⠀⠀⠀⠀⠀⠀⠀⠀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. 1 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 2 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 3 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 4 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 5 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. 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 Evolution of Human Walking.pdf

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Anthropologists once thought that the ancestors of modern humans began

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KarishmaB

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VeritasKarishma

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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

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)

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 !

Option (A) would still include the aspect of why bipedal walking did evolve (nuclear family) while option (D) wouldn't. The centre stage is taken by bipedal locomotion and everything else is discussed in relation to that.
Though in that case, I would argue between (A) being too generic and (D) being too specific and hence, who knows if that would pass the GMAC filters.

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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?

The highlighted part is incorrect. Nuclear family is not a more crucial step than development of tools in bipedal walking. Nuclear family could be the reason why bipedal walking developed. Development of brain/tools may have had nothing to do with bipedal walking.
But a big part of the passage talks about bipedal walking predating brain enlargement. So by saying "chronological relationship" and "certain key aspects", it covers everything.

I do understand that (A) feels a bit generic but it does cover the passage as a whole.

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KarishmaB

Hi Karishma,
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
For primary purpose, why we can't assume "human evolution" as transition to walking upright. The last sentence of the para mentions that "the transition to bipedal walking may have occurred as long as ten million years ago, at the time of the earliest hominids, making it a crucial initiating event in human evolution"
And nuclear family could be the reason why bipedal walking developed so transition to nuclear family structure was a crucial event that led to walking upright than development of tools that was thought earlier.

Thank you so much for your help

4. The passage suggests that, in comparison with the hominid australopithecines, modern humans are
D. more well suited to a nuclear family structure

Why D or E is incorrect?

If the transition to a nuclear family structure could be the reason for bipedal walking, modern humans are more suited to a nuclear family structure than are australopithecines. Please help to reject D.

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?
I selected E but was not sure about the correct reason to reject A & C.
Why A & C are incorrect?
A. Their brains were smaller than the brains of present-day chimpanzees.
"By contrast, the head of Lucy`s baby could have been no larger than that of a baby chimpanzee" - Their brains could be same or smaller than the brains of chimpanzees. So this option doesn't cover the possibility of having same size.
C. Their mating patterns and family structure were closer to those of present-day chimpanzees than to those of modern humans.
Can we say that passage shared no info about mating patterns and family structure of present day chimpanzees? Please help.

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KarishmaB
Hi Karishma,
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
For primary purpose, why we can't assume "human evolution" as transition to walking upright. The last sentence of the para mentions that "the transition to bipedal walking may have occurred as long as ten million years ago, at the time of the earliest hominids, making it a crucial initiating event in human evolution"
And nuclear family could be the reason why bipedal walking developed so transition to nuclear family structure was a crucial event that led to walking upright than development of tools that was thought earlier.

Thank you so much for your help

The passage does not say or imply that 'nuclear family' was a more crucial event than tools. It talks about the possible chronological relationship between diff events and bipedal walking. Also, 'bipedal walking' is called an initiating crucial event, not nuclear family even if it may be the reason for bipedal walking.
Just think - if you were to summarise the passage to someone in 2 lines, how would you do it?

You would say - the author is telling us that bipedal walking did not come about after brains enlarged and humans made tools. It happened much earlier and because they started living in nuclear families.
So it gives 'the chronological relationship between bipedal locomotion and certain other key aspects of human evolution.'

The passage is not written to impress upon you that nuclear family was more crucial than stone tools.

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KarishmaB GMATNinja

4. The passage suggests that, in comparison with the hominid australopithecines, modern humans are
D. more well suited to a nuclear family structure

Why D or E is incorrect?

If the transition to a nuclear family structure could be the reason for bipedal walking, modern humans are more suited to a nuclear family structure than are australopithecines. Please help to reject D.

The only thing the passage says is that australopithecines was better suited to bipedal walking than modern humans.
We don't know which ones are more suited to nuclear family.
Nuclear family concept needed bipedal walking and that is how bipedal walking evolved. Modern humans also walk on two feet, whether their body is less or more suited to it, doesn't matter. What other factors play a role in making humans more or less suited to nuclear family, we don't know. So we cannot say whether australopithecines or modern humans are more suited to nuclear families.
When we have a perfect answer in (B) which is given to us in the passage, why would we even consider options (D) and (E) for which there is no information.

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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?
I selected E but was not sure about the correct reason to reject A & C.

Why A & C are incorrect?
A. Their brains were smaller than the brains of present-day chimpanzees.
"By contrast, the head of Lucy`s baby could have been no larger than that of a baby chimpanzee" - Their brains could be same or smaller than the brains of chimpanzees. So this option doesn't cover the possibility of having same size.

C. Their mating patterns and family structure were closer to those of present-day chimpanzees than to those of modern humans.
Can we say that passage shared no info about mating patterns and family structure of present day chimpanzees? Please help.

Note the question stem:
(passage) suggests that which of the following was true for the hominid ...

You need to find support for the correct option in the passage.

Whether a statement could be true or not is not the point. Does the passage say/suggest that it was true for the hominid?
There is no mention of brains smaller than chimp's and family structures and mating patterns of chimps in the passage so eliminate.

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