托福聽力
Questions: 43 through 46 Listen to a part of talk in a biology class. We've looking at fear from a biological perspective, and someone asked whether the tendency to be fearful is genetic. What some studies done with mice indicate that mammals do inherit fearfulness to some degree. In one study, for instance, a group of mice was placed in a brightly lit open box with no hiding place. Some of the mice wandered around the box and didn’t appear to be bothered about being so exposed. But other mice didn’t move. They stayed up against one wall which indicated that they were afraid. Well, when fearful mice, or you might say anxious mice like the ones who stayed in one place, when mice like these were bred with one another repeatedly, after about twelve or so generations, then all of the offspring showed similar signs of fearfulness And even when a new born mouse from this generation was raised by a mother and with other mice who were not fearful, that mouse still tended to be fearful as an adult. Now why is this? Well it’s thought that specific genes in an animal’s body have an influence on anxious behavior. These are genes that are associated with particular nerve-cell receptors in the brain. And the degree of overall of fearfulness in the mammal seems to depend in large part on the presence or absence of these nerve-cell receptor. And this appears to apply to humans as well by the way. But while a tendency towards anxiety and fear may well be an inherited trait, the specific form that the fear takes has more to do with the individual’s environment. So a particular fear, like a fear of snakes or the fear of spider, say, is not genetic, but the overall tendency to have fearful responses, is.