托福考试阅读加试之达尔文进化论(原文).pdf

托福考试阅读加试之达尔文进化论 原文 Observing Natural Selection Witnessing natural selection would not have seemed possible to Darwin because he assumed natural selection was too slow and gradual for our short term minds to perceive Yet later biologists have been able to witness flashes of evolutionary change In the late 1980s for example biologist David Reznick began to use the guppies that swim in the streams of Trinidad forests in natural experiment At lower elevations these guppies face the assault of predatory fishes but the ones in higher waters live in peace because few of the predators can move upstream past the waterfalls and craggy rocks Like all animals guppies have a timetable for their lives how long they take to reach sexual maturity how fast they grow during that time how long they live as adults Theoretical biologists have predicted that the life history of animals can evolve if mutations that alter it bring the animals more reproductive success Reznick put their predictions to the test In ponds with a lot of predators guppies that grow fast should be more successful than slow growing ones With the threat of death hanging over a guppy it will grow as quickly as possible so that it can start mating as soon as possible and have as many offspring as possible Of course the strategy comes with a heavy price By growing so quickly a guppy may shorten its own natural life span and by quickly giving birth to babies female guppy cannot take time to support her offspring with energy which put them at risk of dying young But Reznick reasoned that the threat of an early death offset by other risk To see whether this trade off was real Reznick relocated guppies that were being terrorized in the downstream by putting them in pools with relatively few predators Eleven years in these conditions produced guppies that were on average in less of a rush They took 10 percent longer to mature than their ancestors and were over 10 percent heavier by the time they were fully grown They were also laying smaller broods of eggs but each of the new guppies that hatched from those was bigger nSometimes nature runs evolutionary experiments of its own without any help from humans whatsoever nIn 1973 Peter and Rosemary Grant husband and wife biologists arrived on the Galapagos Islands to study the effects of natural selection on the birds Most years on the Galapagos the weather follows a standard pattern nFor the first five months of the years it is hot and rainy followed by a cool dry period nBut in 1977 the wet season never came A periodic disturbance of the Pacific ocean called La Nina altered weather patterns over the Galapagos causing a disastrous drought On Daphne Island where the Grants worked the drought was lethal Out of the 1 200 medium ground finches Geospiza fortis that lived on the Island more that 1 000 died But the Grants discovered that the decimation was not random G fortis lives mainly on seeds which it cracks with its strong beak Small G fontis can break only small seeds but larger birds have beaks that are strong enough to break big ones The drought had lingered for a few months the small finches ran out of small seeds and began dying off But the big finches managed to survive because they could eat seeds that the smaller ones couldn t get to In particular they depended on a plant called caltrop which grows spiked shells to protect it seeds The survivors on the 1977 drought mated in 1978 and the Grants could see evolution s mark on their offspring A new generation of G fortis was born and the Grants student Peter Boag discovered that on average their beaks were 4 percent larger than those of the previous generation The big beaked finches which had fared better during the drought had put their trait to their offspring altered the profile of the population In the years since the drought the finches changed In 1983 for example there was a season of heavy rain abundant seeds favored finches with smaller beaks and Grants found that by 1985 their average size had dropper 5 percent The finches can change quickly but it seems that are swinging back and forth like a pendulum 中文大意 关于natural selection Darwin认为是长期且渐进的 后来 科学家却在短时间内目击witness 词汇题 到进化 接着用两个relatively short evolution s examples 来support natural selection 1st 人为控制条件 有一种鱼guppy 在predator多的时候 长得快 但代价是life span变短 不过研究人员认为 这代价被其他危险抵销offset 词汇题 了 然后 再将一部分放入predator少的pool中 offspring发生了很多changes 比如比它们的ance stor size上要大 下egg少了 等等 2ed 自然条件变化 我们需要做的只是observe 讲的是finch 有关它们beak的大小的 又举了一个bird的例子 一对夫妇学者在一个群鸟研究一种雀鸟 有一年岛上发生致命的lethal 词 汇题 干旱 他们发现 当干旱 drought 时 鸟的大量死亡decimation 词汇题 并不是随机的 那 些有大而硬的beak的bird往往能生存下来 这样一来这一地区的这种bird很快都有了大而硬的bea k 干旱的时候小种子少 嘴小的鸟死了 嘴长的鸟存活 存活的鸟和第二年的鸟交配 后代的鸟 嘴整体变长 雨量又充足的时候 又足够小种子 这个时候 新出生的鸟的鸟嘴又变短了 考题 1 According to paragraph 1 compared to the views of modern biologists Darwin s view of natural selection was limited by his belief that 答案 A natural selection only occurred over a very long period of time IS natural selection could only be witnessed in some species 2 The word witness in the passage is closest in meaning to 答案 A observe 3 The word offset in the passage in meaning to 答案 D balanced 4 Which of the following reason is mentioned in paragraph 3 to explain why growing fast is an advantage for guppies that live in ponds with many predators 答案 A They will product more offspring 5 What is the author s primary in presenting the information in paragraph 3 答案 C To explain Reznick s reasoning about why it would be an advantage for guppies with predators to mature quickly 6 All of the following are mentioned in paragraph 4 as change in the guppy population eleven years after guppies were transferred to upstream ponds EXCEPT 答案 B More offspring were produced 7 The word lethal in the passage is closest in meaning to 答案 C deadly 8 The word decimation in the passage is closest in meaning to 答案 A destruction 9 According to paragraph 6 what disadvantage did small beaked finches have compared to large beaked fiches 答案 A Small beaked finches were not able to crack open the large seeds 10 According to paragraph 7 the new generation of G fortis on average differed from earlier population in 答案 B the size of their beaks 11 According to paragraph 8 how short term changes to the environment affect the r natural election of traits in G fortis 答案 A Short term changes result in quick reversals of the trait selected 12 How were the results of the natural experiment with the finches similar