原新聞網址： http://www.nytimes.com/2011/02/15/science/15obfrog.html?ref=science 原文: Dollo’s Law, a theory proposed by the scientist Louis Dollo in the 1800s, states that when a particular trait is lost in a species, it never comes back. Dollo這位科學家曾在1800年提供了一套理論，說明了當一個物種的特徵 若是消失了，此特徵將不會再出現。 It’s one explanation for why humans no longer have tails, birds and turtles are toothless and snakes have stayed limbless. 這也是說為什麼人們已經不會有尾巴，鳥類與烏龜沒有牙齒，蛇維持著沒有 腳。 But a new analysis, done by a researcher at Stony Brook University, found that while frogs lost teeth in the lower jaw at least 200 million years ago, a particular type of marsupial tree frog regained those lower teeth about 20 million years ago. 但是最近有一份新的研究指出，在兩億年前青蛙已經失去了下顎的牙齒，但是 有一種特殊型態的樹蛙卻在兩千萬年前再次獲得牙齒。 “It’s a very clear-cut case of re-evolution because of the large time span,” said John Wiens, the Stony Brook biologist who authored the paper in the journal Evolution. 這將是一個非常明顯的再次演進，因為有非常大的time span。(time span不知道 如何翻譯?) Dr. Wiens analyzed DNA samples of 170 modern and fossilized frogs to approximate the dates of loss and re-evolution of the teeth. Dr.Wiens分析一百七十種近代的DNA試片(覺得有點怪怪的翻譯!!)，與化石蛙 去估計失去牙齒的日期與觀察牙齒的再次演進。 Most frogs have teeth on their upper jaws, which may have made the re-evolution in the tree frog, known as Gastrotheca guentheri, easier, Dr. Wiens said. 大多數的青蛙在上顎都有牙齒，這樣會促使樹蛙在下顎也衍生出牙齒。 “They already had teeth in the upper jaw, so they had the enamel, dentine and other necessities,” he said. “There was a way to facilitate new teeth after 200 million years.” 這些青蛙在上顎已經有了牙齒，因此他們擁有了砝郎質、象牙質，還有其他 的材料。兩億年後，有一個方法讓他們重新配置他們的牙齒。 The species is the only known modern frog species with lower teeth, though certain other species with upper teeth do have toothlike structures on the lower jaw. 這些擁有下顎牙齒特徵的蛙只出現在近代的青蛙上，其他擁有上顎牙齒的 青蛙並不一定會有此特徵。 “That’s a big question now: What’s keeping the other frogs from developing real teeth on the lower jaw?” Dr. Wiens said. 問題在於，甚麼會讓某些品種的青蛙在下顎無法長出牙齒? 閱讀獲得的心單字: enamel:砝瑯質 dentine:象牙質 應該還有很多要修正地方，請各位大大多給建議。 --

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