2020托福听力练习：驯化家猪或含野生祖先基因（下载）

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　　The standard story told about domesticating wild animals goes something like this:humans selected individuals with a desired trait—docility, for example and bred those animals together to produce offspring even more docile than their parents.

　　Eventually the breeders created a genetic bottleneck that separated domestic animals from their wild relatives.

　　And they brought their livestock along as they spread across Europe and Asia.

　　But now a group of scientists has demonstrated that the story is far too tidy—at least when it comes to pigs.

　　Pigs were domesticated from wild boar at least twice, in Anatolia in present day Turkey and in the Mekong Valley in China, both about 9,000 years ago.

　　They arrived in Europe about 7,500 years ago.

　　For this study, researchers focused on European pigs.

　　They evaluated more than 600 genomes from European and Asian wild boars and domesticated pigs.

　　And they found that, in Europe, the story of a bottleneck separating domestic from wild animals does not fit the genetic data.

　　Rather, the model that does fit indicates that there was a frequent flow of genes from wild European boars into the domestic population.

　　In other words, boars and pigs kept finding ways to get together.

　　The most likely scenario for the development of the modern pig genome includes gene flow from some species of European wild boars that are now extinct.

　　But their genes live on, on the farm.

　　The research is in the journal Nature Genetics.

　　The authors hope this study will prompt the use of genetics to evaluate the domestication history for other species, including dogs and horses.

　　They say the incorporation of contemporary and ancient DNA into these modeling scenarios will help elucidate the timing of the domestication of plants and animals and, “ultimately substantially enhance knowledge of this fascinating evolutionary process.”