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Our very ancient animal ancestors had tails.
我们非常古老的动物祖先有尾巴。
Why don't we have them now?
为什么我们现在没有尾巴呢？
From the time of Charles Darwin, a scientist from the 1800s who studied evolutionary biology, scientists have questioned why and how this happened.
自19世纪研究进化生物学的科学家查尔斯·达尔文以来，科学家就一直在质疑这种现象发生的原因和方式。
The answer is somewhere around 20 million or 25 million years ago.
答案是大约在两千万年或两千五百万年前。
That was the time apes, the group of animals humans are part of, split from another animal group, monkeys.
那是人类所属的类人猿从另一个动物群体猴子中分离出来的时期。
During that split, our branch of the tree of life lost its tail.
在那次分离中，我们生命之树的分枝失去了尾巴。
Now, scientists have identified at least one of the genetic differences that led to this change.
如今，科学家已经确定了导致这种变化的至少一个基因差异。
"We found a single mutation in a very important gene," said Bo Xia.
夏波（音译）说：“我们在一个非常重要的基因中发现了一个突变”。
He is a geneticist at the Broad Institute and helped write the study recently released in the publication Nature.
他是布罗德研究所的遗传学家，帮助撰写了最近发表在《自然》杂志上的这篇研究论文。
The researchers compared the genomes of six kinds of apes, including humans, and 15 kinds of monkeys with tails to find important differences between the groups.
研究人员比较了包括人类在内的六种类人猿和15种有尾巴的猴子的基因组，以找出这两个群体之间的重要差异。
Once they identified an important mutation, they tested their theory by using the gene-editing tool CRISPR.
一旦他们发现了一个重要的突变，他们就使用基因编辑工具CRISPR来验证他们的理论。
They used it to change the same place in embryos of an animal often used in laboratories, mice.
他们用它改变了一种经常用于实验室里的动物——老鼠——的胚胎中的相同位置。
Those mice were born without tails.
那些老鼠生来就没有尾巴。
Xia said, however, that other genetic changes may also play a part in losing tails.
夏说，然而，其他基因变化也可能是导致尾巴脱落的原因之一。
Another mystery: Did having no tails help these ape ancestors – and eventually, humans – survive?
另一个谜团：没有尾巴是否帮助这些类人猿祖先以及最终帮助人类生存下来？
Or was it just a chance mutation in a population that survived for other reasons?
或者，这只是一个因其他原因幸存下来的种群中的一个偶然突变？
"It could be random chance, but it could have brought a big evolutionary advantage," said Miriam Konkel.
米里亚姆·康克尔说：“这可能是偶然的，但它可能带来了巨大的进化优势。”
She is an evolutionary geneticist at Clemson University, who was not involved in the study.
她是克莱姆森大学的进化遗传学家，没有参与这项研究。
As to why having no tails may have helped our ancestors, there are many interesting theories.
至于为什么没有尾巴可能帮助了我们的祖先，有很多有趣的理论。
They include some that link being tailless to learning to walk upright.
其中包括一些将无尾与学会直立行走联系在一起的理论。
Rick Potts directs the Human Origins Project of the Smithsonian Institution in Washington, D.C.
里克·波茨是华盛顿特区史密森学会人类起源项目的负责人。
He was not involved in the research.
他没有参与这项研究。
Potts suggests being tailless may have been a first step toward some apes standing upright, even before they left the trees.
波茨认为，没有尾巴可能是一些猿类在离开树木之前直立行走的第一步。
Not all apes live on the ground today.
如今，并不是所有的猿类都生活在地面上。
Orangutans and gibbons are tailless apes that still live in trees.
猩猩和长臂猿是无尾猿，仍然生活在树上。
But Potts notes that they move very differently than monkeys, who move along the tops of branches, using their tails for balance.
但波茨指出，它们的移动方式与猴子非常不同，猴子沿着树枝顶端移动，用尾巴保持平衡。
Those apes hang below branches, holding onto the branches with their arms while hanging largely upright.
这些类人猿悬挂在树枝下，用手臂抓住树枝，而大部分是直立的。
New York University biologist Itai Yanai helped write the study.
纽约大学生物学家以太·亚奈参与撰写了这篇研究论文。
He said that losing our tails was clearly a large change.
他说，失去尾巴显然是一个巨大的变化。
But the only way to truly know the reason "would be to invent a time machine," he said.
但他说，真正了解原因的唯一方法是“发明一台时光机”。
I'm Gregory Stachel.
格雷戈里·施塔赫尔为您播报。
译文为可可英语翻译，未经授权请勿转载！
