Our ancient animal ancestors had tails. Why not us?

Washington: Our ancient animal ancestors had tails. Why not us?

About 20 million or 25 million years ago, when apes split from apes, our branch of the tree of life dropped its tail. Since Darwin’s time, scientists have wondered why and how this happened.

Now, researchers have identified at least one key genetic change that caused this change.

“We found a mutation in a very important gene,” said Bo Xia, a geneticist at the Broad Institute and co-author of a study published Wednesday in the journal Nature.

The researchers compared the genomes of six species of apes, including humans, and 15 species of tailed monkeys, to pinpoint key differences between the groups. Once they identified a key mutation, they tested their theory by using the gene-editing tool CRISPR to fix the same location in mouse embryos. Those rats were born without tail.

Xia cautioned that other genetic changes may also play a role in tail loss.

Another mystery: Did having no tail actually help these ape ancestors – and eventually, humans – survive? Or was it simply an accidental mutation in a population that had flourished for other reasons?

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

There are several interesting theories as to why not having a tail might have helped – including some that link being tailless to humans eventually learning to walk upright.

Rick Potts, who directs the Smithsonian Institution’s Human Origins Project and was not involved in the research, suggests that going tailless may have been the first step in some apes adopting an upright body posture even before they left the trees.

Today not all monkeys live on land. Orangutans and gibbons are tailless apes that still live in trees. But Potts notes that they move very differently than monkeys, which leap to the tops of branches while using their tails for balance. Those monkeys hang low on the branches, swinging between them and hanging quite upright.

Losing our tails was clearly a major transition, said New York University biologist Itai Yanai, a co-author of the study. But the only way to know the cause definitively “would be to invent a time machine,” he said.

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