Why do our eyes open wide when we feel fear? And why do our eyes become narrow when we express disgust  ? According to a new research, it has something to do with survival. In a recently published paper, researchers concluded that expressions of fear and disgust changed the way human eyes gather and focus light. They argued that these changes were the result of evolutionary development and were intended to help humans survive, or at least discover, very different dangers. In order to test their hypothesis  ,researchers examined two dozen volunteer college students with standard eye-exam equipment, and asked them to show expressions of fear and dislike. It was found that when the students widened their eyes, more light was admitted and their field of vision was expanded. When they wrinkled their noses in disgust, their eyes narrowed. This had the effect of blocking out more light but focusing on a specific point. Although some scientists have admitted that emotional expressions are intended primarily to communicate information, expressions of fear and disgust seem to perform different visual functions. "Eye widening may help to find a potential danger that requires much attention. And this would agree with the hypothesized function of fear," said researchers. "On the other hand, eye narrowing may help to distinguish and avoid different kinds of dangers, such as disease carriers and dirty foods. And this would agree with the hypothesized function of disgust." These findings supported naturalist Charles Darwin's view that expressions are not necessarily for communication and are not arbitrary  ."If our expressions were arbitrary, they would show little cross-cultural relationship." researchers said. "But actually, our expressions probably have some universal   functional principles." The main idea of the text is that   _  .
emotional expressions change with cultures expressions of fear and disgust aid human survival evolutionary development causes changes of human eyes evolutionary development results in emotional expressions