托福閱讀真題Official 54 Passage 2（三）

托福閱讀真題Official 54 Passage 2（三）

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 5 of 14

According to paragraph 2,what suggests that human activity played a role in the extinction of mammals about 11,000 years ago?

A.Climate changes that would have favored human population expansion occurred at the time of the extinctions.

B.The presence of human hunters had caused animal extinctions in other time periods.

C.There was a pattern of climate change earlier than 11,000 years ago that had not caused animal extinctions.

D.Harmful climate changes 11,000 years ago would have required humans to hunt larger numbers of animals for food.

正確答案：C

題目詳解

題型分類：事實信息題

原文定位：根據(jù)11,000定位到第二句和第三句。

選項分析：

原句為“盡管發(fā)生了這些變化，但像11,000年前那樣的大型哺乳動物的大規(guī)模滅絕在之前的400,000年里并沒有發(fā)生過。唯一重大的區(qū)別就是這些大型哺乳動物的人類捕食者在11,000前的美洲出現(xiàn)”，這兩句都為第一句主題句的解釋，證明氣候變化沒有影響動物滅絕。C選項a pattern of climate change對應(yīng)第一句warming trends had happened before，C選項not caused animal extinctions對應(yīng)第二句massive extinction of large mammals…not occurred。

A選項，human population expansion無中生有。

B選項，other time periods無中生有，第二段只說了11,000年前，一個人類存在的時間。

D選項，required humans to hunt無中生有。

Question 6 of 14

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.

A.A computer model was designed to determine how long it would have taken for a small group of hunters to spread across North America.

B.A computer model showed that it was possible for a small group of hunters to spread across North America and kill off game animals in just 300 years.

C.According to a computer model,people coming into North America 12,000 years ago had to kill game animals in order to feed their population.

D.According to a computer model,about 12,000 years ago conditions enabled a small group of hunters to enter and cross North America in about 300 years.

正確答案：B

題目詳解

題型分類：簡化句子題

原文分析：簡化題考察找主干和邏輯的能力，原文為“與研究員合作的電腦模型顯示，在大約300年的時間內(nèi)，在合適的條件下，12000年前一小群獵人流入東部波尼吉亞就可能席卷北美并消滅動物來喂養(yǎng)迅速增長的人口”。本句的重要信息在后半部分模型顯示了什么。

選項分析：

B選項a small group of hunters對應(yīng)原句a small influx of hunters；wiped out對應(yīng)原句kill off，“計算機模型顯示，一小群獵人可能在僅僅300年的時間里，分散在北美地區(qū)并消滅動物”。與原句重要意思相符。

A選項，determine how long無中生有，模型只演示了一個時間。

C選項，had to kill game animals不是本句重點，原句用的是wiped out game animals來顯示使動物很快滅絕。并且缺乏句子主干信息spread across North America。

D選項，缺少句子主干信息wiped out game animals。

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