About 11,000 years ago, all of North America’s megafauna became extinct.
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.
第七段：M表明缺乏证据因为人类的扩张和动物的灭绝发生得太快来支持模型。G反驳举例：New Zealand moa的灭绝，遗骸形式的考古证据非常丰富。G还表明大部分大型食草动物灭绝证据不是很清楚，许多更老的属可能在12,000年前就已经灭绝了。
选项B 错误，原文未提及 the Clovis society developed spears in order to hunt发展长矛是为了猎杀动物来养活人口；
选项D错误，Scientists have proven that...错误，证据还不是很清楚；
选项E 错误，是否是人类导致的灭绝的证据都还不是十分的清楚，而E选项说人类导致the moa的证据比人类导致大型哺乳动物灭绝的证据多，错误；