一般开始为老观点,后面作者给出与之对立的新观点。通常文章对老观点持负面评价,对新观点持正面评价。
According to a theory advanced by researcher Paul Martin, the wave of species extinctions that occurred in North America about 11,000 years ago, at the end of the Pleistocene era, can be directly attributed to the arrival of humans, i.e., the Paleoindians, who were ancestors of modern Native Americans. However, anthropologist Shepard Krech points out that large animal species vanished even in areas where there is no evidence to demonstrate that Paleoindians hunted them. Nor were extinctions confined to large animals: small animals, plants, and insects disappeared, presumably not all through human consumption. Krech also contradicts Martin's exclusion of climatic change as an explanation by asserting that widespread climatic change did indeed occur at the end of the Pleistocene. Still, Krech attributes secondary if not primary responsibility for the extinctions to the Paleoindians, arguing that humans have produced local extinctions elsewhere. But, according to historian Richard White, even the attribution of secondary responsibility may not be supported by the evidence. White observes that Martin's thesis depends on coinciding dates for the arrival of humans and the decline of large animal species, and Krech, though aware that the dates are controversial, does not challenge them; yet recent archaeological discoveries are providing evidence that the date of human arrival was much earlier than 11,000 years ago.
观点:研究者PM的理论认为,物种灭绝潮可以直接归于人类到来。
观点:但是人类学家SK指出(反驳)大型物种在一些没有证据表明人类捕食了它们的地方消失了。
观点:SK进一步指出小动物、植物、昆虫消失了,很可能不全因为人类消耗。
观点:SK也反对PM把气候变化排除在物种灭绝潮的解释之外。
观点:SK认为人类如果不是物种灭绝潮的主要原因的话,那应该是次要原因。
观点:历史学家RW认为“人类是物种灭绝的次要原因”的观点无证据支持。
解释:RW观察到PM的观点基于人类到来和物种灭绝的时间重合,而SK,尽管意识到这种时间的争议,却并为质疑这个争议;最新数据表明,人到来的时间就是远早于11000年前。