Official 54 Passage 3


Overkill of the North American Megafauna


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.

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  • 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.
正确答案: B

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  • 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-Indiansa 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.

  • 数千年前,在过去的北美,所有巨型动物——猛犸象和巨熊这些大型动物——都消失了。对此事件的一个解释是,当第一批美国人从亚洲迁移过来时,他们狩猎巨型动物以至于使其灭绝。这些人,他们使用的独特的矛头在首次被发现后,人们把他们称为克洛维斯族人,这些人能够使用这些食物源来扩展他们的人口,并且很快的充满了整个大陆。然而,许多科学家反对这种“更新世过度捕杀”假说。现代人对动物确实具有如此剧烈的影响,但难道只有石矛等武器的古代人也同样能造成无数种动物的灭绝吗?在公元前11000年前后,北美洲有35个属或种群(以及许多单个物种),在古印第安人在美洲出现和扩张后不久就灭绝了。(27属全部消失,另有8个属于局部灭绝,幸存下来只生活在北美以外的地区)。


    我们不知道。 生态学家保罗•马丁(Paul S. Martin)提出将更新世末期大型哺乳动物灭绝与人类捕食相关联的模式。 研究人员J.E Mosimann与他合作撰写了一个计算机模型的研究报告,报告显示在大约300年的时间里,条件正确的话,12,000年前在Beringia东部的小量涌入的猎人波浪式地快速传播到北美洲,消除野兽以养活其新增的人口。


    许多学者继续支持这种说法。 例如,地质学家Larry Agenbroad已经绘制出了那个时期的克洛维斯遗址的位置,以及考古遗址的分布,在这些地方已经发现了羊毛猛犸遗体,这些都可以在考古学和纯粹生物学的文章中体现出来了。这些分布显示出明显的同步性(同时发生)。

    然而,这种模式存在很多问题。 值得注意的是,虽然有几个遗址令人印象深刻,但实际上很少有考古证据能支持它。1982年,马丁写到,他自己承认自己缺乏证据; 例如,在那个时候,在克洛维斯遗址发现的只有38只个体猛犸象的遗骸。在那之后,几乎没有其它的猛犸象被发现;但是仍然有不到20个克洛维斯遗址,其中一头或多头猛犸象的遗体已经被发现,其中数百万中的一些小部分必然会在过度屠杀的情况下被杀害。

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    B选项a small group of hunters=a small influx of hunters;wiped out=kill off,计算机模型显示,一小群猎人可能在仅仅300年的时间里,分散在北美地区并消灭动物。因此B选项正确对应原文信息。