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Scientists have been debating this question for a long time.
科學(xué)家們圍繞這個問題已經(jīng)爭論了很長的時間。
Some believed that snakes evolved on land,and that their ancestors were small,burrowing lizards.
一些科學(xué)家認為蛇從陸地上進化而來，它們的祖先是小的，穴居的蜥蜴。
And others believed that snakes evolved fromthe mosasaurs, giant swimming lizards that lived 144 to 65 million years ago.
另一些科學(xué)家認為蛇由滄龍進化而來，滄龍是生活在一億四千四百萬年前至六千五百萬年前的一種巨型水生蜥蜴。
Except it's difficult to analyze the genes of the extinct mosasaurs.
分析已經(jīng)滅絕的滄龍的基因是非常困難的。
So instead, scientists at Penn Stateanalyzed the genes of their closest living relatives, the monitor lizards.
所以賓夕法尼亞州立大學(xué)的科學(xué)家們分析了它們現(xiàn)存的最近親屬巨蜥的基因。
In fact, these scientists examinedgenetic material representing all nineteen living lizard families, and seventeen of the twenty-five familiesof living snakes.
實際上，這些科學(xué)家們檢查了代表所有19種現(xiàn)存蜥蜴家族以及蛇的25種現(xiàn)存家族中的17種基因材料。
They analyzed the differences in genetic structure that inevitably result from the slight mutations that develop over time.
他們分析了隨著時間的推移，遺傳結(jié)構(gòu)中不可避免的微小變化所帶來的差異。
This enabled them to map a genetic family tree.
這讓他們能夠繪畫出一個基因家譜圖。
They discovered that snakes aren'tclosely related to monitor lizards.
他們發(fā)現(xiàn)了什么呢？他們發(fā)現(xiàn)了蛇與巨蜥并沒有密切的關(guān)系。
Now, because the mosasaurs– the monitor lizards' ancestors–werethe only marine lizards around when snakes evolved, snakes must have evolved from lizards living onland.
現(xiàn)在，因為滄龍-巨蜥的祖先-是蛇進化時周圍唯一的海洋蜥蜴，所以蛇應(yīng)該是從在陸地上生活的蜥蜴進化而來。
There's a strong correlation between the burrowing lifestyle and very small limbs or the complete lossof limbs.
從穴居生活到非常小的四肢，再到完全喪失四肢，這之間的關(guān)聯(lián)非常強。
Some burrowing lizards have reduced limbs and some have lost one or both pairs.
一些穴居蜥蜴的四肢減少，一些已經(jīng)失去了一個或者所有的四肢。
After all,you could fit into much smaller openings if you didn't need a pelvis or shoulders to support your limbs.
畢竟,你需要適應(yīng)更小的通道，如果你不需要骨盆或肩膀來支撐你的肢體。
