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 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 primary purpose of the passage is to
*内容概述： 文章开头说女性的草根运动时期和他们对新文明意识的看法的核心来自于美国在大推进时期的社会改革。接着进一步解释在这一时期中产白人女性改革者取得的成就。接下来笔锋一转，在童工问 题上不同阶级女性看法不同。改革者认为必须剔除，但工人阶级则认为童工法会让家庭里干活的人变少，生活难以为继。最后是作者的评价，承认改革者要求不适用童工是正确的，但他们没有考 虑到工人阶级的家庭经济状况 *文章类型：人文历史 *文章套路：对比解释说明 --------------------------------------------------------------- *题目类型：主旨题
*选项分析：主旨题去看全文内容概述。本文的目的就是文章的结尾处说的中产阶级改革者没能够理解公认阶级的经济状况。因此正确答案是D
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