【BBC新闻词汇】狗狗的生命
Summary：Scientists who have traced the ancestry of the domestic dog say they've worked out why man's best friend loves to chew bones. Researchers from the national university of Colombia found that dogs' jaws and teeth started to grow larger about 8 million years ago, when the animals first started hunting in groups. This gradual transformation is what turned our favourite pets into what the scientists called 'hypercarnivores'.
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http://t1.g.hjfile.cn/listen/201304/20130421095119345842.mp38 million years ago, a shift in the climate caused more barren, open landscapes to spread across the globe. And without the cover of trees, large animals grouped together for protection.
This, the scientists say, was when wild dogs started to work together, teaming up to drive big prey out of the herd. The Colombian team examined the skulls of more than 300 dog species, building a timeline that revealed how their jaws and teeth had evolved.
This showed that the wolves from which our domestic dogs descend started to change when they began to hunt in packs. From then on, the dogs with the biggest teeth and the most powerful jaws were most likely to succeed in overpowering their prey, so they passed their hypercarnivorous genes on to the next generation.
The researchers say that this is what's given our pet dogs such good evolutionary reasons to really enjoy chewing on bones.
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