[ti:How Did Human Ancestors Lose Their Tails?]
[al:Science & Technology]
[ar:VOA]
[dt:2024-03-03]
[by:www.voase.cn]
[00:00.00]Our very ancient animal ancestors had tails. Why don't we have them now?
[00:09.22]From the time of Charles Darwin, a scientist from the 1800s who studied evolutionary biology, scientists have questioned why and how this happened.
[00:26.46]The answer is somewhere around 20 million or 25 million years ago. 
[00:34.55]That was the time apes, the group of animals humans are part of, split from another animal group, monkeys.
[00:45.13]During that split, our branch of the tree of life lost its tail.
[00:53.69]Now, scientists have identified at least one of the genetic differences that led to this change.
[01:03.45]"We found a single mutation in a very important gene," said Bo Xia. 
[01:12.27]He is a geneticist at the Broad Institute and helped write the study recently released in the publication Nature.
[01:25.32]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. 
[01:43.14]Once they identified an important mutation, they tested their theory by using the gene-editing tool CRISPR.
[01:54.00]They used it to change the same place in embryos of an animal often used in laboratories, mice.
[02:04.23]Those mice were born without tails.
[02:09.25]Xia said, however, that other genetic changes may also play a part in losing tails.
[02:19.24]Another mystery: Did having no tails help these ape ancestors - and eventually, humans - survive? 
[02:31.33]Or was it just a chance mutation in a population that survived for other reasons?
[02:40.08]"It could be random chance, but it could have brought a big evolutionary advantage," said Miriam Konkel. 
[02:50.68]She is an evolutionary geneticist at Clemson University, who was not involved in the study.
[03:01.27]As to why having no tails may have helped our ancestors, there are many interesting theories. 
[03:10.36]They include some that link being tailless to learning to walk upright.
[03:16.82]Rick Potts directs the Human Origins Project of the Smithsonian Institution in Washington, D.C. 
[03:28.06]He was not involved in the research. 
[03:32.10]Potts suggests being tailless may have been a first step toward some apes standing upright, even before they left the trees.
[03:45.33]Not all apes live on the ground today. Orangutans and gibbons are tailless apes that still live in trees.
[03:56.14]But Potts notes that they move very differently than monkeys, who move along the tops of branches, using their tails for balance. 
[04:08.90]Those apes hang below branches, holding onto the branches with their arms while hanging largely upright.
[04:18.63]New York University biologist Itai Yanai helped write the study.
[04:26.42]He said that losing our tails was clearly a large change. 
[04:33.12]But the only way to truly know the reason "would be to invent a time machine," he said.
[04:42.02]I'm Gregory Stachel.