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1、GRE写作素材之打哈欠的奥秘考生想要在GRE写作中写出优秀的文章，就一定要积累较多的材和写作技巧，下面就给大家整理的一篇GRE写作素材题材，希望大家取得理想的成绩。The mystery of yawningAccording to conventional theory, yawning（打哈欠）takes place when people are bored or sleepy and serves the function of increasing alertness(机敏) by reversing, through deeper breathing, the drop in bl
2、ood oxygen levels that are caused by the shallow breathing that accompanies lack of sleep or boredom. Unfortunately, the few scientific investigations of yawning have failed to find any connection between how often someone yawns and how much sleep they have had or how tired they are. About the close
3、st any research has come to supporting the tiredness theory is to confirm that adults yawn more often on weekdays than at weekends, and that school children yawn more frequently in their first year at primary school than they do in kindergarten.根据传统理论，当人们无聊或者困倦时就会打哈欠。伴随睡眠不足或无聊的是浅呼吸，而浅呼吸会降低血液中氧的含量。打哈
4、欠可以通过深呼吸逆转这一点，增加血液中氧的含量从而达到提高警觉性的功能。但遗憾的是，少量关于打哈欠的科学研究并没有找到任何打哈欠频率与个人睡眠时长或者疲劳程度之间的联系。最近所有用于支持疲劳理论的研究是为了确认成人在工作日比在周末打哈欠的频率更高；学生在小学一年级比在幼儿园时打哈欠的频率要高。Another flaw（瑕疵） of the tiredness theory is that yawning does not raise alertness or physiological activity, as the theory would predict. When researcher
5、s measured the heart rate, muscle tension and skin conductance （皮肤电传导）of people before, during and after yawning, they did detect some changes in skin conductance following yawning, indicating a slight increase in physiological activity（生理活性）. However, similar changes occurred when the subjects were
6、 asked simply to open their mouths or to breathe deeply. Yawning did nothing special to their state of physiological activity. Experiments have also cast serious doubt on the belief that yawning is triggered by a drop in blood oxygen or a rise in blood carbon dioxide. Volunteers were told to think a
7、bout yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide. If the theory was correct, breathing air with extra carbon dioxide should have triggered yawning, while breathing pure oxygen should have suppressed yawning. In fact, neit
8、her condition made any difference to the frequency of yawning, which remained constant at about 24 yawns per hour. Another experiment demonstrated that physical exercise, which was sufficiently vigorous（精力充沛的） to double the rate of breathing, had no effect on the frequency of yawning. Again the impl
9、ication is that yawning has little or nothing to do with oxygen.疲劳理论的另一个缺陷是打哈欠并不如该理论所预期的那样提高警觉性或生理活动。研究人员在（志愿者）打哈欠的前、中、后三个阶段均测量了心率、肌肉张力以及皮肤传导性，而他们测得皮肤传导性在打哈欠后的确存在一些变化，这一变化表明生理活动有轻微的增强。但是，在实验者被要求只是张开嘴或深呼吸时，皮肤传导性也发生了相似的变化。打哈欠对于生理活动的状态并无特殊作用。实验结果也对“打哈欠是由血液中氧含量下降或由血液中二氧化碳含量上升所引起的”这一论断产生了严重怀疑。志愿者被告知当他们吸入
10、普通空气、纯氧或者是含有高于正常水平的二氧化碳的空气混合物时要想着打哈欠。如果疲劳理论是正确的，那么当人吸入额外的二氧化碳时，应该能够激发打哈欠；当吸入纯氧时应该能够抑制打哈欠。但实际上，在这两种条件下，打哈欠的频率并无任何差异，均维持在稳定的约24个每小时。另一个实验证明，即使是可以让呼吸频率翻倍的剧烈运动对于打哈欠频率也毫无影响。这再一次说明打哈欠几乎或完全与氧气无关。A completely different theory holds that yawning assists in the physical development of the lungs early in life,
11、 but has no remaining biological function in adults. It has been suggested that yawning and hiccupping（打嗝） might serve to clear out the fetuses（胎） airways. The lungs of a fetus secrete a liquid that mixes with its mothers amniotic（羊水） fluid. Babies with congenital（先天的） blockages （堵塞）that prevent thi
12、s fluid from escaping from their lungs are sometimes born with deformed lungs. It might be that yawning helps to clear out the lungs by periodically lowering the pressure in them. According to this theory, yawning in adults is just a developmental fossil with no biological function. But, while accep
13、ting that not everything in life can be explained by Darwinian evolution, there are sound reasons for being skeptical of theories like this one, which avoid the issue of what yawning does for adults. Yawning is distracting, consumes energy and takes time. It is almost certainly doing something signi
14、ficant in adults as well as in fetuses. What could it be?一个完全不同的理论认为，打哈欠有助于早期肺部的发育，但是对于成年人来说并无任何生理功效。这也暗示了打哈欠和打嗝或许能够清理胎儿的呼吸道。胎儿的肺会分泌一种混合着母亲羊水的液体。当患有先天性肺不张的婴儿的肺部阻止这种液体从肺中流出时，这些婴儿出生时肺部就会变形。打哈欠很可能是通过周期性的降低肺部压力，帮助清除肺部中的这些液体。按照该理论，成年人打哈欠只是一个没有生理功效的发育阶段的化石。但是，当人们已认同达尔文的进化论并不能解释所有现象时，我们有充分的理由去怀疑这一没有解释成年人打哈
15、欠的问题的理论。打哈欠是分散精力的，费时又耗力。但是，几乎可以肯定是，打哈欠不仅对胎儿，对成年人也有重要的作用。那么，究竟是什么作用呢？The empirical evidence（实验性证据）, such as it is, suggests an altogether different function for yawningnamely, that yawning prepares us for a change in activity level. Support for this theory came from a study of yawning behavior in eve
16、ryday life. Volunteers wore wrist-mounted devices that automatically recorded their physical activity for up to two weeks: the volunteers also recorded their yawns by pressing a button on the device each time they yawned. The data showed that yawning tended to occur about 15 minutes before a period of increased behavioral activity. Yawning bore no relationship to sleep patterns, however. This accords with anecdotal evidence （轶事证据）that people often yawn in situations where the
