GMAT阅读文章“古今食肉兽牙齿破碎率”深度分析

蘧凤东

　　阅读建议：
　　1） 北京新东方建议读者先按自己的节奏阅读文章并做完题目，再看文章分析及题目讲解。
　　文章及题目：
　　A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36，000 to 10，000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.
　　In considering possible explanations for this finding， the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores-in particular， more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low， at least seasonally， or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.
　　1. The primary purpose of the passage is to
　　(A) present several explanations for a well-known fact
　　(B) suggest alternative methods for resolving a debate
　　(C) argue in favor of a controversial theory
　　(D) question the methodology used in a study
　　(E) discuss the implications of a research finding
　　2. According to the passage， compared with Pleistocene carnivores in other areas， Pleistocene carnivores in the La Brea area
　　(A) included the same species， in approximately the same proportions
　　(B) had a similar frequency of tooth fractures
　　(C) populated the La Brea area more densely
　　(D) consumed their prey more thoroughly
　　(E) found it harder to obtain sufficient prey
　　3. According to the passage， the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by
　　(A) the aging process in individual carnivores
　　(B) contact between the fossils in the pits
　　(C) poor preservation of the fossils after they were removed from the pits
　　(D) the impact of carnivores' teeth against the bones of their prey
　　(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills
　　4. The researchers' conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that
　　(A) the older an individual carnivore is， the more likely it is to have a large number of tooth fractures
　　(B) the average age at death of a present-day carnivore is greater than was the average age at death of a Pleistocene carnivore
　　(C)in Pleistocene carnivore species， older individuals consumed carcasses as thoroughly as did younger individuals
　　(D) the methods used to determine animals' ages in fossil samples tend to misidentify many older individuals as younger individuals
　　(E) data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores
　　5. According to the passage， if the researchers had NOT found that two extinct carnivore species were free of tooth breakage， the researchers would have concluded that
　　(A) the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits
　　(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits
　　(C) Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcasses
　　(D) all Pleistocene carnivore species differed behaviorally from present-day carnivore species
　　(E) predator densities during the Pleistocene era were extremely high
　　1. 文章初读：（只读各段首句）
　　第一段首句：
　　A recent study has provided clues to predator-prey dynamics in the late Pleistocene era.
　　翻译：一项最近的研究为更新世晚期的捕食者-猎物动力学提供了线索。
　　评：给出了文章的大背景，研究提供了关于P时代晚期捕食者-猎物动力学的线索。所谓捕食者-猎物动力学，是研究捕食者数量和猎物数量的动态联系的，争取用数学模型来描述和解释两者之间的动态关系。
　　第二段首句：
　　In considering possible explanations for this finding， the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples.
　　翻译：在考虑这个发现的可能解释时，研究者对人口统计学错误不予理会，因为在化石样本中，（使用的）更老的个体（样本）并未超过适当比例。
　　评：关键词possible explanations for this finding，点出了本段的的作用是探讨对上段提到的发现的各种可能的解释。基本可以判断为解释型文章。
　　2. 文章精读（精读各句，把握逻辑关系）
　　第一段：（标记重要逻辑关系词及态度评价词）
　　A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36，000 to 10，000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.
　　In considering possible explanations for this finding， the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores-in particular， more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low， at least seasonally， or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.
　　翻译：
　　一项最近的研究为更新世晚期的捕食者-猎物动力学提供了线索。研究者对比了现存肉食动物同生活在36，000至10，000年前的肉食动物以及保存在洛杉矶Rancho La Brea天然沥青坑的肉食动物的牙齿断裂的数量。与现存物种相比，已灭绝物种的破损频率明显更高。
　　在考虑这个发现的可能解释时，研究者对人口统计学错误不予理会，因为在化石样本中，（使用的）更老的个体（样本）并未超过适当比例。他们不同意保存错误，因为两个完全没有牙齿破裂的物种证明了断裂不是由坑内磨损引起。他们也排除了地域错误因为从其他更新世地区采集到的牙齿破损数据同La Brea的数据类似。研究者认为最可能的解释是已灭绝肉食动物和现存肉食动物间的行为差异--特别是因为已灭绝物种咀嚼动物残骸更加彻底，那时的捕食者牙齿与猎物骨骼有更多的接触。这种对动物残骸的彻底咀嚼向研究者暗示：或者（当时）缺乏猎物，至少是季节性缺乏，或者因为捕食者密度相对较高捕食竞争很激烈，而且动物残骸失窃率也很高。
　　重要阅读技巧：
　　要快速把握本文，最关键的一个技巧是在读第二段前半段，即关于三种不靠谱的解释的时候，要学会略读和跳读。第二段开头几句话呈现出明显的排比结构，以三组“负评价动词+because”组成：“dismissed…because…； rejected…because…； ruled out…because…”。第一次阅读文章读到此处时，应选择跳读，只看科学家们排除什么解释（即三个bias），而不细看because后面的内容。迅速找到接下来说的most plausible的解释，再详读。当题目考到三种不靠谱解释内部的逻辑关系时，才回头细看because分句解题。此技巧归结为一句话，即：连续出现的并列或排比结的细节内容可跳读。
　　读完文章后，可做如下笔记，整理各句大意及句间关系：
　　Recent study：
　　Tooth fracture： present < RLB
　　Explanations：
　　demog. bias Ө
　　preserv. bias Ө
　　local. bias Ө
　　behavioral diff. ⊕
　　“ low prey / intense competition
　　3. 做题：　1. The primary purpose of the passage is to
　　(A) present several explanations for a well-known fact
　　(B) suggest alternative methods for resolving a debate
　　(C) argue in favor of a controversial theory
　　(D) question the methodology used in a study
　　(E) discuss the implications of a research finding
　　评：　1)主旨题：正确答案为(E)。本文属于解释型文章，全文态度应为正态度或无态度，因此应排除负态度选项。
　　2)错项分析：
　　(A)： 无中生有：文中并没有提到这是个well-known fact
　　(C)： 无中生有：文中并没有resolve a debate。
　　(D)： controversial是负评价词，选项属于负评价选项，应排除。
　　(E)：question作动词意为质疑，是负评价词，选项属于负评价选项，应排除。
　　2. According to the passage， compared with Pleistocene carnivores in other areas， Pleistocene carnivores in the La Brea area
　　(A) included the same species， in approximately the same proportions
　　(B) had a similar frequency of tooth fractures？

(c) Populated the La Brea area more densely
　　(D) consumed their prey more thoroughly
　　(E) found it harder to obtain sufficient prey
　　评：　1)直接细节题：正确答案为(B)。题干中出现compared with…， P carnivores in LB area…，问的是比较关系，比较主体是P carnivores in LB area，参照对象是P carnivores in other areas。定位至文中15行说local bias处，找到”similar“，即可选到同义转述的正确答案(B)。
　　2)错项分析：
　　(A)： 无中生有：文中并没有提到species 内的proportions。

　　(C)：
无中生有：文中并没有比较谁比谁更dense，属于无关比较。
　　(D)：
混淆文意：此选项是古今肉食动物的对比，而不是题目所问的不同地区的古代肉食动物之间的对比。这是经典错项！
　　(E)：
无中生有：文中没有指明谁更难获得足够食物。
　　3. According to the passage， the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by
　　(A) the aging process in individual carnivores
　　(B) contact between the fossils in the pits
　　(C) poor preservation of the fossils after they were removed from the pits
　　(D) the impact of carnivores' teeth against the bones of their prey
　　(E) the impact of carnivores' teeth against the bones of other carnivores during fights over kills
　　评：
　　1)直接细节题：正确答案为(D)。题目问造成LB地区的古代肉食动物的高发破齿率的真正原因是什么，而全文正是都在探讨这个问题，排除了三种错误的解释，给出了靠谱的解释。因此应直接定位到第二段后半段说most plausible explanation处，选上原句的同义转述项即为正确答案(D)。做此题，是属于带着正确答案去选择，因此没必要纠结排除错误选项怎么错，而应该迅速找到正确选项，选择即可。
　　4. The researchers' conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that
　　(A) the older an individual carnivore is， the more likely it is to have a large number of tooth fractures
　　(B) the average age at death of a present-day carnivore is greater than was the average age at death of a Pleistocene carnivore
　　(C)in Pleistocene carnivore species， older individuals consumed carcasses as thoroughly as did younger individuals
　　(D) the methods used to determine animals' ages in fossil samples tend to misidentify many older individuals as younger individuals
　　(E) data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores
　　评：　1)逻辑削弱题：正确答案为(D)。做逻辑削弱题的三个步骤：i) 回文中定位处，找因果关系；ii) 找原因反方向；iii) 原因反方向即为正确选项。注意，做逻辑削弱题，没必要挨个分析错误选项，只需迅速找到正确答案即可。好，以此题为例，按照解题三板斧，一步一步来选出正确选项。
　　首先，根据题干中”demographic bias“，定位至第二段开头处的demographic bias。找到因果关系词because。
　　然后，找寻因果反方向。文中说可以排除demographic bias的理由是老年个体没有在化石样本中过多出现。则咱们可以做出简单推理：如果老年个体在样本中过多出现了，则不能排除demographic bias。
　　最后，选到正确答案，应提到老年样本过多出现、(D)选项说把老年样本当作年轻样本算进去统计中了，也就是说老年样本过多出现。
　　5. According to the passage， if the researchers had NOT found that two extinct carnivore species were free of tooth breakage， the researchers would have concluded that
　　(A) the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits
　　(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits
　　(C) Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcasses
　　(D) all Pleistocene carnivore species differed behaviorally from present-day carnivore species
　　(E) predator densities during the Pleistocene era were extremely high