There are five fingers in one hand, why is there only two thumbs?

This question is really good. Sometimes what we do every day is too familiar to be ignored. As an orthopedic surgeon, we know the importance of thumb when we are not in contact with clinic, which accounts for 50% of the whole finger function. Without thumb, we can't do many fine movements, such as hugging, and the quality of life will be obviously reduced. Thumb total cut injury can be rated as grade 6 in industrial injury identification, which is a very high level, showing the importance of thumb. Although I knew at school that my thumb had two phalanges and my other fingers had three phalanges, I never thought about why. Therefore, after seeing this problem, I felt particularly interested, so I quickly consulted the relevant literature, but there were different opinions. Some people say that in the process of evolution, in order to better use fingers, the thumb slowly became like this; Some people say that God arranged it this way, but the following statement is quite interesting. Today is not a popular science, but a possibility of why this happened.

Thumb has two explanations as follows: there are 39 "homologous" genes in the construction of human stem cells, which determine the growth position of arms and the number of cervical vertebrae, and are called "Hox" genes.

As early as 525 million years ago, some homologous genes participated in the formation of limbs, and began to participate in the formation of fingers after1.300 million years. Birds have wings and feet, while humans have hands and feet.

The tissues of our limbs at embryonic level are regulated by these Hox genes, which are distributed on four chromosomes. When the moment of finger development comes, these genes will be activated by a series of amplifiers, which act as a control tower, triggering the expression of four homologous proteins. D 13 gene is the closest gene to the control tower. It receives all instructions, and the protein it expresses prevents genes from acting on gene lines in the thumb-D12, d 1 1 and d 10. Because the thumb is at the end of the hand, only the Hox gene in the first position is expressed. On other fingers, these four homologous genes can work normally. Because of this genetic "short circuit" structure, the thumb has only two phalanges.

Does it look like a gobbledygook ... Dr. Xie will explain it to you briefly, although it is not quite right, but it can be convenient for you to understand: this situation is equivalent to a chief designer building five buildings, and he handed over these five tasks to five subordinate designers, four of which completed the tasks well, but one designer suddenly had a short circuit ... Others built 30-story buildings respectively, and he only built 20 floors. However, it is such a mistake that this 20-story building has played the most important role. Isn't it interesting?

Although it can be explained that the thumb has two segments, it seems that 100% cannot be proved to be correct. Although we humans can be the spirit of all things, not 100% is the correct design, and many accidents have created our current design.

For example, the retina of our human eyes is much worse than that of squid. If you look carefully at the picture below, you will find that the photoreceptor cells in squid eyes are the outermost layer, while our human photoreceptor cells are behind nerve fibers. This structure leads to blind spots in our eyes, while octopus does not.

But anyway, fortunately, natural selection has given us a very useful thumb. Without the thumb, the function of our hands will be lost too much, which will seriously affect our lives! However, genes are always good at playing jokes on us humans. Some patients have three thumbs instead of two! This situation is called three-finger thumb! This congenital malformation can be traced back to 1559 at the earliest. It has been proved that there is a mutant chromosome 7q36. When the gene mutates, it will lead to the appearance of three-fingered thumb. Look at the picture below, this is not a picture of ps, this is a classic photo of three-fingered thumb. In fact, such patients are not uncommon. Many patients do not take treatment, because there will be a slight weakening of strength when holding objects. Many patients think that it will not affect their daily life, which is people's adaptability.

Some patients with three-fingered thumb underwent surgery for aesthetic requirements.

To sum up, the creator has completed its design for both the phalanges of two fingers and three fingers, and we have adapted to this design. Sometimes excessive pursuit of designers' ideas has nothing to do with the lives of ordinary people. What we need to do is to protect our fingers and let them serve us more. what do you think?