揽瓜阁阅读做题小分队 第146天 多态性

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In nearly all human populations, a majority of individuals can taste the artificially synthesized chemical phenylthiocarbonide (PTC). However, the percentage varies dramatically—from as low as 60 percent in India to as high as 95 percent in Africa. That this polymorphism is observed in nonhuman primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant, bitter substances, such as certain toxic plants.

A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations, 90 percent of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which nonhuman primates—and to a lesser extent humans—pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.

1. It can be inferred from the passage that human populations vary considerably in their
(A) sensitivity to certain bodily odors.
(B) capacity for hearing.
(C) ability to assimilate artificial chemicals.
(D) vulnerability to certain toxins found in plants.
(E) ability to discern bitterness in taste.

2. Which of the following provides the most reasonable explanation for the assertion in the first paragraph that evolutionary history “obviously” did not act on PTC?
(A) PTC is not a naturally occurring chemical but rather has been produced only recently by scientists.
(B) Most humans lack sufficient taste sensitivity to discriminate between PTC and bitter chemicals occurring naturally.
(C) Variability among humans respecting PTC discrimination, like variability respecting earwax, cannot be explained in terms of evolutionary adaptivity.
(D) The sense of taste in humans is not as discriminating as that in nonhuman primates.
(E) Unlike nonhuman primates, humans can discriminate intellectually between toxic and nontoxic bitter substances.

3. Which of the following best expresses the main idea of the passage?
(A) Artificially synthesized chemicals might eventually serve to alter the course of evolution by desensitizing humans to certain tastes and odors.
(B) Some human polymorphisms might be explained as vestigial evidence of evolutionary adaptations that still serve vital purposes in other primates.
(C) Sensitivity to taste and to odors have been subject to far greater natural selectivity during the evolution of primates than previously thought.
(D) Polymorphism among human populations varies considerably from region to region throughout the world.
(E) The human senses of taste and smell have evolved considerably over the course of evolutionary history.

参考答案：

EAB

斯麦尔糖

ead

svwma

E
A
D-B

Erebuslee

1 A
2 C
3 B

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品尝一个东西的不同显示出evolutionary election
介绍另外一个突出例子-cerumen variability
EAB

梦校offer和全奖

文章结构
提出整体现象—转折说明局部差异——举例—提出观点——举例说明观点＋对比——结论回应观点——举例——再次强调观点
文章内容：
提出大部分人类可以尝出PTC——但是...在不同地区人群中该比例波动大——举例印度和非洲——在非人类身上也发现的体态多样性表明存在进化选择_举例苦味道和有毒植物——举例耳垢（欧洲和中国作对比）——结论：耳垢多样性表明了进化选择对人体多样性的影响——举例耳垢和气味的关系——强调人类进化过程中受到进化选择的影响
作者态度和意图：
证明人类体态差异性受到进化自然选择的影响
反思
-第2题错误很重要的原因是当时在读的时候没有搞明白PTC在原文的作用是什么，因为突然看到出现了一个新的名词 polymorphism，不知道PTC与其关系。下次遇到这种情况有两种解题方法，从内容入手，一定要看懂这个长难句“That this polymorphism is observed in nonhuman primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant, bitter substances, such as certain toxic plants. 首先不知polymorphrism，但是发现用了指示代词“that”，这就说明that polymorphism是对前面味觉识别地区差异性的总结。再看TPC前面用的是although，表示让步，说明although引导的句子与前面意思相反，前面句子再说“这种体态差异被发现在非人类物种中揭示了长时间进化历史”，那就说明PTC没有揭示长时间的进化历史（说明和进化没有关系=没有受到进化的影响），题目也是问有什么证据表示PTC没有受到进化论的影响，A选项进行回答“人工合成物”，这个答案也在第一句关于PTC的定义中明确‘the artificially synthesized chemical phenylthiocarbonide ’。从结构上来看，作者写PTC是为了引出不同地区人对于识别PTC的差异——引出主要观点：多态性揭示了进化的长期影响（自然选择）而不是PTC被影响造成了这种差异——只要证明PTC不是自然物即可。
-第三题错误的原因我认为是没有理解推测题的核心。推测不会选择文中细节，一定是具有概括意义的选项，然后发现有一些选项文中没有提及可以排除，而且残证据这个说法也非常的准确，因为原文基本都是猜测的语气，比如使用perhaps。

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AEE

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EAC