导读：据英国《卫报》报道，日前，一位全球生物多样性专家表示，目前人类活动造成的负面影响已超越了新物种的进化速度，这也就意味着全球生物种类将会越来越少。一直以来，自然资源保护专家都认为，目前全球生物正面临“第六次物种大灭绝”的危险，而造成这一严峻形势的主要因素则包括人类对自然保护区的破坏、大肆捕猎、疾病的传播及全球气候变暖等等，这些因素大都同人类活动相关。
对应考题：2010.01.15北美托福阅读题
Dinosaurs were surely fantastic creatures, but you’d be hard pressed to find someone who wishes Tyrannosaurus rex were alive and roaming the streets. If dinosaurs weren’t extinct, humankind probably would be. All in all, the dinosaur extinction is something we should be happy about, at least from a human survival perspective. So sorry, T. Rex, you’re not one of the things we pine to resurrect.
Unfortunately, there have been some not-so-ancient extinctions that we really should regret happening. Most of the species that have gone kaput in recent history have met their doom at human hands. And although, at the time, we thought we could do without these creatures, many of them could have helped us, or at least provided us with an interesting spectacle. The following 10 animals are all species that have died out in recent recorded history. And they’re all creatures that, for one reason or another, we should miss.
There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. "Just as each species is unique," write Beverly and Stephen Stearns, "so is each extinction... the causes for each are varied—some subtle and complex, others obvious and simple". Most simply, any species that is unable to survive or reproduce in its environment, and unable to move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors.
Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the nature-nurture debate. The question of whether more extinctions in the fossil record have been caused by evolution or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction argues for a mathematical model that falls between the two positions. By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause. When concerns about human extinction have been raised, for example in Sir Martin Rees' 2003 book Our Final Hour, those concerns lie with the effects of climate change or technological disaster.
Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and are attempting to combat further extinctions through a variety of conservation programs. Humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of new predators and food competitors, overhunting, and other influences. According to the World Conservation Union (WCU, also known as IUCN), 784 extinctions have been recorded since the year 1500 (to the year 2004), the arbitrary date selected to define "modern" extinctions, with many more likely to have gone unnoticed (several species have also been listed as extinct since the 2004 date).
中文背景：
生物灭绝实际上是其演化过程的一部分，如今地球上所有存在过的物种中，只有近2%至4%还生活在世界各个不同地方。研究人员通过考察化石记录发现，在地球35亿年的历史时间中，生物的灭绝速度应该是平均每年每100万个物种中，有1个物种会灭绝。但是，从1500年开始，有过正式记录的灭绝物种却只有869个，因为科学家只能够识别全球500万至3000万物种当中近200万种生物。因此，科学家在测算生物灭绝速度的时候，实际上只是算出了已知生物的灭绝速度，而已知生物又只是自然界生物总数的一小部分。与此相比，2004年，IUCN所测算出的数据则是通过对比以往5次“生物大灭绝”的数据，才下此结论。当前地球上的物种消失与历史上的生物灭绝事件很相似，甚至速度更快，有调查显示，地球上平均每1小时就有1个物种灭绝，灭绝速度超过了以往任何一次，只不过这一次生物的灭绝主要是受人类活动的影响。
在地球的生命演化史上，曾经历过五次大规模的生物灭绝：第一次物种大灭绝发生在距今4.4亿年前的奥陶纪末期，大约有85%的物种灭绝；第二次发生在距今约3.65亿年前的泥盆纪后期，海洋生物遭到重创；发生在距今约2.5亿年前二叠纪末期的第三次物种大灭绝，是史上最大最严重的一次，96%的物种灭绝了，其中90%的海洋生物和70%的陆地脊椎动物灭绝；第四次发生在距今1.85亿年前，80%的爬行动物灭绝；第五次则发生在距今6500万年前的白垩纪，统治地球达1.6亿年之久的恐龙遭到灭绝。
