#17 - Humankind would not have survived, as it clearly has

[Administrator]

Complete Question Explanation

Parallel Reasoning—SN. The correct answer choice is (A)

The first sentence states that if our ancestors had not been motivated by the desire to sacrifice themselves, then humankind would not have survived. But the same sentence also points out that humankind clearly has survived. The contrapositive of the first sentence tells us that if humankind has survived, then our ancestors were motivated by the desire to sacrifice themselves. Thus, if this desire to sacrifice is a form of altruism, then our ancestors were at least partially altruistic.

The premises in the stimulus provide two conditional statements that can be connected to form a chain relationship. The premises also establish that the initial sufficient condition has been met (humankind has survived), which supports the conclusion that the ultimate necessary condition must also be met. The argument, when reworded, is structured as follows:

• Premise (1): Desire to sacrifice Survive
  
  Premise (2): Desire to sacrifice Form of altruism
  
  These two premises form the following conditional chain:
  
  Survive Desire to sacrifice Form of altruism
  
  Premise (3): Survived
  
  Conclusion: Ancestors Altruistic

Answer Choice (A): This is the correct answer choice. The premises here tell us that some students raise their grades. According to the contrapositive of the first sentence, if students raise their grades, then they must increase the amount of time they study. Since increased study time requires good time management, then it can be concluded that some students manage their time well. The logic in this answer choice matches the stimulus and can be diagrammed as follows:

• Premise: Increase Time Studying Raise Grades
  
  Premise: Increase Time Studying Good Time Management
  
  These two premises form the following conditional chain:
  
  Raise Grades Increase Time Studying Good Time Management
  
  Premise: Some Students Raise Grades
  
  Conclusion: Some Students Have Good Time Management

Answer Choice (B): This answer choice represents flawed reasoning and therefore fails the Validity Test. The first sentence claims that if organisms do not consume other organisms to obtain carbohydrates, then they are capable of manufacturing their own carbohydrate supply. This does not mean that organisms that do consume other organisms for carbohydrates are not capable of manufacturing their own carbohydrates. This would be a Mistaken Negation of the original rule and therefore does match the reasoning in the stimulus.

Answer Choice (C): The premises in this answer choice cannot form a conditional chain and fail the Premise Test.

Answer Choice (D): This reasoning in this answer choice is very similar to the stimulus, as the two premises can be linked together to form a conditional chain:

• Resources Depleted Replaced More power

However, the premises need also establish that the requirement for more power was not met (just like the premises in the stimulus establish that humankind did survive). However, the author of answer choice (D) only assumes that more power cannot be obtained; she does not explicitly say so. Therefore, there is no evidence to conclude that the resources will become depleted.

Answer Choice (E): This answer choice fails the Conclusion Test as the conclusion claims there must be either one of two possibilities. The conclusion in the stimulus claims that our ancestors were at least partially altruistic. The stimulus did not establish that either one of two possibilities must occur.

[reop6780]

The correct answer is A.

While A is more appealing than the rest of the answers, I was hesitant about it.

The problem for me is that I could not find the counterparts for the last sentence in answer A.

Stimuli : sacrifice-> survive. Sacrifice->children.
But sacrifice is a form of altruism. some ancestors were partially altruistic.

A: Increase time->increase grade. Increase time-> time management.
But some raise grade. some manage time.

While the stimuli touch sufficient condition, "sacrifice," answer A touches a necessary condition of "grade." Also, the stimuli brings a new factor, "altruism," answer A connects two existing necessary conditions.

Still, they are somehow similar?

In what way?

[KelseyWoods]

Hi reop!

I think your diagramming might be a little off here and that's why it's giving you trouble. Let's walk through it together:

The first sentence in our stimulus says that humankind would not have survived if our ancestors hadn't sacrificed. That would be diagrammed like this:
/ancestors sacrifice /humankind survive

The contrapositive would be:
humankind survive ancestors sacrifice
That's the reverse of what you had, I think.

The next sentence could be diagrammed as:
sacrifice altruism

And you could apply that specifically to the ancestors:
ancestors sacrifice ancestors altruism

You can chain those together to get:
humankind survive ancestors sacrifice ancestors altruism

We know that humankind has survived (the stimulus states "it clearly has") so we can follow the chain down and get to the conclusion that our ancestors were altruistic.

Now let's look at answer choice (A). The first sentence would look like this:
/increase study time /raise grades

The contrapositive would be:
students raise grades students increase study time

The second sentence would look like this:
increase study time good time management

We can apply that specifically to students:
students increase study time students good time management

You can link those two statements together:
students raise grades students increase study time students good time management

We know that some students raise their grades (3rd sentence) so we can follow the chain down to get to the conclusion that some students have good time management.

With that diagramming, I think you can see how very similar answer choice (A) actually is to the stimulus. The order of presentation is a little different (the sentence in (A) that some students raise their grades matches the "it clearly has" part from the first sentence of the stimulus and the last sentence of the stimulus matches the 2nd and 4th sentences of (A) in combination) but the structure is the same.

Hope this helps!

Best,
Kelsey

[15veries]

This is a tough parallel question...

So I guess I have a question about "some" in the stimulus.
Although I understand A is the best matching, I still feel it is not a parfect match due to small differences between the stimulu and A.
It does not have to be true if the stimulus did not use "some " or "most" answer choice should not use them either I guess?
As long as they have match within answer choice ("some" students do raise their grades. So "some" students manage their time well) and as long as the structure match, it is allowed? I tend to check most, some, the word strength in conclusion etc for parallel question, but maybe this stragtegy does not work always?

Or...
the "some" part in A actually match "a form of" and "partially" in the stimulus?

[Kristina Moen]

Hi 15veries,

In the LSAT world, the word "some" means one or more. You can contrast "some" with "none." We call these logical opposites. "Some" can be 1/100, 50/100, 70/100, 99/100, etc. It is everything BUT zero or none.

So in the LSAT world, "some" would be parallel to "at least partially." It means everything but zero or none.

Here, the conclusions are parallel because they indicate that at least PART of some greater whole (students, ancestors) have a characteristic.

Hope this helps!

[lathlee]

Hi. What does the sentence of "when doing so would ensure survival of their children or other close relatives do?" (Fro now, i will refer as doing so( I agree with other comments that a is the best match but i also was heditant but for me, due to this sentence cuz "when doing so" contains sufficient condition indicator therefore i thought this question stem contains the following conditional relationahip: when doing so had not motivated humankind would not have survived. not altuism

[Adam Tyson]

You're trying too hard to put every aspect of this argument into the conditional chain, lathlee. Relax, let it come more naturally! Yes, that "when doing so" statement has conditional elements, and they go something like this:

Sacrific Self Chidren Survive

This is because "doing so" refers to sacrificing oneself, and "ensuring" is a necessary condition indicator.

Having done this, where did it get us? Not far. We learn that there are some instances where sacrificing oneself ensures the survival of your children. Is survival of children sufficient for something else here? No. Is something else sufficient for sacrificing oneself? Sort of, yes - we would not have survived as a species if that did not happen, or:

Sacrifice Self Species Survives

So the contrapositive gives us:

Species Survived Sacrifice Self Children Survive

That's kind of a tautology, a self-proving statement, because it's really just saying that we, the descendants of our ancestors, have survived, proving that our ancestors did stuff to ensure that we survived, which means we survived. Not very helpful to chase this down, is it?

Your diagram appears to be stringing together some things that are conditional with others that are not, simply because they appear in the sentence in a certain order. If I were to read your diagram as a sentence, it would be:

"If our ancestors sometimes sacrificed themselves, then they were not motivated to do so, then we would not have survived, which would then prove no altruism."

Forget the order of the terms, lathlee, and focus on the logical relationships. What are the statements that you can paraphrase in "if...then" form? If our ancestors had not been motivated to sacrifice themselves, then what? If we survived as a species, then what?

One final note, and that is that you said you agreed that the correct answer was the best match, but you still hesitated. Don't do that! When you know an answer is the best match for what you need it to be, even if you do not understand it, do not hesitate, but select that answer with confidence and a light heart, knowing that you are moving on to more questions and more correct answers! That's how you win at this test. He who hesitates is lost!

Re-read the official explanation here, and if needed then read Kelsey's excellent breakdown, to see the right way to tackle the conditional relationships here. Don't just blindly string words and phrases together based on word order, but base those diagrams on logical relationships (and paraphrasing in if...then form when you need to in order to understand them).

Good luck!

[jmramon]

Hi,

I get why A is the best answer, although I'd appreciate some clarification too. I had trouble when it came to matching "partially altruistic" from the stimulus to "some students" in answer A. I see now that each reference described the quantity of a group having a similarity, but at first I thought "partially altruistic" from the stimulus meant "kind of altruistic" (like saying I'm ambivalent, or perhaps partially tired) . Also, the previous mention in the stimulus that our ancestors sacrificed themselves for the survival of their children and close relatives made me further think that "partially" meant "kind of" in this context because it was self-serving in a way. How would you go about interpreting this information and not make my mistake?

[Claire Horan]

Hi jmramon,

That's an interesting question. "Partially altruistic" could potentially mean that one individual is somewhat altruistic or that part of the group is altruistic. There may also be other possible interpretations. In this context, we are talking about humankind, which is a group made up of individuals. What would "kind of altruistic" mean in that context? The stimulus discusses ancestors' altruism as when they sacrificed themselves for their children or close relatives. I think that would lead more towards the interpretation that at least some individuals were altruistic.

But, practically speaking, I don't think it makes a big difference for solving the problem. It's important to note when phrases can be interpreted in multiple ways, but I don't think reading the phrase as meaning "kind of altruistic" would lead you to any of the other answer choices. As a result, you would have eliminated all of the answer choices. At that point, the best thing to do would be to start over, reread the stimulus, and look for a more accurate or different interpretation of the stimulus.

So to answer your question of how to avoid similar misinterpretations in the future, try not to make assumptions and note ambiguity when you see it.

Good luck!

[akanshalsat]

So where I'm confused for this question is the fact that the last sentence of the stimulus is talking about the "sacrifice" portion when connecting to the altruistic which is connecting the 2nd term in the conditional statement we made (the contrapositive) to the third term in the stimulus (altruism), but the paragraph in A, the last sentence is relating the first term (raise their grades) of the conditional statement to the "manage the times wisely" which is the third term