Unit 5 Into the wild
对于动物的灭绝，很多人猜测是气候的原因，其实，有时候人类才是动物生存最大的威胁。我们要保护动植物，与它们和谐相处。
Climate change, not human hunting, may have wiped out the thylacine (袋狼), according to a new study based on DNA from thylacines' bones.
The meat-eating marsupials (有袋动物) died out on mainla
nd Australia a few thousand years ago, but survived in Tasmania, an island of southeast Australia separated from the mainland, until the 1930s. Until then, scientists had believed the cause of this mainland extinction (灭绝) was increased activity from native Australians and dingoes (Australian wild dogs)．
Scientists behind the University of Adelaide study, which was published in the Journal of Biogeography on Thursday, collected 51 new thylacine DNA samples from fossil bones and museum skins — the largest data set of thylacine DNA to date. The paper concluded that climate change starting about 4,000 years ago — in particular drier seasons caused by the weather systems
known as El Ni?o — Southern Oscillation (南方涛动) — was likely the main cause of the mainland extinction.
The ancient DNA showed that the mainland extinction of thylacines was rapid, and not the result of loss of genetic diversity. There was also evidence of a population crash in thylacines in Tasmania at the same period of time, reducing their numbers and genetic diversity.
Associate Professor Jeremy Austin said Tasmania would have been protected from mainland Australia's warmer, drier climate due to its higher rainfall. He argued that climate change was “the only thing that could have caused, or at least started, an extinction on the mainland and caused a population crash in
Tasmania.”
“They both happened at about the same time, and the other two things that had been talked about in the past that may have driven thylacines to extinction on the mainland were dingoes and humans. So the only explanation left is climate change. And because the population crash happened at the same time and the species went extinct on the mainland, our argument is that there's a common theme there and the only common theme is that there is this change in climate.”
外研版英语必修一同步解析Unit 5 Into the wild
