In my opinion, the correct answer is E.
An assumption is what is absolutely necessary for the conclusion to hold. In other words, the assumption is the unstated premise of the argument. While there are several assumptions made in an argument (all of which have to be true), only one will be present in the answer choice. So, the trick to spot one is not to find the choice that validates the conclusion, but to find the choice that is an essential piece of information for the conclusion to be true
. Also, along with supporting the conclusion, the assumption must also link the premises with the conclusion. Negating the assumption will destroy the argument.
The question asks for an assumption. Hence, the argument will consist of premises and conclusion.
Breaking down the argument structure as premises and conclusion, we have;
Premise 1: Joey (newborn kangaroo), born after a short gestation period of 39 days, (at birth
) does not have well-developed hindlimbs
However, Joey's forelimbs are well developed so that
(i.e. the purpose of well developed forelimbs is that) Joey can climb from cloaca into its mother's pouch
for further development.
Premise 2: The recent discovery is that ancient marsupial lions were also born with only their forelims developed
Conclusion: This discovery (of ancient marsupial lions) supports the hypothesis that newborn marsupial lions must also have needed to climb into their mother's pouch
(Please note the underlined keywords that are crucial in the line of reasoning in the argument and that represent the core point of the argument).
So here we go. The important words here are so that
The argument's line of reasoning is that, as development of only forelimbs in kangaroos is for the purpose of Joey's climbing in its mother's pouch, the development of only forelimbs in ancient marsupial lions also implies that they needed to climb into their mother's pouch.
One of the assumptions made here is that the one definite purpose that only the forelimbs would develop in ancient marsupial lions would be to climb into their mother's pouch
We will look for a choice that ties together premises and conclusion.
[A] All animals that are born after a short gestation period are born with some parts of their bodies underdeveloped. - The choice is too broad. In fact, this choice has no links to the conclusion. the author does not assume that anything about all animals born after a short gestation period. In fact, the author does not mention the gestation period of ancient marsupial lions being short either! The conclusion would hold even if this choice were not true. Hence, this is not an assumption.
[B] Well developed forelimbs would have been more advantageous to ancient marsupial lions than well developed hind limbs would have been. - The author does not assume this. Even if well developed forelimbs were not more advantageous than well developed hindlimbs, the conclusion would hold true. This choice is too broad in that term advantageous does not suggest that the advantage was specifically for the purpose to climbing into the mother's pouch. Also, this choice has not link to the conclusion.
[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.
This seems close but not accurate. This choice does address the conclusion. However, it does not bridge the gap between the premises and the conclusion. Paleontologists are beyond the scope of the argument. This does not address the line of reasoning, though it addresses the conclusion. That paleontologists would be able to find the evidence if the assumption were not true, is not
an assumption here.
This is a trap choice - close but wrong. Strategically placed before the correct one
[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. - Beware! This is a trap choice. This suggests that the the only means of climbing into mother's pouch is having only well developed forelimbs. HOWEVER, the assumption is actually that atlease one definite purpose of well developed forelimbs is climbing into the pouch.
Further, it is possible that the lions or Joey had other means to climb into the pouches, in addition to well developed forelimbs. The argument foes not deal with them. It only says that the purpose of forelimbs was climbing in the pouch.
[E] Newborn marsupial lions would not have had only their forelimbs developed if this development were of no use to the marsupial lions - This choice is broad but decent. Use
here does not indicate climbing into the mother's pouch. Negating this would mean that newborn lions may have had only their forelimbs developed even if this development were of not use to them. This is it! This version destroys the argument that the puspose of development of forelimbs was to climb into the pouch, as negating the choice indicates the possibility that the development may have been purposeleess.
This choice might be too broad or inadequate in that the term use
is too broad. However, it is one of the subtle assumptions made in drawing the conclusion!
Hope this post helps!
Your kudos will let me know.