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What kind of body is perfect? In fact, the “perfect individual” has never existed: from goose bumps to men’s nipples to snoring, many physiological features of the human body are the legacy of evolution…

Which is the most perfect human body in the world? Is Michelangelo’s David? Or was Vinturvius written by Da Vinci? Or can you look modern and look for modern bodybuilding athletes?

Unfortunately, even the eight abdominal muscles pursued by modern aesthetics are actually the products of the evolutionary process. The muscle characteristics of the connective tissue division are commonly owned by fish, and most of the muscles of the terrestrial spinal cord animal have lost the phenomenon of segmentation. However, such remnants still exist in the rectus abdominis muscle.

Segmented muscles of human rectus abdominis and zebrafish

Although it sounds unbelievable, none of the entire Homo sapiens species can be considered perfect. “Perfect human body” is simply a false proposition. After all, the human body is not created by God according to his own preferences. Even human beings who consider themselves as the most advanced are full of flaws. This is a fact that is hard to accept for perfectionists and supporters of creationism.

In general, if you want to understand history, you must look for the remains left over from the birth and development of civilization. But to understand the history of evolution, we don’t need to go to the wilderness to look around and see if we can.

Human beings are generally considered to be highly evolved advanced creatures, which are different from the body form and the way of life. Despite this, there are many organ remains in our bodies, and each one is related to evolution.

Evolutionary ear in the ear

Some of these relics are already familiar.

For example, at the end of the appendix, when we first learned about it from our parents, the “useless” and “excessive” labels were already affixed. The appendix is ​​located at the back end of the cecum, originally used by mammals as an organ for the digestion of plant fibers. It later lost its status because of the change in diet. (Note: The appendix is ​​not a completely unnecessary and useless organ. Modern studies have found that the appendix has an immune function, and it can also provide a shelter for some probiotics to protect the health of the intestinal flora.)

Another example is the human ear, which is a well-preserved evolutionary site, and the exquisite artifacts are amazing. The first is the Darwinian point at the outer edge of the ear, with a small protrusion on the inner edge of the upper part of the helix.

It is the ear tip of higher animals. Humans no longer have such sharp ears, but they still retain this part.

Below the pinna, we also retained three moving ear muscles. This is obviously our mammalian ancestors used to control the direction of the auricle in order to better alert the danger. However, the human ear has long changed and there is basically no possibility of changing the orientation. The three muscles have become furnishings. Many people are unable to control these three dynamic ear muscles. Only a few people can regain their skills and use the legacy of this ancestor.

Apart from these obvious ancient ruins on the ear, there are still some organs that we talk about every day but do not know that it is an evolutionary remnant.

The truth of goose bumps

Goosebite is a reaction that we often see. It may be frightened or cold. Perhaps some people will not actively explore the significance of this reaction, at best, in the biological textbooks to remember “skeletal muscle shivering, piloerection, increased thyroid hormone secretion,” the human body cold mechanism.

In fact, standing hair muscles are the muscles that allow hairs to stand upright. For our furry ancestors, it is a normal operation to get fried with some external stimuli. However, our human hair is not very competitive and has not been able to thrive. Although muscle is still the muscle, hairiness is no longer that hair. Many animals still retain the “fried hair” reaction. The most common is that cats erect their hair in fear and make themselves appear as large as possible.

And people have more complex and sophisticated emotions than these animals. The reason for playing chicken skin is not limited to fear. It may be that you read the wonderful sentence that you read in your novel, or you may hear an amazing melody, which obviously has nothing to do with fear. The reaction of pili muscles may help us to find the origin of these advanced emotions. After all, the chicken skin is also the natural reaction after completing the “harmonious life”.

Why do men also have nipples?

In addition, the existence of some extra organs can directly refute supporters of creationism.

The Bible tells us that God, according to his own image, used dust to pinch out a man and gave him life. Afterwards, God felt that one person was too lonely. Then he made a woman with a rib of a man. If the story is true, why do men need to have breastfeeding organs that resemble women? Is it because of God’s own efforts to nurture the offspring? Or is there anything special about God’s nipples?

This question is not a good one. Darwin did not explain this issue well as chairman of the alliance of creationism. He only put forward a speculation that the former mammals were both parents and breast-feeding offspring, and later only for some reason did the male nipples degenerate.

The fundamental reason why men are born with nipples is that the default gender for human development is women. This sex determination mechanism comes from the XY sex chromosome we are familiar with.

In the first four weeks of embryonic development, there is no gender distinction, and all genes are coded according to the X chromosome. The genes for the nipples and breasts are on the autosomal chromosomes. Therefore, both men and women will have long nipples. It was not until the fifth week that embryos began to form gonadal organs, but this is still no gender distinction. In the seventh week, the sex-determining gene on the Y chromosome was expressed and the gonad began to develop into the testis. If it is a female baby without a Y chromosome, wait until the 13th week when the gonads will develop into the ovaries according to the default female gender.

In simple terms, the development of mammary glands is completed before the sex differentiation of the embryos, even if the mammary glands are useless to men, and it is not convenient to delete them later. This also shows that the male breast is not a degenerative organ, but only maintains the undeveloped state before puberty. If stimulated by estrogen, it can still develop into a fully functional breast-feeding organ.

The developmental mechanism of human embryos may be to increase developmental efficiency. After all, saving the embryonic development time can bring about greater chance of survival. But this also brings some obvious flaws.

Gonadal position causes hernia

Although the testicles of males are located near the penis, the spermatic cords that connect the two have a large circle in the abdominal cavity. This causes men to be more prone to suffocation and some of the intestines may fall into the scrotum and cause immense suffering.

The reason is that the gonads of human ancestors grow at higher positions. For example, the gonads of sharks grow near the liver. The gonads that form in the early stages of human embryos are still the same, but we all know that both the female ovaries and the male testicles have to be positioned lower. Therefore, in the process of fetal development, the gonads continue to move downwards, just like the re-evolution. For women, the ovaries only need to move down to the lower abdomen, while the male’s testicles have to be moved out of the abdominal cavity. This process will inevitably lead to errors.

There are many factors that cause the baby’s testicles to remain in the scrotum when the final fetal development is complete, known as cryptorchidism. The testicles they hide in their bodies are difficult to produce sperm normally because of the high ambient temperature, and they are dozens of times higher than normal testes.

However, the normal testis is not necessarily perfect. As the testicles descend through the weakened area of ​​the body wall down to the scrotum, this process not only allows the spermatic cord to circle the pubic bone, but also leaves a fragile breach in the body wall. When the abdominal pressure rises, the intestine may break through the weak body wall and fall into the scrotum. The increase in abdominal pressure may be due to children crying or coughing. Adults gradually become more prone to cramps due to the increase in body wall thickness. Clinically, in addition to male-specific scrotal hernias, male inguinal hernias have a much higher prevalence than females, roughly 12:1.

The truth of hiccups

Fish ancestors did not simply dig a hernia pit, but they also gave us a burp gift to our amphibian ancestors. (burp: evolutionary defects from amphibious ancestors “) hiccups here are not the kind of hiccups that eat enough to spare the excess air in the stomach, but the involuntary muscle spasmodic hiccups. We inherited the phrenic nerves that control the respiration of fish ancestors, and inherited the reflex of closing the trachea when breathing from amphibian ancestors.

The fish are gill breathing, and the gill is located near the neck. Therefore, the phrenic nerves that control the breathing follow the principle of proximity and emit from the neck. To amphibians, they have evolved their lungs and can breathe on land.

The outer gills of tadpoles

However, amphibian larvae still lack water and there is a stage where gills and lungs coexist. For example, tadpoles usually breathe through the gills before metamorphosis, but they have the lungs at the same time, and the phrenic nerve must close the trachea in control of breathing to ensure that the water does not enter the lungs. This protection mechanism has also been passed on to humans, but humans have no gills. When this protection mechanism is activated, there will be hiccups.
From the gill to the lung, the phrenic nerve control organs have moved down a lot, but the starting point of the nerve is in the original neck. This means that the way of phrenic nerve will be very winding, and the length of nerve fibers is extraordinary. Any problem will cause hiccups.

Recurrent laryngeal nerve break through cognition

If the neck is far away from the chest, it is understandable to pull a long nerve. The famous recurrent laryngeal nerve may break through your bottom line.

The recurrent laryngeal nerve sends out a large number of structures from the brain, connecting the neck, which mainly control the movement of the throat, including swallowing behavior and daily voicing.

In principle, from the brain to the throat path is very short, there should be no difference. But in fact, both the left and right recurrent laryngeal nerves have taken a surprising detour.

The back of the laryngeal nerve on the right is to go down the carotid artery, and the left laryngeal nerve is further extended down to the heart, around the aorta and back to the larynx, which is the name of the recurrent laryngeal nerve. This unimaginable layout is once again inseparable from our fish ancestors.

Our recurrent laryngeal nerve belongs to the fourth vagus nerve in the ancestors, under the sixth arch, and the two nerves and arteries do not interfere with each other. Here we can get to the terrestrial animals, where the sixth artery arches move back to the chest, and the recurrent laryngeal nerve has to be bypassed from under it.

Humans should be glad that their necks are short and the recurrent laryngeal nerve is not too long. Look at the long neck of giraffe, and the laryngeal recurrent nerve is 4.56 meters long. I am afraid it is the heaviest animal to suffer.

In fact, although we always claim to be a miracle in the history of biological evolution, we are the highest ranking creature on earth. But the cruel reality still reminds us that mankind is, in a sense, a fish, a frog and a beast. If we walk a million years, we will still be a primitive creature of the magic version. Although we have more functions, there will be more hidden dangers in the process of modification. There are no advantages and disadvantages between the sophisticated and sophisticated animals and the ancient simple creatures billions of years ago.

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