Those who lacked a strong fear response were more likely to be killed, leaving the more timid and careful to pass their genes onto the next generation.How do scientists explain why shivering over such scary things is fun?

• 也正是由于恐惧，我们才得以在数百万年的进化过程中生存至今。那些对恐惧缺乏强烈反应的物种往往丢掉性命，而那些胆小或谨慎的却存活下来并将它们的基因传至下一代。