托福閱讀真題Official 54 Passage 2（四）

托福閱讀真題Official 54 Passage 2（四）

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 7 of 14

Which of the following best describes the results of the research discussed in paragraph 4?

A.Scientists used mathematical models to show that most of the extinctions occurred in areas where humans had recently arrived.

B.Scientists established that the main population of North Americans who hunted lived in Canada during the time of the megafauna extinctions.

C.Scientists used numerical models to confirm that a small population of humans could have caused big-game extinctions in a relatively short period of time.

D.Scientists used statistics to prove beyond doubt the currently accepted view that human hunters were the main cause of the megafauna extinctions.

正確答案：C

題目詳解

題型分類：事實(shí)信息題

原文定位：根據(jù)the results of the research定位到最后一句。

選項(xiàng)分析：

最后一句的結(jié)論是人類最初接觸大型生物到其滅絕是在279年到1157年之間。C選項(xiàng)a small population對(duì)應(yīng)第一句a population of 100 humans，big-game extinctions對(duì)應(yīng)最后一句big-game extinction，a relatively short period of time對(duì)應(yīng)最后一句between 279 and 1,157 years。

A選項(xiàng)，where humans had recently arrived無(wú)中生有，第四段只討論了初始100人的情況。

B選項(xiàng)，the main population…lived in Canada無(wú)中生有。

D選項(xiàng)，the main cause of the megafauna extinctions過(guò)于極端，只討論了人類會(huì)導(dǎo)致滅絕，但沒(méi)有說(shuō)人類是主要原因。

Question 8 of 14

Which of the following statements about Larry Agenbroad’s work is implied in the discussion in paragraph 5?

A.Agenbroad showed that Mosimann and Martin’s estimates of the amount of time needed to drive big-game to extinction were correct.

B.Agenbroad’s maps were the first to indicate the ages of the Clovis sites.

C.Agenbroad reinforced the idea that humans could have caused the extinctions.

D.Agenbroad’s studies of wooly mammoths led to his discovery of Clovis sites.

正確答案：C

題目詳解

題型分類：推論題

原文定位：根據(jù)Larry Agenbroad定位到第二句。

選項(xiàng)分析：

定位句是一個(gè)例子：“LA繪制了不同時(shí)期克洛維斯遺址的位置，以及不同時(shí)期猛犸象遺體的分布。這些分布顯示出明顯的同步性”。例子一般用于前文觀點(diǎn)的解釋，而C選項(xiàng)reinforced the idea對(duì)應(yīng)第一句continue to support，the idea that humans could have caused the extinctions對(duì)應(yīng)第一句the idea that humans could have caused the extinctions。

A選項(xiàng)，the amount of time無(wú)中生有，第五段沒(méi)有提279到1157年。

B選項(xiàng)，the first to過(guò)于極端，文中沒(méi)有提示是第一個(gè)。

D選項(xiàng)，led to“導(dǎo)致”，邏輯關(guān)系錯(cuò)誤，兩者沒(méi)有因果關(guān)系。

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