Skip to Main Content

June 2007, Logical Reasoning 2, Question 25


Question 25, when a question asks you for the criticism that the reasoning and argument is vulnerable to, it as a flaw question. Flaw questions involve finding the error in an argument, which of course means understanding the argument first, knowing its conclusion, knowing its evidence and seeing the way that the evidence doesn't quite prove the conclusion. The hence flags the conclusion at the end, or at least the first part of it, hence the anthropologists' claim is false.

But you have to double back to the first sentence to know what the claim is that's false. So there are some anthropologists out there who argue that humans could not have survived prehistoric times if they hadn't evolved the ability to cope with diverse natural environments. The evidence that the author gives against this follows the word however.

However, there is considerable evidence that Australopithecus afarensis, a prehistoric species related to early humans, also thrived in a diverse array of environments but became extinct. The flaw of this argument is a really common one, confusing necessity with sufficiency. If we chart this out in formal logic, you might be able to see it a little bit easier.

The anthropologists have a claim that in order to survive, you have to be able to evolve to cope with a lot of different environments. But that's not the claim that the author of this argument is disproving. The author is disproving a different claim, that If you evolved to cope with a bunch of environments you will survive. Clearly that didn't happen, because the Australopithecus evolved to cope with a lot of different environments, and it didn't survive.

But disproving the statement that we have in blue is not the same thing as disproving the statement that we have in red. Something can be necessary without being enough to guarantee something. So let's look for that in the answer choices. So answer choice A, now answer choice A is exactly what we were looking for. The flaw was confusing sufficiency with necessity.

Required means necessity, sufficient means sufficiency. This is exactly what we wanted. So since it's our answer, we can glance at the other answers just to see why they're wrong. Answer choice B, well, the argument doesn't assume that for every living species with a certain characteristic there must be a dead species that has that same characteristic.

It just has two species that have the same characteristic. Answer choice C misdescribes the argument. The argument didn't try to prove that all species will survive. It's trying to prove that because one of them didn't survive that something wasn't required for survival. Answer choice D, the argument doesn't fail to consider this possibility, it accepts it.

This species must have had some characteristic that lessens its survival chances or else it wouldn't have survived. And finally, answer choice E, this answer uses the word necessary, but not in the right way. It's describing a different flaw, a flaw of overgeneralizing a cause from a single instance.

So because something happened here, it must always happen. That wasn't our argument here, so the answer was answer choice A

Read full transcript