a goat population is through a diverse gene pool.

Hope that helps. Let me know if you have any other questions!

Lily on August 13, 2013

So ....

Some ascription:
increase # G (DGP) -> increase freq. S

However ... So author thinks differently

P: increase freq. -> Rs
:. Increase freq. S ->Rs(sm>lg => ~DGP)