Q20 - The ability of mammals to control

[ManhattanPrepLSAT1]

You're understanding of this one is about the same as I would have if I encountered it on a test. i'd know that answer choice (C) didn't seem necessary, but I wouldn't pause long enough to find out why. That said, in review, it's always good to go back and look a bit deeper.

The issue with answer choice (C) is that it's too precise. The argument concludes that controlling the temperature of the chemical reactions in the brain is a factor in the development of intelligence, but the argument never concludes, suggests, or assumes that it's an essential element of developing intelligence. Beware of answer choices that are too strong on Necessary Assumption questions. Answer choice (C) says that controlling the temperature of the chemical reactions is necessary to developing intelligence, and while the argument concludes that it's a factor in developing intelligence, it never suggests that it's necessary.

Notice how answer choice (D) is presented in much weaker language. It says that the development of intelligence is not independent of the chemical reactions in the brains, but this doesn't say what the relationship is, just that a relationship exists.

So answer choice (C) says precisely what the relationship is, while answer choice (D) simply says that a relationship exists. Which one is necessary? The exact relationship outlined in answer choice (C) need not be true, but that a relationship exists between intelligence and chemical reactions in the brain as outlined in answer choice (D) does.

Let's look at the incorrect answers:

(A) is true, at least according to my understanding of the world, but that doesn't make it the correct answer. This does not connect the temperature of chemical reactions with the development of the brain or intelligence.
(B) need not be true. While the conclusion may be about mammals, that does not restrict intelligence to only mammals.
(C) represents a connection between the right ideas but does so too precisely. Even if mammals whose brains are subject to uncontrolled temperature swings could develop intelligence, this would not undermine the conclusion that controlling such temperatures is a factor in the development of the brain and intelligence.
(E) represents a negation of information in the evidence, but not the gap between the evidence and the conclusion. Relevant? Yes. Necessary? No.

Hope that helps!


#officialexplanation

[kmewmewblue]

I was able to eliminate (A),(B) and (E).

(C) does not seem right, but I cannot articulate the reason why.
So as to why (D) is right.

Thanks.

[alana.canfield]

I think another reason (C) is wrong is that to me the stimulus is talking about the development of brains and the development of intelligence. Answer (C) is just about supporting intelligence in and of itself, not about the development of intelligence.

[griffin.811]

In addition to what Matt said, I think C's scope is actually too wide.

Our argument is about the temperature necessary for the brains of MAMMALS. Need it be true that NO brain can support intelligence under uncontrolled temps? Absolutely not. It just needs to be true that MAMMALS brains cannot.

Would love to hear what you all think

[tpham]

Premise 1: "The brain is a chemical machine, all chemical machine reactions are temperature dependent"

Premise 2: any organism that can control it's body temperature can assure that these reactions occur at the proper temperatures

Conclusion: The ability of mammals to control their internal body temperatures is a factor in the development of their brains and intelligence

The question type is assumption, so we know to look for new information that is presented in the conclusion; in this case, the development of intelligence, as the development of the brain has already been mentioned. The conclusion states...blah blah blah...brains AND intelligence, so in order for the conclusion to be valid, the author must assumed that the development of intelligence is not independent from the development of the brain. Thus (D) correctly assumes this notion.

(A) External Factors? irrelevant
(B) Does not help the conclusion as we want to focus on either brain or intelligence
(C) Not about whether the brain can support intelligence
(E) Unpredictable chemical processes? irrelevant

[Mab6q]

Although I got this question right, my reasoning was off. When looking for the flaw in the argument, I thought the author was equating chemical machine with chemical reaction. However, from reading some explanations, it seems like you guys went ahead and equated the two, as well as equating temperature dependent with can control its body temperature. In essence, I am having a hard time spotting the right flaw in the argument. At times, I am too strict with the terms in the premises even when it is okay to equate two terms that are related such as the chemical machine and chemical reaction. Any suggestions?

[rinagoldfield]

Thanks, Mab. You’re right that it’s often difficult to determine which term shifts are warranted.

One good rule of thumb: be extra wary of new, different terminology in the conclusion. For example, the conclusion in this argument talks about intelligence. Intelligence really isn’t touched upon anywhere else in the argument. This should set off “flaw” alarm bells in your mind. Indeed, the main gap in this argument is the jump from “intelligence” to all of that chemical and temperature stuff.

Another good rule of thumb: subcategories of a bigger concept are usually ok. Here, there is a jump from “chemical machine” to “chemical reactions.” This is a small shift, but anything chemical includes reactions, by definition. So “chemical reactions” is an ok subcategory of “chemical thing.”

Hope this helps.

[PhoebeL747]

(E) represents a negation of information in the evidence, but not the gap between the evidence and the conclusion. Relevant? Yes. Necessary? No.



#officialexplanation

Thank you for your super clear explanation. But isn't (E) a contrapositive of the second premise rather than a negation?

[LSATN100]

The problem with (C) lies in its wording. The conclusion is about "the development of their brains and intelligence." Brain and intelligence are parallel terms. But answer choice (C) states "the brain cannot support intelligence," which distorts the relationship between brain and intelligence.
"The development of intelligence" is not equal to "the intelligence supported by the brain."

[RamseyM415]

To use the classic "Laura Damone method" of negation for (C), it goes something like this:

There is one case in which the brain can support intelligence even if the chemical reactions within it are subject to uncontrolled temperatures.

Negating it this way, you can clearly see that this does not wreck the argument that "the ability...is a FACTOR."

Remember that a negation is just a minimal nonconforming case.