《托福考试阅读加试之达尔文进化论(原文)》由会员分享，可在线阅读，更多相关《托福考试阅读加试之达尔文进化论(原文)（6页珍藏版）》请在金锄头文库上搜索。
1、 http:/托福考试阅读加试之达尔文进化论（原文）Observing Natural SelectionWitnessing 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
2、. 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
3、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 ev
4、olve 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
5、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
6、 offspring with energy, which put them at risk of dying young. But Reznick reasoned, that the threat ,of an early death offset http:/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 f
7、ew 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 g
8、uppies 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
9、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,
10、 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
11、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 t
12、hey could eat seeds that the smaller ones couldnt http:/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 evolutions mark on their offspring. A new generation of G.
13、 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
14、 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
15、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 evolutions 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
16、，比如比它们的ance http:/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beak。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，
