【导语】 专家指出：地球上的动植物物种正以前所未有的速度消失，而无论是它们栖息地的丧失、污染，还是全球变暖带来的间接影响，祸根都源于人类。
北部白犀牛 小嘴狐猴
Extinction is for ever!
As almost everyone knows，to become extinct is to be gone for ever.Even before man's arrival on Earth，species became extinct quite naturally.Natural extinction happens when a species decreases in numbers gradually but steadily at the end of its evolutionary period on Earth.The length of this period depends on how well a species can get used to changes around it.This process of extinction can take a very long time—sometimes several million years—and the extinction of one species is immediately followed by the appearance of another in a continuous cycle.
