Scientists uncover why humans lost their tails 25 million years ago

Our ancestors lost their tails about 25 million years ago, but scientists have recently found what caused the mutation that changed the course of primate history.

Researchers at New York University determined it all came down to a single snippet of DNA that apes and humans share, but is missing from monkeys.

The discovery lives in the gene TBXT, which is involved with tail length in certain animals, and when a small portion of DNA called AluY was inserted, tails were lost.

Although the reason for the tail loss is uncertain, some experts propose that it may have better-suited life on the ground than in the trees.

Our ancestors lost their tails about 25 million years ago, but scientists have recently found what caused the mutation that changed the course of primate history

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

More than 100 genes had been linked by past work to the development of tails in various vertebrate species, and the study authors hypothesized that tail loss occurred through changes in the DNA code of one or more of them.

AluY snippets are also called 'jumping genes' or 'mobile elements because they can move around and insert themselves repeatedly and randomly in human code.

The elements are also responsible for for regulation of tissue-specific genes and can change the way a gene is expressed.

In the new study, researchers identified two jumping genes in TBXT that are found in great apes, leading to the hypothesis that AluY had randomly inserted itself with the code tens of millions of years ago.

To uncover the mystery, researchers inserted jumping genes into mice, finding tails of offspring were missing entirely

The team found also found that the jumping gene altered the tail length in one of the mice

To uncover the mystery, researchers inserted jumping genes into 63 mice, finding tails of offspring were either shorter or missing entirely.

Any advantage that came with tail loss was likely powerful, the researchers said, because it may have happened despite coming with a cost.

Specifically, researcher found a small uptick in neural tube defects in mice with the study insertion in the TBXT gene.

Even more, an AluY insertion remained in the same location within the TBXT gene in humans and apes resulting in the production of two forms of TBXT RNA.

And one form is likely what contributed to the tail loss.

Professor Jef Boeke, from NYU Langone Health, said: '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.' 

The discovery lives in the gene TBXT , which is involved with tail length in certain animals, and when a small portion of DNA called AluY was inserted, tails were lost

Gorillas, chimpanzees and humans are believed to have lost their tails when they moved away from Old World monkeys, the researchers said. 

Following this evolutionary split, the group of apes that includes present-day humans evolved the formation of fewer tail vertebrae, giving rise to the coccyx, or tailbone. 

Although the reason for tail loss is uncertain, some experts propose that it may have better suited life on the ground than in the trees. 

Famed naturalist Charles Darwin discovered the change in human and our ancestors' anatomy in his 19th century book The Descent of Man, but could not be certain the coccyx was an ancient tail.

'I believe the Os coccyx gives attachment to certain muscles, but I cannot doubt that it is a rudimentary tail,' Darwin wrote.