We know that when a chicken becomes a die-in, it becomes a synonym for male external genitalia.
But in fact, the chicken does not have the part of Tintin. They have only cloaca. The way they mate with the mother bird is to reproduce in the cloaca of both sides, and the whole process is really "rubbing into it" and extremely fast, scientists call it "the cloacal kiss".
The ancestors of chickens and other birds began with tintin, many primitive birds, ancient jaw species, such as: emus, emus, ostrich, they all had a well-developed tintin, along the biological evolutionary route, birds formed two branches: one is a goose duck, including ducks with a spiral structure of tintin, they not only have tintin, but also unusually developed, and are spiral-shaped, in general, like the male South American hard-tailed duck, the average length is 22 cm, which can exceed half the length of the body. Records have shown that the hard-tailed duck in South America, which is the most inverse size, can reach 42.5 centimeters, which is longer than its own body length.
The other is the order Heliomorphs, which are mostly terrestrial birds that lack a tintin structure, with 97% of birds having tintin.
This is a mystery in the history of evolution, the vast majority of birds gave up the power of the male, abandoned their own Tintin, so why do ducks still have Tintin?
Scientists were confused at first, they thought it was because the chicken's tintin cells stopped dividing, but after research, it was not.
Researchers from Florida State University in the United States and the University of Reading in the United Kingdom published an online article in Current Biology to analyze the reasons for the shortening or disappearance of the external genitalia of birds, and believe that the expression of the Bmp4 gene in the distal interstitial of the reproductive nodules of chickaceous birds makes the reproductive nodules apoptosis, and eventually leads to the degradation of their external genitalia.
Scientists in the chicken and duck embryos after careful observation found that chicken and duck embryos in the early stage of development in a similar way to form tintin, it is difficult to distinguish the difference between the two, a few days after the chicken embryo original tintin structure began to expand, but the development will be abruptly interrupted, and then reverse atrophy. When they are born, chickens and chicken-related species remain only cloaca, not external tintin. But the duck's tintin continued to grow.
This special protein is the Bmp4 gene, scientists do not know why the Bmp4 gene is doing this, but scientists have found through experiments that Bmp4 is also involved in other important features in birds, such as controlling the origin of bird feathers and tooth loss, especially the Bmp4 gene can affect the size and appearance of the beak, so scientists speculate that the loss of tintin may be a side effect of this, which may be an important reason why chickens give up tintin.
The research is significant for humans, birds and humans, who use many of the same genes for development, humans also have genes that regulate the growth and biological function of Sertoli cells in the human testicles, and the BMP4 molecule is the second molecule known to promote thymus regeneration. The researchers found that BMP4 is produced by certain cells in the thymus gland. This molecule can signal to other cells in the thymus gland to initiate the expression of genes that promote development and repair. The study of the same genes in different species can give us a better understanding of the "pluripotency" of genes.
In addition, humans also have genetic diseases with Tintin anomaly, and the study of birds may also help human happiness.
In addition, the evolution of the reproductive system is very rapid and efficient, and it is more susceptible to genetic defects than other organs. Although the probability of genes causing malformations in newborns is high, we still lack genetic research at the molecular level, which not only gives us a better understanding of how genes work, but also gives us a better understanding of the causes of malformations.
That talk about chickens without Tintin, so why did ducks evolve a spiral-shaped Tintin structure?
The male duck came out spiraling (counterclockwise) because it is more adaptable and can adapt to the linear structure and the counterclockwise structure polyline structure.
Because they often force the female duck to reproduce, the female duck, in order to resist, developed a spiral-shaped reproductive tract (or fallopian tube) form, making it difficult for the male to inseminate at the fertilization site and the sperm store of the fallopian tube, thus gaining the right to choose, which means that without my consent, the male duck will not be able to continue his genes.
Such an outcome is unacceptable to the male duck, and in The Selfish Gene, the author writes that the meaning of all living things is to perpetuate the structure of genes. The same goes for male ducks. To facilitate access to the labyrinthine fallopian tubes of female mates, some male ducks develop spiral-shaped tintins.
Many people think that the study of duck tintin is meaningless, and scientists believe that the study of this aspect may have significant application value in the future.
But the way ducks reproduce also poses a problem, with other jealous male ducks going over to peck at the tintin of the breeding male duck, or even biting off the entire tintin stem. Such a high mortality rate of breeding ducks is a headache for the livestock industry.
To make a simple summary, although scientists have found that chickens do not have Tintin, ducks have a reason because of the Bmp4 gene. But why chickens and ducks evolved in this way remains a mystery in evolutionary history.