June 2007 LSAT Question Explanations June 2007 - Sec 3 - LR...

June 2007 - Sec 3 - LR - Q25

Video Transcript:

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Question 25.
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Some anthropologists argue that the human species could not have survived prehistoric
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times if the species had not evolved the ability to cope with diverse natural environments.
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However, there is considerable evidence that Australopithecus afarensis, a prehistoric
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species related to early humans, also thrived in a diverse area of environments, but became
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extinct.
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Hence, the anthropologists' claim is false.
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So argument or facts?
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Clearly, we have an argument.
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'Hence' will be our structural indicator the conclusion being the anthropologists' claim
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is false.
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What was this anthropologists' claim?
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You notice, the first sentence tells us some anthropologists argue that human species could
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not have survived prehistoric times if the species had not evolved the ability to cope
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with the diverse natural environments.
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We know 'if' introduces sufficient, so not evolved the ability to cope with diverse
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natural environments.
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Then the necessary condition would be, could not have survived prehistoric times, so survived
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prehistoric times negated.
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The contrapositive would tell us that to survive prehistoric times they must evolve the ability
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to cope with the diverse natural environments.
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So that is the anthropologists' claim, you notice it is a general principle.
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And then, the author gives us a premise that he believes disproves this general principle,
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and that is the example of Australopithecus afarensis, a prehistoric species related to
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early humans that also thrived in a diverse array of environments, but became extinct.
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So basically, Australopithecus afarensis had the ability to survive in diverse array of
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environments, so evolved the ability to cope in diverse array of environments and also
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tells us that they became extinct, so they did not survive prehistoric times.
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And takes that to conclude, therefore the anthropologists' claims is false.
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So let's take a closer look.
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The anthropologists claim here is a sufficient and necessary statement.
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How do we disprove a sufficient and necessary statement?
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Well, imagine that I told you that all berries are red, how would you prove me wrong?
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You would show me a blueberry.
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Maybe a boysenberry, right?
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An idea there is you would be showing me a berry that is not red.
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So to disprove a sufficient and necessary statement, you want to show sufficient can
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exist without necessary.
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So in order for this author to correctly disprove this anthropologists' statement, he would
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have to show either a creature that survived prehistoric times, but that did not evolve
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the ability to cope with diverse natural environments.
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Or, a creature that did not evolve the ability to cope with diverse natural environments,
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but survived prehistoric times.
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And you notice the example of the Australopithecus afarensis, shows us neither of those.
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Instead you see a species that has evolved the capacity to deal with a diverse array
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of natural environments, but that did not survive prehistoric times.
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And you notice, based on the principle having evolved the ability to cope with a diverse
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array of natural environments is our necessary condition.
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It tells us nothing about whether this species has survived or not survived prehistoric times.
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We cannot go backwards, don't just reverse!
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So you notice here, the author is assuming that the general principle is the reverse.
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That if we have evolved the ability to cope with diverse natural environments, then we
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survive prehistoric times.
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Because the example of Australopithecus afarensis shows us evolved the ability to cope with
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diverse natural environments, but did not survive natural prehistoric times and that
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would be correct then because we would be showing sufficient without necessary.
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But again, it's not correct because that is not what the anthropologists are claiming,
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they're claiming the reverse of that, so clearly we have a flawed argument.
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And now that we have a clear understanding of this mistake, again, the author is reversing
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or mistaking sufficient for necessary.
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So the reasoning in the argument is most vulnerable to criticism, on the grounds that the argument
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most vulnerable to criticism we have an Errors in Reasoning question.
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So we've identified the error, don't just negate or mistaking sufficient from necessary
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so let's go find the answer choice that explains that flaw.
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(A) confuses a condition being required for a given result to occur in one case with a
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condition being sufficient for such a result to occur in a similar case.
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You notice confusing what is required for what is sufficient mistaking sufficient
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for necessary which is exactly what we saw in the passage, so (A) would be the correct
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answer.
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Again, because to disprove sufficient and necessary, you must show sufficient without
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necessary.
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This case, the author showed us necessary without sufficient and that is not correct.
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We know nothing about sufficient based on whether or not necessary is present.
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So the author is clearly reversing this statement assuming that it said the reverse, because
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then his evidence would have shown sufficient without necessary and would've disproved the
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anthropologists' claim if this was their claim but it's not.
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So again you notice the mistake here is they are reversing sufficient and necessary conditions.
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So (A) would be the correct answer.
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But again let's just make sure.
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(B) takes for granted that if one species had a characteristic that happened to enable
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it to survive certain conditions, at least one related extinct species must have had
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the same characteristic.
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You notice that's clearly not happening in this passage.
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That is not the assumption, it is not taking that for granted.
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So (B) would be out.
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(C) generalizes from the fact that one species with a certain characteristic survive certain
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conditions that all related species with the same characteristic must have survived exactly
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the same conditions.
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And actually the author is not doing that at all because they showed us a related species,
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Australopithecus afarensis that did not survive prehistoric times.
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So, (C) clearly does not apply and (C) would be eliminated.
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(D) fails to consider the possibility that Australopithecus afarensis had one or more
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characteristics that lessens its chances of surviving prehistoric times and that is clearly
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not what's going on.
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That is true, but it's not the flaw.
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The problem here is that the anthropologist's general principle is not refuted by the author's
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evidence because the author's evidence would only refute the reverse of the anthropologists'
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claim so that's the problem.
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(D), you could argue it's true he does do that but that's not the logical flaw, so do
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not pick it as the correct answer.
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Moving to (E), fails to consider the possibility that even if a condition caused the result
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to occur in one case, it was not necessary to cause the result to occur in a similar
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case and again clearly out.
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This is not a cause and effect argument, so how can (E) be the correct answer?