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RC - Two hypothesis - Weaken Question

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gauravgundal Really wants to Beat The GMAT! Default Avatar
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RC - Two hypothesis - Weaken Question Post Mon Jan 24, 2011 1:35 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Two opposing scenarios,
    the “arboreal” hypothesis and
    the “cursorial” hypothesis, have
    Line traditionally been put forward con-
    (5) cerning the origins of bird flight.
    The “arboreal” hypothesis holds
    that bird ancestors began to fly
    by climbing frees and gliding
    down from branches with the
    (10) help of incipient feathers: the
    height of trees provides a good
    starting place for launching flight,
    especially through gliding. As
    feathers became larger over time,
    (15) flapping flight evolved and birds
    finally became fully air-borne.
    This hypothesis makes intuitive
    Sense, but certain aspects are
    Troubling. Archaeopteryx (the
    (20) earliest known bird) and its
    maniraptoran dinosaur cousins
    have no obviously arboreal
    adaptations, such as feet fully
    adapted for perching. Perhaps
    (25) some of them could climb trees,
    but no convincing analysis has
    demonstrated how Archaeopteryx
    would have both climbed and
    flown with its forelimbs, and there
    (30) were no plants taller than a few
    meters in the environments where
    Archaeopteryx fossils have been
    found. Even if the animals could
    climb trees, this ability is not
    (35) synonymous with gliding ability.
    (Many small animals, and even
    some goats and kangaroos,
    are capable of climbing trees
    but are not gliders.)
    Besides,
    (40) Archaeopteryx shows no obvious
    features of gliders, such as
    a broad membrane connecting
    forelimbs and hind limbs.
    The “cursorial”(running)
    (45) hypothesis holds that small
    dinosaurs ran along the ground
    and stretched out their arms for
    balance as they leaped into the
    air after insect prey or, perhaps,
    (50) to avoid predators. Even rudimentary
    feathers on forelimbs
    could have expanded the arm’s
    surface area to enhance lift
    slightly. Larger feathers could
    (55) have increased lift incrementally,
    until sustained flight was gradually
    achieved. Of course, a leap
    into the air does not provide the
    acceleration produced by drop-
    (60) ping out of a tree; an animal
    would have to run quite fast
    to take off. Still, some small
    terrestrial animals can achieve
    high speeds. The cursorial
    (65) hypothesis is strengthened by
    the fact that the immediate theropod
    dinosaur ancestors of
    birds were terrestrial, and they
    had the traits needed for high
    (70) lift off speeds: they were small,
    agile, lightly built, long-legged,
    and good runners. And because
    they were bipedal, their arms
    were free to evolve flapping flight,
    (75) which cannot be said for other
    reptiles of their time.

    -----------------------------------------------------------------
    The passage presents which of the following facts as evidence that tends to undermine
    the arboreal hypothesis?
    A. Feathers tend to become larger over time
    B. Flapping flight is thought to have evolved gradually over time
    C. Many small animals are capable of climbing trees.
    D. Plants in Archaeopteryx’s known habitats were relatively small
    E. Leaping into the air does not provide as much acceleration as gliding out of a
    tree

    IMO: D
    With POE, I got down to C and D.
    I am not able to justify why answer choice C is wrong.
    The line no. 36 does mention about the small animals and their ability to climb trees , this may undermine 'arboreal hypothesis'.

    Can anyone help me to answer my silly query of what can be the reason to eliminate answer choice C?

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    hja379 Really wants to Beat The GMAT!
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    Post Mon Jan 24, 2011 3:39 am
    The passage mentions small animals to make a point that climbing tree alone does not equal to flying.
    Goats and kangaroos might not have even existed during the period of Archaeopteryx. I don't think
    choice C undermines the arboreal hypothesis.

    What is the OA?

    AIM GMAT GMAT Destroyer! Default Avatar
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    Post Mon Jan 24, 2011 6:46 am
    Both the options C and D undermine the arboreal hypothesis .

    Option C says that that period had small trees , so gliding from trees isnt the option , that directly doubts the arboreal hypothesis .

    Now option D says that small animals were also able to climb trees , but infact acc to C if the trees were not large enough then how wud small animals glide ?

    So the degree of undermining is more for D Smile .

    Hope you get my point.

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    ashforgmat Rising GMAT Star Default Avatar
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    Post Sat Jan 29, 2011 4:04 am
    I guess its D since both C and D undermine the arboreal hypothesis but as per the passage many small animals are able to climb trees even "Goats and Kangaroos" can climb trees...hence it may be possible that small animals were able to climb trees in those times.

    But as per D there were trees taller than a few metres where the fossils of arboreal ancestors have been found ...there is no other fact which undermines the short tree evidence hence IMO D beats C...

    whats the OA?

    prachich1987 GMAT Destroyer!
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    Post Sat Jan 29, 2011 5:12 am
    +1 for D
    Please post the OA along with the source

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    Post Tue Feb 01, 2011 9:35 am
    IMO C

    Perhaps
    (25) some of them could climb trees,
    but no convincing analysis has
    demonstrated how Archaeopteryx
    would have both climbed and
    flown with its forelimbs, and there
    (30) were no plants taller than a few
    meters in the environments where
    Archaeopteryx fossils have been
    found. --- Means the plants were very small and they could easily climb them. Perhaps these plants were taller than them.[/b]

    (Many small animals, and even
    some goats and kangaroos,
    are capable of climbing trees
    but are not gliders.) -- Here the author says that despite the fact that these plants were small, some animals did manage to climb (like the small animals)

    Since the passage already states the animals were small, you should infer from the first part and undermine the author's argument.

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    Post Wed Feb 02, 2011 10:42 am
    I vote C. Source please!

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    Post Thu Mar 03, 2011 9:49 pm
    IMO : C
    OA please

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    Post Wed Apr 06, 2011 11:21 pm
    IMO D.

    Please post the OA.

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    Post Thu Apr 07, 2011 8:28 am
    I believe the answer is D.

    Why is C incorrect? Because it doesn't undermine the hypothesis. The passage states

    Quote:
    The “arboreal” hypothesis holds
    that bird ancestors began to fly
    by climbing frees and gliding
    down from branches
    with the
    (10) help of incipient feathers: the
    height of trees provides a good
    starting place for launching flight,
    especially through gliding
    Your bolded section states

    Quote:
    (Many small animals...
    are capable of climbing trees
    but are not gliders
    .
    Obviously this undermines the hypothesis. However (C) just says "many small animals are capable of climbing trees" which, in and of itself is neutral (or possibly supports) the hypothesis. This answer is, as the CR Bible calls it, a shell game (presenting something from the passage that is slightly tweaked or leaves out some crucial detail)

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    Post Tue May 17, 2011 1:35 pm
    Wow this is a really tough choice between C and D, and I really don't think I can call it either way.
    What is the source for this question and what is the OA?

    Thanks

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    Post Wed May 18, 2011 2:29 am
    tgou008 wrote:
    Wow this is a really tough choice between C and D, and I really don't think I can call it either way.
    What is the source for this question and what is the OA?

    Thanks
    It's not a tough choice, unless you make it one by second guessing yourself instead of aggressively eliminating. ldoolitt got it right: the fact that small animals can climb does not in and of itself undermine the arboreal hypothesis. For C to be correct, it needs to present the entire undermining fact: that many small animals can climb but cannot fly.

    also, D is clearly a piece of evidence used to undermine the hypothesis - the earliest known bird did not have trees high enough to glide from, so it probably developed flight in a different way. Once you have D, there really is no reason to go and talk yourself into choosing a trap answer choice such as C.

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    Post Thu May 19, 2011 12:28 am
    I go with C, though D also looks tempting!

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    Post Fri Feb 24, 2012 7:14 pm
    Actually D doesn't even weaken the stimulus. I mean just because there are no trees tall enough near the fossil doesn't mean that the bird couldn't climb tall trees elsewhere right?

    C does a good job at weakening the argument. The author needs to prove both climbing and gliding to prove the first theory. He only succeeds at the climbing part. Answer choice C forces him to answer gliding part of the argument.

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    Post Sun Apr 01, 2012 7:24 am
    Climbing tree is not the license for flying or gliding

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