We share a lot of genes with other primates – but not for tails (Pictures: Getty)
Scientists now know why human ancestors lost their tails 25 million years ago – and it’s down to a single snippet of DNA, a new study revealed.
The researchers discovered the genetic change in our ancient ancestors which could explain why humans don’t have tails like monkeys.
The study, published in the journal Nature, compared the DNA of tail-less apes and humans to tailed monkeys and found an insertion – a type of genetic change – of DNA shared by apes and humans, but missing in monkeys.
More than 100 genes had been linked by past work to the development of tails in various vertebrate species, and the study authors from NYU hypothesised that tail loss occurred through changes in the DNA code or mutations of one or more of them.
Remarkably, say the researchers, the new study found that the differences in tails came not from gene mutations, but instead from the addition of a DNA snippet called AluY into the gene’s code in the ancestors of apes and humans.
‘Our study begins to explain how evolution removed our tails, a question that has intrigued me since I was young,’ said Dr Bo Xia, a graduate from NYU Grossman School of Medicine.
When the research team engineered a series of mice to examine whether the insertion of a gene called TBXT affected their tails, they found a variety of tail effects – including some mice born without tails.
Would you like a tail? (Pictures: Getty)
Further research showed that an insertion – addition – to the TBXT gene, AluY, influenced different tail lengths.
They then found an AluY insertion that remained in the same location within the TBXT gene in humans and apes resulting in the production of two forms of TBXT RNA – a copy of DNA used in cell reproduction.
One of these, they theorise, directly contributed to tail loss.
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.
Any advantage that came with tail loss was likely powerful, the researchers say, because it may have happened despite coming with a cost.
Specifically, the research team found a small uptick in neural tube defects in mice with the study insertion in the TBXT gene.
‘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, like those involved in spinal bifida, which are seen today in one in a thousand human neonates,’ said Professor Itai Yanai.