New Delhi, India

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There was a time when humans had tails, but thanks to evolution, certain changes ensured that the tail vanished. Nearly 25 million years ago, the tails of human beings disappeared. Scientists have now found out what exactly happened that led to this change during the evolution process.

The secret behind the disappearance of the tail was discovered by researchers from New York University Langone Health. 

They identified a single snippet of DNA, which is commonly found in apes and humans but has been missing from monkeys. The new study was published in the prestigious journal Nature.

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"Our study begins to explain how evolution removed our tails, a question that has intrigued me since I was young," said lead study author Bo Xia.

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The answer is present in the gene TBXT which is present in the tail length in certain animals.

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As per the study, the gene was not found in humans, not due to mutation but because another genetic code "snippet" known as AluY was randomly inserted inside non-tailed apes and early humans during prehistoric times, as per the study.

How the gene affected tail length?

The new gene was observed to affect tail lengths. When it was paired with TBXT, the new gene created two types of ribonucleic acid, which are important for cellular structure and led to the disappearance of tails in people and apes.

"This finding is remarkable because most human introns carry copies of repetitive, jumping DNAs without any effect on gene expression, but this particular AluY insertion did something as obvious as determine tail length," said Dr Jef Boeke, the Sol and Judith Bergstein Director of the Institute for Systems Genetics, as reported by the New York Post.

AluY snippets are also known as "jumping genes" or "mobile elements" since they are able to move around and insert themselves repeatedly and in random order in human code.

Watch: Study: Apes like to tease their friends

The scientists used mice to test their theory and inserted AluY into 63 of them. It was found by the researchers that the tails of offspring were either completely missing or had shortened.

These experiments proved that tail loss may also coincide with an increase in neural tube defects which can cause diseases like spina bifida in people. In this disease, the spine does not properly align with the spinal cord.

 "Future experiments will test the theory that in an ancient evolutionary trade-off, the loss of a tail in humans contributed to the neural tube birth defects," study author Dr Itai Yanai said.

(With inputs from agencies)