Anthropologists once thought that the ancestors of modern humans began

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.

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.

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.

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.

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.

SajjadAhmad, bb :

I think there is an issue with statistics of the questions. I mean accuracy and corresponding percentage of correct/incorrect answers.
For example , %age correct for Question no. 4 option B is only 4%, this means only 4% of people clicked that option, but when I see correct/wrong accuracy it shows 50%-50%. Please have a look. This can be seen in mostly GMAT advanced questions IMO.
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This happens when OA has been changed later on, when OA gets changed the statistics get distorted and that is the main reason.

SajjadAhmad,
hello, can you kindly provide a better explanation for Q1. I cant rule out option D, though I found option A to be equally good.

I am not an expert but I can share my 2 cents thought on this problem with you.
The first part of option D is fine "analyze anatomical evidence of bipedal locomotion". However, the second part just mentions small detail about the passage "to show that the large brain of modern humans developed at a later stage of evolution than was previously believed".
So A is a sure winner.

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

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?

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.

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.
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sunny91
Just like you, I had to decide between A and D

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 starts with:
Anthropologists once thought that the ancestors of modern humans began to walk upright because it freed their hands to use stone tools.

Both A and D are true but "D" although it is true, it is narrow in scope.
This is a type of Trap in Primary Purpose Questions, giving you true answers but narrow in scope and doesn’t give broader perspective. I eliminated this answer choice on this basis.
A is a broader choice and True as well.


I eliminated "D" as
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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!
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Can you please explain in q1 (Primary purpose) why is option C incorrect?

Thanks
Kritika

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

Support for this statement cannot be found in this passage, nowhere in the passage the author is arguing that the "nuclear family structure is more crucial than stone tools"

argument has been made only for "bipedal walking was a crucial event".


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.
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GMATNinja, SajjadAhmad, GMATNinjaTwo, bm2201 VeritasKarishma

Hi - For 3, why not C ?

Reviewing the OA solution posted, the OA solution says there are notable differences in shape between the australopithecine pelvis and the pelvis of modern human beings.

However, doesn't the red font below indicate the australopithecine pelvis and the pelvis of modern human beings are actually similar (what's the red font below then saying?)


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.

Hi jabhatta@umail.iu.edu,

Sure the bones of Lucy are more similar to the corresponding bones of the modern humans, but option C mentions the "shape of pelvis", the difference of which can be inferred from the lines" Lucy’s wide, shallow pelvis is actually better suited to bipedal walking than is the rounder, bowl-like pelvis of the modern human", implying that there is a difference between the shape of Pelvis of Lucy and the modern humans, but the method of locomotion seems to be similar.


Hope This Helps.
Thanks.