The tail is a standard body "accessory" that most vertebrates have. According to the "theory of evolution," humans originally have it. What is the reason that humans now have coccyxes but no tails?
The latest paper published on the life science online reading website bioRxiv uses genes as the research object and explores the secret of human beings gradually "getting off their tails" in the course of evolution.
The tail, for many animals, is an essential part of the body for survival. After throwing off their tails, humans obviously reproduced better than other animals, and finally became a unique creature that dominates the earth.
So, how exactly did such a great leap forward in the body happen?
Gene variation theory
In February 2021, the British "Royal Society Open Science" magazine published a paper discussing the fossils of Purgatorius mckeeveri, the oldest known primate to date.
Fossils show that this monkey lived in the Cretaceous period about 66 million years ago, the same time as the extinction of the dinosaurs.
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Such monkeys have flexible and mature tails, which should be convenient for them to live on the tree canopy. The tail is so important to monkeys that it has such a critical function that after so many years, most monkeys and other primates still have tails.
However, the skeletal fossils of the original Proconsul, the most primitive ape about 20 million years ago, have been discovered so far that it has no tail.
Why do humans and their close relatives lose their tails?
According to the latest paper published on the life science online reading website bioRxiv, a group of researchers from New York University found that some genes play a role in the early stages of embryonic development, instructing stem cells to develop into important bone structures, such as the neck and waist. , And the vertebral chain and muscles that ultimately form the tail.
The human tailbone is considered to be the result of evolution: the human ancestors who walked out of the forest no longer need the tail that crawls among the branches to maintain the balance of the body.
Researchers say that about 30 genes are now known to be the basis for tail development in different species.
When the researchers compared the DNA of six species of tailed monkeys with the DNA of nine species of tailed monkeys, they found a genetic mutation shared by apes and humans, but missing in monkeys.
The mutation affected is a gene called TBXT.
Therefore, one explanation is that about 20 million years ago, an ancient ape was born with this genetic mutation, reproduced more and passed this gene to offspring, and eventually became a decisive feature of the ape genome.
In order to verify that this genetic mutation is related to the loss of the tail in humans, the researchers conducted experiments on mice. Some of these genetically modified mouse embryos have not developed tails, and some have very short tails.
Therefore, scientists say that the TBXT gene mutation is not the only reason that humans have a tailbone but not a tail. There must be other genetic mutations that have led to this structural feature of humans.
The function of the tail
The ocean is the birthplace of life on earth, which is the most mainstream consensus in scientific development so far. According to the "evolution theory" of life, the tail of an animal evolved from the tail fin of a fish.
During the Cambrian period 500 million years ago, fish lived in the ocean, and the role of the fish tail was to advance and adjust the direction.
In the evolution of life, the tail has different functions for various animals: the cow uses the tail as a fly swatter, the crocodile stores fat on the tail, the peacock uses the tail for courtship, and the monkey uses the tail to maintain balance...
However, there are also many animals that have lost their tails during evolution: koalas, guinea pigs, gorillas, frogs...
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Although humans do not have tails, they have left traces of tail evolution, and human embryos have tails in the early stages of development.
The human tail is most obvious from the 31st to the 35th day of gestation, and the size is about one-sixth of the embryo itself. When the embryo develops to the ninth week, the tail stops growing and degenerates into a tail bone.
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According to the theory of "evolution", when the human ancestors "threw off" their tails, when they moved from the forest to the grassland, the external environment no longer needed a balanced tail on the branches, and the energy needed to maintain the tail was saved inside the body; When being chased by a beast, there is one missing "handle" to be caught.
In the book "The Descent of Man, and Selection in Relation to Sex" first published in 1871, the famous British scientist Charles Darwin noticed this feature of the human body and wrote Dao: In some rare and abnormal situations, the tailbone will grow into the shape of a tail.
The latest research results explain the "throwing off" of the tail in humans from the perspective of genetic mutations, perhaps answering the "process" question of "how" humans do not have a tail, but it still fails to reveal the fundamental question of "why there is no" tail. .
From this point of view, the endless debates between "theory of evolution" and "theory of creation" just show that human beings have been exploring the origin of the universe and life.