来自《耶鲁大学开放课程：心理学导论 第10集 第10集》

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  You typically do not need to
  你根本不需要
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  because they do not want to have sex with one another.
  因为他们之间也没这想法
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  Now, this is--actually also illustrates
  这事实上也展示了
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  the difference between proximate and ultimate causation.
  引信和终极导因的区别
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  So, you think for yourself,
  所以自己想想
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  "Eew. Do I want to have sex with my sister?"
  我想和我妹妹做爱吗
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  You don't think to yourself, "I would prefer not to,
  你不会想说 我不会这么做
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  for the offspring that we will create will be nonviable
  因为我们的后代是无法存活
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  and it'll be a waste of my reproductive efforts."
  这也浪费我的生育精力
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  Rather, you think, "Eew,"
  而是 你认为
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  because at a gut level you respond.
  因为你会本能地反感
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  And this sort of instinctive response
  这种本能反应