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Why do humans not have tails? A major genetic mutation that led to the evolution of Homo sapiens

چرا انسان‌ها دم ندارند؟ جهش ژنتیکی بزرگی که به تکامل هوموساپینس ختم شد

Throughout the Earth’s natural history, our ancestors had tails for about half a billion years. Fish used their tails to swim in the Cambrian seas and oceans, and millions of years later evolved into primates. Primates helped them maintain their balance in the forests while jumping from one branch to another in the Eocene forests. But later, about 25 million years ago, these tails were removed from the bodies of living things and disappeared.

Charles Darwin first noticed this change by studying the anatomy of ancient humans, but how this change remained unanswered. Until a team of researchers in a study noticed a genetic mutation that caused the tail to be removed from the body of living things. Interestingly, when the researchers created the mutation in the mice, their tails no longer grew and disappeared.

This dramatic change in anatomy had a profound effect on our evolution. Our ancestors’ tail muscles evolved into a network in the pelvis. Millions of years ago, when human ancestors stood and walked on their own two feet, this muscle was ready to support the weight of their limbs while standing.

Rhesus monkey

Although it is not possible to prove exactly why this mutation caused the death of our ancestors, it can be said that it is strong evidence for this. Darwin surprised the Victorian people by announcing that we humans evolved from primordial primates. He noted that although humans and chimpanzees do not have distinct tails, they both have a few smaller vertebrae that extend after their pelvis, which is actually a structure called the tail.

Since then, paleontologists have found fossils that confirm this information. The oldest primates date back to 66 million years ago. In their anatomy, there was a full tail that helped maintain their balance on the trees. Today, most primates, such as lemurs and almost all apes, still have tails, but no tails have been found in the fossils of 20-million-year-old chimpanzees.

To understand how humans and chimpanzees lost their tails, we need to look at how this organ forms in the bodies of other living things. During fetal formation, a number of major genes are activated, forming different parts of the spine to form distinct parts such as the neck and lumbar region. In the lower part of the fetus, a small tail begins to grow and special vertebrae, muscles and nerves are formed inside it.

Researchers have so far found more than 30 different genes in different species of animals, from iguanas with very long tails to Menx cats with short tails, that have a direct effect on tail formation. All of these genes are involved in shaping the rest of the fetus, and researchers are still trying to learn more about the unique activity of these genes in shaping the tail of the fetus.

Researchers believe that when a genetic mutation occurred on one or more of these genes, our human ancestors lost their tails. To understand these mutations, they compared the dienes of six species of tailless chimpanzees with nine species of tailed monkeys, and eventually found a mutation in a chimpanzee gene called TBXT that was common to humans and did not exist in apes.

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Comparison of fetuses of different animals

This TBXT gene was one of the first genes discovered by scientists about a hundred years ago. At the time, many scientists were trying to create observable genetic mutations by damaging animals, plants, and microbes in order to detect more genes.

In 1923, Russian geneticist Nadezhda Dobrovolskaya-Zavadskaya exposed several male mice to X-rays and allowed them to reproduce. He later observed a genetic mutation in a number of new mice that caused them to have shorter tails. Subsequent experiments also showed that this mutation occurred on the TBXT gene.

However, the mutation that this group of researchers found had never been seen before. The mutation contained 300 genetic codes that occurred in the TBXT gene. This part of the world was shared between chimpanzees and humans, and happened in exactly the same part of their genome.

To prove this theory and to show that this genetic mutation caused the death of the human tail, the researchers genetically engineered a number of mice in the TBXT gene to make a mutation that occurred in humans. When the mice hatched, most of them had no tails and a few had short tails.

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The group speculates that such a leap occurred by accident in chimpanzees about 20 million years ago, causing them to have short tails or no tails at all. However, this creature has survived without a tail and has been able to progress and pass this mutation on to the next generation. Eventually, this mutated TBXT gene became the normal gene for chimpanzees and humans.

Researchers say that the reason for the growth of the tail instead of the tail in our anatomy is not just the TBXT mutation, but there are several other reasons for it. In the experiments, the mice had tails of different sizes, but all human tails were the same and did not differ much. In the meantime, other mutations must have occurred in other genes to create this final shape and create the same anatomy in us.

Even if geneticists fully explain how our tail was lost, the “why” remains. The first chimpanzees were larger than monkeys, and their large size made it easier for them to fall to the ground than trees, and most of them might eventually die as a result of these falls. It would be very difficult to explain why chimpanzees that did not have tails did not suffer from a major evolutionary defect.

In addition, losing the tail posed great risks. The researchers found that a mutation in the TBXT gene not only destroys the tail, but also causes a defect in the spinal cord. However, the extinction of the tail was able to give chimpanzees a great evolutionary advantage and lead to the evolution of humans.

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