Anthropologists once thought that the ancestors of modern humans began

Question

⠀⠀⠀⠀⠀⠀⠀⠀Anthropologists once thought that the ancestors
⠀⠀⠀ of modern humans began to walk upright because
⠀⠀⠀ it freed their hands to use stone tools, which they
⠀⠀⠀ had begun to make as the species evolved a brain of
(5)⠀⠀increased size and mental capacity. But discoveries
⠀⠀⠀ of the three-million-year-old fossilized remains of
⠀⠀⠀ our hominid ancestor Australopithecus have yielded
⠀⠀⠀ substantial anatomical evidence that upright walking
⠀⠀⠀ appeared prior to the dramatic enlargement of the
(10) brain and the development of stone tools.

⠀⠀⠀⠀⠀⠀⠀⠀Walking on two legs in an upright posture (bipedal
⠀⠀⠀ locomotion) is a less efficient proposition than walking
⠀⠀⠀ on all fours (quadrupedal locomotion) because several
⠀⠀⠀ muscle groups that the quadruped uses for propulsion
(15) must instead to provide the biped with
⠀⠀⠀ stability and control. The shape and configuration
⠀⠀⠀ of various bones must likewise be modified to allow
⠀⠀⠀ the muscles to perform these functions in upright
⠀⠀⠀ walking. Reconstruction of the pelvis (hipbones) and
(20) femur (thighbone) of “Lucy”, a three-million-year-old
⠀⠀⠀ skeleton that is the most complete fossilized skeleton
⠀⠀⠀ from the australopithecine era, has shown that they
⠀⠀⠀ are much more like the corresponding bones of the
⠀⠀⠀ modern human than like those of the most closely
(25) related living primate, the quadrupedal chimpanzee.
⠀⠀⠀ Lucy’s wide, shallow pelvis is actually better suited to
⠀⠀⠀ bipedal walking than is the rounder, bowl-like pelvis of
⠀⠀⠀ the modern human, which evolved to form the larger
⠀⠀⠀ birth canal needed to accommodate the head of a
(30) large-brained human infant. By contrast, the head of
⠀⠀⠀ Lucy’s baby could have been no larger than that of a
⠀⠀⠀ baby chimpanzee.

⠀⠀⠀⠀⠀⠀⠀⠀If the small-brained australopithecines were not
⠀⠀⠀ toolmakers, what evolutionary advantage did they
(35) gain by walking upright? One theory is that bipedality
⠀⠀⠀ evolved in conjunction with the nuclear family:
⠀⠀⠀ monogamous parents cooperating to care for their
⠀⠀⠀ offspring. Walking upright permitted the father to
⠀⠀⠀ use his hands to gather food and carry it to his mate
(40) from a distance, allowing the mother to devote more
⠀⠀⠀ time and energy to nurturing and protecting their
⠀⠀⠀ children. According to this view, the transition to
⠀⠀⠀ bipedal walking may have occurred as long as ten
⠀⠀⠀ million years ago, at the time of the earliest hominids,
(45) making it a crucial initiating event in human evolution.

RC62100.01-10
1. The primary purpose of the passage is to

A. present an interpretation of the chronological relationship between bipedal locomotion and certain other key aspects of human evolution
B. compare the evolutionary advantages and disadvantages of bipedal locomotion to those of quadrupedal locomotion
C. argue that the transition to a nuclear family structure was a more crucial step in human evolution than was the development of stone tools
D. analyze anatomical evidence of bipedal locomotion to show that the large brain of modern humans developed at a later stage of evolution than was previously believed
E. use examples of muscle and bone structure to illustrate the evolutionary differences between modern humans, australopithecines, and chimpanzees

RC62100.01-20
2. The passage suggests that proponents of the theory mentioned in lines 35–38 assume that which of the following steps in human evolution occurred most recently?

A. Development of a nuclear family structure
B. Transition from walking on all fours to walking upright
C. Dramatic enlargement of the brain
D. Use of the hands to gather and carry food
E. Modification of propulsive muscles to provide stability and control in locomotion

RC62100.01-30
3. According to the passage, the hominid australopithecine most closely resembled a modern human with respect to which of the following characteristics?

A. Brain size
B. Tool-making ability
C. Shape of the pelvis
D. Method of locomotion
E. Preference for certain foods

RC62100.01-40
4. The passage suggests that, in comparison with the hominid australopithecines, modern humans are

A. less well adapted to large group cooperation
B. less well adapted to walking upright
C. more agile in running and climbing
D. more well suited to a nuclear family structure
E. more well suited to cooperative caring for their offspring

RC62100.01-50
5. The theory mentioned in lines 35–38 suggests that which of the following was true for the hominid ancestors of modern humans before they made the transition to walking upright?

A. Their brains were smaller than the brains of present-day chimpanzees.
B. They competed rather than cooperated in searching for food.
C. Their mating patterns and family structure were closer to those of present-day chimpanzees than to those of modern humans.
D. Males played a more significant role in child rearing than they played after the transition to walking upright.
E. Females' ability to nurture and protect their offspring was limited by the need to find food for themselves.

Show Spoiler

Source : JOURNAL ARTICLE
Evolution of Human Walking
C. Owen Lovejoy
Scientific American
Vol. 259, No. 5 (NOVEMBER 1988), pp. 118-125
Published by: Scientific American, a division of Nature America, Inc.
https://www.jstor.org/stable/24989268
Page Count: 8

Attachment:

Evolution of Human Walking.pdf [600.28 KiB]
Downloaded 385 times

Show Answer Question #1

Official Answer

A

Show Answer Question #2

Official Answer

C

Show Answer Question #3

Official Answer

D

Show Answer Question #4

Official Answer

B

Show Answer Question #5

Official Answer

E

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gmatt1476 · Accepted Answer

Official Explanation

RC62100.01-50

5. The theory mentioned in lines 35–38 suggests that which of the following was true for the hominid ancestors of modern humans before they made the transition to walking upright?

A. Their brains were smaller than the brains of present-day chimpanzees.
B. They competed rather than cooperated in searching for food.
C. Their mating patterns and family structure were closer to those of present-day chimpanzees than to those of modern humans.
D. Males played a more significant role in child rearing than they played after the transition to walking upright.
E. Females' ability to nurture and protect their offspring was limited by the need to find food for themselves.

Inference

The theory mentioned in lines 35–38 holds that bipedality evolved among modern humans' hominid ancestors specifically because it granted monogamous couples the ability to cooperate in the care of their offspring.

According to this theory, because they could now walk upright, fathers were able to use their hands to gather food and carry it to their mates from a distance. This in turn allowed mothers to expend greater amounts of time and energy to the nurture and protection of their children.

This implies that prior to the development of walking upright, mothers had to spend more time acquiring their own food, and therefore less time nurturing and protecting their offspring.

A. According to the passage, the brains of baby australopithecine hominids were no larger than the brains of baby chimpanzees. This in no way implies that the brains of these ancestors were smaller than those of chimpanzees. Nothing in the passage indicates that the theory would disagree with this.

B. The theory states that walking upright allowed for cooperation for food within a monogamous couple; a simple lack of cooperation does not imply that these ancestors necessarily competed for food. For example, these groups could have engaged in cooperative hunting, just as many nonbipedal animals are now.

C. The theory does suggest that prior to the development of bipedality, these ancestors were not as capable of cooperative care. However, this still does not imply that their mating patterns and family structures were more similar to those of chimpanzees than to those of modern humans.

D. The theory actually suggests the opposite: that bipedality developed because it allowed for greater cooperative care among hominid parents.

E. Correct.  As discussed above, the development of bipedality allowed fathers to assist mothers in acquiring food. This, thereby, freed up time and energy for mothers to nurture and protect their offspring.

The correct answer is E.

gmatt1476 · Answer

Official Explanation

RC62100.01-10

1. The primary purpose of the passage is to

A. present an interpretation of the chronological relationship between bipedal locomotion and certain other key aspects of human evolution
B. compare the evolutionary advantages and disadvantages of bipedal locomotion to those of quadrupedal locomotion
C. argue that the transition to a nuclear family structure was a more crucial step in human evolution than was the development of stone tools
D. analyze anatomical evidence of bipedal locomotion to show that the large brain of modern humans developed at a later stage of evolution than was previously believed
E. use examples of muscle and bone structure to illustrate the evolutionary differences between modern humans, australopithecines, and chimpanzees

Main idea

To discern the primary purpose of a passage requires an understanding of the key messages within the passage. The passage states that a once-favored view was that modern human beings' ancestors began to walk upright around the same time that they began to use stone tools.

However, this argument has been weakened by archaeological discoveries indicating that these ancestors began to walk upright before the enlargement of the brain that led to the development of such tools.

Furthermore, the passage indicates that these ancestors had a shallow pelvis that would actually suit walking upright better than the bowl-shaped human pelvis, a development that allows for children to be born with larger brains and therefore heads.

Given that walking upright is less efficient than walking on all fours, the passage suggests that some sort of evolutionary advantage came from walking upright; the passage suggests that this advantage may have been that it allowed monogamous parents to cooperate in the care of offspring.

A. Correct.  As the review above indicates, the passage is primarily concerned with the chronological relationship between bipedal locomotion and certain other important developments in human evolution, such as fitness for cooperative parental roles.

B. While the passage does mention the relative efficiency of bipedal and quadrupedal locomotion, it does so primarily to motivate the larger purpose of the passage. That is, it justifies the need to explain the development of bipedal locomotion. In other words, if bipedal locomotion were more efficient rather than less efficient, this efficiency boost would be sufficient to explain its evolution.

C. The passage does not discuss whether the development of the nuclear family or the development of stone tools was the more crucial step in human evolution. Rather, it simply rules out the development of stone tools as an explanation for the development of bipedal locomotion and proposes the transition to a nuclear family as a possible explanation.

D. The passage does present such evidence, but it does so merely as one step in pursuit of the primary purpose of presenting the chronological relationships among the evolution of bipedal locomotion and other key human developments.

E. The passage does use such examples, but it does so merely as one step in pursuit of the overall, primary purpose of presenting the chronological relationships among the evolution of bipedal locomotion and other key human developments.

The correct answer is A.

GMATNinja · Answer

Question 1

To answer primary purpose questions, first think through the structure of the passage. Why did the author write each paragraph?

Here's a structural breakdown of this passage:

Paragraph 1: The author  introduces an old theory . This theory held that humans started making stone tools, and then began walking on two legs so their hands would be free to use those tools. Then, the author  undermines this old theory.  He/she says that the timeline is all wrong -- in fact, people started walking on two legs BEFORE they made stone tools.
 
 Paragraph 2: The author  provides more info to undermine the old theory . He/she talks about fossils that support the idea that bipedalism happened BEFORE stone tools.
 
 Paragraph 3: The author  introduces a new theory to explain why people started walking on two legs:  so that parents could better care for their young as part of a nuclear family. The author then discusses what this theory could mean for the timeline of human evolution.

Overall, then, the author is mainly interested in using the timeline of various events in human evolution to explain why we started walking on two legs.

Let's see how the answer choices stack up:
 
This looks pretty good! The author discusses the timeline of stone tool usage and the formation of the nuclear family, and uses this timeline to interpret the relationship of these things to bipedalism. Keep (A) for now.
 
The author does discuss the advantages and disadvantages of walking on two legs, but that's not his/her  primary  purpose. He/she is much more interested in the timeline of various components of human evolution, and how that answer the question of  why  we move to bipedalism. Eliminate (B).
 
The author says that the nuclear family structure was a "crucial" step in human evolution, but he/she never compares this to the importance of the development of stone tools. That component could be just as crucial. We don't get a comparison of importance, we only get a relative timeline of events. For that reason, we can eliminate (C).
 
Lucy's bones don't suggest that our large brains developed LATER than was previously believed -- they just show that bipedalism developed EARLIER than was previously believed. Early anthropologists could be 100% correct about the timeline of brain growth, but wrong about when we transitioned to two legs. (D) is out.
 
Again, this just doesn't capture the main purpose of the passage. The author talks about different bone and muscle structures in these various species, but his/her primary purpose is to use timelines to explain why we became bipedal. Eliminate (E).

(A) is the correct answer to question 1.

gmatt1476 · Answer

Official Explanation

RC62100.01-20

2. The passage suggests that proponents of the theory mentioned in lines 35–38 assume that which of the following steps in human evolution occurred most recently?

A. Development of a nuclear family structure
B. Transition from walking on all fours to walking upright
C. Dramatic enlargement of the brain
D. Use of the hands to gather and carry food
E. Modification of propulsive muscles to provide stability and control in locomotion

Inference

The passage states that fossilized remains provide anatomical evidence that upright walking, which required a modification of propulsive muscles to provide stability and control in locomotion, occurred before the dramatic enlargement of the brain.

Proponents of the theory mentioned in lines 35–38 argue that walking upright may have evolved alongside the nuclear family structure because it allowed for cooperative caring for infants, which would have required the use of hands to gather and carry food. Thus, the dramatic enlargement of the brain was the most recent of the developments listed among the answer options.

A. Proponents of the theory mentioned in lines 35–38 hold that the dramatic enlargement of the brain occurred more recently than the development of walking upright, which happened alongside the development of a nuclear family structure.

B. Proponents of the theory mentioned in lines 35–38 hold that the dramatic enlargement of the brain occurred more recently than the transition from walking on all fours to walking upright.

C. Correct.  Proponents of the theory mentioned in lines 35–38 hold that the dramatic enlargement of the brain was the most recent of these developments to occur.

D. Proponents of the theory mentioned in lines 35–38 hold that the dramatic enlargement of the brain occurred more recently than the use of hands to gather and carry food, which occurred alongside the development of walking upright.

E. Proponents of the theory mentioned in lines 35–38 hold that the dramatic enlargement of the brain occurred more recently than the modification of propulsive muscles to provide stability and control in locomotion, which is a key factor in the development of walking upright.

The correct answer is C.

gmatt1476 · Answer

Official Explanation

RC62100.01-30

3. According to the passage, the hominid australopithecine most closely resembled a modern human with respect to which of the following characteristics?

A. Brain size
B. Tool-making ability
C. Shape of the pelvis
D. Method of locomotion
E. Preference for certain foods

Supporting idea

The passage directly states that australopithecines walked upright (used bipedal locomotion), as human beings do.

A. The passage states that the dramatic enlargement of the brain among hominids occurred after the australopithecine era; it follows that the size of the australopithecine brain did not closely resemble that of the modern human brain.

B. The passage states that stone-tool-making ability did not develop until some time after the australopithecine era. The passage suggests that study of Australopithecus indicates that there is substantial evidence that upright walking appeared prior to . . . stone tools.

C. The passage specifies notable differences in shape between the australopithecine pelvis and the pelvis of modern human beings.

D. Correct.  As noted above, the passage indicates that australopithecines walked upright, or used bipedal locomotion, as modern human beings do.

E. The passage does not indicate the types of foods preferred by australopithecines.

The correct answer is D.

gmatt1476 · Answer

Official Explanation

RC62100.01-40

4. The passage suggests that, in comparison with the hominid australopithecines, modern humans are

A. less well adapted to large group cooperation
B. less well adapted to walking upright 
C. more agile in running and climbing 
D. more well suited to a nuclear family structure 
E. more well suited to cooperative caring for their offspring

Inference

The information needed to answer this question is contained in the second paragraph. This is the only place in the passage where comparisons between australopithecines and modern human beings occur; the passage points out (1) that the pelvis and the femur of australopithecines are more similar to those of modern humans than they are to those of chimpanzees, the most closely related living primate, and (2) that the pelvis of australopithecines is better suited for bipedal locomotion than is the pelvis of modern humans.

A. The passage makes no mention of large-group cooperation.

B. Correct.  As discussed above, the passage notes that the modern human pelvis is less suited for bipedal locomotion than was the australopithecine pelvis. This suggests that, in comparison with australopithecines, modern humans are less well adapted to walking upright.

C. The fact that australopithecines were better suited for walking upright than modern humans are would suggest if anything that australopithecines would also be better suited than humans to running and climbing (rather than vice versa). Regardless, the passage provides no clear evidence of whether modern humans or australopithecines were more agile.

D. In the third paragraph, the passage suggests that australopithecines may have been physically well suited to a nuclear family structure. The passage gives no information as to whether australopithecines were more or less physically well suited to such a structure than are modern humans.

E. In the third paragraph, the passage suggests that australopithecines may have been physically well suited to cooperative caring for their offspring. The passage gives no information as to whether they were more or less physically well suited to such caring than modern humans.

The correct answer is B.

gdatta · Answer

GMATNinja  Can you please assist in understanding the logic behind Q No. 2 here

gmatapprentice · Answer

Can anyone explain why D is wrong in Question 5? The father is now focused on obtaining food post bipedal evolution and now mother is rearing the infants. What am I missing?

BoundMan · Answer

permitted the father to
⠀⠀⠀ use his hands to gather food and carry it to his mate
(40) from a distance, allowing the mother to devote more
⠀⠀⠀ time and energy to nurturing and protecting their
⠀⠀⠀ children. 
 VeritasKarishma  This is for question 5.
 How can we infer option E here?  May be the father was just being friendly and the Female's ability was not limited.
E. Females' ability to nurture and protect their offspring was limited by the need to find food for themselves.

KarishmaB · Answer

The passage clearly says that the father gathering food "allowed" the mother to devote more time to nurture and protect. So food gathering was something that limited her 'nurture and protect time' previously. Now when the father started doing it, she had more time.
So option (E) is correct.

GMATNinja · Answer

Question 2

Anthropologists once thought that "the ancestors of modern humans began to walk upright because it freed their hands to use stone tools, which they had begun to make as the species evolved a brain of increased size and mental capacity."

However, new evidence showed that humans began walking upright long  before  their brains got bigger. So it is not possible that humans started walking upright in order to use stone tools, because their mental capacity was not yet big enough to make/use stone tools!

The theory mentioned in question #2 addresses this issue by coming up with another explanation: "bipedality evolved in conjunction with the nuclear family."

So, the timeline of that theory goes something like this:
  Humans evolved to walk on two legs  at the same time  as they evolved to live as nuclear families 
 THEN, their brains began to grow and they started using stone tools

In the answer choices, we are looking for the most recent step in human evolution:
 
As discussed above, these two things happened in conjunction with one another. Hmm, that makes it difficult to say which one would come more recently. Eliminate (A) and (B).

This definitely happened AFTER humans developed a nuclear family structure and transitioned to walking upright, so we can feel good about getting rid of (A) and (B). Let's keep (C) for now, and see whether anything more recent comes along.

Proponents of the new theory believed that the whole reason that humans evolved to walk upright was to gather and carry food, so this development must have occurred  with  the transition from walking on all fours to walking upright. That puts (D) at the same time as (A) and (B), which occurred BEFORE (C). (D) is out.

This is mentioned in the passage as a REQUIREMENT for transitioning from walking on all fours to walking upright. So, this certainly could not occur  after  humans made that transition. That means that (E) definitely occurred before (C).

We're left with (C) as the most recent development, and (C) is the correct answer to question #2.

Question 5

The theory states that "walking upright permitted the father to use his hands to gather food and carry it to his mate from a distance, allowing the mother to devote more time and energy to nurturing and protecting their children."

Can we infer from this that, when they walked on all fours, "males played a more significant role in child rearing than they played after the transition to walking upright"?

Not really. It is possible that quadrupedal males helped with child rearing, but it's also possible that they were deadbeat dads and just left the mothers to raise the kids solo. Mothers would not have had as much time and energy to nurture their children, but that does not mean that fathers actually helped them out -- maybe it was just a tough life for quadrupedal moms, who had to both gather food  and  raise the kids.

The theory in lines 35-38 doesn't suggest that males helped more with child rearing before they became bipedal, so (C) is out.

I hope that helps!

mSKR · Answer

For question no. 4 , why not D or E

1.) 
please see the bold lines. EVOLVED means from australopithecines to MODERN HUMANS. So it is clearly a reference that NOW MALES can use hands and Females can spend more time, so certainly it seems that modern humans are MORE SUITED to NUCLEAR FAMILY STRUCTURE than before australopithecines due to EVOLUTION .

2.) Modern humans walk on 2 legs for so many ages, what more can be evolved in bipedality ? Normal thought would be how even australopithecines can be well suited to bipedality . Even australopithecines structures were not straigh as MODERN HUMANS.

3. ) in the passage, it is mentioned 
Just by one line that pelvis is suitable for bipedal walking SHOULD NOT MEAN that modern humans are less well adapted to walking upright. There maybe 100s of other factors that decide final suitability.
OFcourse, their pelvis structure maybe suitable but maybe their BACKBONE or Body weight doesnt make it suitable for bidepal walking.

I am already in shock with the correct answer choice of B.

GMATNinja ,  GMATNinjaTwo ,  bm2201   VeritasKarishma  ; PLEASE GIVE YOUR MUCH-NEEEDED OPINION.

Thanks!

KarishmaB · Answer

The question is - what does the passage suggest?

The passage says that 
Lucy’s wide, shallow pelvis is actually better suited to 
⠀⠀⠀ bipedal walking than is the rounder, bowl-like pelvis of 
⠀⠀⠀ the modern human, which evolved to form the larger 
⠀⠀⠀ birth canal needed to accommodate the head of a 
large-brained human infant.

So the modern human's pelvis evolved to form the larger birth canal though Lucy's pelvis was better suited to walking. It may feel against what we think of when we say "evolution" but the passage clearly mentions it. To accommodate another feature (larger birth canal), the human body had to take a hit on a more suitable pelvis for walking.

The point is that our preconceived notions need to be kept aside while reading the passage.

Also the passage does not mention whether modern humans are better suited to nuclear family structure. It just says that bipedality and nuclear family evolved together i.e. came into being at the same time.

Ranasaymon · Answer

Sajjad1994   GMATRockstar   VeritasKarishma   ChiranjeevSingh

I am stuck between option A and D. Why is the primary purpose of the passage not D?

1. The primary purpose of the passage is to

P-1: Old view; Smart 1st-> then walk upright
New View: new discovery-> New view-> walk upright 1st-> smart(brain dev) next

p-2: Why upright? 
lucy's similarity and dissimilarity with modern and with chimp

p3: 
Why walk upright? 
-> family theory

A. present an interpretation of the chronological relationship between bipedal locomotion and certain other key aspects of human evolution

D. analyze anatomical evidence of bipedal locomotion to show that the large brain of modern humans developed at a later stage of evolution than was previously believed

KarishmaB · Answer

Anthropologists once thought that the ancestors 
⠀⠀⠀ of modern humans began to walk upright because 
⠀⠀⠀ it freed their hands to use stone tools, which they 
⠀⠀⠀ had begun to make as the species evolved a brain of
(5)⠀⠀increased size and mental capacity. But discoveries 
⠀⠀⠀ of the three-million-year-old fossilized remains of 
⠀⠀⠀ our hominid ancestor Australopithecus have yielded 
⠀⠀⠀ substantial anatomical evidence that upright walking 
⠀⠀⠀ appeared prior to the dramatic enlargement of the 
(10) brain and the development of stone tools.

Says that bipedal walking came much earlier than previously believed (not that larger brain developed later than previously thought). 
Bipedal walking happened before brain enlargement and tools development.

⠀⠀⠀⠀⠀⠀⠀⠀ Walking on two legs in an upright posture (bipedal 
⠀⠀⠀ locomotion) is a less efficient proposition than walking 
⠀⠀⠀ on all fours (quadrupedal locomotion) because several 
⠀⠀⠀ muscle groups that the quadruped uses for propulsion 
(15) must instead to provide the biped with 
⠀⠀⠀ stability and control. The shape and configuration 
⠀⠀⠀ of various bones must likewise be modified to allow 
⠀⠀⠀ the muscles to perform these functions in upright 
⠀⠀⠀ walking. Reconstruction of the pelvis (hipbones) and 
(20) femur (thighbone) of “Lucy”, a three-million-year-old 
⠀⠀⠀ skeleton that is the most complete fossilized skeleton
⠀⠀⠀ from the australopithecine era, has shown that they 
⠀⠀⠀ are much more like the corresponding bones of the 
⠀⠀⠀ modern human than like those of the most closely 
(25) related living primate, the quadrupedal chimpanzee. 
⠀⠀⠀ Lucy’s wide, shallow pelvis is actually better suited to
⠀⠀⠀ bipedal walking than is the rounder, bowl-like pelvis of 
⠀⠀⠀ the modern human, which evolved to form the larger
⠀⠀⠀ birth canal needed to accommodate the head of a 
(30) large-brained human infant. By contrast, the head of 
⠀⠀⠀ Lucy’s baby could have been no larger than that of a 
⠀⠀⠀ baby chimpanzee.

Evaluates anatomical features which show that bipedal walking started much earlier and brains were small at that time.

⠀⠀⠀⠀⠀⠀⠀ ⠀If the small-brained australopithecines were not
⠀⠀⠀ toolmakers, what evolutionary advantage did they 
(35) gain by walking upright? One theory is that bipedality
⠀⠀⠀ evolved in conjunction with the nuclear family: 
⠀⠀⠀ monogamous parents cooperating to care for their 
⠀⠀⠀ offspring. Walking upright permitted the father to 
⠀⠀⠀ use his hands to gather food and carry it to his mate 
(40) from a distance, allowing the mother to devote more 
⠀⠀⠀ time and energy to nurturing and protecting their 
⠀⠀⠀ children. According to this view, the transition to 
⠀⠀⠀ bipedal walking may have occurred as long as ten 
⠀⠀⠀ million years ago, at the time of the earliest hominids, 
(45) making it a crucial initiating event in human evolution.

Questions why bipedal walking developed then if not to hold tools? It helped fathers carry food from a distance. So nuclear families started at that time and hence bipedal walking came into being.

Now consider:
1. The primary purpose of the passage is to

A. present an interpretation of the chronological relationship between bipedal locomotion and certain other key aspects

Correct. It is all about bipedal locomotion. It shows chronology of bipedal walking in relation to some other aspects - brain enlargement, tools development, nuclear family

D. analyze anatomical evidence of bipedal locomotion to show that the large brain of modern humans developed at a later stage of evolution than was previously believed

The passage doesn't focus on showing that brains evolved later. It shows that bipedal walking evolved earlier and discusses another factor that might have led to it.

Answer (A)

mSKR · Answer

HI  VeritasKarishma

Please give your comments on C option also. I was more inclined to choose C over A. 
What mistake was I doing? 
In 1st para, it says for human evoluation , stones tools didn't play more role 3 million years ago than needs of a nuclear family 10 millions years ago.
In fact in 1st paragraph, they have kind of argument ( xxxx, but yyyy)
Please suggest how to get rid of C and choose A confidentially .

Thanks!

KarishmaB · Answer

The passage doesn't discuss the relative importance of each development. It mentions these developments in relation to bipedal walking. It aims to tell you when and why did bipedal walking evolve. 
Note that the passage mentions bipedal walking on and on in every paragraph so it is highly likely that the main point revolves around that. But (C) doesn't even mention it. That should give you a hint that (C) is not correct.

mSKR · Answer

I realized my mistake, I associated human evolution with bipedal walking. 
 
C'. argue that the transition to a nuclear family structure was a more crucial step in  bipedal walking by ancestors  than was the development of stone tools

Do you think C' could be possible primary purpose, better than A?

penco · Answer

Thanks for this amazing explanation.  VeritasKarishma 
I selected D because I thought if we proved brain enlargement happened later, it would ultimately prove the question in first para that walking happened prior to that. That is clearly not the case and I certainly felt into that trap.

I know that official questions are already constructed at an expense of $2000 and upwards and play well with our psychology.
But what if option D was inverted to say " analyze anatomical evidence of bipedal locomotion to show that Walking evolved at earlier stage than using tools or brain enlargement. "
Would it still be fair to choose option A or GMAC is already smart enough to not let that happen !

Regards !

Anthropologists once thought that the ancestors of modern humans began

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Anthropologists once thought that the ancestors of modern humans began

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