In 200 Years Cows May Be the Biggest Land Mammals (哺乳动物) on the Planet

Around 13,000 years ago North America had a wider variety of mammals than modern Africa. There were multiple horse species, camels and some now-extinct animals. And such _________ creatures were not just found in North America. On every continent mammals on average were a lot larger from around 2.5 million until about 11,700 years ago.

Scientists have long debated what caused all these large creatures to go extinct while many of the smaller ones _________. A team of researchers led by biologist Felisa Smith analyzed evidence from millions of years’ worth of mammalian extinctions and found that on each continent large mammals started to _________ around the same time humans first showed up.

If the extinction trend continues, many more large mammals will soon disappear as well, as the primary threats from humans have _________ from overhunting to indirect processes such as habitat loss. The largest land mammal 200 years from now could well be the domestic cow, Smith’s research suggests. In their new study Smith and her team analyzed a database of all land mammals that lived from 65 million years ago until today. “We found _________ no effect of climate on mammalian extinction over 65 million years,” she says. But starting around 125,000 years ago and continuing until today, large mammals have been more likely to go extinct than smaller ones, the researchers found.

The average _________ of surviving mammals has decreased as a result. And those large-mammal extinctions are tightly coupled with the _________ of humans. For most of mammalian _________ history, an animal’s size was not predictive of its extinction risk. That _________ only appeared once humans began to live alongside large mammals.

This finding does not mean climate-related changes could not have __________ some wildlife populations, enabling humans to more easily bring about their eventual downfall. __________, it suggests the greater likelihood of large mammals going extinct is tied to human activities. The animals that evolved without the risk of hunting from humans were suddenly faced with a new __________. They simply could not __________ fast enough to survive the invasion of humans.

Smith says the lesson to be learned from the new findings is that our ancestors prepared us to be extremely skillful killers. “What’s __________ now,” she says, “is that some of us are comfortable enough, have a high enough standard of living, that we can start thinking about our use of the Earth.” Rather than simply behaving as __________, many of us are now in a position to become environmental protectors.

Angela Pozzi didn’t like seeing plastic rubbish washing up on the shore near her home in Bandon, Oregon. So she started an organization and called it Washed Ashore: ______ to Save the Sea.

Here’s how it works: Volunteers help clean up Oregon’s 300 miles of ______. Then, ______only plastics from the beach cleanup, Ms. Pozzi and her staff and volunteers create sculptures of sea animals.

In the sculptures, viewers can see what each piece was ______ it became part of the artwork. They know that every bit—comb, plastic boot, bottle cap, bottle or ______ —was found on a beach.

Plastics, unlike wood, cotton, and other ______ materials, don’t ______ into anything useful to other living things. ______, they stay for years in the oceans. Some sea animals eat plastic objects that look like food. Others are ______ in plastic nets or packaging.

Ms. Pozzi says, “I want to create sculptures that make people take a look and think, ‘______ come there can be this much trash on the beach?’ ______, the Washed Ashore sculptures will make people ______ their plastic purchases and be aware of how much they should pay for them in the end.”

Surprisingly, one of the Washed Ashore’s sculptures, Turtle Ocean, received a ______ honor. It was ______ at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C. Ms. Pozzi says, “Until we run out of ______ on the beach, the work will continue.”

In 2014, a sophomore student at the National Academy of Chinese Theatre Arts went with friends for a birthday celebration to Beijing Zoo. Little did he know that a chance _________ at the aquarium (水族馆) there would light a lifelong passion.

Fast-forward to today, Xu, a Beijing native, has _________ to the tropical island of South China’s Hainan province, where he serves as a coral _________ for a Sanya-based tropical biological laboratory attached to the Chinese Academy of Sciences.

Each day, he spends several hours diving deep under the waves to observe and _________ the growth and development of the creatures that _________ him all those years ago. Xu, who is nicknamed “coral man”, is _________ engaged on such social media platforms as Sina Weibo, where he regularly shares visually amazing photos and entertaining videos of corals. He aims to _________ individuals to take action in protecting coral reefs(珊瑚礁) and the oceans as a whole.

For Xu, who had been studying Peking Opera since childhood, becoming a coral conservationist was an _________ turn of events. After he first saw corals at the aquarium, he began to _________ the local market to learn about coral __________ from merchants who sell decorative plants, fish and corals. He also __________information online. Before long, he had set up a small fish tank at home and started cultivating a coral.

“The coral organism is quite sensitive to its environment and has extremely high __________ for water quality,” recalls Xu. “When I started growing coral, its state was not __________.” But as Xu gained more __________ about coral, including how to control factors like water temperature and pH levels, his coral gradually started to flourish. He also learned that coral reefs are known as “tropical rainforests” and “underwater gardens” of the ocean, providing a __________ for a quarter of all sea creatures.