Some identical twins have been adopted and brought up in different homes. With identical genes but a different home environment, scientists can study twins to see how much a particular feature depends on the genes we inherit. For example, we know that eye problems, like short­sightedness, are mostly genetic.But resistance to pain is largely dependent on experiences. Genes also influence our eating habits. Identical twins brought up apart often like to eat at the same time of day and feel full after eating the same amount. Non­identical twins in similar circumstances have more varied eating habits. Identical twins are also more likely to follow the same patterns for marriage and divorce than non­identical twins.

　　Scientists are trying to identify the different genes that influence our behaviour. Some people are thrill­seekers and get into risk­taking and adventurous activities.They take up extreme sports like bungee jumping and possibly take drugs. Scientists have discovered a gene which affects this.

　　We could ask，“Are our lives determined by our genes or our upbringing？” Scientists are learning more all the time, but it is certainly true that both are important in making us who we are.

　　【语篇解读】 本文主要介绍基因和生活经历对人的外貌、性格等的形成所起的作

　　用。

　　40. What is the main idea of the first paragraph?

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