OG RC #2 Pleistocene Carnivores

[mundasingh123]

A recent study has provided clues to
predator-prey dynamics in the late Pleistocene
era. Researchers compared the number of tooth
fractures in present-day carnivores with tooth
fractures in carnivores that lived 36,000 to 10,000
years ago and that were preserved in the Rancho
La Brea tar pits in Los Angeles. The breakage
frequencies in the extinct species were strikingly
higher than those in the present-day species.
In considering possible explanations for this
finding, the researchers dismissed demographic bias
because older individuals were not overrepresented
in the fossil samples. They rejected preservational
bias because a total absence of breakage in two
extinct species demonstrated that the fractures
were not the result of abrasion within the pits.
They ruled out local bias because breakage data
obtained from other Pleistocene sites were similar
to the La Brea data. The explanation they consider
most plausible is behavioral differences between
extinct and present-day carnivores-in particular,
more contact between the teeth of predators and
the bones of prey due to more thorough
consumption of carcasses by the extinct species.
Such thorough carcass consumption implies to
the researchers either that prey availability was
low, at least seasonally, or that there was intense
competition over kills and a high rate of carcass
theft due to relatively high predator densities.

[mundasingh123]

7. The researchers' conclusion concerning the absence
of demographic bias would be most seriously
undermined if it were found that
(A) the older an individual carnivore is, the more
likely it is to have a large number of tooth
fractures
(B) the average age at death of a present-day
carnivore is greater than was the average age at
death of a Pleistocene carnivore
(C) in Pleistocene carnivore species, older
individuals consumed carcasses as thoroughly
as did younger individuals
(D) the methods used to determine animals' ages in
fossil samples tend to misidentify many older
individuals as younger individuals
(E) data concerning the ages of fossil samples
cannot provide reliable information about
behavioral differences between extinct
carnivores and present-day carnivores
OG EXPLANATION

Logical structure
Begin by looking at the section on demographic
bias. Lines 11-13 state that demographic bias has
been ruled out as an explanation because older
individuals were not overrepresented in the fossil
samples.
This implies that older carnivores would
be expected to have more tooth fractures than
younger ones.
To answer this question, read each
answer choice to find the one statement that
undermines the researchers' conclusion. If the
method to determine age in the fossil samples is
faulty and older carnivores are misidentified as
younger ones, then demographic bias cannot be
dismissed.

D Correct. If older individuals have been
misidentified as younger ones, then a higher
proportion of older individuals undermines
the researchers' conclusion.
E Neither the diff erences nor the data are
relevant to the researchers' conclusion about
the proportion of older Pleistocene
carnivores.

I didnt understand how the bolded lines is implied .

[mundasingh123]

The Passage says that

In considering possible explanations for this
finding, the researchers dismissed demographic bias
because older individuals were not overrepresented
in the fossil samples.

Doesnt this mean that a lot of younger fossils had been taken to be old by mistake .So That only strengthens the conclusion because despite so many fossils being mistakenly grouped under old had more tooth fractures than present day carnivores

In contrast with the OG explanation for E , if the methods used to find the ages were faulty , there is a high chance that many old oldfossils were mistakenly assumed to be young , so if we assume that older fossils have higher number of tooth fractures , we could erroneously come to a conclusion that the behavioural chacteristics of pleistocene carnivores were different from those of present day carnivores[/quote]

[lunarpower]

1) watch the APRIL 28, 2011 video here, if you haven't seen it yet:
https://www.manhattangmat.com/thursdays-with-ron.cfm

2) once you've watched that video, you'll understand that the correct answers to inference and detail questions should be
* found directly in the vicinity of the relevant facts;
* equivalent to statements that are already in the passage.

the problem is about "demographic bias", so that's your mental "search string" -- basically, pretend you're google and go through the passage until you find "demographic bias".

you'll find this:
the researchers dismissed demographic bias
because older individuals were not overrepresented
in the fossil samples.

you're looking to *undermine* this reasoning.
because this reasoning has only 1 premise (the bolded part), the *only* direct way to undermine this reasoning is for that 1 premise to be false.
therefore, you know that you're looking for a choice that says "well, actually, older individuals WERE overrepresented".
hence (d), the only answer choice that says that sort of thing.

[mundasingh123]

i on Does this also answer the small questions that i raised at https://www.beatthegmat.com/inferences-a ... 83532.html
By

* equivalent to statements that are already in the passage.

ou mean , its not a big Inference that we must make but rather a paraphrase of whats in the passage .

[lunarpower]

i on Does this also answer the small questions that i raised at https://www.beatthegmat.com/inferences-a ... 83532.html
By

* equivalent to statements that are already in the passage.

ou mean , its not a big Inference that we must make but rather a paraphrase of whats in the passage .

the two question types ("according to the passage" and "inference / suggestion") are VERY closely related. both of them require you to stay extremely close to the content of the passage.
the only real difference is this:

* "according to the passage" questions pretty much require you to regurgitate the exact content of the passage -- i.e., so that the principal challenge lies in finding that content and/or determining which content is relevant to the question vs. which content is irrelevant.

* "inference/suggestion" questions usually require you to go one small step beyond the information in the passage... but when i say "small step", i'm talking about really, really small steps. for instance, if the passage says "i'm shorter than my brother", then the inference might be "my brother is taller than i am". or, if the passage says "individual statistics were not kept in sport X until 1963", then the inference might be "before 1963, only group statistics were kept in sport X".
so, basically, you're still not creating anything new -- you're just flipping around existing statements into new combinations/permutations, and/or seeing the "flipside" of existing statements.

the MENTALITY for both of these questions is almost exactly the same -- i.e., a mentality of sticking with exactly the information that you already have. therefore, it's not necessarily even important to understand the distinction made above; it's much more important to understand that you have to have the same approach to both question types.

(i'm answering here because i'm not really a fan of having separate, extra threads for **related** questions -- if you are raising an issue that is highly relevant to the thread at hand, then you should just post that issue in the same thread!)

[mundasingh123]

Hi Ron ,
i ll make sit a point to post similar quests on the same thread .
Ron , I came across an inference question ,the answer to which , i found was not just a paraphrase of the content in the passage but an assumtion .
This is regarding the RC on terrestrial snakes.

In arboreal
snakes, however, which dwell in trees and often
assume a vertical posture, the average distance

from the heart to the head can be as little as 15
percent of overall body length. Such a location
requires that blood circulated to the tail of the
snake travel a greater distance back to the heart,
a problem solved by another adaptation. When
climbing, arboreal snakes often pause
momentarily to wiggle their bodies, causing waves
of muscle contraction that advance from the lower
torso to the head. By compressing the veins and
forcing blood forward, these contractions
apparently improve the fl ow of venous blood
returning to the heart.

Q20 is

20. It can be inferred from the passage that which of the
following is true of species of terrestrial snakes that
often need to assume a vertical posture?
(A) They are more likely to be susceptible to
circulatory failure in vertical postures than are
sea snakes.
(B) Their hearts are less likely to be located at the
midpoint of their bodies than is the case with
sea snakes.
(C) They cannot counteract the pooling of blood in
lower regions of their bodies as effectively as
sea snakes can.
(D) The blood pressure at their midpoint decreases
signifi cantly when they are tilted with their
heads up.
(E) They are unable to rely on muscle contractions
to move venous blood from the lower torso to
the head.

The OG assumes that if terrestrial snakes assume the vertical posture quite a lot , then their bodies will have to adapt to the requirements in just the same way as arboreal snakes' bodies did .
The Exact Explanation from the OG is

Inference
Th is question requires using information given
about how arboreal snakes, which are frequently
in vertical postures, have adapted to gravity's
infl uence to make an assumption that other
terrestrial snakes that are frequently in these
postures are likely to have similar adaptations.
The passage implies that sea snakes have hearts at
the midpoint of their bodies because the water's
pressure gradients help distribute blood evenly. It
then illustrates that arboreal snakes have hearts
closer to their heads to help keep blood fl owing to
their brain when they are in vertical postures.
A Th e passage does not suggest that any of the
snakes mentioned are ill-adapted to their
particular environments.
B Correct. Th e passage states that arboreal
snakes have hearts close to their heads and
not at the midpoints of their bodies, so it is
reasonable to conclude that any terrestrial
snake that frequently assumes vertical
postures would be unlikely to have hearts at
their bodies' midpoint.
C As with option (A), the passage does not
suggest that any species of snake is illadapted
to its environment.
D Th e passage states that sea snakes lose
pressure at their midpoints when they are
tilted on land with heads up but that
terrestrial snakes do not have this problem.
E Because arboreal snakes use muscle
contractions to circulate blood when they
are vertical, it is likely that most terrestrial
snakes that frequently assume vertical
postures also have this capability.
Th e correct answer is B.

[mundasingh123]

The OG Explanation makes a sort of a prediction here that terrestrial snakes will have to adapt to their requirements just as the arboreal snakes did.

[lunarpower]

The OG Explanation makes a sort of a prediction here that terrestrial snakes will have to adapt to their requirements just as the arboreal snakes did.

"arboreal snakes" (= snakes that live in trees) are a type of "terrestrial snake" (= snakes that live on land). the contrast is between snakes that live on land (terrestrial snakes) and those that live in water (sea snakes); arboreal snakes are part of the former group.

yes, you need to make the basic assumption that arboreal snakes are not somehow fantastically unique -- in other words, you have to assume that they have a certain number of traits in common -- but these questions are allowed to operate with certain commonsense assumptions.

[mundasingh123]

Ron,

"arboreal snakes" (= snakes that live in trees) are a type of "terrestrial snake"

Isnt this outside information . I and many others , i am sure, wouldnt know this .
and isnt the assumption a prediction ?

[lunarpower]

Ron,

"arboreal snakes" (= snakes that live in trees) are a type of "terrestrial snake"

Isnt this outside information . I and many others , i am sure, wouldnt know this .

nah, no outside knowledge -- the only thing you need here is the definition of the word "terrestrial", which, while not necessarily an easy word, is well within the bounds of words that you could be expected to know.
(you don't need to have memorized the definition of the more exotic word "arboreal", because the passage tells you that those guys live in trees)

and isnt the assumption a prediction ?

i guess -- but it's based on the general idea that, if similar things/animals/etc are in similar situations, then they will be similar in the relevant ways. this is not true 100% of the time, but it's generally true unless there is a really specific, tangible reason why it shouldn't be true.

--

i don't know whether i asked already, but which other choice did you think was a serious contender?
(even if you don't think an answer choice is perfect, "much better than all other choices" is still good to go)

[mundasingh123]

i chose A . This question took me 248 seconds .
I chose A because in sea snakes , the heart is midway between the body and the tail whereas in terrestrial snakes , the heart is close to the head . Therefore , Terrestrial snakes have to put in extra effort to circulate their blood back to the head from the tail . Sea snakes have to put in less effort . So in Terrestrial snakes ,there is a higher prossiblity that the blood would accumulate in the tail causing problems for them

[lunarpower]

i chose A . This question took me 248 seconds .
I chose A because in sea snakes , the heart is midway between the body and the tail whereas in terrestrial snakes , the heart is close to the head . Therefore , Terrestrial snakes have to put in extra effort to circulate their blood back to the head from the tail . Sea snakes have to put in less effort . So in Terrestrial snakes ,there is a higher prossiblity that the blood would accumulate in the tail causing problems for them

the passage says basically the direct opposite of choice (a): "When [sea snakes are] removed from the water and tilted at various angles with the head up, however, blood pressure at their midpoint drops significantly, and at brain level falls to zero." --> in other words, sea snakes WILL have *total* circulatory failure in vertical postures.
choice (a) is therefore impossible.
(it also goes against the whole idea described for terrestrial snakes, which is that terrestrial snakes are adapted to being in vertical positions while sea snakes are not.)

[GMATMadeEasy]

@lunarpower: Nothing to do with the question under discussion here but following this thread I have gone through your thursday video about inferenes. But I didnt know how to communicate to you for few questions after having watched thursday video. As ussal no surprise , you have brought down the monster RCs to their knees.And thanks for the spectrum analysis,which is amazing.

Few things I want to communicate :

1. One passage that is related to maps of non-native americans has some error in second paragraph? I could not figure out where and how after which in that paragraph sentence is composed and looks like either punctuation is missing or something is wrong. well - that something wrong very well might be me , but I thought no harm in checking with you.

2. An important and interestign thing I noticed is that how dense they make those paragraphs, full of information presented in complicate and normalized way.(there is no single RC in all OGs as complicated as those in GMATPrep) People have attempted to teach speed read etc but no one has ever tried to help for effective read - as far as i know of course. One aspect is to ignore detail but can't there be an another effective way to read sentences or let's say group of words effectively? Some people talk about visual cues and also talk about looking at whole line a a go. But all these approaches try to ignore the semantics of language and rely more on ohter information. A particular approach ,reading effectively based on semantics, might vary a bit from language to language but underlying structures/methodologies should have some clue for a given language providing some guiding rules such as always look for subject and verb. Would you consider something of that sort for next thursday video or it is too vague to ask for?

To quote from OG12 under test taking strategies:

Remember that comprehension -not speed- is the critical success factor when it comes to
reading comprehension questions.

Question is what contributes to good comprehension ? and how this can be worked assuming already good understanding of language grammatically and lexicographically.

[mundasingh123]

i chose A . This question took me 248 seconds .
I chose A because in sea snakes , the heart is midway between the body and the tail whereas in terrestrial snakes , the heart is close to the head . Therefore , Terrestrial snakes have to put in extra effort to circulate their blood back to the head from the tail . Sea snakes have to put in less effort . So in Terrestrial snakes ,there is a higher prossiblity that the blood would accumulate in the tail causing problems for them

the passage says basically the direct opposite of choice (a): "When [sea snakes are] removed from the water and tilted at various angles with the head up, however, blood pressure at their midpoint drops significantly, and at brain level falls to zero." --> in other words, sea snakes WILL have *total* circulatory failure in vertical postures.
choice (a) is therefore impossible.
(it also goes against the whole idea described for terrestrial snakes, which is that terrestrial snakes are adapted to being in vertical positions while sea snakes are not.)

No ron, i thought sea snakes would have no problems when when they assume the vertical posture in water .