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

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

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问题 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. 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 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 must instead be adapted 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 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 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 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 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 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, making it a crucial initiating event in human evolution.  
The passage suggests that, in comparison with the hominid australopithecines, modern humans are
选项 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
答案B
解析 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.
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