2015届高考英语一轮复习课时作业34 Unit 4（人教版选修7）_高考复习指南

2015届高考英语一轮复习课时作业34 Unit 4（人教版选修7）

　　Robert Wayne of the University of California, Los Angeles, and Jennifer Leonard of the Smithsonian Institute, used DNA material—some of it unearthed by miners in Alaska—to conclude that today’s domestic dog originated in Asia and accompanied the first humans to the New World about 10, 000 to 15, 000 years ago. Wayne suggests that man’s best friend may have enabled the tough journey from Asia into North America. “Dogs may have been the reason people made it across the land bridge, ”said Wayne. “They can pull things, carry things, defend you from fierce animals, and they’re useful to eat. ”

　　Researchers have agreed that today’s dog is the result of the domestication(驯化)of wolves thousands of years ago. Before this recent study, a common thought about the precise origin of North America’s domestic dog was that Natives domesticated local wolves, the descendants(后代)of which now live with people in Alaska, Canada, and the Lower 48.

　　Dog remains from a Fairbanks-area gold mine helped the scientists reach their conclusion. Leonard, an evolutionary biologist, collected DNA from 11 bones of ancient dogs that were locked in permafrost(永冻层)until Fairbanks miners uncovered them in the 1920s. The miners donated the preserved bones to the American Museum of Natural History in New York City, where they remained untouched for more than 70 years. After borrowing the bones from the museum, Leonard and her colleagues used radiocarbon techniques to find the age of the Alaska dogs. They found the dogs all lived between the years of 1450 and 1675 A. D. , before Vitus Bering and Aleksey Chirikov who were the first known Europeans to view Alaska in 1741. “The bones of dogs that wandered the Fairbanks area centuries ago should therefore be the remains of pure native American dogs, ”Leonard said. The DNA of the Fairbanks dogs would also expose whether they were the descendants of wolves from North America.