For years, scientists have pondered the question: Why is our species lacking a tail, especially when our ancient ancestors did? Researchers say after doing too much struggle they have finally discovered the genetic mechanism responsible for our taillessness and the tailed condition of our ape ancestors. It appears to be related to a mutation in an important gene.
Tails have been a common feature in most vertebrates for more than half a billion years, and their disappearance may have had advantages as our ancestors moved from aquatic habitats to terrestrial environments, according to scientists.
By comparing the DNA of two groups: monkeys, which have tails, and the hominids humans, and monkeys, which do not. They found a mutation in a gene called tbxt that was present in humans and apes but not in monkeys.
To determine the effects of this mutation, researchers genetically modified laboratory mice for this trait. The tails of these mice were either shortened or completely lost. For the first time, we have been able to propose a plausible scenario for the genetic mechanism that led to our ancestors, said Etai Yanai, a geneticist and systems biologist at New York University Langone Health, who led the study, published in the journal Nature.
Surprisingly, such a large physical change can be caused by such a small genetic change. The absence of a tail may have better balanced the body for orthograde locomotion and eventually bipedal walking, says BoXia, a geneticist and biologist at Harvard University and the Broad Institute.
According to the researchers, the mutation that led to the end of the tail occurred about two and a half million years ago, when the first apes arose from the ancestors of monkeys.
Our species, Homo sapiens, appeared about three hundred thousand years ago. Humanoids today include humans, the ‘large apes’ – chimpanzees, bonobos, gorillas, orangutans – and the ‘small apes’ – gibbons. The earliest hominids, called proconsuls, were tailless. Hominoids evolved the formation of low-tailed vertebrae, eliminating the external tail.
Remains of the tail remained in humans. A bone at the lower end of the spine called the coccyx or tailbone, is formed from what remains of the tail. For many vertebrates, tails have aided functions such as locomotion—think fish and whale propulsion—and defense—as dinosaurs used their spiked tails as weapons. Some monkeys and some other animals already have tails that can grasp objects such as tree branches.
When you live in trees, tails can be beneficial, says Yanai. As you move to Earth, it may become unnecessary. The benefits of tailing off come at a cost. Because a gene can contribute to multiple functions in the body, changes that benefit one part may be harmful to another.
In this case, genetically modified mice showed a slight increase in severe birth defects of the spinal cord, called neural tube defects which is similar to spina bifida in humans. It is an interesting experiment to wonder if humans could have evolved with a tail.
