Scientists discover why humans lost their tails 25 million years ago
Our ancestors lost their tails about 25 million years ago, but scientists have recently discovered what caused the mutation that changed the course of primate history.
Researchers at New York University have determined that it all comes down to a single piece of DNA that monkeys and humans share, but which monkeys lack.
The discovery is in the gene TBXT, which is involved in tail length in certain animals, and when a small part of the DNA called AluY was inserted, tails were lost.
Although the reason for tail loss is uncertain, some experts suggest that life on the ground may be more suitable than in the trees.
Our ancestors lost their tails about 25 million years ago, but scientists have recently discovered what caused the mutation that changed the course of primate history
The study’s corresponding author Bo
More than 100 genes had been linked by previous research to the development of tails in several vertebrate species, and the study authors hypothesized that tail loss occurred through changes in the DNA code of one or more of them.
AluY fragments are also called “jumping genes” or “mobile elements” because they can move around and insert themselves repeatedly and randomly into human code.
The elements are also responsible for the 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 occur in great apes, leading to the hypothesis that AluY had randomly inserted itself with the code tens of millions of years ago.
To unravel the mystery, researchers put jumping genes into mice, finding that offspring’s tails were completely missing
The team also found that the jumping gene changed tail length in one of the mice
To unravel the mystery, researchers inserted jumping genes into 63 mice, finding that the offspring’s tails were shorter or missing altogether.
Any benefit associated with tail loss was likely powerful, the researchers said, because it could have happened despite there being a cost.
Specifically, the researcher found a small increase in neural tube defects in mice with the study insertion in the TBXT gene.
In fact, an AluY insertion remained in the same location within the TBXT gene in humans and monkeys, resulting in the production of two forms of TBXT RNA.
And one form likely 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 determining of tail length.’
The discovery is in the gene TBXT, which is involved in tail length in certain animals, and when a small part of the DNA called AluY was inserted, the tails were lost.
Gorillas, chimpanzees and humans are believed to have lost their tails as they moved away from Old World monkeys, the researchers said.
After this evolutionary split, the group of apes, which includes today’s humans, developed the formation of fewer tail vertebrae, creating the coccyx or tailbone.
Although the reason for the loss of the tail is uncertain, some experts suggest that life on the ground may be more suitable than in the trees.
Famed naturalist Charles Darwin discovered the change in the anatomy of humans and our ancestors in his 19th century book The Descent of Man, but could not be sure that the coccyx was an ancient tail.
“I believe that the coccyx of Os gives attachment to certain muscles, but I cannot doubt that it is a rudimentary tail,” Darwin wrote.