英語語言學(xué)習(xí)：狗狗的進(jìn)化史
Olivia Willis: It’s the evolution debate that’s divided the scientific community for decades: dogs, where they come from and how they came to be, has largely remained a mystery. But researchers in Sweden may have finally cracked the code. With the report released last month showing that human domestication of dogs is twice as old as previously thought. The paper, published in Current Biology, has found that dogs split from wolves at least 27,000 years ago, and possibly up to 40,000 years ago. 40,000, it’s astonishing really, when you consider that the conventional domestication of most animals—say goats or cattle—happened just 10 to 12,000 years ago.
The new findings were based on a bone fragment found in Siberia, and revealed a new species of wolf that was a side branch of the common ancestor of modern wolves and dogs. Scientists compared the differences between the genome of the ancient wolf and those of modern wolves and dogs, and built a family tree showing the two had split much earlier than previously thought. However the study, while impressive, wasn’t able to conclude much about the domestication process itself. Understanding where, when, and exactly how humans developed a close companionship with what are otherwise wild and fierce creatures, remains a hotly contested bone of contention. Early signs of domestication emerged in the late 1970s when scientists in northern Israel discovered a puppy buried in the arms of a human under a 12,000-year-old home, suggesting that dogs were domesticated in the Middle East, shortly before people took up farming.
But it wasn’t long before other evidence suggested domestication took place in Asia, or even Europe. It was Peter Savolainen, a Swedish professor of evolutionary genetics, who created the world’s first canine DNA database. He conducted a study that examined DNA sequence variation among 654 domestic dogs. Through his research, Savolainen began to recognise a pattern that eastern Asian dogs were more genetically diverse, a trademark of ancient origins. Further study in 2009 led Savolainen to conclude that dogs had originated from a region south of China’s Yangtze River, less than 16,500 years ago, when humans were transitioning from hunters and gatherers, to farming and agriculture. Although his team couldn’t decipher just how or why they’d been domesticated, Savolainen was confident that he’d solved the basic canine question. But not everybody was convinced. Robert Wayne, and evolutionary biologist at the University of California, believes that Savolainen’s approach of using only modern DNA is a gross oversight.
Wayne says that any genetic diversity in modern Asian dogs—the crux of Savolainen’s theory—is not necessarily an indication of ancient origins, but rather a result of human colonisation, as dogs regularly interbred with wolves and canines from other regions. Wayne instead focused his attention on ancient DNA, and in 2013 his team published the most extensive analysis of ancient dog and wolf genomes to date, and concluded that dogs had evolved from an ancient group of wolves in Europe. Somewhere between 19 and 32,000 years ago. So the mystery of dog domestication remained, that’s when scientists Greger Larson and Keith Dobney stepped in and things got even more interesting. Larson and Dobney had grown frustrated over the continued disputes about canine origins because no studies—especially those of Savolainen and Wayne—were combining both ancient and modern DNA and using a broad range of geographic samples.
So Larson and Dobney set to work, attempting to analyse as many samples as possible, from as many places as possible. Combining ancient DNA analysis, with modern techniques. So far they’ve analysed more than 3,000 specimens, and their first and highly anticipated paper is due to be published in coming months. They hope to finally determine when and where wolves transitioned from wild animals of the forest to man’s beloved, best friend.
Robyn Williams: More than 40,000 years ago, I’ll bet you. Olivia Willis on the story reported in The New Scientist this week on page 12, and is the cover story of the journal Science, on 17th of April. And so for the rest of The Science Show, big data: computers, and later, dating. For first we go way back.
