美国科学60秒 SSS 2013-02-18

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　　Alan Mann, a Prinston University physical anthropologist² at the annual meeting of the American Association for the Advancement³ of Science in Boston on February 15.

　　Some thousands of years ago, there was a random⁴ mutation⁵. It suppressed the calcification⁶ of the third molar, a wisdom teeth. So many of you, and many of your children, have grown to adulthood⁷ without the apperance of third molars. Now that particular mutation has increased in frequency so that in some populations more than 40% people have one or more absent third molars. So you might ask the question: How did that develop because obviously you have an apparent third molar if you follow survival of the fetus⁸, then you are gonna fall over holding your mouth and dying in agony.

　　Reproduction of the fetuses⁹ – what is it all about? In other words, differential reproduction. How will this work? Well, one evening, a person, who has had serious chronic pain with impacted third molars, perhaps of lower third molar, impacting into the mandibular canal(下颌管), causing a lot of pain. The partner comes up and says: How about a bout¹⁰ of reproduction, dear? And the person says: Not tonight, dear, my jaws¹¹ are killing¹² me.

　　That is in fact a revolutionary scenario¹³; and because that would produce fewer offspring in those people, the prequency of this feature would increase over time.

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