People without tails? Scientists identify genetic mutation behind the condition
The mutation that led to the loss of the tail occurred about 25 million years ago.
Washington:
Director James Cameron’s “Avatar” films features a species of blue creatures shaped like humans except for a tail. So why does our species lack a tail, given that our evolutionary ancestors in the primate lineage had tails?
Scientists on Wednesday discovered what may be the genetic mechanism behind the tailless condition of us and our ape ancestors — a mutation in a gene that aids in embryonic development. The tail has been a feature of most vertebrates for more than half a billion years, and its loss may have been an advantage as our ancestors moved from trees to the ground, he said.
The researchers compared the DNA of two groups of primates: monkeys, which have tails, and hominoids – humans and apes – which do not have tails. They found a mutation in a gene called TBXT that was present in people and apes but absent in monkeys. To test the effects of this mutation, researchers genetically modified laboratory mice to have this trait. The tail of these rats was either reduced or did not survive at all.
New York University said, “For the first time, we propose a credible scenario for the genetic mechanism that led to the loss of our ancestors’ tails. It is surprising that such a large physical change could be caused by such a small genetic change.” ” Langone Health geneticist and systems biologist Itai Yanai, who helped lead the study published in the journal Nature.
The absence of a tail may have left the body better balanced for orthograde — upright — walking and ultimately bipedalism, said the study’s lead author, geneticist and systems biologist Bo Xia of Harvard University and the Broad Institute.
According to researchers, the mutation that caused the loss of the tail occurred about 25 million years ago, when the first apes evolved from ape ancestors. Our species, Homo sapiens, appeared about 300,000 years ago.
The evolutionary lineage that led to apes and humans diverging from the lineage that led to today’s Old World monkeys, a family that includes baboons and macaques. Hominoids today include humans, the “great apes” – chimpanzees, bonobos, gorillas, orangutans – and the “small apes” – gibbons. The earliest known hominoid, called Proconsul, was tailless.
Hominoids evolved to have reduced tail vertebrae, losing an external tail. Remnants of the tail remain in humans. A bone at the base of the spine called the coccyx or tailbone is formed from the fused remains of the tail vertebrae.
For many vertebrates, a tail has helped with functions such as locomotion – think of propulsion by fish and whales – and defense – such as with dinosaurs that wielded tails with clubs or spikes. Some monkeys and some other animals have long tails that can hold onto objects such as tree trunks.
“The tail can be beneficial when you live in trees. As you move to the ground, it can become more of a liability,” Yanai said.
It seems that the benefits of acting without thinking also have a price. Because genes can contribute to many functions in the body, mutations that confer an advantage in one area may be harmful in another.
In this case, the modified mice showed a small increase in serious birth defects in the spinal cord, called neural tube defects, which resemble spina bifida in people.
“This suggests that the evolutionary pressure to lose the tail was so high that, despite creating the possibility of this condition (neural tube defect), we lost the tail,” Yanai said.
It’s an interesting thought experiment to consider whether humans could have evolved with a tail. Alas, the Na’vi people of “Avatar” are science fiction.
“I’m a fan of James Cameron’s ‘Avatar’ — it’s just a beautiful world, and the Na’vi people use their tails to communicate directly,” Zia said. “I hope I get to ask James why he created Na’vi people with tails.”
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)