Biologist Ernst Mayr defined aspeciesas “an actually or potentially interbreedingpopulationthat does not interbreed with other such populations when there isopportunityto do so.” Akeyevent in theoriginof manyspeciesis the separation of apopulationwith itsgenepool (all of the genes in apopulationat any one time) from other populations of the samespecies,therebypreventingpopulationinterbreeding. With itsgenepoolisolated, aseparatepopulationcan follow its ownevolutionarycourse. In theformationof manyspecies, theinitialisolation of apopulationseems to have been a geographicbarrier. Thismodeof evolving newspeciesis called allopatricspeciation.

Many factors canisolateapopulationgeographically. A mountain range mayemergeandgraduallysplitapopulationof organisms that caninhabitonlylowlandlakes, certain fish populations might becomeisolatedin this way. Similarly, a creepingglaciermaygraduallydivide apopulation, or a land bridge such as the Isthmus of Panama may form andseparatethemarinelife in the ocean waters on either side.

Howformidablemust a geographicbarrierbe to keep populations apart? It depends on theabilityof the organisms to moveacrossbarriers. Birds and coyotes can easily cross mountains and rivers. Thepassageof wind-blown treepollenis also not hindered by such barriers, and the seeds of many plants may be carried back and forth on animals. Incontrast, small rodents may find a deepcanyonor a wide river aneffectivebarrier. For example, the GrandCanyon, in the southwestern United States,separatethe range of the white-tailedantelopesquirrelfrom that of the closely related Harris’antelopesquirrel. Smaller, with a shorter tail that is whiteunderneath, the white-tailedantelopesquirrelinhabits deserts north of thecanyonand west of the Colorado River in southern California. Harris'antelopesquirrelhas a more limited range in deserts south of the GrandCanyon.

Geographic isolation creates opportunities for newspeciesto develop, but it does not necessarilyleadto newspeciesbecausespeciationoccurs only when thegenepool undergoes enough changes toestablishreproductivebarriers between theisolatedpopulationand its parentpopulation. The likelihood of allopatricspeciationincreases when apopulationis small as well asisolated, making it more likely than a largepopulationto have itsgenepool changedsubstantially. For example, in less than two million years, small populations of stray animals and plants from the South American mainland that managed tocolonizethe Galapagos Islands gave rise to all thespeciesthat nowinhabitthe islands.

Whenoceanicislands are far enough apart topermitpopulations toevolvein isolation, but close enough to allowoccasionaldispersions tooccur, they are effectively outdoor laboratories ofevolution. The Galapagos islandchainis one of the world's greatest showcases ofevolution. Each island was born from underwater volcanoes and wasgraduallycovered by organisms derived from strays that rode the ocean currents and winds from other islands and continents. Organisms can also be carried to islands by other organisms, such as sea birds that travel long distances with seeds clinging to their feathers.

Thespecieson the Galapagos Islands today, most of whichoccurnowhere else, descended from organisms that floated, flew, or were blown over the sea from the South American mainland. Forinstance, the Galapagos islandchainhas a total of thirteenspeciesof closely related birds called Galapagos finches. These birds have many similarities but differ in their feeding habits and theirbeaktype, which is correlated with what they eat. Accumulatedevidenceindicates that all thirteenfinchspeciesevolved from a single smallpopulationof ancestral birds that colonized one of the islands. Completelyisolatedon the island after migrating from the mainland, the founderpopulationmay have undergonesignificantchanges in itsgenepool and become a newspecies. Later, a few individuals of this newspeciesmay have been blown by storms to a neighboring island. Isolatedon this second island, the second founderpopulationcould have evolved into a second newspecies, which could later recolonize the island from which itsfoundingpopulationemigrated. Today each Galapagos island hasmultiplespeciesof finches, with as many as ten on some islands.

Questions:
question_stem: The word “key” in the passage is closest in meaning to
choices: tag: A
text: early

tag: B
text: crucial

tag: C
text: noticeable

tag: D
text: frequent
answer_key: B
explanation: 【题目翻译】段落中的“key”一词最接近于下列哪个选项？
A：早期的
B：关键的
C：显而易见的
D：频繁的

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“key”,定位到原句“A key event in the origin of many species is the separation of a population with its gene pool (all of the genes in a population at any one time) from other populations of the same species, thereby preventing population interbreeding.”。

【词汇解析】词汇“key”的意思是“关键的”,带入到原句中，原句的意思是“许多物种起源时的一个关键事件是有着自己的基因库的种群（任何时候这个种群的所有基因）与该物种其他种群分离，因此阻止了种群间交配。”

【选项分析】
A：早期的。不符，错误
B：关键的。同义替换，正确
C：显而易见的。不符，错误
D：频繁的。不符，错误

question_stem: The word “initial” in the passage is closest in meaning to
choices: tag: A
text: best

tag: B
text: usual

tag: C
text: first

tag: D
text: actual
answer_key: C
explanation: 【题目翻译】段落中的“initial”一词最接近于下列哪个选项？
A：最好的
B：通常的
C：第一
D：真正的

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“initial”,定位到原句“In the formation of many species, the initial isolation of a population seems to have been a geographic barrier. ”。

【词汇解析】词汇“initial”的意思是“最初的”,带入到原句中，原句的意思是“在许多物种的形成过程中，最初的种群隔离似乎来自一种地理上的屏障。”

【选项分析】
A：最好的。不符，错误
B：通常的。不符，错误
C：第一。同义替换，正确
D：真正的。不符，错误

question_stem: According to paragraph 1, allopatric speciation is possible when
choices: tag: A
text: a population contains all the different genes present in a species at a particular time

tag: B
text: a population becomes isolated due to the presence of a geographic barrier

tag: C
text: genetic mixing begins to occur in previously separate populations of a species

tag: D
text: a species is successful in crossing a geographic barrier
answer_key: B
explanation: 【题目翻译】根据第1段，当什么时候异域物种变得可能？
A：一个种群包含一个物种在特定时间存在的所有不同基因。
B：由于地理屏障的存在，种群变得孤立。
C：一个物种先前分离的种群开始发生遗传混合。
D：一个物种成功地穿越了地理屏障。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据 allopatric speciation 定位至原文 the initial isolation of a population seems to have been a geographic barrier. This mode of evolving new species is called allopatric speciation.意思是“最初的种群隔离似乎是一个地理障碍。这种新物种进化模式被称为异域物种形成”。

【逻辑分析】说明种群的隔离和地理障碍有关。

【选项分析】
A.文章未提到，故错误。
B.文章中 have been a geographic barrier 对应 B 选项中的 the presence of a geographic barrier. 所以 B 选项正确。
C.文章中提到基因分离后，未提到到基因混合，故错误。
D.文章第一段未提及，故错误。

question_stem: How is paragraph 2 related to paragraph 1?
choices: tag: A
text: Paragraph 2 points out a number of ways in which the phenomenon of geographic isolation mentioned in paragraph 1 can occur

tag: B
text: Paragraph 2 identifies discoveries that led to the conclusion presented in paragraph 1 that geographic isolation has played a role in the origin of many species

tag: C
text: Paragraph 2 provides evidence supporting the statement in paragraph 1 that a population can follow its own evolutionary course once its gene pool becomes isolated

tag: D
text: Paragraph 2 explains why the term “allopatric” was adopted to describe the method of speciation described in paragraph 1
answer_key: A
explanation: 【题目翻译】第2段与第1段有何关联？
A：第2段指出了第1段中提到的地理隔离现象的几种发生方式
B：第2段确定了导致第1段所述结论的发现，即地理隔离在许多物种的起源中发挥了作用。
C：第2段提供了证据支持第1段中的说法，即一旦一个种群的基因库被分离，它就可以遵循自己的进化过程。
D：第2段解释了为什么采用“异域的”这个术语来描述第1段中描述的物种形成方法。

【判定题型】：根据题目问法，题目询问 xxx 组成或构成方式/段落与段落的关系/某一段在全文中所起的作用，故判断本题为组织结构题。

【内容分析】根据第二段第一句话 Many factors can isolate a population geographically.可知接下来的整段内容都将围绕能引起异域种化的因素或途径。而后列举的 mountain range, creeping glacier, land bridge 都是进一步的对其进行解释说明。

【选项分析】
A.与文章内容相符，故正确。
B.第二段并未确定第一段观点。因为第二段开头还说“有许多因素”。故错误。
C.文章未提到“它就可以遵循自己的进化过程”。故错误。
D.文章未解释，故错误。

question_stem: In paragraph 3, the author contrasts a variety of organisms to illustrate which of the following points?
choices: tag: A
text: Geographic barriers are less likely to keep apart populations of plants than populations of animals.

tag: B
text: Geographic barriers are more likely to keep apart populations of large organisms than populations of small organisms

tag: C
text: Some members of a species are able to cross geographic barriers, while other members of the same species are not.

tag: D
text: The effectiveness of geographic barriers in keeping organisms apart depends on an organism’s ability to move across barriers.
answer_key: D
explanation: 【题目翻译】在第3段中，作者对比了各种有机体，以说明以下哪一点？
A：与动物种群相比，地理屏障不太可能将植物种群隔离开来。

B：地理屏障比小生物更容易使大生物种群分开。

C：一个物种的某些成员能够跨越地理屏障，而同一物种的其他成员则不能。

D：地理屏障保持生物体分离的有效性取决于生物体跨越屏障的能力。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据 organisms 定位至原文 How formidable must a geographic barrier be to keep populations apart? It depends on the ability of the organisms to move across barriers.意思是“一个地理屏障必须有多强大才能使种群分开？这取决于生物体跨越屏障的能力。”。

【逻辑分析】说明了一个物种会不会产生隔离与其自身跨越屏障能力有关。

【选项分析】
A.第三段未把动植物作比较。故错误。
B.第三段未把小大生物种作比较。故错误。
C.未提及同一物种中的成员，故错误。
D.与文章相符，正确。文章中 How formidable must a geographic barrier be to keep populations apart 对应 D 选项中的 The effectiveness of geographic barriers in keeping organisms apart. 所以 D 选项正确。

question_stem: Paragraph 3 supports the idea that white-tailed antelope squirrels and Harris' antelope squirrels have which of the following in common?
choices: tag: A
text: They are the two smallest rodents now found in the southwestern United States.

tag: B
text: They have white coloring underneath their tails

tag: C
text: They cannot cross the Grand Canyon

tag: D
text: They cannot survive in desert conditions
answer_key: C
explanation: 【题目翻译】第3段支持白尾羚羊松鼠和哈里斯羚羊松鼠有以下哪一个共同点？
A：它们是目前在美国西南部发现的两种最小的啮齿动物。

B：它们的尾巴下面有白色。

C：它们不能穿过大峡谷

D：它们不能在沙漠中生存。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据 white-tailed antelope squirrels 定位至原文 For example, the Grand Canyon, in the southwestern United States, separate the range of the white-tailed antelope squirrel from that of the closely related Harris’ antelope squirrel.意思是“例如，美国西南部的大峡谷，将白尾羚羊松鼠的范围与密切相关的哈里斯羚羊松鼠的范围分开”。

【逻辑分析】可知，科罗拉多大峡谷将白尾巴羚羊松鼠和哈里斯羚羊松鼠隔绝开了

【选项分析】
A.文章里未说是“最小的啮齿动物”，故错误。
B.文章只说白尾羚羊松鼠尾巴很短且下面是白色的，故错误。
C.符合文章，这两种羚羊松鼠的共同特点就是无法跨越科罗拉多大峡谷。正确。
D.哈里斯羚羊松鼠的生活范围更为有限，位于大峡谷以南的沙漠地区。所以这种动物是可以在沙漠生活的。故错误。

question_stem: The word “undergoes” in the passage is closest in meaning to
choices: tag: A
text: experiences

tag: B
text: allows

tag: C
text: prevents

tag: D
text: causes
answer_key: A
explanation: 【题目翻译】段落中的“undergoes”一词最接近于
A：经历
B：允许
C：阻止
D：导致

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“undergoes”,定位到原句“Geographic isolation creates opportunities for new species to develop, but it does not necessarily lead to new species because speciation occurs only when the gene pool undergoes enough changes to establish reproductive barriers between the isolated population and its parent population. ”。

【词汇解析】词汇“undergoes”的意思是“ 经历，忍受”,带入到原句中，原句的意思是“地理隔离为新物种的进化创造了机会，但这并不一定会形成新物种，因为物种形成只有在基因库发生足够大的变化，被隔离的种群与亲本种群之间出现繁殖障碍（即不能交配繁殖）时才发生。”

【选项分析】
A：经历。同义替换，正确
B：允许。不符，错误
C：阻止。不符，错误
D：导致。不符，错误

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information
choices: tag: A
text: Geographic isolation is sometimes but not always the reason for the creation of reproductive barriers between a parent population and the populations descended from it

tag: B
text: Genetic changes in a geographical isolated population do not necessarily make the population look different enough from its parent population to be considered a new species

tag: C
text: Geographical isolation allows the separated populations to evolve independently of each other and so can lead to the formation of new species

tag: D
text: Geographic isolation can lead to new species only if the gene pool of the isolated population changes enough to prevent it from reproducing with the parent population
answer_key: D
explanation: 【题目翻译】下面哪句话最能表达文章中突出显示的句子中的基本信息？错误的选择会以重要的方式改变意义，或遗漏重要信息。
A：地理隔离有时但不总是造成亲本种群和其后代种群之间生殖障碍的原因。

B：地理隔离种群的遗传变化不一定使种群看起来与其亲本种群有足够的差异，因而被认为是一个新物种。

C：地理隔离使分离的种群彼此独立进化，从而形成新的物种。

D：只有当隔离种群的基因库发生足够的变化，阻止其与亲本种群繁殖时，地理隔离才能产生新的物种。

【判定题型】：根据题目问法，题目要求选择和高亮句意思逻辑都最为接近的句子，故判断本题为句子简化题。

【句子分析】注意句子中的转折和因果关系，句子主干出现在转折后面，且要注意 only 后面的内容。句子大意为，只有当物种被隔绝的基因库改变的足够多来防止它们和亲本种群繁殖时，地理隔绝就会产生新的物种。

【选项分析】
A.原句未把地理隔离作为后代种群之间生殖障碍的原因。故错误。
B.原句未提到和其亲本种群有足够的差异，故错误。
C.原句未提到独立进化。故错误。
D.符合句子意思，正确。

question_stem: According to paragraph 4, why does the size of a population affect the likelihood of allopatric speciation?
choices: tag: A
text: Because smaller populations are more likely than larger ones to become geographically isolated

tag: B
text: Because the gene pool of a small isolated population is more likely to undergo substantial change than is the gene pool of a larger population

tag: C
text: Because a small isolated population can become a new species with substantially less change to its gene pool than would be required by a larger population

tag: D
text: Because smaller populations are more likely to be made up of stray animals or plants than larger populations are
answer_key: B
explanation: 【题目翻译】段落中的“undergoes”一词最接近于以下哪个选项？
A：经历
B：允许
C：阻止
D：导致
[判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“undergoes”,定位到原句“Geographic isolation creates opportunities for new species to develop, but it does not necessarily lead to new species because speciation occurs only when the gene pool undergoes enough changes to establish reproductive barriers between the isolated population and its parent population. ”。

【词汇解析】词汇“undergoes”的意思是“ 经历，忍受”,带入到原句中，原句的意思是“地理隔离为新物种的进化创造了机会，但这并不一定会形成新物种，因为物种形成只有在基因库发生足够大的变化，被隔离的种群与亲本种群之间出现繁殖障碍（即不能交配繁殖）时才发生。”

【选项分析】
A：经历。同义替换，正确
B：允许。不符，错误
C：阻止。不符，错误
D：导致。不符，错误

question_stem: The word “managed” in the passage is closest in meaning to
choices: tag: A
text: were able

tag: B
text: were forced

tag: C
text: arrived

tag: D
text: expanded
answer_key: A
explanation: 【题目翻译】文章中的“managed”一词最接近于下列哪个选项？
A：能够

B：被迫

C：到达

D：扩大

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“managed”,定位到原句“For example, in less than two million years, small populations of stray animals and plants from the South American mainland that managed to colonize the Galapagos Islands gave rise to all the species that now inhabit the islands.”。

【词汇解析】：词汇“managed”的意思是“设法完成”,带入到原句中，原句的意思是“例如，从南美大陆流浪而来，成功移居到加拉帕戈斯群岛的动物和植物小种群，在不到二百万年的时间就进化出了现在岛上存在的所有物种”。

【选项分析】
A：能够。同义替换，正确

B：被迫。不符，错误

C：到达。不符，错误

D：扩大。不符，错误

question_stem: Paragraph 5 supports the idea that the Galapagos island chain was able to become "one of the world's greatest showcases of evolution" primarily because of
choices: tag: A
text: the richness of the volcanic soil of each of the islands in the chain

tag: B
text: the distance of the individual islands from each other and from the mainland

tag: C
text: the relativity long time it took for the islands to become covered by organisms

tag: D
text: the outdoor laboratories that scientists have built on the islands to study evolution
answer_key: B
explanation: 【题目翻译】第5段支持加拉帕戈斯岛链之所以能够成为“世界上最伟大的进化展示之一”的观点，主要是因为
A：链中每个岛屿的火山土壤丰富
B：各岛屿之间和大陆之间的距离
C：相对论使岛屿被生物所覆盖的时间很长
D：科学家在岛上建立的研究进化的户外实验室

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据“one of the world's greatest showcases of evolution”定位至原文前一句话 When oceanic islands are far enough apart to permit populations to evolve in isolation, but close enough to allow occasional dispersions to occur, they are effectively outdoor laboratories of evolution.意思是“当海洋岛屿相距足够远，允许种群单独进化，但距离足够近，允许偶尔发生分散时，它们实际上是室外进化实验室”。

【逻辑分析】岛屿之间的距离和陆地的距离最完美的诠释了进化。

【选项分析】
A.火山土壤丰富不是主要原因。故错误
B.符合原文，正确。
C.覆盖的时间不是主要原因。故错误
D.最伟大的进化展示与科学家的实验室无关。故错误

question_stem: According to paragraph 6, what is true about the thirteen species of Galapagos finches?
choices: tag: A
text: All thirteen species are now found on most of the Galapagos Islands

tag: B
text: All thirteen species are descended from the same population of ancestral birds

tag: C
text: All thirteen species evolved on the island that was originally colonized by finches from the mainland.

tag: D
text: All thirteen species occur only in small, completely isolated populations.
answer_key: B
explanation: 【题目翻译】根据第6段，关于加拉帕戈斯雀的13个物种正确的是哪项？
A：目前在加拉帕戈斯群岛的大部分地区都发现了13种物种。

B：这13种鸟类都是同一个族群的祖先。

C：这13个物种都是在岛上进化而来的，岛上最初是由大陆的雀鸟聚居的。

D：这13个物种都只在小的完全隔离的种群中出现。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据 thirteen species 定位至原文 Accumulated evidence indicates that all thirteen finch species evolved from a single small population of ancestral birds that colonized one of the islands.意思是“积累的证据表明，所有13种雀鸟都是由一小部分祖先鸟类进化而来，这些祖先鸟类曾栖息在其中一个岛屿上。”。

【逻辑分析】：结合题目问法和出题句，进行逻辑分析。

【选项分析】
A.并不是每个岛都发现了13种，文章只说“有些岛上达到了10种”。故错误。
B.与原文相符，正确。
C.文章未提及这13个物种是否都是在岛上进化而来。故错误。
D.并不是 only in small。故错误。