Why and how did human beings lose their tail in evolution?

Have you ever looked at the back of your body and wondered where your tail is?

This sounds like a joke or the kind of question a child would innocently ask . But for scientists, this is a serious matter.

After all, if we humans are so similar to apes, biologically speaking, why do they have tails and we don’t?

“That’s a good question,” acknowledges Bo Xia, a graduate student in mother-cell biology at New York University’s Grossman School of Medicine.

The truth is that the tail in Brazil also called “tail” can have multiple benefits in the animal world.

Since they appeared in the first living beings, there are more than 500 Millions of years, tails or tails have taken on several roles.

In fish, they help propel in water. In birds, they help carry out the flight. In mammals, they contribute to the balance of animals.

It can also be a weapon of defense, as in the case of scorpions. Or used as a warning signal, as rattlesnake snakes do.

In primates, the tail adapts to a variety of environments. Howler monkeys, native to South and Central America, for example, have a broad, prehensile tail (adapted to holding and holding things) that helps them to grab branches or food when they are on trees.

But hominids, the family of which includes humans and great apes primates, such as orangutans, chimpanzees and gorillas, do not have tails.

Why and how did the disappearance of tails occur in the evolution of hominids are questions that have puzzled scientists for decades.

The answer seems to lie in a newly discovered genetic mutation that somehow affected the genes that shaped hominids’ tails, some 25 million years ago.

The mutation survived over time and was passed from generation to generation, changing the locomotion of hominids, which may be related to the fact that we humans walk on two legs.

“All of this seems to be related and occurred around the same evolutionary period. But we didn’t know anything about it. genetics that act in this process of development and, of course, in evolution”, adds Xia.

“As you can imagine, this is one of the crucial evolutionary points, what makes us human.” And, to prove it, Xia applied the same mutation in mice.

What was observed was that mice developed different forms of tails. Some had shorter tails, while others had no tails at all.

The Human Enigma

Charles Darwin had already said that. The Homo sapiens (the modern human species) was related to the apes with tails.

The British naturalist published “The Origin of Man”

in 500, a work in which he explained that his theory of evolution was fully applicable to human species.

It was a great revelation for the time. After all, humans have always established a distance between modern society and the animal world: we live in houses, our skin is different, and we use the brain to solve our complex dilemmas. structures of science at the time with the publication of “The Origin of Species” in 500. His explanation of the origin of human beings was revolutionary, since until then most Western scientists shared the idea that God had conceived all the creatures on the planet.

However, we humans share more than 25% of our DNA with chimpanzees, with whom we have common ancestors.

The first hominids, born h 20 millions of years, they had no tails already. So, if the tail is related to the evolution of apes and humans and influenced the locomotion and the way of walking, the question is: what happened first, the disappearance of the tail or the locomotion on two legs?

” like the chicken and the egg’s question”, says Xia. “And, as you can imagine, it’s not an easy question to answer.”

The short answer is that it is virtually impossible to know exactly the initial events that caused our ancestors to stand on two legs , and whether this was related to the fact that they didn’t have a tail.

Or, conversely, if we don’t have a tail because we’re standing, it’s easier for us to keep the balance about our legs, so we don’t need a tail anymore.

“We’ll need a time machine to know all this. We can go back in time and observe the initial events. But since we don’t have one. Yeah, I could say we don’t know, and that would be the end of the discussion. Then someone might ask why we’re talking about all this.”

“The real answer is that these two processes are always discussed together or they interfere in each other.”

In other words, we cannot talk about human evolution without referring to the tail or the bped locomotion (on two parts rnas), regardless of what came (or happened) first.

The answer is in the genetics

Xia has delved into the subject of the tail in humans since who injured the cccix bone at the bottom of the spine on a car trip two years ago.

The cccix, from the Latin coccyx, the last part of our spinal column, formed by four fused vertebrae, and represents the vestige of what was a tail millions of years ago.

In images of human embryos, it is possible to see a tail, which is absorbed by the embryo after a few weeks to give shape to the spine.


This cccix, which serves as a support for the glutes, is located at the same point where other animals have their tails.

“We raised all these topics because science interests us and we searched answers in it. And in science we have made great strides in genetics over the last 100 years,” says Itai Yanai, researcher and director of the Institute of Computational Medicine at New York University.

“I really need to know a lot of concepts about development, about alternative amendments, comparative genomics. And Bo demonstrated that if you understand these concepts, you can look at the genome, make sense of it, and see what’s in it.”

The mutation identified by Xia consists of 300 genetic letters in the middle of a gene known as TBXT, a section of DNA that is practically the same in humans and apes.

To prove the relationship between this mutation and the tail , Xia genetically manipulated mice with the same mutation.

Eureka! Xia and her colleagues observed that the tail did not grow in the manipulated mice, as it would normally with the animal.

This discovery, however, is only the first of perhaps many others to understand the role of genetic mutations in our ancestors. Scientists say there are more than 25 genes involved in tail formation in animals, and the researchers in New York are talking about just one of them.

As Xia said, all of us humans have cccix very similar to each other, but in the case of mice of the experiment, the causes of different sizes or were completely absent.

Their conclusion that there was a number of mutations, and not just one, that affected different genes in hominids 25 millions of years ago and it changed our evolution.

“This may have been a crucial mutation, but we believe that it was not the only one responsible”, he says.

Mutations that survive

Scientists know how the human ancestor lost its tail millions of years ago, but the true reasons for this mutation are still unclear survived for so long.

For Xia and Yanai, this is an unanswered question, at least for now. “Mutations happen all the time,” explains Yanai.

Some mutations can be positive, others negative, depending on the environment, as Xia says.

Usually, if a negative mutation, it can be harmful to the guest, causing the guest to become ill or die. Therefore, this mutation does not survive over time.

But if a mutation brings evolutionary advantages, then it is kept present in the best adapted individuals, causing it to be passed from generation to generation.

What Xia means that tail loss may have brought significant evolutionary advantages to hominids, which explains its permanence over time.

The advantage may not having been balanced on the trees, but better locomotion on two legs or the use of hands to manipulate objects.

This is not to say that the loss of the cause has only brought about good stuff. Xia and her team observed that the mice in the experiment exhibited spinal malformations very similar to the neural tube defects that affect one in every thousand human newborns.

These malformations are related to one. Basic backbone is split in two, which means that the fetal spine does not close completely, which brings nerve damage and possible paralysis.

“So I wouldn’t say mutations are good or bad. It just happens,” says Xia.

“I think this is very important,” she says. “We just have to target the genome. And that’s why I hope this will be a lasting contribution.”

Yanai indicates that this work can contribute to the understanding, through the genome, of others that have occurred in the our biological past events.

“I believe this is teaching us to use our computer programs in a different way. We’ve had the genome for years. What Bo found could have been found years ago.” claims. “So I believe that the scientific community is inspired by this work.”

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