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CR - negates potential argument weakener

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karthikpandian19: Legendary Member; Posts: 1665; Joined: Thu Nov 03, 2011 7:04 pmFollowed by: 70 members; Thanked: 165 times

by karthikpandian19 » Tue Jul 10, 2012 12:17 am

A newborn kangaroo, or joey, is born after a short gestation period of only 39 days. At this stage, the joey's hind limbs are not well developed, but its forelimbs are well developed, so that it can can climb from the cloaca into its mother's pouch for further development. The recent discovery that ancient marsupial lions were also born with only their forelimbs developed supports the hypothesis that newborn marsupial lions must also have needed to climb into their mothers' pouches.

The argument in this passage relies on which of the following assumptions?

(A) All animals that are born after a short gestation period are born with some parts of their bodies underdeveloped.

(B) Well developed forelimbs would have been more advantageous to ancient marsupial lions than well developed hind limbs would have been.

(C) If the newborn marsupial lion did not climb into its mother's pouch, then paleontologists would be able to find evidence of this fact.

(D) Newborn marsupial lions that crawled into their mothers' pouches could not have done so had they not had only their forelimbs developed at birth.

(E) Newborn marsupial lions would not have had only their forelegs developed if this development were of no use to the marsupial lions.

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Source: Beat The GMAT — Critical Reasoning | Tue Jul 10, 2012 12:17 am

Kasia@EconomistGMAT: GMAT Instructor; Posts: 646; Joined: Mon May 21, 2012 7:08 amFollowed by: 143 members; Thanked: 322 times

by Kasia@EconomistGMAT » Tue Jul 10, 2012 3:58 am

The correct answer is E. It is the only statement of all answer choices that supports the conclusion. Were it not true that the developed forelimbs had been of importance to the marsupial lions, the argument would fall apart because that would mean that newborn marsupial lions cannot be compared to newborn kangaroos.

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karthikpandian19: Legendary Member; Posts: 1665; Joined: Thu Nov 03, 2011 7:04 pmFollowed by: 70 members; Thanked: 165 times

by karthikpandian19 » Tue Jul 10, 2012 5:02 pm

OA is E

The passage states that newborn kangaroos ("joeys") have underdeveloped hind limbs but fully developed forelimbs. These forelimbs allow the joey climb into its mother's pouch. The passage also states that newborn ancient marsupial lions also had developed forelimbs and undeveloped hind limbs. From this, the passage concludes that the newborn marsupial lion also needed to climb into its mother's pouch.

We are asked to find the assumption underlying this argument. This argument assumes that the only reason why the newborn marsupial lion would have been born with only its forelimbs developed is that it needed to crawl into its mother's pouch. The answer should address this assumption.

Choice A claims that all animals with short gestation periods have underdeveloped newborns. However, we know only that the marsupial lion was born with part of its body underdeveloped; the argument doesn't rely on this being true for all such animals.

Choice B claims that well developed forelimbs would have been more advantageous than well developed hind limbs for marsupial lions. However, the argument does not rely on the relative value of forelimbs and hindlimbs, but rather the particular purpose of forelimbs.

Choice C claims that paleontologists would be able to figure out that marsupial lions did not climb into their mother's pouch. However, the argument does not rely on the ability of paleontologists to discover such evidence. If this assumption were false (and paleontologists were unable to find evidence to disprove the argument's conclusion), the argument could certainly still be true.

Choice D (once we eliminate the double negative) states that newborn marsupial lions needed to have developed forelimbs, and only forelimbs, in order to crawl into their mothers' pouches. This is a purely hypothetical situation with regards to the argument: marsupial lions may have been able to climb into pouches regardless of the number of limbs they had developed, and the development of forelimbs may have only aided in this process. This idea negates the assumption without undermining the argument.

Choice E claims that there must be some reason that newborn marsupial lions had only their forelimbs developed. In order for the argument to hold up, this must be the case; if newborn lions possessed developed forelimbs for no reason at all, then the presence of these forelimbs couldn't tell us anything about the lions' behavior.

Choice E is correct.

karthikpandian19 wrote:A newborn kangaroo, or joey, is born after a short gestation period of only 39 days. At this stage, the joey's hind limbs are not well developed, but its forelimbs are well developed, so that it can can climb from the cloaca into its mother's pouch for further development. The recent discovery that ancient marsupial lions were also born with only their forelimbs developed supports the hypothesis that newborn marsupial lions must also have needed to climb into their mothers' pouches.

The argument in this passage relies on which of the following assumptions?

(A) All animals that are born after a short gestation period are born with some parts of their bodies underdeveloped.

(B) Well developed forelimbs would have been more advantageous to ancient marsupial lions than well developed hind limbs would have been.

(C) If the newborn marsupial lion did not climb into its mother's pouch, then paleontologists would be able to find evidence of this fact.

(D) Newborn marsupial lions that crawled into their mothers' pouches could not have done so had they not had only their forelimbs developed at birth.

(E) Newborn marsupial lions would not have had only their forelegs developed if this development were of no use to the marsupial lions.

Regards,
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON

---If you find my post useful, click "Thank"

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