Our very ancient animal ancestors had tails. Why don’t we have them now?

我们非常古老的动物祖先有尾巴。为什么我们现在没有它们？ 

From the time of Charles Darwin, a scientist from the 1800s who studied evolutionary biology, scientists have questioned why and how this happened. 

从 1800 年代研究进化生物学的科学家查尔斯·达尔文 (Charles Darwin) 时代起，科学家们就一直质疑这种现象为何以及如何发生。 

The answer is somewhere around 20 million or 25 million years ago. That was the time apes, the group of animals humans are part of, split from another animal group, monkeys. During that split, our branch of the tree of life lost its tail. 

答案是大约 2000 万或 2500 万年前。那时，猿猴是人类的动物群体，与另一个动物群体猴子分开。在那次分裂中，我们生命之树的树枝失去了尾巴。

Now, scientists have identified at least one of the genetic differences that led to this change. 

现在，科学家们已经确定了至少一个导致这一变化的遗传差异。 

“We found a single mutation in a very important gene,” said Bo Xia. He is a geneticist at the Broad Institute and helped write the study recently released in the publication Nature. 

“我们在一个非常重要的基因中发现了一个突变，”夏波说。他是布罗德研究所的遗传学家，并帮助撰写了最近在《自然》杂志上发表的这项研究。 

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. Once they identified an important mutation, they tested their theory by using the gene-editing tool CRISPR. They used it to change the same place in embryos of an animal often used in laboratories, mice. Those mice were born without tails. 

研究人员比较了包括人类在内的六种猿类和 15 种有尾巴的猴子的基因组，以发现这些群体之间的重要差异。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 测试了他们的理论。他们用它来改变实验室常用动物——小鼠——胚胎中的同一位置。这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. 

不过，夏说，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? Or was it just a chance mutation in a population that survived for other reasons? 

另一个谜团：没有尾巴是否有助于这些猿类祖先以及最终人类的生存？或者这只是由于其他原因幸存下来的种群中的偶然突变？ 

“It could be random chance, but it could have brought a big evolutionary advantage,” said Miriam Konkel. She is an evolutionary geneticist at Clemson University, who was not involved in the study. 

“这可能是随机的机会，但它可能带来巨大的进化优势，”米里亚姆·康克尔说。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. They include some that link being tailless to learning to walk upright. 

至于为什么没有尾巴可能对我们的祖先有帮助，有很多有趣的理论。其中一些将无尾与学习直立行走联系起来。 

Rick Potts directs the Human Origins Project of the Smithsonian Institution in Washington, D.C. He was not involved in the research. Potts suggests being tailless may have been a first step toward some apes standing upright, even before they left the trees. 

里克·波茨 (Rick Potts) 是华盛顿特区史密森尼学会人类起源项目的负责人。他没有参与这项研究。波茨认为，无尾可能是一些猿类直立站立的第一步，甚至在它们离开树林之前也是如此。 

Not all apes live on the ground today. Orangutans and gibbons are tailless apes that still live in trees. But Potts notes that they move very differently than monkeys, who move along the tops of branches, using their tails for balance. Those apes hang below branches, holding onto the branches with their arms while hanging largely upright. 

今天，并非所有猿类都生活在地面上。猩猩和长臂猿是仍然生活在树上的无尾猿。但波茨指出，它们的移动方式与猴子非常不同，猴子沿着树枝顶部移动，用尾巴来保持平衡。这些猿类悬挂在树枝下方，用手臂抓住树枝，同时基本上直立悬挂。 

New York University biologist Itai Yanai helped write the study. He said that losing our tails was clearly a large change. But the only way to truly know the reason “would be to invent a time machine,” he said. 

纽约大学生物学家 Itai Yanai 帮助撰写了这项研究。他说，失去尾巴显然是一个很大的变化。但他说，真正了解原因的唯一方法“就是发明一台时间机器”。