托福阅读真题Official 54 Passage 2（二）

托福阅读真题Official 54 Passage 2（二）

Overkill of the North American Megafauna

Thousands of years ago,in North America’s past,all of its megafauna—large mammals such as mammoths and giant bears—disappeared.One proposed explanation for this event is that when the first Americans migrated over from Asia,they hunted the megafauna to extinction.These people,known as the Clovis society after a site where their distinctive spear points were first found,would have been able to use this food source to expand their population and fill the continent rapidly.Yet many scientists argue against this“Pleistocene,the period between about 2.5 million and 11,700 years ago during which humans first appeared on Earth,overkill”hypothesis.Modern humans have certainly been capable of such drastic effects on animals,but could ancient people with little more than stone spears similarly have caused the extinction of numerous species of animals.Thirty-five genera or groups of species(and many individual species)suffered extinction in North America around 11,000 B.C.,soon after the appearance and expansion of Paleo-Indians,a group of hunters active in America during the late Pleistocene,throughout the Americas(27 genera disappeared completely,and another 8 became locally extinct,surviving only outside North America).

Although the climate changed at the end of the Pleistocene,warming trends had happened before.A period of massive extinction of large mammals like that seen about 11,000 years ago had not occurred during the previous 400,000 years,despite these changes.The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals.Was this coincidence or cause-and-effect?

We do not know.Ecologist Paul S.Martin has championed the model that associates the extinction of large mammals at the end of the Pleistocene with human predation.With researcher J.E.Mosimann,he has co-authored a work in which a computer model showed that in around 300 years,given the right conditions,a small influx of hunters into eastern Beringia 12,000 years ago could have spread across North America in a wave and wiped out game animals to feed their burgeoning population.

The researchers ran the model several ways,always beginning with a population of 100 humans in Edmonton,in Alberta,Canada,at 11,500 years ago.Assuming different initial North American big-game-animal populations(75–150 million animals)and different population growth rates for the human settlers(0.65%–3.5%),and varying kill rates,Mosimann and Martin derived figures of between 279 and 1,157 years from initial contact to big-game extinction.

Many scholars continue to support this scenario.For example,geologist Larry Agenbroad has mapped the locations of dated Clovis sites alongside the distribution of dated sites where the remains of wooly mammoths have been found in both archaeological and purely paleontological contexts.These distributions show remarkable synchronicity(occurrence at the same time).

There are,however,many problems with this model.Significantly,though a few sites are quite impressive,there really is very little archaeological evidence to support it.Writing in 1982,Martin himself admitted the paucity of evidence;for example,at that point,the remains of only 38 individual mammoths had been found at Clovis sites.In the years since,few additional mammoths have been added to the list;there are still fewer than 20 Clovis sites where the remains of one or more mammoths have been recovered,a minuscule proportion of the millions that necessarily would have had to have been slaughtered within the overkill scenario.

Though Martin claims the lack of evidence actually supports his model—the evidence is sparse because the spread of humans and the extinction of animals occurred so quickly—this argument seems weak.And how could we ever disprove it.As archaeologist Donald Grayson points out,in other cases where extinction resulted from the quick spread of human hunters—for example,the extinction of the moa,the large flightless bird of New Zealand—archaeological evidence in the form of remains is abundant.Grayson has also shown that the evidence is not so clear that all or even most of the large herbivores in late Pleistocene America became extinct after the appearance of Clovis.Of the 35 extinct genera,only 8 can be confidently assigned an extinction date of between 12,000 and 10,000 years ago.Many of the older genera,Grayson argues,may have succumbed before 12,000 B.C.,at least half a century before the Clovis showed up in the American West.

Question 3 of 14

Why does the author compare Modern humans with ancient people?

A.To argue that modern people have continued to have drastic effects on animal species

B.To illustrate how people from different historical times treated animals differently

C.To question the idea that ancient people could have hunted the megafauna to extinction

D.To emphasize that modern people are more successful hunters than ancient people were

正确答案：C

题目详解

题型分类：修辞目的题

题干分析：考察句子之间的关系；根据Modern humans和ancient people定位到第一段倒数第二句。

选项分析：

定位句说“现代人类当然能够对动物产生如此剧烈的影响，但是仅仅拥有石矛的远古人类是否也同样导致了众多物种的灭绝呢?”这句说提到了古代技术不发达，可能无法造成灭绝，用于支持前一句观点，反对本文第一个观点“最初的美洲人使巨型动物灭绝”。即C选项。

A选项，continued to have drastic effects无中生有。

B选项，treated animals无中生有，前半句只说了能够造成大的影响，但没有说如何对待动物。

D选项，modern people are more successful hunters无中生有，只说了现代人能造成影响，没有说因为他们是成功的猎人而造成影响。

Question 4 of 14

In using the word“coincidence”in the passage,the author refers to events that occurred

A.after a period of many years

B.subsequent to a prediction

C.from time to time

D.at the same time and by chance

正确答案：D

题目详解

题型分类：词汇题

选项分析：

coincidence表明前文提到的事情可能是“巧合，同时存在”，对应D选项。也可以根据coincidence与cause-and-effect意义一定不相同选择，不是“原因和结果”，那就是“by chance：偶然”，对应D选项。

A选项after a period of many years：多年后；

B选项subsequent to a prediction：预测后；

C选项from time to time：不时。

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