Unit 5 Into the wild 全单元课件+讲义+课本录音+练习-2021-2022学年高一英语外研版（2019）必修第一册

Humans pushed cave bears to extinction 语篇导读 约两万年前，穴居熊神秘地走向灭绝。都是气候变化惹的祸吗？科学家有了新的发现…… Cave bears, true to their name, slept and wintered in caves. The biggest cave bears measured 2,000 pounds, hundreds of pounds larger than the largest brown bears alive today. Now the bears' bones are scattered (散布) in the caves where they once lived. They went extinct around 20,000 years ago. What killed off the bears is a question that's gotten a lot of attention from scientists. A study published in the journal Scientific Reports showed that humans played a large role in their extinction. “It's a very nice study that shows something quite profound (深刻的) happened to the global cave bear population around 40,000 years ago,” said Axel Barlow, a professor from the University of Potsdam, in Germany. He has sought long and hard to uncover the mystery of the bears' disappearance. Studies showed this bear population remained stable from 200,000 to 50,000 years ago. At around 40,000 years, it began to crash. 20,000 years later, cave bears disappeared. Some researchers have proposed that climate change felled the bears. Ice sheets advanced and shrank during the Pleistocene Epoch, the period from 2.6 million to 11,700 years ago. Wear on the bears' teeth suggests the animals mostly ate plants. If vegetation (植物) shifted with the ice cycles, perhaps the bears struggled with smaller food supplies. But, the study authors note, in Europe between 200,000 to 50,000 years ago, the climate cooled and warmed twice without any apparent effect on the bears. Instead, the population crash began at the same time as the arrival of modern humans in Europe. Physical evidence shows humans killed the bears. More than ten years ago, scientists discovered the tip of a weapon in a cave bear's body. “Looking at the effect of climate change and humans on the large creature can tell us a lot about the general process and results of large mammal (哺乳动物) extinction,” Axel Barlow said. “Studying the past to save the futu