【英语时差8,16】小狗躺下前为什么要转圈圈？（在线收听）

 Why Dogs Turn In Circles Before Lying Down Ever wonder why dogs turn around in circles before lying down? Almost all domestic and wild dogs show this behavior as they prepare to curl up and lie down. There are many legends that claim to explain this stereotyped behavior. But there are almost no experiments that actually test these claims–in part because such hypotheses would be difficult to verify experimentally. The most commonly repeated story is that the behavior is an evolutionary hold-over from dogs’ wild ancestors. Circling may have been necessary to trample down tall vegetation and shoo away any pests hiding in the grass, making the ground more comfortable to lie on. Others theorize that dogs in the wild preferred to sleep with their nose into the wind. Circling allowed dogs to determine wind direction. The simplest explanation is that turning in circles is just a way to orient the body into a tight curled posture as the dog lies down. What scientists do know is that the behavior is an example of what has traditionally been called a “fixed action pattern.” Fixed action patterns are stereotyped behaviors that are exhibited by all members of a particular species. These behaviors are triggered by some external or internal stimulus, and once triggered, the pattern usually continues to completion. Yawning is a good example. Yawns can be triggered by others yawning near you, or by an internal cue. Once started, a yawn is very difficult to stop. Most fixed action patterns are not as inflexible as the name suggests, and can often be modified subtly by experience or environment. For dogs turning in circles before lying down, factors such as age, surroundings, or other individual differences may change the exact behavioral pattern. But the basic action pattern is likely an inborn and hard-wired one.