Scientists have been baffled for decades by the lack of tails in humans.

For years, scientists have been puzzled by one question: Why don’t humans have tails, when other primates in our evolutionary line do?

Researchers have discovered the potential genetic cause for the lack of tails in humans and our primate predecessors. This is due to a mutation in a gene important for the development of embryos. While tails were a common trait among many species for millions of years, the absence of a tail may have served as an evolutionary advantage as our ancestors transitioned from living in trees to living on land.

The scientists analyzed the genetic makeup of two categories of primates: monkeys, which possess tails, and hominoids – humans and apes – which lack them. They identified a genetic alteration in a gene known as TBXT, which was present in humans and apes but not in monkeys. In order to observe the impact of this mutation, the scientists genetically engineered lab mice to express this characteristic. As a result, the mice either had a shorter tail or no tail at all.

“In a groundbreaking study published in Nature, our team has presented a potential explanation for the genetic process responsible for the disappearance of the tail in our early ancestors. It is remarkable that a seemingly minor genetic alteration could result in such a significant anatomical transformation,” stated Itai Yanai, a geneticist and systems biologist from New York University Langone Health and a key researcher on the project.

According to Bo Xia, lead author of the study and a geneticist and systems biologist at Harvard University and the Broad Institute, the lack of a tail may have improved body balance for upright movement and, eventually, walking on two feet.

According to the scientists, the change in genetic makeup that resulted in the loss of tails occurred approximately 25 million years ago, coinciding with the evolution of the first apes from their monkey predecessors. Our human species, Homo sapiens, emerged around 300,000 years ago.

The family of Old World monkeys, which includes baboons and macaques, diverged from the evolutionary lineage that eventually led to apes and humans. Today, the hominoid category includes the “great apes” such as chimpanzees, bonobos, gorillas, and orangutans, as well as the “lesser apes” such as gibbons. Proconsul, the earliest known hominoid, did not have a tail.

The hominoid species underwent a process of developing a smaller number of tail vertebrae, resulting in the loss of a visible tail. However, remnants of a tail can still be observed in humans. The coccyx, also known as the tailbone, is a fused structure formed from the remnants of tail vertebrae located at the base of the spine.

For many vertebrates, a tail has helped with functions like locomotion – think of propulsion by fish and whales – and defense – as with dinosaurs that wielded tails with clubs or spikes. Some monkeys and some other animals have prehensile tails that can grasp objects like tree limbs.

According to Yanai, having a tail may be beneficial when living in trees, but once transitioning to land, it can become a disadvantage.

The benefits of having no tail seem to come at a price. Since genes can play a role in various functions of the body, mutations that provide an advantage in one area may be harmful in another.

In this particular scenario, the altered mice exhibited a slight rise in significant birth abnormalities known as neural tube defects, which resemble human spina bifida, affecting the spinal cord.

Yanai stated that due to significant evolutionary pressure, the decision to eliminate the tail was made despite the potential risk for neural tube defects.

It is a thought-provoking exercise to contemplate whether humans could have developed tails through evolution.

Source: independent.co.uk