Scientists have put forward many hypotheses about bilateral symmetry advantage. For example, this symmetry can make animals move effectively in a purposeful and intentional direction, move to food sources or favorable environments, and stay away from danger. Bilateral cooperation can promote the improvement of sensory organs, such as eyes and ears, which helps symmetrical bodies to concentrate on sports.
Another popular hypothesis is that the evolution of symmetry helps to choose a mate. Experiments on birds and insects show that females prefer to mate with males with the most symmetrical decoration. For example, female peacocks prefer male peacocks with long and symmetrical tails, while domestic swallows prefer male swallows with long and symmetrical tails.
The left and right surfaces of symmetrical creatures are symmetrical, but the symmetry is not perfect. First of all, the shape or position of internal organs are not all symmetrical, and even the face is not completely symmetrical.
Asymmetric animal
Sponges are completely asymmetrical; Another example is fiddler crabs. One male claw is more than ten times bigger than the other.
Another example is the narwhal. The male's left tooth protrudes up to 3 meters, like a horn, while the right tooth is very small.
Flatfishes are symmetrical at first, but as adults, their eyes will move to one side of their faces, so that they can lie flat in the sand to prevent predators from attacking from above.
Cross-billed bird, the upper and lower beaks cross together.
A: Some animals do have obviously asymmetrical bodies, such as flounder, fiddler crab, hermit crab, butterfly of Yin and Yang, sperm whale and conch.
Ignoring the details, most animals on the earth are almost symmetrical in appearance. For example, people, giant pandas, and most fish are plane symmetrical. This is because when animals walk and exercise, symmetrical bodies are more likely to achieve left-right balance, thus achieving labor-saving effects.
For animals in the ocean, when the body is symmetrical and swimming fast, the resistance on both sides of the body is the same, and the balance of the body is easier to control; But the world is full of miracles, and there are some exceptions to biological evolution.
right-eyed flounder
The flounder's eyes are on one side, which is different from the crawling rays. The side of the flounder with eyes is extremely asymmetrical. This peculiar body structure also creates the interesting life habits of flounder.
The flounder swims with its eyes up, and when hunting, it lies on the seabed with sand, only showing its eyes; In fact, when the flounder just hatched, its eyes grew on both sides. When it grows to about 3 cm, one eye begins to move to the other side, and finally both eyes grow to one side.
Fiddler crab
The obvious characteristics of fiddler crabs are large and small claws [× o] and high eyes, and the large claws can be used as weapons for defense and attack; But only the male crab's claws are big and small, and the female crab's two small claws are symmetrical.
If the male crab loses its big claw, it will grow a small claw in its original place, and the original small claw will continue to grow into a big claw.
Yin-yang butterfly
The butterfly of Yin and Yang has a protruding tail stalk on one wing, but not on the other wing. This butterfly is hermaphrodite, half female and half male.
Silurus gracilis
Hermit crabs live in the shells of animal carcasses. Compared with common crabs, hermit crabs have a longer body, an asymmetrical body and a bigger foot.
sperm whale
Sperm whale's head accounts for one third of its body, and its head is more like a cuboid. The left and right skulls are asymmetrical, and the left bony nostril is larger than the right one, so its appearance looks very uncoordinated.
trumpet shell
Molluscs with shells, such as conch, snail, oyster, etc. Having an asymmetrical body and a spiral shell.
Wrong, this is a joke played by Leonardo da Vinci. One of the sketches is considered to be the masterpiece of Mona Lisa, with a size of 34*25㎝, which is not much larger than A4. Vitruvian, a circle around the human body, to illustrate his view on the symmetrical structure of the human body! He dissected many animals, including human corpses, and drew some sketch notes, no worse than today's medical school. This guy is called the highest IQ person in human history by some researchers, but his genius is limited to scientific and technological means! In his time, we couldn't observe such a small difference. In fact, all animals, even creatures, have asymmetric structures! I have always wondered if Leonardo da Vinci realized this difference, but in that era, it was still possible to regard it as a symmetrical structure in painting. The actual difference of a few centimeters is not so important in painting, but drawing a hand and foot is not' beautiful'. It was an era of pursuing truth, and this' truth' was a visual relative value. Leonardo da Vinci is also a black-hearted man (some psychologists and human behavior experts have analyzed it)
I work like a knife. In the concept of China people, a knife has a unilateral edge, so it is asymmetrical. It is more difficult than a sword to consider the balance of the axis (horizontal) line, not just the vertical (tree) line between the blade and the handle, so I have made great efforts on the symmetry problem, and the tool is not that simple! Symmetry and asymmetry also have many interesting reasons!
The most familiar example of symmetry is man himself. Leonardo da Vinci chose the human body to explain symmetry. Let's start here. The first is appearance, no one is absolutely symmetrical, even the completely symmetrical face made by computer looks terrible! Then there is the function, no one is as flexible as his right hand, and his left and right legs are as long and as hard! Functionally, everyone has active hands, eyes and legs. Many examples can be quoted from people. From the inside out, the left and right functions of the brain are different, and the internal organs are not the same size even if they are symmetrically distributed. This is complicated for many reasons!
But in the final analysis, there is only one root cause, energy saving!
If the government can produce two brands and one team, it will also work hard on the word "saving". If one organization does not do much work, it is a reasonable choice for another organization to take care of it. Although sometimes the effect is poor or even counterproductive, in theory, it is a good choice to weaken a creature when it is sufficient, provided that it is sufficient! ! !
People and other living things exist by energy, which is not produced by life itself. The energy of life on the earth comes from the sun, which can flow among all kinds of life through the food chain. Under the pressure of reproduction, in a broad sense, all living things on the earth are competing with each other. If a mathematical model is established, the total amount of energy that the earth gets from the sun in a short period of time is a nearly constant value, then how to make good use of the energy that it can get is an eternal problem that all living things can't avoid! Then, in the face of this problem, if even distribution is an unreasonable choice, we can regard most of the vital signs of the left and right structures as spare parts for one to the other! Hehe, hands cooperate well, but not everything needs two hands. If one hand is accidentally lost, the ability of the other hand will be strengthened under the pressure of life! Such examples abound in real life. From this perspective, we can see a life feature called ability compensation. Conversely, can one hand be regarded as a spare part of the other? ! Since there is a' spare tire', then, hehe, look at the car. Why don't many cars have full-size spare tires? The reason is the same!
But why are the structures of many creatures basically symmetrical?
In addition to standby, it is balance, balance and energy saving, which is the inherent contradiction of most living things. From a philosophical point of view, balance itself is also a kind of energy saving. Single-arm structure has the disadvantage of single function, which also affects the movement of living things. Why do most industrial robots have a single-arm structure? Because they rarely need to move! The more urgent the need for mobility, the closer it is to absolute equilibrium. Why do you need to change tires one by one? This is also a fact! Plants that don't need to be moved can grow into Huangshan welcoming pine!
I use plants as an example because plants are relatively simple, and there are too many reasons for the symmetry and asymmetry of animals. This has been written a lot, and it is objectively estimated that 80% people don't want to read it! But don't mention that there are no two identical leaves in the world. Everyone can tell the truth, but why? There are many reasons for the asymmetry of blades, including aerodynamics and fluid dynamics. The best state of leaves is that more areas face the sun. Plants are different from animals, and most of them can only be considered from the modeling effect, so the asymmetry of leaves is extremely complicated, and the growth position is highly oriented. They don't have the nervous system and movement structure like animals, but they seem to have the ability to think, just taking the influence of the wind on the leaves. They have a set of their own coping methods. When the breeze blows, the leaves are offset by the swing of the petiole, which basically does not affect photosynthesis. When the wind is strong, they will turn the leaves to avoid being blown away. After all, it takes energy to grow a leaf. When the clouds cross, they will fold in half or sag, and save themselves by shrinking their faces! The asymmetry of leaves is the result of balance, and no two identical leaves are also the result of balance. If you use a computer to analyze, it will not require much less calculation than the sand mold, so learning to paint, whether it is good or not, and learning the way of thinking and observation of painting will make you see the world more clearly!
To be sure, I may go back. After all, my original intention is to share, so don't throw negative energy at me in a stupid way!
Yes, there is.
There are not a few animals with obviously asymmetrical shapes, and there are only a handful. For example, flounder, two eyes must be on the same side of the head, in pairs.
For example, the male crab of fiddler crab has two claws, one big and one small. Big claws can scare enemies, fight for courtship, and small claws can only sell cute. . . .
Another example is the sperm whale.
The skull of sperm whale is obviously asymmetrical from left to right. They only have the left nostril to breathe smoothly, so the left nasal bone is obviously developed, the left nostril is bigger, and the right nasal bone is degraded.
These animals can find obvious asymmetry from their appearance.
However, it is true that in order to move faster, better and more balanced, organisms have to undergo symmetrical cell division from the development of fertilized eggs, but most animals are basically symmetrical in size. But this kind of symmetry, also can't do perfect symmetry. For example, most people's left and right faces can't be completely symmetrical. If you don't believe me, you can copy and paste the left face or the right face of your photo to the other side, and you will find it completely different from what you are now!
But this slight asymmetry looks more comfortable. If a person's left face and right face are completely symmetrical, the effect will be a little … worse.
As for the visceral distribution of organisms, it is even more impossible to achieve complete symmetry.
Like people. . . . . The internal organs as a whole are asymmetrical. Although all organs such as lungs and kidneys are symmetrical, one on each side, the positions of the heart, stomach and liver are actually asymmetrical in the human body.
Most living things, including people, are symmetrical, but there are many forms of symmetry on the earth, such as wired symmetry, such as jellyfish, face symmetry, such as most advanced animals, and a little symmetry, such as viruses.
The symmetry of life on the surface of the earth comes from the uniformity of space. If a creature is born asymmetrical, it is likely that it will not be able to keep its balance under the action of gravity. What we call symmetry is actually an approximate symmetry, and it refers to the symmetry in appearance. Take the human body as an example, it is indeed symmetrical in appearance, but it is not absolute. People's left hand and right hand, left foot and right foot are generally different in size, and if human internal organs are involved, there is no symmetry at all, so what we call symmetry is only general symmetry.
But there are also some creatures that are asymmetrical and asymmetrical in appearance. Most of these creatures live in the ocean or water, such as flounder, conch, hermit crab and so on.
right-eyed flounder
The flounder is a strange-looking fish. Strangely, its two eyes are on one side of its head, and its body is very flat and oval. The left side of its body is light brown and its abdomen is light. In fact, the treasure fish we often eat is commonly called halibut, which is also a kind of halibut.
Silurus gracilis
Hermit crab is a kind of crab with snail shell as carrier. It doesn't dig its own hole, but lives in a snail's shell. Hermit crabs, except for a few species, are generally asymmetrical in body and tail joints.
trumpet shell
Conch is no stranger to us. Generally, animals with soft bodies are often asymmetrical and their shells are spiral.
In addition, some creatures are asymmetrical, such as sponges, but some people think that sponges are radiation symmetrical creatures. In addition, shells do not seem to be symmetrical creatures.
Have you found that basically all animals are symmetrical? Are there any asymmetrical animals?
Most animals we see every day, even ourselves, are basically symmetrical, unless there are some disabilities! But most people are not exactly the same, such as face, eyes and nostrils, and even girls' breasts. The general situation is one big and one small, even the position is high and low! Of course, we don't care about these details today, but there is a question, why are we symmetrical? What other asymmetric species are there?
First, why should humans be symmetrical?
In fact, there is not only a kind of left-right symmetry, but also radiation symmetry, such as corals, starfish, and of course many asymmetric species! From the evolutionary history of organisms, we can know that there are two kinds of body symmetry from eukaryotes, one is bilateral symmetry and the other is radial symmetry. Animals with radial symmetry are generally pie-shaped or bucket-shaped, and generally have only two layers of bodies, such as coelenterate jellyfish and echinoderms starfish! But bilateral symmetry has three layers. Theoretically, bilateral symmetry is more advanced than radiation symmetry of animals! Of course, this is an important reason, so what else?
Since the Ordovician 550 million years ago, animals have evolved into symmetrical bodies. In order to survive, the nervous system and sensory organs will evolve with higher requirements, and the development of the head will appear in the direction of the trunk, because this is the most convenient and quick source of danger perception! Of course, it is still too early for the earliest mammals to appear at this time, but it is obvious that mammals have inherited these symmetrical structures and brain evolution from 5.5 years ago!
We found the source of human left-right symmetrical structure, but the brain is actually divided into left and right brains, which is mainly due to the evolution and development of human sensory and motor organs, and it is also a trend to gradually tend to fine division of labor!
Division of labor between human brain and nervous system
Second, are there any asymmetric animals?
Although humans seem to be symmetrical, the distribution of internal organs and the division of labor in the brain are symmetrical, but their functions are quite different! In addition, many seemingly asymmetrical animals are actually radiation symmetrical or left-right symmetrical:
1. For example, a flounder has only one eye on the same side, because it lives near the bottom of the sea, and it is useless if the other eye is not on the same side!
2. There is also a hermit crab, that is, the pliers are relatively large, but they are also symmetrical as a whole! This is also the result of functional evolution!
3. Animals with symmetric and asymmetric radiation, such as jellyfish and sponges, but some people think that they are symmetric and shells seem asymmetric!
Most animals on the earth are indeed symmetrical in appearance, which makes the animals we see every day symmetrical. However, life is complicated and diverse, and because of the competition for survival, there are several "crooked melons and cracked dates", and two eyes can grow on one side of the face.
There are about 6.5438+0.5 million kinds of animals on the earth. It is not excluded that some animals live far away from human beings and are difficult to be found. In terms of biological composition, it can be roughly divided into vertebrates and invertebrates. Vertebrates have a spine that runs through the head and tail. The joint structure of the spine makes the organism more active in two directions, but less active in the other two directions. For example, the human spine is more active in the front and back, and the fish spine is more active in the left and right or up and down, which makes the structure of many vertebrates symmetrical. This structure is called left-right symmetry, which is roughly like a dotted line in the middle of a piece of paper, making the organism.
Living around humans, creatures that are easy to be found, such as cats, dogs, chickens, ducks, geese, pigs, sheep, cows and donkeys, are all vertebrates, so people think that all creatures are symmetrical. The symmetry of biology is easy to move, but it will also be affected by environmental factors such as survival competition, and some special cases have appeared. For example, the adult flounder, with asymmetrical shape, is a typical representative, which has been mentioned by many respondents. Although external symmetry is common in vertebrates, there are many asymmetries in internal organs. A research team found that a certain gene plays a role in inducing body asymmetry in vertebrates, and controls organs to wind or rotate in the same direction by controlling the formation of a myosin.
(ordinary sponge)
Most invertebrates are symmetrical, including radial symmetry and radial symmetry. The former allows animals to move in all directions, such as starfish and other animals. The latter also makes it easier for living things to move in one direction, such as flies, crabs, shrimps and other animals. However, among invertebrates, many of them are asymmetric because of their primitive phyla, such as common sponges. If you look at the appearance alone, there are really not many asymmetric animals.
After thinking about it, it seems that all animals in nature are really symmetrical and have a central axis, which can divide animals into two. After thinking for a long time, I really can't find an asymmetric animal. This is just like the physical laws of nature, which emphasize parity conservation, but only a few fields are not conserved.
I think there are several reasons why animals are symmetrical:
First, symmetry can keep the body in sufficient balance.
This should be easy to understand. Asymmetric objects must not be as balanced as symmetrical objects. Symmetrical animals, the center of gravity is above the axis of symmetry, above the local body midline, so that the two sides of the animal will be more stable, will not sink left and right, "standing" unstable.
Second, the development process of animals determines that animals are symmetrical.
We all know that animals are developed from fertilized eggs. The first fertilized egg has only one cell, and then it is divided into two, two into four, four into eight, and so on. The number of cells is always even. In this way, every cell of the same kind divides in the same state every time, and there is no factor that will lead to their asymmetry, so the final result of development is symmetry.
Questioner, have you never eaten asymmetry, have you never seen it?
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Have you ever eaten Duobao fish stewed at home? Do you pull the fish head symmetrically?
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Have you ever tried fried fish? Look at the fish head before eating. How do fish eyes grow?
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Steamed salmon,
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Small mouth fish,
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Die fish head
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Roasted starfish
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Eat sea urchins raw
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Gabaxia
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Silurus gracilis
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trumpet shell
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river snail
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The above is the asymmetry I have ever eaten.
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The world is asymmetrical,
Life is asymmetrical.
Information is asymmetric,
Love is asymmetrical.
As for the topic that everyone found, basically all animals are symmetrical, so are there asymmetric animals? My personal opinion is that most animal species do have body symmetry, but there are still some special species that are asymmetric. Why do you say that?
Because most animals' body shapes and postures are symmetrical physiological manifestations, the main reason is that the process of survival activities needs the balance of the body's center of gravity, and the performance characteristics of animal survival activities mainly include: walking, swimming, walking, jumping, jumping and flying. The performance characteristics of these different survival activities determine the evolutionary development direction of natural selection. No matter what kind of ecological performance characteristics are established, they are all around the balance of the body's center of gravity in the process of activity, constantly increasing the coordination of the body's activity process and effectively helping animals find food and survive. Therefore, most animal species can evolve symmetrical ecological phenomena.
However, some special animal species are asymmetric, such as left-handed fish, snails, butterflies, tidal crabs, starfish, corals, hermit crabs and anemones. These animal species do not have symmetrical ecological phenomena, mainly because they all live in special environments, or they are pretending; Or water flow factors; Or defend against natural enemies; Let's rest assured to eat. What kind of special living environment can create special animals suitable for your special living environment?