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

admin2022-10-18  8
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 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?
选项 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.
答案E
解析 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.
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