Are you curious, Most mammals have tails, but humans do not?
In fact, tens of millions of years ago, the common ancestor of humans and other primates had tails. Many modern primates, such as monkeys and lemur , still have tails, but the ancestors of modern humans and apes such as chimpanzees and gorillas have abandoned the body structure of the tail.
So why do some primates retain their tails, but humans and apes do not? Scientists have always wanted to figure out this problem.
Written | Mindy Weisberger
compiled | spruce
editor | poplar / trees
map source | Livescience / Wikipedia
The human embryo has a tail
In fact, when we were embryos, we had tails. tail This feature can be traced back to the earliest vertebrates on earth, so in the early embryonic development of , we will have a tail briefly.
Not only humans, but all vertebrates in the world are like this. But after about 8 weeks, the tails of most human embryos will disappear completely.
Scientists pointed out that the tail will undergo the process of cell apoptosis . This is a kind of programmed death, a natural process in the development of multicellular life. After that, there are only three or four vertebrae left in the tail.
Sometimes,Human babies also have tails at birth, but this is very rare. A 2012 study pointed out that this tail is embryonic remnants, not a real tail.
The fake tail covered with skin contains muscles, nerves, blood vessels and connective tissue , but it does not have bones and cartilage, and is not connected to the spinal cord like a real tail.
But how do humans lose their tails? For Dr. Xia Bo of the Grossman School of Medicine of New York University, this is a question he has been thinking about since he was a child. Dr. Xia is an expert in the study of human development, disease and evolutionary genetic mechanisms.
"When I was a child, I wanted to know why almost all animals have tails, but I don't." Dr. Xia said. In the summer of 2019, after his tailbone was injured, Dr. Xia decided to investigate this question more closely: How did humans lose their tails during evolution?
gene mutation leads to the disappearance of the tail
The skeleton restoration model of the former Consor ape | Image source: Guérin Nicolas
8p 8 span 8 and the earliest known human span
5br 5br
The tailless ancestor of the genus is a primate called , the proto-consour ape ,Lives in Africa during the Miocene period (5.3 million to 23 million years ago) in .
But Dr. Xia and his colleagues believe that the disappearance of the tail may be traced back to earlier - about 25 million years ago, when the evolution of humans and apes took different paths.
They compared the genetic data of 6 species of human family and 9 species of monkey family to find possible tail-related differences. A possible candidate gene appears in a small piece of DNA in the "Alu sequence" (a repetitive gene sequence).
This gene is hidden in the TBXT genome , which can jump from one position in the gene sequence, which affects the synthesis of span 8 to another. This mutation is present in the genomes of apes and humans, but not in the genomes of monkeys.
Subsequently, scientists used CRISPR gene editing technology to copy this mutation into the mouse TBXT gene. It was found that the tail lengths of the mice after gene editing varied from normal to no tail at all.
Although the mutation did affect their tails,But this did not make them completely lose their tails. Scientists realized that there are other genes that play a role in the loss of tails in primates. Moreover, scientists believe that the appearance of this mutation is a key factor in the disappearance of the tail.
Scientists pointed out that The loss of tails of early humans and apes is an evolution that helped them transition to upright walking.
Can we still grow a tail
_spanspan 8 Say, tail is actually a kind of advantage, can play many roles. "During the jump, the tail can help the body maintain balance," she added, "it can also keep the body stable while moving, foraging, and even sleeping."
primate Sometimes the tail can also be used as a tool. For example, white-headed capuchin monkey will use its tail to absorb the water in the tree hole, and then suck the water from the tail. Primates can also use the tail as a pillow or quilt, and even use the tail in social activities.
The little monkey will wrap his mother’s body or tail with his flexible tail.They also pull the tail of their companions when they play. Titi even entwines his tail with his mating partner to express his love.
Just because the tail has so many uses, humans without tails might think that they should have more tails. So is it possible for us to grow a tail again? Unfortunately, we lost our tail a long time ago, it is impossible to grow back.
25 million years is really too long. During this long period of time, the genes related to the tail in our body have long lost their function, and all the DNA required for tail development has also been lost. .
"Unfortunately, even if we fix all the genetic mutations that caused us to lose our tail, we still may not be able to grow our tail again." Dr. Xia said.
[Singularity Science is the copyright partner of Science Illustrated, a European classic popular science magazine, focusing on reporting exciting cutting-edge technological developments, allowing readers to see the future ahead of time. ]
reference
[1] https://www.livescience.com/why-dont-people-have-tails
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