VOA科学技术2024--How Did Human Ancestors Lose Their Tails?

How Did Human Ancestors Lose Their Tails?

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

　　From the time of Charles Darwin, a scientist from the 1800s who studied evolutionary¹ biology, scientists have questioned why and how this happened.

　　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.

　　Now, scientists have identified at least one of the genetic² differences that led to this change.

　　"We found a single mutation³ 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.

　　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 embryos⁵ of an animal often used in laboratories, mice. Those mice were born without tails.

　　Xia said, however, that other genetic changes may also play a part in losing tails.

　　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?

　　"It could be random⁶ 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.

　　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.

　　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 standing⁷ upright, even before they left the trees.

　　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.

　　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.

　　Words in This Story

　　tail – n. the part of an animal's body that extends from the animal's back end

　　mutation – n. the part of an animal's body that extends from the animal's back end

　　edit – v. to make changes

　　embryo⁴ – n. a human or animal in the early stages of development before it is born or hatched

　　random – adj. in a way that does not follow a particular plan or pattern

　　advantage – n. something (such as a good position or condition) that helps to make someone or something better or more likely to succeed than others

1 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• Life has its own evolutionary process.生命有其自身的进化过程。
• These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。

2 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

3 mutation   

n.变化，变异，转变

参考例句：

• People who have this mutation need less sleep than others.有这种突变的人需要的睡眠比其他人少。
• So far the discussion has centered entirely around mutation in the strict sense.到目前为止，严格来讲，讨论完全集中于围绕突变问题上。

4 embryo   

n.胚胎，萌芽的事物

参考例句：

• They are engaging in an embryo research.他们正在进行一项胚胎研究。
• The project was barely in embryo.该计划只是个雏形。

5 embryos   

n.晶胚；胚，胚胎( embryo的名词复数 )

参考例句：

• Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段，而且其行为象胚。 来自辞典例句
• Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句

6 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

7 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。