#22 - Biologist: Some speculate that the unusually high

[alee]

Hi,

I have a question about Q22. Section 2 (June 1997). I am trying to 'rule out' the wrong answer options based on the techniques from the logical reasoning bible. I understood the stimulus as following:
Prem: Some speculate that evolutionary pressure to increase diversity of gene pool causes unusually high frequency of small goats in island populations

Prem: However, in general reproductive success of a trait causes frequency of that trait in a population

Conclusion: Therefore, it is actually the case that 'reproductive success of small goats' causes unusually high frequency of small goats...

Question stem: the biologist's view, if true, provides the most support for which of the following?

A is a shell answer ('diverse gene pool' explanation is *not* the explanation of the biologist). B is an opposite answer. C is an opposite answer because it were true, than the biologist's view fails to explain why large goats, rather than small appear in greater frequency in these populations. E is out of scope.
1.-Is this ^ a correct application of the techniques in ruling out the wrong answers?

2. I am not sure exactly why D is correct is it because if we *assume the truth of the biologist's view* than the 'diverse gene pool' factor is *not* the cause of a greater frequency of small goats in these populations (instead the cause is reproductive success of these goats).

Thanks!

[Steve Stein]

Thanks--let's break down the biologist's argument into simple terms:

Some claim island goats have evolved to be smaller, in order to increase their number and ensure a diverse gene pool.

But there is only one way goats would evolve (and make the trait of being small more common), and that would be for smaller goats to have greater success reproducing.

So, the biologist disagrees with the claim that the goats have evolved to increase their numbers by becoming smaller--evolution doesn't work that way--the individual goats don't sense the need for greater numbers and respond with smaller offspring.

Instead, what has lead to smaller goats on average must be some factor other than evolutionary pressure. This is provided by correct answer choice (D), which states that evolutionary pressure would not cause smaller goats to become more common.

Choice A is an Opposite Answer: take a look at the wording--it is a perfect logical opposite of correct answer D.

Choice B is incorrect because greater reproductive success could lead to a greater frequency of small goats in island populations.

Choice C, if true, would not support the biologist's view and would appear to present a paradox, because smaller goats are more frequent in island populations.

Choice E provides that reduction in the average size of the population is necessary. As you point out though, this is irrelevant, because the question is whether evolutionary pressure could have led to that size reduction.

Tough one! Let me know whether this makes sense--thanks!

~Steve

[GLMDYP]

Hi Powerscore! I'm just wondering how (D) can fit into the stimulus? What does it mean by saying "does not have the effect of increasing the frequency of a gene for small size"?
Thanks!

[Ron Gore]

GLMDYP,

This is a Must Be True question. The correct answer will be either a restatement of one of the statements in the stimulus, or will be an inference permitted by the combination of one or more of the statements.

The wording in your question, "how (D) can fit into the stimulus" may indicate a difficulty you are having. In a Must Be True question, you are not bringing the information from the answer choice up into the stimulus. Rather, you look at the information in the stimulus to see if it supports that language in the answer choice.

In this case, the stimulus told you 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." Because that is the "only" kind of evolutionary pressure (or cause), then no other evolution pressure produces the small goat. Choice (D) reflects this by stating we can infer that evolutionary pressure to ensure a diverse gene pool does NOT have the effect of increasing the frequency of a gene for small size.

In other words, the stimulus told use that there was only one possible cause for the effect of the unusually high frequency of small goats. Answer choice (D) says that this other potential cause is not the case, which is consistent with their being only the one provided in the stimulus. Therefore, (D) is information supported by the stimulus.

[BostonLawGuy]

Greetings and thanks for the useful information on this perplexing question. Since I have not seen any information on what a correct diagram would look like and this question is full of conditional logic, I am curious to know how my diagram has led me to the wrong answer choice.

increase population of small goats reprod. success of trait

evol. pressure to increase small goat size sm. goats achieve greater reprod. success

The correct answer seems to indicate that my above reasoning is a mistaken reversal. However, I thought that the language in the stimulus regarding "the only kind of reproductive pressure..." indicates a necessary condition. But, obviously designating it to a necessary condition as I did above led to the wrong answer choice.

Any clarification would be appreciated .

[James Finch]

Hi BLG,

This is a complicated question to break down, because we see both causal and conditional reasoning represented. The biologist is attempting to refute a causal argument (evolutionary pressure to create a diverse gene pool caused the unusually high frequency of small goats in island populations) by applying a conditional statement to this specific situation:

Greater Frequency Trait (GFT) Reproductive Success Trait (RST)

Applying that to the small-goats-on-islands example (SG = Small Goats):

GFTSG RSTSG



Which would mean that the actual cause of the smaller sizes of goats on islands, according to the biologist, is the greater reproductive success of the smaller goats, as the stimulus states. In summary, the stimulus is rebutting a causal argument using conditional reasoning to show an alternate cause for the effect.

This alternate cause implies that the evolutionary pressure to increase the number of goats is not the actual cause (the reproductive success of small goats is). That inference lines up exactly with answer choice (D), which is the correct answer.

Hope this helps!

[BostonLawGuy]

You're awesome, thanks!